pediatric ventilator stephaniepediatric ventilator stephanie technical manual january 2003 1. ......

Pediatric Ventilator

Stephanie

Technical Manual January 2003

1

CONTENT Basic Principles .........................................................................................................................4

1.1 Structure ....................................................................................................................4 1.1.1 Control Unit Module .............................................................................................5 1.1.2 Electronic Module .............................................................................................5 1.1.3 PC Module............................................................................................................8 1.1.4 Electric Power Supply Module ............................................................................8 1.1.5 Battery Module..................................................................................................9 1.1.6 Pneumatics Module ...........................................................................................9 1.1.7 Patient Component ..........................................................................................10 1.1.8 Test Module.....................................................................................................10 1.1.9 Valve Actuation...............................................................................................11

1.2 Functional Operation...............................................................................................11 1.2.1 Gas Supply ......................................................................................................12 1.2.2 Electric Power Supply.....................................................................................12

Technical documentation Power Pack/Mains Power ..............................................................12 1.2.3 Generation of the Ventilation Pattern .............................................................16 1.2.4 Heating and Humidifying Ventilatory Gases ..................................................17 1.2.5 Monitoring...........................................................................................................18 1.2.6 Control.............................................................................................................18

2 Mechanical Structure ......................................................................................................19 2.1 General ....................................................................................................................19 2.2 Assembly and Disassembly.....................................................................................20 2.3 Assembly pictures for Exchange of Stephanie-Moduls ..........................................21

3 Pneumatics ......................................................................................................................42 3.1 General ....................................................................................................................42 3.2 Pneumatics module .................................................................................................42

3.2.1 Pneumatics schema .....................................................................................43 3.2.2 Sensor Electronic..........................................................................................44

3.2.2.1 Signal designation .......................................................................................44 3.2.2.2 Operating function.......................................................................................44

3.2.3 Assembly and Disassembly.............................................................................46 3.3 Test Block ...............................................................................................................47

3.3.1 General ............................................................................................................47 3.3.2 Assembly and Disassembly.............................................................................48

3.4 Patient Component ..................................................................................................49 3.4.1 General ............................................................................................................49 3.4.2 Functional operation........................................................................................49 3.4.3 Assembly and Disassembly.............................................................................51

3.5 Patient Hose System................................................................................................51 3.6 Measurement of Pressure and Volume Flow ..........................................................52 3.7 Aerosol System .......................................................................................................53 3.8 Ventilatory-Gas Humidifying .................................................................................53

4 Electronic ........................................................................................................................53 4.1 General ....................................................................................................................53 4.2 Control Unit.............................................................................................................54

4.2.1 Therapy Control Module.................................................................................54 4.2.2 Monitor Control Module .................................................................................55

4.3 PC Module...............................................................................................................55

2

4.3.1 PC Circuit Boards............................................................................................55 4.3.2 VGA Card .......................................................................................................55 4.3.3 PC Interface.....................................................................................................55

4.3.3.1 Signal Designations.....................................................................................56 4.3.3.2 Operational functioning...............................................................................56

4.4 Electronics Block ....................................................................................................58 4.4.1 Microcomputer ................................................................................................58

4.4.1.1 Signal designations......................................................................................58 4.4.1.2 Operational functioning...............................................................................60

4.4.2 Monitoring (watchdog.....................................................................................61 4.4.2.1 Signal designations......................................................................................61 4.4.2.2 Functional operation....................................................................................62

4.4.3 Sensor Module.................................................................................................64 4.4.3.1 Signal Designations.....................................................................................64 4.4.3.2 Operational functioning...............................................................................65

4.4.4 Power amplifier ...............................................................................................67 4.4.4.1 Signal designations......................................................................................67 4.4.4.2 Operational function....................................................................................68

4.5 Power Supply ..........................................................................................................72 4.5.1 Power supply module ......................................................................................72

4.5.1.1 Signal designations......................................................................................72 4.5.1.2 Operational function....................................................................................73

4.5.2 Battery Module....................................................................................................73 4.6 Valve Actuation.......................................................................................................74

5 Safety Concept ................................................................................................................75 5.1 General ....................................................................................................................75 5.2 Safety Design of the Ventilators .............................................................................75 5.3 Mandatory Parameters to be monitored and tested .................................................76 5.4 Adjustment and Treatment of Limit Valves............................................................76

5.4.1 General ............................................................................................................76 5.4.2 Pressure ...........................................................................................................76 5.4.3 Respiratory Minute Volume............................................................................77 5.4.4 Insp. O2 concentration: ...................................................................................77 5.4.5 Temperature ....................................................................................................78

5.5 Alarm Response ......................................................................................................78 5.5.1 General ............................................................................................................78 5.5.2 Alarm suppression...........................................................................................79 5.5.3 Status graphic of the alarm system..................................................................79 5.5.4 Alarm table......................................................................................................81

6 Failure Mode Analysis ....................................................................................................84 6.1.1 Control Unit.....................................................................................................84

3

Basic Principles

1.1 Structure

Using the modular structure, this section will briefly deal the individual functional modules

and their interaction.. Detailed descriptions and explanations of the individual functionalities

of the modules are given in the sections that follow.

As shown in the Appendix (modular display, Stephanie), theStephanie consists of several

components or modules :

• Control unit module,

• Electronic module,

• PC module,

• Pneumatics module,

• Electric power supply module,

• Patient component,

• Actuator for the ventilator valve.

4

1.1.1 Control Unit Module

The control unit module is positioned on the front side of the Stephanie unit. It is lectern-

shaped and is comprised of all the adjustment and settings elements in the form of switches,

potentiometers and keys (push-buttons). Furthermore, these are grouped for the various

therapy settings and for monitoring.

The control unit module, ie the control elements, transmits the information to the central

controller in the electronic block module.

On a 10.4" TFT flat screen, all monitoring results are displayed in alphanumerical form of all

ventilation parameters being monitored; time functions of ventilatory pressure, volume flow

and volume are displayed in graphical form.

The screen display is directly controlled by the PC module.

1.1.2 Electronic Module

The electronic module consists of the circuit boards: pressure sensor circuit boards, power

amplifier, monitoring (watchdog) as well as the central processing unit.

5

The sensor circuit board has two pressure sensors for regulating and monitoring ventilatory

pressure, one differential pressure sensor that, together with the pneumotachograph head,

carries out volume measurement, and amplifiers for evaluating thermistor signals for

ventilatory-gas humidifying.

The Microcomputer (MC) is the essential core of the unit controlling all therapy

functionalities provided by the Stephanie unit. It processes the information given via the

control module received from the adjustment and settings elements and transfers these on to

the serial port interface RS 232 to the PC module.

The microcomputer generates the digital control algorithms for pressure regulation and

volume regulation. For doing this, it receives information from the pressure and volume flow

sensors of the sensor ciruit board as actual values and compares these to the pre-set or target

values of the ventilatory pattern generator. As a result of the control algorithm, a corrective

signal is generated, which – amplified by the power amplifier – activates the valve actuation.

This changes the pistion position of the inspiration/expiration valve until the target and pre-

set values precisely correspond to each other.

The microcomputer also takes on the regulation of respiratory-gas humidifying. Temperature

signals provided by the sensor circuit board serve as actual values, and the target value is

generated by the temperature control algorithm. Depending on regulating deviations, power

6

transistors located in the electric power module switch on or off the heating element in the

humidifier and/or hose.

The power amplifier amplifies the analogue signal generated by the microcomputer which, in

turn, activates the valve actuation. By means of feedback of the path signal of a positional

transducer coupled with the valve actuation, a path control loop is created, which greatly

improves the dynamic of the valve actuation.

Circuit board monitoring / supervision (watchdog) serves functionality monitoring, and

oversees the microcomputer, the power supply as well as the PC module. It contains the so-

called watchdogs, that are rhythmically activated by both units, and if failure occurs, switches

the entire unit over to an emergency mode, in which the safety valve is activated and the

patient can at least spontaneously breathe ambient air.

If the alarm limit is exceeded, it activates an audible alarm.

In addition, this circuit board contains the power transistors for activation of the magnetic

valve (solenoid).

7

1.1.3 PC Module

h00000000

120 240

Sauerstoffsensor

®

M - 11

2x4AT

Reset

h00000000

12024 0

Sauerstoffsensor

®

M - 11

2x4AT

Reset

The PC Module houses a complete personal computer, 586 DX 66.

It fulfills two tasks:

• Monitoring of the microcomputer,

• Monitoring of ventilatory parameters and pre-set alarm limits.

The sensor signals generated by the sensor circuit board are evaluated independent of the

microcomputer and the monitoring parameters are alphanumerically displayed in a dedicated

field on the monitor display screen.. It coordinates the visual alarm with the alarm status, that

are recognized either by the PC module itself or by the microcomputer.

In addition, the PC module generates the screen display of ventilatory pressure, volume and

volume flow as a function of time.

1.1.4 Electric Power Supply Module

The electric power supply module supplies the electric current necessary for the operation of

the ventilation unit. It contains all monitoring switching devices as well as power transistors

for switching on/off the heating elements of the respiratory-gas humidifier and ventilation

hoses.

8

1.1.5 Battery Module

h00000000

120 240

Sauerstoffsensor

®

M - 11

2x4AT

Reset

The battery module contains a 24 V lead storage battery, which, in the event of power failure,

ensures continued operation of the ventilation unit for a short period of time.

1.1.6 Pneumatics Module

Pneumatik-Block

The pneumatics module contains all the pneumatic components that are necessary for

processing the respiratory gas, including respiratory gas mixer, valves, pressure regulator, etc.

It is pneumatically connected to the patient component via a plug coupling.

9

1.1.7 Patient Component

The patient component contains all the pneumatic components of the patient circuit (loop),

which must be sterilised. In particular, these are: the inspiration/expiration valve housed in a

ventilation valve unit, safety valve as well as an injector. It additionally integrates the

heater/humidifier of the patient gas.

1.1.8 Test Module

The test module contains an electromagnet via which the safety valve of the patient

component is activated; it also contains a lever for switching the ventilator over to manual

operation, as well as for calibration for Compliance and Resistance, for testing the entire

system during the unit system selftest.

10

1.1.9 Valve Actuation

The valve actuation is carried out by an electrodynamic converter. It is activated by the power

amplifier and is coupled with the ventilatory valve unit by means of magnetic force.

1.2 Functional Operation

"Operational Diagram, Entire System"

Gassupply

Pistonvalve

Watch dogforCPU

Ventilationpres.Ventilationflow

Pressuresensor(control circuit)

Flowsensor(control circuit)

TubesystemPatient

(Monitor)

Gasblender

DAC1 El. dyn.Drive

Bidirectionel Transfer of all Adjustmentparameter and Alarms

HP-Alarm

HP-Alarm

FiO2-Sensor

Sensor 2

MP-Alarm

Supervisionof

vent. pressure

Supervision of- Apnoe- Diskonnektion-Temperatur

-FiO2

Supervisor-Programm of Microcomputer Supervisor-Programm ofPC - Module

- FiO2,- Apnoe- Diskonnektion- Temperatur

visual display of- Information

- AlarmsGraphical indication

of breathingcurves

and ventilation parameter

Plausibilitycheck of

Adjustments

Ext. watch dog

für Monitor

LP-Alarm

presuresensorAir and O2

Net voltage

"disk on chip"for Programm

Zeroing ofFlowsensor

cycl.Zeroing.

Supervision

reg.distanceSensor 1Way measurement

system (WMS)

Valves forAir and O2

Manual ventilationoutlet

switch over valveManual-mechanical

manualhandleautomatic

Substitution in case oflGasfailure

watchdog

ADC

ADC

DAC2

ADC

8bitBus

ADC of PC

Micro-Computer PC-Modul

mitMonitor

Emergencyvalve

Funktion diagram of hole unit"STEPHANIE"

audibleSignal

Supervision ofaudible Signals

Speaker 1

Speaker 2

internalVoltage forSupervision

watchdogPC

poweramplifier

Display-ElementsUser-Elements

Front panelADC

Akku-Modul

Temperatur

Patient gashumidifier

and warmer

ADC Temp.-Sensor Temp.-Sensor(Monitor)

Voltagesupervision

Voltage generator

Power supply

Floppy disk

Hard disk

Pneumatik - Modul

ADC

in Pn.-Module

Monitorparameter

SafetyRelais

Pressuresensor

reg.distance

(control circuit)

Supervision- transmissionerror MC/PCUserelements

Supervision ofSupervision

ofvent. pressure

Emergency valve

11

1.2.1 Gas Supply

The gas supplies, compressed air (Air) and oxygen (O2) are fed in the pneumatics module via

magnetic valves (solenoids) to the oxygen/air mixer and can be used either for mechanical or

manual ventilation. The current (actual) oxygen concentration is monitored by the oxygen

sensor and evaluated by the PC module.

Pressure sensors, together with the central processor, monitor supply pressures for CA and

O2.

1.2.2 Electric Power Supply

Technical documentation Power Pack/Mains Power 1. General description The power pack module of the STEPHANIE provides the equipment with the necessary

supply voltage 5 V, +/- 12 V and 24 V, and regulates the charging of the internal battery as

well as the switch-over from mains power supply to battery operation. Furthermore, it

generates monitoring signals including re-set signals for the controller of the STEPHANIE.

All voltages are generated with switching regulators from a unstabilized intermediate circuit

voltage in the range of 22 – 28 V, that is taken either from rectified secondary voltage of a

transformer, or from the internal battery of the equipment.

2. Transformer A safety transformer from the company Marek is used to generate the secondary voltage. The

transformer can be operated on 230 V or 100 V respectively, and provides secondary 22 V at

7 A. Compliance with the requirements of EN 60601 for equipment with a protective rating of

1 has been tested. In addition, the transformer is equipped with an over-heating safety device.

The rectified secondary voltage serves as intermediate circuit voltage for generating other

supply voltages as well as directly providing power supply for the heating system.

12

3. Generating supply voltages The supply voltages necessary for the STEPHANIE (5V / 4A and +/-12/2A) are taken from

the intermediate circuit voltages with switching regulators (see circuit diagram, sheet 1).

Types LM2679 from National Semiconductor (NSC) were used. Voltages of 5V and 12V are

generated by the downwards adjustment control, the 12 voltage by means of inversion of the

+12V voltage. The load on the 12V regulator does not increase in this case, because the 12V

supply is essentially only alternately loaded. The design of the switching and the selection of

additional components is in accordance with the circuit recommendations of NSC. Cooling of

the regulator is effected by means of a copper surface on the printed circuit board. The

maximal measured temperature in immediate proximity of the 5V regulator (having the most

load) amounted to approximately 70ºC. (maximal permissible temperature, 115ºC).

The thermal load on the other components is lower.

Additionally, all voltages are filtered through a LC module. Because of a special sensitivity of

the power amplifier to interference of the –12V supply (leads to noise at the patient

component), a significantly greater inductivity (4mH) was used than that for the other

voltages.

The 5V and 12V regulators can be switched off via a shut-down input (STB2) (see "Control").

4. Charging circuit, switch-over to battery operation For maintaining voltage supply in the event of mains power failure, the STEPHANIE is

equipped with two series connected batteries (each 12V /1.3 ampere hour). A voltage of

approximately 27.6V is necessary to charge the batteries which slightly difffers according to

temperature.

As the intermediate circuit voltage from the mains can lie below as well as above this value, a

regulator is used for battery charging that operates both upwards and downwards (component

at U5, Circuit Diagram, sheet 1). The circuit is similar to an application of the company

Linear Technologies.

The maximal output current of the charging circuit is limited to a value of approximately 0.3A

via R16 and Q3. Battery charging can also be switched on or off via a shut-down signal (AK-

SHDN).

The switch-over between mains power supply and battery operation is effected by a relay

(K1, Circuit Diagram, sheet 1). By means of this relay, the equipment can also be switched

off in the event of error or malfunctioning, by using the Re-set key S1. This forces the relay

13

into the mains position. If the mains power is also switched off, the STEPHANIE software

shuts the equipment down.

5. Heating Control The circuit breaker for the two heating systems of the STEPHANIE are also built in to the

power pack module. They are Profets from the company, Infineon: (U6, U7, Circuit Diagram,

sheet 1). They are Mosfets with protective and monitoring functions.

The components are short-circuit proof and equipped with thermal overload protection.

They switch the intermediate circuit voltage over to heating resistors.

6. Control

Monitoring of the power pack and the generation of the control signals for the controller is via

the microprocessor (Motorola 68HC11, ICI, Circuit Diagram, sheet 2).

Because of practicality, the processor is used as the use of assembled discrete components is

somewhat costly. The possibility of programming proves to be useful as well, because the

temporal control of the signals has proven to be critical. The program is written in Assembler

and filed (stored) in the program memory of the processor.

Generated and evaluated are the following signals:

14

Outputs:

- Two power OK signals (POK1/2) These signals are set when all supply voltages lie within the default limits. These are: 5V :4.8 – 5.2V 12V :11 – 13V -12V :-11 – -13V Intermediate circuit voltage : 18- 37V The voltages are led through voltage multipliers to the A/D converter inputs of the processor and the processor controls the compliance with the limit values. The POK signals are logical HIGH (5V) for correct functioning, and LOW (0V) for malfunctioning. POK1 is used as RESET for the controller of the STEPHANIE. A correct start of the controller was only achieved, when this signal was set with a delay of 200 ms.

- Two signals for battery check (BATOK, BATLOW) These signals serve as watchdog for the battery. BATOK becomes HIGH, when the battery voltage is at least 22V. BATLOW becomes LOW, when the voltage fall below 18V.

- A mains power failure signal (PFAIL)

This output becomes LOW, when the secondary voltage of the transformer falls below 18V.

- Inputs: Mains switch-off/shut-down (SHDN) This signal causes the STEPHANIE to shut down the power supply unit. The mains/battery switch-over relay is put into battery operation mode, in this mode battery charging is switched off. SHDN is used to briefly switch over to battery operation during the test routine after starting up the equipment to test the flawless functioning of the battery.

- Standby operation (STB)

In standby mode, all functions of the equipment, apart from battery charging, are deactivated. Input corresponds to a software shutdown. The switch-over mains/battery is put into mains position, the voltage regulator for supply voltages are switched off (the internal control signal STB2 is set to LOW). Battery charging mode remains on. Evaluation of standby signal proved to be problematic, because the STEPHANIE switching circuit generated no clearly defined signal. During normal operational mode, there is a voltage of approximately 4V, that drifts to smaller values after switch-over to standby, without a clear switch-over. Therefore, the evaluation takes place also with a A/D converter. If the voltage exceeds 3V, normal operation is switched off. Switch-over to standby takes place when the voltage falls below 2V.

15

- Inputs for heating control (HZ1ON, HZ2ON, HZDIS) HIGH signals at HZ1ON, HZ2ON switch on the respective heating, under the condition that HZDIS is not activated and the unit is being operated on mains power. In battery operation, the heating systems are switched off to increase operation time.

7. Actions to be taken in the event of power failure

If the processor detects a fall in secondary voltage below 18V, there is an automatic switch-

over to battery-powered operation via the switching of relay K1. Here, a relay can be used,

because of the large supportive condensator at the input (C22, 10000uf), the intermediate

circuit voltage only falls slowly.

As soon as mains power has been restored, switch-over to mains power takes place and

battery charging is switched on once again.

8. Safety controls

For protection against transient interruptions, all voltage outputs are equipped with voltage

surge diodes. Secondary and battery voltages are secured with 47V protection diodes, the +/-

12V voltages with 15V diodes and the 5V with 6.8V diodes.

Problems with reversed polarity are kept below approximately 0.7V.

1.2.3 Generation of the Ventilation Pattern

The central control regulates the pressure, volume flow regulating circuits for generating the

ventilation pattern desired.

It receives from the control elements of the control unit the desired ventilation parameters and

from these generates, via the controller program, all the analogue and digital control signals

necessary for carrying out the tasks involved in the therapy.

For this purpose, actual values of ventilation pressure and volume flow are collected by the

analogue-digital converter (ADUs) of the central control (microcomputer) and are via control

16

algorithms converted into an analgoue control signal for the power amplifier. This regulates,

via the valve actuation, the control valve in the patient loop.

Mandatory monitoring of the ventilation pressure is carried out by the PC module via a

second pressure sensor.

To ensure a high quality of performance of monitoring the pressure and volume flow

regulator circuits, a high valve actuation dynamic is of absolute necessity. For this, there is

the path control circuit, in which the position of the control valve is tracked by means of an

optical positional transducer, and is fed back to the input of the power amplifier.

For reasons of safety, the positional transducer is a dual system and the position signal is fed

to the central control by System 2. By comparing the pre-set (target) valve (output DAC1 of

the central control) with the actual position, a complex monitoring of the ADU – DAU path of

the central control is obtained including power amplifier, actuator and control valve.

1.2.4 Heating and Humidifying Ventilatory Gases

Heating and humidifying ventilatory gases are also coordinated by the central control. A

temperature sensor at the exit side of the humidifying chamber and one at the exit side of the

inspiration hose heating element provide the actual temperature valve to the central control.

The central control generates, according to a pre-set temperature value and according to a

temperature control algorithm, the control signal, from which the power transistors for both

heating circuits are switched.

A third temperature sensor serves as monitor. For safety reasons, it is also evaluated by the

PC module.

17

1.2.5 Monitoring

Together with the display screen, the PC module serves and supports

• monitoring of the proper functioning of the central control, and

• monitoring of the ventilation pattern

• alphanumerical display of measured ventilation parameters as well as alarm statuses.

The PC is coupled with the central control via a serial interface port and receives the setting

parameters of the control unit, including those of the alarm statuses of the central control, and

also transmits its own alarm statuses as well as the monitoring parameters to the central

control..

1.2.6 Control

The central control and PC module take on, independent of one another, the monitoring of

safety-relevant parameters and statuses in line with current standards.

Both units classify alarm statuses via independent alarm systems, into alarms of high and

medium priority and then feed these data to the circuit board. This triggers an audible alarm

and, should the situation or error be endangering, switches off the emergency air valve for

reasons of patient safety.

Monitoring the central control and PC module themselves is carried out by watchdogs, that, in

the event of malfunctioning or failure, also lead to shut-down followed by appropriate

corrective action.

The audible warning system has a backup system so that in the event of failure of the first

audible system, the second system will trigger the alarm.

18

2 Mechanical Structure

2.1 General

„Mechanical Structure“.

The Stephanie consists of the housing, in which a rack is inserted. Positioned on this rack are

the PC module, pneumatics module and electric power supply module arranged as plug-ins.

The circuit boards of the electronic module are individually inserted in the lower tier of the

rack. The latter are covered at the rear side of the unit by the battery module.

The control unit serves as the front cover of the housing unit.

Connections between the individual electronic units are in the form of wiring backplane, ie

circuit boards, and connection cables. A specific of the Stephanie is the drive of the

oxygen/air mixer positioned in the pneumatics module. As the setting element belonging to it

is positioned on the control unit, a toothed-belt drive serves as a mechnical coupling to both

components.

All functional units of the patient circuit such as valve actuation, patient component and the

test module are mounted to a robust mounting plate on the right-hand sidewall of the

Stephanie. The valve actuation is positioned inside the patient component and the test module

on the exterior of the housing.

Below the lowest tier insert, there are two blowers mounted for providing cooling of the

inside of the unit. RPMs of the blowers and therewith the cooling performance, are regulated

by thermistors that are positioned at temperature-critical points in the unit.

19

2.2 Assembly and Disassembly

The housing consists of an L-shaped basic body, formed by the right sidewall and the base

plate, the left sidewall and the housing cover. Normally, it need not be completely

disassembled for servicing.

If it is necessary to gain access to the backplane or to the control unit, only the cover need be

removed.

To remove the cover, loosen the two long hexagon socket screws (3mm) that are accessible

through the large bores on the rear wall of the cover. The cover is carefully pulled forward

approximately 3 mm, so that the tongues located on the underside of the cover can be freed

from the pins mounted to the housing. Following this, the cover can be lifted from the

housing. Make sure that the control unit does not tip forward. After loosening M4

countersunk screws on the lowerside of the control unit, the control unit is carefully pulled

forwards and hung in the hing pins of the unit. Now the control unit can be swung forward

and all components of the backplane as well as the control unit are accessible.

Assembly is carried out in reverse order. Only make sure that while inserting the control unit,

the potentiometer axis of the FiO2- drive must be inserted into the correct sleeve.

20

2.3 Assembly pictures for Exchange of Stephanie-Moduls

Please take care and secure, that all cables and screws you remove will be reconnected in

exactly the same way and position.

1.

2.

21

3.

2 1

4.

22

5.

6.

23

7.

8.

24

9.

10.

25

11.

12.

26

13.

14.

27

15.

16. Pneumatic-Modul

28

17.

18.

29

19.

20.

30

21.

22.

31

23.

24.

32

25.

26.

33

27.

28.

34

29.

30.

35

31.

32.

36

33. PC-Modul

34.

37

35.

36.

38

37. power supply unit

38.

39

39. battery unit

40.

40

41.

41

3 Pneumatics

3.1 General

The pneumatic system of the Stephanie consists of three main componnents, the pneumatics

module, patient component together with the patient loop, and the test block.

3.2 Pneumatics module

„Pneumatics module, top view“,

The pneumatics module is an insert that contains all the pneumatic elements that do not

directly belong to the patient loop. In addition, sensors are located in the pneumatics module.

These sensors measure the pressures of the supply gases, the inspiratory oxygen concentration

as well as the inner temperature of the module.

Structurally, the pneumatics module is a hermetically closed unit within the ventilation unit.

Should it, in the event of malfunctioning or failure, result in an unacceptably high oxygen

concentration within the module, the high oxygen concentration cannot escape to other parts

of the unit. Such concentrations can escape through a number of wide slits in the front plate of

the pneumatics module.

42

3.2.1 Pneumatics schema

Dat um Name ( Ur spr . : ( Er s . f : )Bl .

Bl at t

Nor m

Gepr .Bear b.

Dat um Name

( Ar t i kel nummer

( Benennung)

Maást ab

Wer k s t of f / Hal bz eugHal bf er t i gt ei lRoht ei l

)

Žnder ungZust .

A NA E S T HE S I E

A T E MT HE R A P I E

P Ž DI A T R I ES t eph an

ng)

Mainusch Pneumatic-Block

Stephanie

1 035 65 053

6.10.00

O2-Kalb.21%

Duese

O,3

Air

R1/8 O2

Injektor M5

D1

V2

V3

V4

M5O2-Zelle

MischerR1/8

MischerR1/8

M5Pilot Druck

Mischerausgang

R1/8 Air

M5Drucksensor

V1

R1/8

NW 0.8

NW 0.8

NW 0.8NW 2

R�cksclagventil OV10/DN8

NC

NC

NC

NC

V7 Ventil stromlos ge”ffnet

24 Volt 2 WATT

Druckbereich 2.5 - 6bar

V1 V2 V3 V4 V5 V6 Ventile stromlos geschlossen

V2-V7

V1

Aerosol M5V6

NW 0.8

NC

Flow = 1-40 l/min

P=min ca.2.8bar

NW 0.8

V7NO

Handbeatmung M5

ca 10 l max.

V5R1/8

NW 2

NCDruckregler 150 mbar

O,5

D2

2.8 bar

43

3.2.2 Sensor Electronic

3.2.2.1 Signal designation

Operating voltages

SV_P12LV

SV_P12

SV_N12

Control signals

/ÜW_VPL Actuation of compressed-air valve (-12V)

/ÜW_VO2 Actuation of oxygen valve (-12V)

/ÜW_VINJ1 Actuation of injector valve 1(-12V)

/ÜW_VINJ2 Actuation of injector valve 2 (-12V)

/ÜW_VSubst Actuation of substitution valve (-12V)

/ÜW_VAerosol Actuation of aerosol valve (-12V)

Outlet signals

PM_UP120 Pressure sensor 120 mbar admission pressure

PM_UPl Pressure sensor, compressed-air admission pressure

PM_UO2 Pressure sensor, oxygen admission pressure

PM_UFiO2 FiO2 sensor signal

PM_UTemp Temperature-sensor signal

3.2.2.2 Operating function

The electronics integrated in the pneumatics module is made up of sensors for measuring:

• Oxygen concentration (FiO2),

• Temperature inside the pneumatics module.

• Supply pressure of compressed air,

• Supply pressure of oxygen,

• Admission pressure of ventilatory-gas mixture.

44

All sensors apart from the oxygen sensor and their respective electronic components are fitted

to a circuit board. (see Operating Plan „Electronics, Pneumatics Module“ in Appendix 6).

This circuit board is located inside the pneumatics module in such a way, that a SUB-D plug

connector mounted to the rear side of the circuit board – hermetically sealed – protrudes

through the rear side of the pneumatics module. This allows all electrical connections to be

effected outside the pneumatics module.

Oxygen partial pressure and thus oxygen concentration of the ventilatory-gas mixture (after

pressure regulator PR2) is converted by means of a sensor KE25 (Unitronic) into an electric

current that is amplified by the amplifier U1 by a factor of 100 and held as signal PM_UFiO2

at the outlet.

The thermistor amplifier U2 is, together with thermistor R4, located on the circuit board, a

temperature voltage converter, and serves to determine the inner temperature of the

pneumatics module. Its output signal PM_UTemp is evaluated by the central control. If the

limit value for the inner temperature of 50°C is exceeded an audible and a visual alarm are

triggered.

The pressure sensors for the admission pressure of the compressed air and oxygen as well as

the ventilatory-gas mixture are sensors with integrated electronic, that directly provide the

pressures of the assigned currents PM_UPl, PM_UO2 and PM_UP120 at the outlet.

45

3.2.3 Assembly and Disassembly

Removing the pneumatics module is effected in the following way:

1. Remove the supply hoses for compressed air and oxygen,

2. Position Hand/Ventilator, switch in Ventilator position,

3. Remove patient component,

4. Loosen pneumatic connection sleeve for patient component from the right sidewall with

hexagon socket wrench,

5. Open housing (see Pt. 2.2),

6. Remove toothed belt from toothed gear of the pneumatics module,

7. Remove SUB-D plug from the rear side of the pneumatics module,

8. Remove plug-coupling hose for nebulizer outlet from the inner right sidewall,

9. Loosen the 4 screws on the front plate of the pneumatics module,

10.Pull out the pneumatics module.

After loosening the screws and removing the cover, all components of the module are now

accessible.

If only an inspection of the pneumatics module is to be carried out during ooperation, the

entire module need not be pulled out. It is only necessary to remove the cover and to unscrew

the upper module rails. After that, the module cover can be opened as described above and the

inner parts of the pneumatic module are accessible.

46

3.3 Test Block

3.3.1 General

„Test block, side view“

The so-called test block is mounted on the right sidewall of the basuc unit. On the underside

of the test block there is a screw-on bottle attached filled with copper wool that serves as test

Compliance. Via a pneumatic resistance, it is connected to a connecting union (pipe) found on

the rear side of the test block. When the unit is not in operation or when running the test

program, the Y-piece of the ventilation hose is attached to this connecting union.

47

Using the lever „Hand / Resp“, the unit can be switched over between manual ventilation and

ventilator operation. When the lever is in „Resp“ position, the ventilatory-gas mixture reaches

the patient via the patient component and the patient is mechanically ventilated. When the

lever is in the „Hand“ position, a tappet rod found in the pneumatics module switches the unit

over to manual ventilation. The ventilatory-gas mixture is then provided at the connecting

union below this lever and is led via a hose to the manual ventilation bag. By using a

screwdriver, the volume flow for manual ventilation can be adjusted at the flow control valve.

This becomes visible when the lever is in the „Hand“ position. Otherwise, it is covered by the

lever.

When the lever is in the „Hand“ position, an electric contact is simultaneously activated.

Once activated the optical message "Attention Manual Ventilation!" appears on the display

screen.!“. In addition, the emergency air valve as well as the injectors in the patient

component are switched off, whereby the patient can, generally, spontaneously breathe

ambient air.

Furthermore, the test block is equipped with an electric lifting magnet. When activated, this

closes, via a valve reed, the emergency air valve of the patient component. (see. Patient

component).


The test block can be disassembled by loosening the hexagon socket screws that are

accessible at the side. After loosening the screws the test block can be pulled off and the plug

connection between the test block and housing removed.

When re-assemblying, make sure that the tappet rod of the switch-over "Hand/Ventilator" is

centrally positioned on the tappet of the pneumatics module.

When replacing the electromagnet (solenoid), loosen the ring nut between the patient

component and the test block by using box or socket spanner (wrench).

48

3.4 Patient Component

3.4.1 General

„ Patient component, inside view“,

The patient component is the actual connection (interface) between the ventilator and the

patient. It is attached on the sidewall of the basic unit in front of the test block and locked in

using a lever.

All pneumatic components of the patient loop are found in the patient component; all these

components must undergo sterilisation.

3.4.2 Functional operation

The ventilatory-gas mixture in the pneumatics module is pressurized to approximately 110

mbar. It is led via a plug coupling, hermetically sealed with o-rings, through the inlet of the

patient component. The ventilatory gas flows through the humidifying bottle filled with

water, and then, warmed and humidified, proceeds to the inspiration valve Vin and from there

is led via the inspiration outlet through the inspiration hose to the Y-piece. The exhaled

ventilatory gas flows through the expiration hose and the expiration inlet to the expiration

valve Vex and from there into the ambient air via an injector.

Valves V1, V2, V3, V4 and V5 form the safety system within the patient component and

prevent, in the event of mechanical malfunctioning, any endangering of the patient.

By means of the excess pressure safety valve V1, the maximum possible excess pressure at

the inspiration outlet is mechanically limited. Here, the opening pressure of valve V1 is

49

adjustable in the range from 20 mbar to approximately 80 mbar by using the toggle found on

the front side of the patient component.

The negative pressure safety valve V4 limits the maxium negative pressure at the expiration

inlet to approximately -10 mbar. It is pre-set by the manufacturer and the opening pressure

cannot be adjusted by the user.

The inspiration outlet and the expiration inlet are connected to the emergency air valve via the

check valves V2 and V3. During normal operation of the ventilator, a lifting magnet

(solenoid) in the test block presses a valve head against the outlet of V5. This disables V2 and

V3. In the event that the unit detects an operational disturbance, the solenoid is deactivated,

the valve head opens the emergency air valve, and the patient can inhale via valve V2 and

exhale via valve V3, whereby the effective dead space is less than 2.5 ml.

The inspiration valve Vin and the expiration valve Vex structurally form a single unit, in that

the inspiration valve opens when the expiration valve closes, and vice versa. This valve unit is

actuated by a valve actuation that is found in the basic unit. The mechanical connection

between actuation and valve unit is by means of magnetic forces. Here, a small magnetic

clamp is attached to the actuation and the side of the valve pistion facing the actuation is

equipped with a thin soft iron plate. When the patient componenet is locked onto the right

side of the housing, the magnetic clamp attracts the valve piston above the soft iron plate and

in this way forms a tight (free of play) connection between actuation and valve unit. Through

a slight crowned design of the soft iron plate, slight tilting of the patient component can be

compensated for, without endangering the safety of the mechanical connection.

When the patient component is separated from the basic unit, the moving part of the valve

actuation found in the basic unit is pulled against a stop until it overcomes the maximum

magnetic force, and the connection between actuation and valve is mechanically broken.

50


The patient component can be completely disassembled.

The bell-shaped valve and the safety valve can be unscrewed by using a coin to loosen the

screws.

3.5 Patient Hose System

"Patient hose system, complete“.

The patient hose system, consisting of heated inspiration hose and expiration hose, is attached

to the ventilatory-gas connection pipes found on the front side of the patient component.

51

Here, it must be ensured that the red hose sleeve coupling of the inspiration hose is on the red

inspiration outlet. At the end of the inspriation hose, a nebulizer pot can be attached, which

then can be connected via an additional hose with the Y-piece.

At the patient end, the temperature sensor is also inserted in to the bore marked red.

The plugs for heating and temperature sensor are pluged into the respective sockets located in

the connection block for heating, pressure measurement and aerosol.

3.6 Measurement of Pressure and Volume Flow

The measurement of pressure and volume flow takes place near the patient between Y-piece

and tube connector. For this, a pneumotachograph head is inserted between both parts. The

differential pressure resulting above the resistor of the PNT-head is a rate for the volume

flow. The differential pressure is led, via two thin tubes, to the pressure sensors (ventilation

pressure) of the sensor circuit board found in the basic unit, and to the differential pressure

sensor (volume flow). The mechanical connection of these hoses to the basic unit is via a Luer

Lock coupling.

For reasons of safety, the measurement of ventilation pressure is via two pressure sensors.

Via valves, the pressure measurement ports of the differential pressure transducer can be

intermittently switched over to ambient air, and during this short time period a zero set

compensation of the volume flow can be carried out. A precise explanation of this calibration

procedure can be found in subpoint 4.3.3 (Sensor Module).

52

3.7 Aerosol System

On the right sidewall there is also a connection union (pipe) for aerosol (see also Pneumatics

Module) and Fig. 3.5.3. When the nebulizer function is activated the therapy ventilatory-gas

mixture at this connection is under a pressure of approximately 2 bar. It is fed to the nebulizer

chamber via a hose attached to this connection. This is to be placed, near the patient, on the

end of the inspiration hose (see also Hose System).

3.8 Ventilatory-Gas Humidifying

Humidifying the ventilatory gas takes place by means of a state-of-the-art procedure, in that

humidifying and warming of the ventilatory gas is done in two steps and via two separate

loops.

4 Electronic

4.1 General

The entire electronic system is housed in the basic unit.

• Control unit,

• Monitor,

• Electric power supply,

• Pneumatics Module,

• Actuator

53

The operational functioning of the individual electronic components can best be described

using the following logic diagrams.

The signal designations are based on the following principle:

The first two letters refer to the signal sources. They are followed by a sub-hyphen and the

subsequent characters that should, if possible, identify the significance of the signal.

Serving as signal sources:

MC : Microcomputer (central control),

PC : PC Module,

ÜW : Monitoring,

LV : Power amplifier,

SM : Sensor module,

PM : Pneumatics module,

SV : Electric power supply module,

AM : Battery module,

RV : Backplane circuit board,

GG : Basic unit.

4.2 Control Unit

The control unit is the communications level (interface) between the user and the equipment.

On the one hand it contains all control elements necessary for the therapeutic operation of the

Stephanie (Therapy Control Module), on the other hand, it also contains the monitor,

consisting of a display screen and its control elements (Monitor Control Module), via which

the user can access all information pertaining to the patient and equipment.

4.2.1 Therapy Control Module

Setting and adjustment elements for the individual parameters are:

• Potentiometer: Tins, Trigger, Vt, Pmax, PEEP, Temp, FiO2, V’osz, fosz, Rv und Ev,

• Switch: Operation mode, inspiration pattern,

• Incre. transmitter: Tex.

• Keys: Insp. Hold, Aerosol, NVI, PVI,

54

The switches are equipped with resistor networks, so that their position, including that of the

potentiometer, is recorded and transmitted to the microcomputer by an analogue-digital

converter via a 16 ibt databus (MC_D0..MC_D15).

The switching state of the keys is stored in a switching circuit and also transmitted via the

databus.

The control signals from the microcomputer for the temporal coordination of the query of the

control elements as well as signalling the LEDs are transmitted via the same databus. The

logic necessary for this is carried out by two programmable logic arrays (PAL).

A failure mode analysis of the control unit is discussed in Section 5.

4.2.2 Monitor Control Module

The following belong to the Monitor Control Module:

Incremental transmitter for menu control of the monitor, as well as the

Keys for Stop, Print, LFD1, Reserve, Alarm Mute.

These signals are evaluated by the PC module and the central control (MC).

4.3 PC Module

The PC module contains a complete industrial standard PC, consisting of the PC circuit

board, a VGA card, floppy-disk drive, harddisk and a bus card as interface between the

processor and the PC. All circuit boards are mounted on a backplane.

4.3.1 PC Circuit Boards

The PC circuit boards supply a PC (486 -33 DX2) and contain all necessary drives and

interfaces for the keyboard and storage systems.

The actual monitoring program is stored on a semiconductor memory (silicon disk). As the

PC card is a commerically manufactured circuit board that is not subject to servicing, its

functioning will not be detailed in this technical manual.

4.3.2 VGA Card

The VGA card contains the entire electronics necessary to drive TFT-VGA display screen.

For detailed information, refer to manufacturer's technical data..

4.3.3 PC Interface

The PC provides the interface between the PC and the ventilator.

55

4.3.3.1 Signal Designations

Operating voltages

SV_P5, SV_0V

Input signals

AIN0...AIN7 8 Analogue inputs

DI0...DI15 16 digital inputs

IGRa, IGRb Inputs for an incremental transmitter

Output signals

DAC0...DAC3 4 Analogue outputs

D01...D15 16 digital outputs

Bus signals

D0...D15 16 Databus signals

A0...A10 11 Addressbus signals

OSC,/IOW, /IOR, BALE, AEN,

RESET.DRV, /IOCS16

Controlbus signals

4.3.3.2 Operational functioning

The PC interface card provides the connection between the address bus and the databus of the

PC as well as analogue and digital input/output signals of the processor.

The analogue-to-digital converter (A3 and A4) allows the AD conversion of 8 analogue

signals with a word size of 12 bits in a voltage range of +/-12V.

Two digital-to-analogue converters (A1, A2) generate four analogue output signals in a

voltage range of +/- 5V using a word size of 12 bits. The exact setting of the reference voltage

is effected via the settings control R1.

56

Via circuits D6 and D7, 16 digital inputs can be read and via D8 and D11 an additional 16

digital outputs can be recorded.

The sequential and combinational control logic for these processes is provided by PALs D3,

D4 and D5.

57

4.4 Electronics Block

4.4.1 Microcomputer

4.4.1.1 Signal designations

Operating voltage

SV_P5, SV_0V

Analogue input signals 10bit (0.5V)

SM_UTemp1 Ventilatory gas conditioning, Temperature 1



PM_UPl Supply pressure, compressed air

PM_UO2 Supply pressure, O2

PM_UTemp Temperature in pneumatics module

RV_UP4 Battery voltage 4V

LV_Usumm1 Positional transducer: cumulative voltage 1

LV_Usumm2 Positional transducer: cumulative voltage 2

Analogue input signals 12 bit (+/-10V)

SM_UP1 Pressure, near patient sensor

SM_UP2 Pressure, near unit sensor

SM_UFlow Volume flow of PNT

PM_UP120 Admission pressure 120 mbar

LV_Us2 Positional transducer: path 2

PM_UFiO2 FiO2 sensor signal

Analogue output signals 12 bit (+/- 12V)

MC_ UDAC1, Analogue output 1

MC_UDAC2 Analogue output 2

58

Digital input signals

/ÜW_RSTMC Restart Microcomputer

SV_PGLV Power amplifier

/NMI Not assigned

/ÜW_5VBFail

/ÜW_PCWD watchdog for PC fail

/RV_SMan Switch, manually switched on

Digital output signals

MC_SD Shut down signal for power supply

MC_INSP Inspiration phase for mechanical ventilation

MC_Heiz1 Heating, humidifier chamber, ON

MC_Heiz2 Heating, hose, ON

MC_RSTAus Blocking of Restart function of ÜW

MC_LVEin Relay on power amplifier, ON

MC_Spk1Ein Signal transmitter 1 on ÜW, ON

MC_NL Emergency air magnet, normal operation

MC_WD Control signal for watchdog on ÜW

MC_HP Alarm, high priority

MC_MP Alarm, medium priority

Bus signals

MC_D0...MC_D15 16 Databus signals

MC_A0...MC_A7 8 Address bus signals

MC_RD, MC_WR, MC_CLK, MC_SEL Control bus signals

Serial interface ports

TXD0, RXD0, TXD1, RXD1 Interface port signals

59


The circuit board of the microcomputer is made up of the following components:

• The actual microcontroller (80C166 from Siemens) with an integrated 10 bit ADU,

• 12 bit ADU, 8 channels (D ),

• 12 bit DAU, 2 channels (D ),

• PAL (D ),

• ROMs (D ),

• RAMs (D ),

• 2 Latch (D ),

• Bi-directional bus driver (D ).

The analogue input signals are collected by the two ADUs and together with the digital input

signals further processed by the microcomputer in line with the program.

At its outputs, it furnishes the corresponding digital control signals and provides the DAU the

information for its analogue output data.

Address bus and databus signals are transmitted via the respective drivers to the outside.

Coordination of the internal processes is ensured by the processor, and by the PAL. In

particular, it generates control signals for the peripheral components.

By means of the adjusting rheostat R1, the reference voltage of the DAU and by means of R6

that of the 10 bit ADU can be set.

The microcomputer is equipped with two ports for serial data transmission RS232.

60

h00000000

120240

Sauerstoffsensor

®

M - 11

2x4AT

Reset

4.4.2 Monitoring (watchdog


Operating voltage

RV_P12, SV_0V, SV_N12LV

Analogue input signals

SA_SPEECH Tone signals for voice output

(not yet installed)

Digital input signals

SV_AkkLOw Battery LOW signal (Ubatt < 21 V)

SV_PG Power good for processor voltage

SV_PGLV Power good for LV voltage

/MC_RSTAus Blocking of Restart function of ÜW

MC_Spk1Ein Signal transmitter 1 on ÜW ON

MC_NL Emergency air magnet, normal operation

MC_WD Control signal for watchdog on ÜW

MC_HP Alarm, high priority

MC_MP Alarm, medium priority

PC_RSTEin Restart_function enable

PC_RSTDrive

Digital output signals

/ÜW_5VBFail Internal voltage 5V fail

/ÜW_5VB1fail Internal voltage 5VB1 fail

/ÜW_RSTMC Restart Microcomputer

/ÜW_RSTPC Restart PC

/ÜW_PCWD PC watchdog responded

/ÜW_MCWD MC watchdog responded

/ÜW_NL Emergency air signal, normal operation

61

ÜW_Spk1_1 Output voltage 1 for speaker 1

ÜW_Spk1_2 feedback input signal 2 from speaker 1

ÜW_SPK2 Output signal for speaker 2

Valve control signals

/ÜW_V0.../ÜW_V10 Negative control signals for the valves

Bus signals

MC_D0...MC_D15 16 data bus signals

MC_A7 Address bus signal

MC_RD, MC_WR, MC_SEL Control bus signals

4.4.2.2 Functional operation

The watchdog circuit board has the following tasks to fulfil:

• Monitoring the proper functioning of PC and MC by processing and evaluating watchdog

signals,

• Generating audible signal sequence for alarm,

• Generating the actuation signal for the emergency air,

• Actuating all magnetic valve in the pneumatics module and basic unit.

Internal power supply

For reasons of safety, the internal voltages for 5V are doubled and the DC-DC transformer

converts the externally supplied voltage RV_P12 into IC21 (5VB) and IC22 (5VB1).

Watchdog monitoring

The PC module and the controller independently transmit, in the course of properly

processing their respective program and at intervals of approx 100..200 ms, watchdog signals

PC_WD and MC_WD, that are evaluated by the watchdog for the PC signal (IC8) and that for

MC signal (IC9). In the event of errors in the program run, the watchdog signal cease and the

PC and/or MC are restarted. During this time a HP (high priority) alarm is triggered, and the

patient has the possibility to spontaneously breathe ambient air via the emergency air valve.

The precise time for running this routine can be read from the status graphs for the watchdog

automaton. It is identical for both the PC and MC systems.

62

The normal state is state 1, the emergency air valve is closed (/ÜW_NLok). If there is no

watchdog signal within the set time-window, the status graph goes over to state 2: the

emergency air valve opens and the PC or MC are restarted via signals /ÜW_RSTPC or

/ÜW_RSTMC. If restartup is successful, the automaton goes over to 3, in which the

emergency air remains open. Only when the next proper WD signal is received, will state 1 be

activated again. If restart was unsuccessful, the WD automaton goes over to state 4, which

can only be exited again by switching the unit off: the emergency air valve remains open and

the HP alarm remains activated.

Generating the audible alarm signal

The audible alarm signal is also generated in an alarm automaton. The signal sequence is

stipulated according EN 475 and for alarms of medium priority (PC_MP, MC_MP) is distinct

from those alarms of high priority (PC_HP, MC_HP). The alarm automaton is made up of the

PALs IC1 and IC2 in connection with a clock generator (IC5).

The output signal of the automaton activates the signal generator SPK1 via the power

amplifier (IC10). This is found in the basic unit and is electrically switched between outputs

ÜW_SPK1_1 and ÜW_SPK1_2. This allows, via the signal (ÜW_SPK1_2) to determine

whether current is actually flowing through the signal generator SPK1 on request/prompt for

audible signaling.. In this respect, signal ÜW_SPK1_2 is actually an input signal and serves

towards monitoring the audible signal routing from input of watchdog switching down to

signal generator SPK1.

In the event of any error within this routing, alarm automaton 2 kicks in and triggers the

audible alarm (ÜW_SPK2) via signal generator 2.

Valve actuation

The magnetic valves (solenoids) in the pneumatics system are actuated by bus signals

(MC_D0..MC_D10) and the respective control. Both registers IC11 and IC12 store the

databytes sent by the MC and control, on their part, the MOSFET power transistors T2..T11

via the optical coupler IC15..IC17. Via their outputs, they switch (ÜW_V0.../ÜW_V10) the

solenoids to - 12V (SV_N12LV). In high-impedance state of the transistors, the valves are

switched off.

Here, there is also a check as to whether the desired switching operation has been at least

electrically executed, or not. For this, there are, in parallel to the outputs of transistors

T0...T10, the control inputs of the optical couplers (IC 18...IC20) are switched via RLC

63

components. When the transistors are in off status low current flows through each solenoid,

which, however, suffices to activate the optical coupler. This signal is transmitted via the bus

drivers IC13 and IC14 and the MC bus signals (MC_D0 ...MC_D10) to the MC. When the

MC generates a control signal for actuating the solenoids, a check is run by the MC after a

transient period of about 10 ms, whether the respective valve has actually been switched. This

provides information on the electrical functional capability of the path, MC - ÜW - valves –

MC, including the respective software.

The emergency air valve is of particular importance among the solenoid valves, as it is not

activated via the bus, but by the alarm automaton and the WD automaton. The emergency air

valve can only be actuated when all units are functioning properly and do not signal a

malfunctioning.

The logic equations for activating the emergency air valve can be found in the operational

diagram.

4.4.3 Sensor Module

The sensor module is a circuit board on which all sensors necessary for the proper functioning

of the Stephanie are mounted, including their respective electronic components. They are the

following:

1 Differential pressure sensor for measuring volume flow,

2 Pressure sensors for ventilatory pressure (HCMX100),

3 Thermistor amplifier for measuring ventilatory-gas temperature,

1 Instrument amplifier,

2 Amplifier.

4.4.3.1 Signal Designations

Operating voltages

SV_P12LV, SV_P12, SV_N12, SV_0V

64

Input signals

MC_UDAC2 MC: DAC-Signal 2

/ÜW_VPNT ÜW: zero point valve PNT ON

GG_UIn1 GG: analogue input 1

GG_UIn2 GG: analogue input 2

GG_Ures1 GG: analogue reserve input 1

GG_Ures2

GG_Rth11 GG: Thermistor 1, terminal1






Output signals

SM_UP1 SM: voltage, pressure 1

SM_UP1Out SM: k. fixed voltage, pressure 1

SM_MP1 SM: measuring pt. 1 (refer. voltage 1.23 V)

SM_UP2 SM: voltage, pressure 2

SM_UFlow SM: voltage, volume flow

SM_UFlowOut SM: k. fixed voltage volume flow

SM_UOut1 SM: output voltage 1

SM_UOut2 SM: output voltage 2

SM_UTemp1 SM: voltage, temperature sensor 1



SM_Ures SM: voltage, reserve

GG: analogue reserve input 2


The functioning of the sensor module is discussed in the following on hand of the operational

diagram FP_SM.

65

Differential pressure sensor

Determining the volume flow is carried out pneumotachographically, whereby the volume

flow to be measured flows through a pneumotachograph head (PNT) and the resulting fall in

pressure above the PNT (the difference between proximal and distal pressure) is converted

into an electrical signal by a piezoresistive differential pressure sensor. The differential

pressure sensor as well as the two sensors for measuring the ventilatory pressure are, from a

pneumatic view, symmetrically arranged. This is necessary so that the ventilatory pressure

does not impede the measurement of the volume (common mode pressure suppression).

The proximal supply pressure P1 reaches, via a distributing manifold, to the proximal

pressure sensor (sensor 2) and via the solenoid valve (valve 2), to the pressure inlet of the

differential pressure sensor (sensor 1).

In the same way the distal supply pressure P2 reaches, via a second distributing manifold, the

distal pressure sensor (sensor 3) and via the solenoid valve (valve 1), the second pressure inlet

of the differential pressure sensor.

The output signal of the differential sensor (sensor 1) is amplified by the instrument amplifier

U1 and is resident at the output as signal SM_UFlow.

A second amplifier A1D provides a short circuit-proof signal SM_UFlowOut for connecting

external equipment.

Bridge supply current for the differential pressure sensor is generated by the reference voltage

source (A1A) in connection with amplifier A1B.

Solenoid valves Valve1 and Valve 2 are electrically actuated in order and switch in

deactivated state a respective pressure inlet of the differential pressure sensor to ambient air.

During normal operation the valves are switched on (/ÜW_VPNT= -12V) and connect the

pressure inlets of the differential pressure sensor with the pressure port for the proximal and

distal pressure.

During a periodical zero point correction, the valves, via the signal /ÜW_VPNT, are

switched off for the duration of approximately 50 ms and the pressure inlets of the differential

pressure sensor are switched over to ambient air. The microcomputer measures the ouput

voltage SM_UFlow and in a compensating procedure, via the control signal MC_UDAC2, the

bridge zero point is modified until SM_UFlow Null reaches zero.

66

Pressure sensors for ventilatory pressure

The output signal of the proximal pressure sensor (sensor 2) is amplified via amplifier A2B (

V=2) to signal SM_UP1 and via a second amplifier A2A (V=1) short circuit-proof to signal

SM_UP1Out.

The distal pressure signal of sensor 3, however, is only converted via amplifier A2C (V=2) to

signal SM_UP2.

The pressure voltage transfer function is:

U/V = 1 + 0.04 * P/mbar.

Thermistor amplifier (temperature measurement)

The instruments amplifiers U3 to U5 form, in connection with the reference voltage source

(MP1) and the bridge resistors R11..R15, a resistive voltage converter by means of which the

signals of the externally located temperature sensors (thermistors) are converted to electical

voltages (SM_UTemp1, SM_UTemp2, SM_UTemp3). The temperature voltage transfer

funtion is:

U/V = 2 + 0.1 *(T/°C - 20°C).

Discrete amplifier (Reserve)

The instruments amplifier U2 enables the amplification of a random signal by the factor

V=100. (use for the measurement of FiO2 in Pulmostar)

Both amplifiers A1C (V=2) and A2D (V=1) are for reserve purposes.

4.4.4 Power amplifier


Voltages

SV_P12, SV_N12, SV_P12LV, SV_N12LV Operating voltages

Input signals

WM_I1PSD1 WM: current 1 from PSD 1

67




MC_UDAC1 MC: Analogue voltage 1

MC_LVEin MC: power amplifier ON

Output signals

LV_USum1 LV: cumulative voltage of positional transd. 1

LV_USum2 LV: cumulative voltage of positional transd. 2

LV_Us1 LV: voltage, path 1

LV_Us2 LV: voltage, path 2

LV_UEDA1 LV: output voltage 1 for EDA

LV_UEDA2 LV: output voltage 2 for EDA

4.4.4.2 Operational function

The power amplifier amplifies the analogue signal supplied by the microcomputer (MC) and

through that controls the moving-coil (electrodynamic) actuation (EDA) for the ventilatory

valve.

In addition, electronic components are on the circuit board for two positional transducers, by

means of which the exact position of the valve piston is determined and with that, via path

feedback, the natural frequency of the EDA can be significantly increased.

Explanatory note on the positional transducer system (Wegmeßsystem/WMS)

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The actual positional transducer system is found on the right sidewall of the Stephanie. It

consists of two position measurement paths, each of which are formed by a luminescence

diode (LED), an optic system and a position sensitive device (PSD). The lightband generated

by the LED and optic is covered by the PSD opposite a crevice located on the valve piston, so

that at the point of the crevice only a narrow light spot appears on the PSD. This spot of light

generates two photoelectric currents, the strength of which both in intensity as well as the

position of the spot of light on the active surface of the PSD can be determined.

The following explains the principle of signal processing. Definitions are

l: Length of the active path of the PSD

x: Position of the lightspot on on the PSD with reference to the initial starting point

I1: Current 1

I2: Current 2,

L: Photo-current of the lightspot.

Equations for the photo-currents:

I1 = k * L * x/l; I2 = k * L * (1-x)/l (Eq1)

Resulting cumulative currents:

Is=I1 + I2 = k * L * 1/l (Eq2)

and the differential current

Id = I1 - I2= k * L * (1-2*x)/l (Eq3)

When the quotients are formed from Id and Is, one receives

69

S = Id/Is = 1 - 2*x. (Eq4)

According to this, the Eq. 4 signal obtained is only proportional to path x and within a certain

range independent of photo-current and physical properties of the PSD.

The following description of circuit design refers to positional transducer system WMS 1.

The operational function of WMS2 is the same.

The photo-currents WM_I1PSD1 and WM_I2PSD1 are converted by amplifiers A1A and

A1B, in connection with resistors R1 and R2, into current-proportional voltages. A1C forms

the sum Us and A1D the difference Ud of these currents. The analogue division curcuit A2

then realises Eq.4 by quotient formation of Us and Ud. Its output signal LV_Us1 is a

measurement for the position of the lightspot on the PSD and is therefore proportional to the

path travel (position) of the piston..

Signal LV_Usumm1 corresponds to the 0.33 fold cumulative voltage after A1C. It serves to

monitor the optical path of the WMS. By means of the adjuster ER1, the electrical zero point

of WMS can be shifted.

The setting of the transfer function of WMS is fixed at U/V = 2 * s/mm, i.e. 1mm travel

difference corresponds to a voltage difference of 2 V.

Power amplifier

The actual power amplifier (LV) is realised by a TDA 2050 (A6). In connection with the

feedback resistors (R33, R41) it has for the input signal an amplification of V=13.6. Input

resistor R33 is, via relay REL1 in its activated state, switched to control input MC_UDAC1

and in deactivated state, via R40, switched to the output of A6. The activation of REL1 is by

means of transistor T1 and the control signal MC_LVEin. The sense of this circuit is that for

reasons of load, the LV and therewith the EDA are only activated when necessary. In certain

emergency situations or when using the Stephanie as a pulmonary-function unit, the LV is

switched off by the MC via the signal MC_LVEin=LOW. This means that the LV can no

longer be activated via its input, and the output current through EDA sinks to values less than

30 mA, which no longer create thermal load.

70

Travel feedback

The output signal of positional transducer 1 is led via a transfer link with PD behaviour (A5A,

A5B) to a further control input for the power amplifier. Der P-part carries back a travel-

proprtional part, and the D-part a speed-proportional part. Via the travel-proportional part, the

overall transfer factor of LV and EDA, concerning travel, and via the speed-proportional part

(ER3) the attenuation can be stipulated. Due to the high loop amplification of this system, the

transfer function LV-EDA is practically only dependent on that of the positional transducer

system, and results

s / Uein = 1 / KWMS = 0.5 mm/V.

This achieves, that, independent of intraindividual parameter fluctuations between the

individual moving-coil actuators, a constant transfer behaviour of the valve actuator is

ensured. That is to say, a change in voltage of MC_UDAC1 by 1 V leads to a change in

position of the EDA of 0.5 mm.

By means of the ER4, an additional stability of the system can be influenced at high

frequencies.

Safety observations

Since the positional transducer system is designed as a dual system, one system is for the

feedback, a second is for checking the system.. Thanks to the good coordination between the

control voltage of the MC (MC_UDAC1) and the position of the control valve, a check can be

run, via the second positional transducer system, as to whether the desired position has

actually been achieved. This comparison check takes place in the MC. This monitoring check

is very complex and entails the entire path MC - LV - actuator – control valve - MC. Its

operational function is: within a certain temporal and voltage error span, the MC checks

whether the generated control voltage of the MC agrees with the voltage of positional

transducer system 2. In the case of deviation, an alarm with high priority is triggered along

with activation of the emergency air system.

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4.5 Power Supply

4.5.1 Power supply module


Voltages:

SV_P5, SV_P12, SV_N12 Operating voltages for the computers

SV_P12LV, SV_N12LV Operating voltages for power amplifier and valves,

SV_P24 Intermediate circuit voltage (24...28V)

SV_HEIZ1 Activated voltage for heating and humidifier,

SV_Heiz2 Activated voltage for hose heating

Monitoring signals:

SV_PG Power good signal of computer voltages

SV_PGLV Power good signal of LV voltages

SV_Netzok Mains voltage is OK

SV_Akkok Battery voltage is OK

SV_AkkLow Battery voltage is less than 20 V

Control voltage:

MC_SD MC: Shut down

/BE_SBER BE: switch position not ready

MC_HEIZ1 MC: Heating 1 ON

MC_HEIZ2 MC: Heating 2 ON

/UW_NL ÜW: emergency air valve not activated

Switch signals

SV_S1a, SV_S1b Switch contact of mains power switch

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4.5.1.2 Operational function

For an explanation of the operational function, see Appendix 7.2: Operational Diagram

FP_SV.

Voltage generation

The input voltage of 220 V is led, via the fuses and the mains power switch to a primary

voltage regulator. If the signal is MC_SD=LOW, it generates an intermediate circuit voltage

of 24 V...28 V (otherwise it is zero). At the same time the charging current for the 24 V lead

battery is generated and the battery is charged.

In the case of /BE_SBER =HIGH, the secondary voltage regulators for the computer voltages

and the power amplifier are switched on.

A contact of the mains power switch is on the outside.

Substitution switch of the battery voltage

If there is a power failure during operation on mains power supply (SV_Netzok=LOW), the

intermediate circuit voltage through the primary regulator becomes zero, and the battery

voltage (24V) is switched via a MosFet to the intermediate circuit. This ensures that there

continue, with no break, all output voltages of the power supply.

Only the heating is not supplied with current during a power failure.

The battery voltage is monitored for compliance within certain voltage parameters and its

state is determined via the respective signals.

Heating voltage generation

The voltages for respiratory gas humidifier and hose heating are obtained via the power-

MosFets directly from the intermediate circuit voltages. Prerequisite for provision of these

heating voltages is that the mains power is on and the systems monitor does not detect an

emergency air situation (SV_Netzok * /UW_NL=HIGH). If this is the case, heating voltages

1 and 2 from the MC can be switched via signals MC_Heiz1,2.

4.5.2 Battery Module

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The battery module is made up of a 24 V rechargeable lead battery, of which the output

voltage (AM_P24) is secured by a 4 A fuse, and is led to the identical inputs of the power

supply module.

4.6 Valve Actuation

The valve actuation is realised by a moving-coil converter similar to that of a loudspeaker.

The drive coil is held by two centering diaphams and is frictionlessly guided.

This drive coil is closed in the direction of the ventilation valve unit by a plate, on which a

small magnetic clamp (D=8.5 mm) is stuck. This magnet forms, in connection with the soft-

iron plate on the valve piston, the mechanical coupling between the valve actuator and the

ventilation valve unit.

When the patient component is connected to the housing, both parts come into magnetic

contact and form a tight hysteresis-free mechanical coupling.

The executed positional feedback, in connection with the valve actuator, has already been

explained in Section 4.3.4. In addition, it allows to check the integrity of the connection

between the valve actuation and the valve piston.

The assembly of the valve actuation is carried out within the unit, whereby using an

adjustment gauge, the adjustment of the position of the positional transducer and the

ventilation valve unit can be conducted.

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5 Safety Concept

5.1 General

The safety concept for the Stephanie is so designed, that it detects a simple error and even in

the case of a double error, switches the ventilator over to a status where the patient is not at all

endangered.

At this stage of development we understand the status of "fail save"; that means that the

patient is secured by the safety valve being activated and this allows the patient to

spontaneously breathe ambient air.

Depending on the cause of the error or malfunctioning, and in line with EN 475, the unit

introduces various forms of visual and audible error signalling and corrective action.

Causes of error and malfunctioning are various. These can be:

• Unit defect of the ventilator des Ventilators (break-down),

• Faulty use of the unit (e.g. disconnection),

• Threatening situation on the patient's side (e.g. apnea),

5.2 Safety Design of the Ventilators

Concerning safety design, the Stephanie is structured as a dual-channel system. The diagram

shows that the microcomputer (central control) and the PC module almost completely, but

independent of one another, take over the mandatory monitoring parameters of the unit and

patient, and when errors are detected trigger audible alarms as well as introduce corrective

action.

In addition, many functional units such as actuator, audible alarming, valve control, etc., are

subject to very complex selftests, the functioning of which has been described in the

respective sections.

Furthermore, the test function of the Stephanie, that must be conducted before using the unit

on the patient, provides a very comprehensive test of the unit. After the test has been

successfully carried out, the unit, based on reliability predictions, can be classified as being

new equipment (prerequisite: constant failure rate).

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5.3 Mandatory Parameters to be monitored and tested

According to DIN EN 794, the mandatory parameters to be monitored and tested are:

1. Functional capability of the equipment.

2. Operating voltages

3. Gas pressure of the central respiratory gas supply

4. Alternative or reserve power supply

5. Inspiratory oxygen concentration

6. Air-passage pressure

7. Minute volume

8. Disconnection

9. Apnea

10. Respiratory gas temperature

5.4 Adjustment and Treatment of Limit Valves

5.4.1 General

The mandatory limit values to be monitored are preferably set by hand (see Operating

Instructions). This has the disadvantage of being time-consuming compared with

automatically set defaults dependent on the preset ventilation parameters. On the other hand,

it has the advantage that a mistakenly false setting of these parameters triggers an alarm, thus

avoids any endangering of the patient.

After the unit has been switched on, limit values are set according to the setup routine.

5.4.2 Pressure

During machine ventilation, the respective peak pressure is monitored in relation to upper and

lower limit values.

During proper functioning of the pressure loop, the upper limit value will normally not be

reached.

Pressure falling below the lower limit value, in the case of disconnection or in comparison to

the preset value of Pmax and VT, will result in "soft lung".

Setting Limit Value

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Setting the limit value is carried out manually.

Setup: Pgob = 30 mbar,

Pgun = 10 mbar.

Error corrective action

Pgob-Alarm:

Visual: "Peak pressure too high !!!"

Audible: HP-Warning tone

Technical: opening of safety valve

Pgun-Alarm:

Visual: "Peak pressure too low, Disconnection ?"

Audible: Warning tone

Technical: no response.

5.4.3 Respiratory Minute Volume

The expiratory minute volume V'ex is monitored in all modes of operation.

Approximately 15 s are selected as a monitoring timeframe.

Setting limit values

Manual setting,

Setup: V’max = 2 l/min,

V’min = 0.2 l/min

Error corrective action

Visual: "Minute volume too low ! Disconnection?"

" Minute volume too high !"

Audible: HP- or MP alarm,

Technical: none

5.4.4 Insp. O2 concentration:

Since a pneumatic mixer is used, the actual preset value is recorded by coupling the mixer

rotary head with an transmitter (Potentiometer).

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The voltage value, corresponding to the potentiometer setting, is the target value, and is

compared to the actual value which is measured by the O2 sensor.


Manual setting,

Setup: FiO2 ob = 50%

FiO2un = 20 %.

5.4.5 Temperature


Setting limit values is carried out manually.

Setup: Tun = 33 °C,

Tob = 38 °C.

Error corrective actions

Visual: " Respiratory gas temperature too high!"

„ Respiratory gas temperature too low!“

Audible: MP - Alarm for a temperature >= 40°C

Technical: For excess temperature > 41 °C longer than 2 min., heater is switched off.

5.5 Alarm Response

5.5.1 General The individual alarm ratings correspond to, in line with DIN EN 475, the various alarm

responses regarding the audible and visual alarm signals as well as the response of the safety

system.

In line with this, there is a distinction between alarms of medium priority and those of high

priority. An alarm of at least medium priority (MHP) means that the alarm begins as medium

priority and then goes over to an alarm of high priority.

The safety system responds by switching off the emergency air valve ( /ÜW_NL), the two

valves for compressed air (/ÜW_VPL) and oxygen (/ÜW_VO2), the central gas supply as

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well as the injector valve (/ÜW_VInj1, /ÜW_VInj2). In this event the patient can at least

spontaneously breathe ambient air.

Visual alarm signalling is via alphanumeric display on the monitor screen. In the event of an

alarm of low and medium priority, it is yellow, alarms of high priority are displayed in red.

Alarm situations that have ended, but have not yet been acknowledged, are displayed in

green.

5.5.2 Alarm suppression

The audible components of alarms of high and medium priority can be suppressed for the

duration of 2 minutes by pressing the "Alarm mute" key.

This suppression applies, however, only for current alarms. When the cause triggering the has

been, in the meantime, remedied, but recurs before this suppression elapses, it is treated as a

new alarm. This also applies to alarms arising due to other causes.

The status of the audible alarm suppression is visually displayed.

5.5.3 Status graphic of the alarm system The behaviour of the alarm automaton can best be described by means of a status graphic.

This also applies to those of the MC and PC..

(Graphic) Glossar

MPALneu MPALneu

MP-OptAnzeige

Gelb

Grün

MP-OptDisplay

Yellow

green

MP-Signalton MP-Signal tone

Kein Alarm No alarm

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Kein Alarm

HP-SignaltonHP-OptAnzeige

(rot)

HP-OptAnzeigeHPAL : rot

/HPAL : grün

HPAL_neu + HPAL_old*Tmute

/HPAL* Mute

/HPAL

MPAL + MHPAL

MP-SignaltonMP-OptAnzeige

MP-OptAnzeigeMPAL: gelb/MPAL: grün

MPALneu +MPALold*Tmute

/MPAL

MHPALold*Tmhp + HPALneu

HPAL/MPAL* Mute

Mute

Mute

HPAL

The status graphic describes the transitions between the individual states/statuses depending

on the kind of (MP, MHP, HP) as well as temporal occurance and the effect of T-Mute key.

The designations in the nodes denote which action is taken during a particular status. The

edge lines represent the condition under which a status transition occurs..

In detail:

HPAL: presence of a HP-Alarm condition

MPAL: presence of a MP-Alarm condition,

MHPAL: presence of a MHP-Alarm condition,

Tmute: Alarm-Mute duration has elapsed,

Mute: Activation of Mute key

Tmhp: Time for transition from a MP-Alarm to HP-Alarm.

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5.5.4 Alarm table The following is a table of Alarm Events evaluated by the Stephanie.

To apply this table:

The alarm designation is identical to the visual alarm message.

The category designates the priority of the alarm (MP, MHP, HP) including the kind of

audible signalling.

Columns 5 and 6 refer to the particular monitoring unit.

The column "Condition" refers to the condition that triggered the alarm event.

The various responses of the safety system are listed in the last column. Definitions

• Safety status 1: the switching off of all valves, including the emergency air valve, so that

the patient can breathe ambient air or be manually ventilated.

• Safety status 2: For CMV ventilation with standard values for CPAP mit PEEP = 2mbar.

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No. Alarm designation Rating Monitoring. Condition Safety system response

Primary energy supply

1 „Mains power failurel“ MHP MC PC /SV_Netzok

2. „Compressed air failure“ MHP MC PC P_Pl < 2.8 bar

3. „Oxygen failure“ MHP MC PC P_O2 < 2.8 bar

4. „Primary gas failure“ HP MC PC (P_Pl < 2.8 bar) & ( P_O2 < 2.8 bar) Stage 1 (all valves OFF)

5. „Respiratory gas failure“ HP MC PC P_120 < 70 mbar Stage 1

6. „Battery discharge“ HP MC PC RV_AkkuLow & /SV_NetzOk Stage 1

Ventilatory parameters

7. „Peak pressure“ When Plim_max is reached for longer than

0.1 s for MC and for longer than 0.2s for

PC

MC switches after 0.1 s to

PEEP level.

PC switches off emergency

air after 0.2s

8. „Cont. high pressure“ HP MC PC Pmean > Pmean lim for longer than 15 s /V_NL for 1sec. After that

start of new inspiration.

Max. 3 attempt, then

/V_NL,/V_PL, /V_O2,

9. „pressure low, Disconn ?“ MHP MC PC Pendinsp < Pmax during machine

inspiration

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No.

Alarm designation Rating Monitoring. Condition Safety system response

10. „AMV high“ MP MC PC Amv > AMV lim max

11. „AMV to low“ MHP MC PC AMV < AMV lim min

12. „Apnea“ MHP MC PC no inspiration start within 15 s

Respiratory gas conditioning

13. „FiO2 too high“ MP MC PC FiO2 > FIO2 lim max

14. „FiO2 too low“ MP MC PC FiO2 < FiO2 lim min

15. „ Temperature too high“ MP MC PC Temp > Temp lim max

16. „ Temperature too low“ MP MC PC Temp < Temp lim min

17. „Temperature > 41°C“ MHP MC PC Temp > 41°C Heating OFF

Hardware error

20. „Controller error “ HP ÜW PC watchdog error Safety status 1

21 „PC error „ almost imposs.. HP ÜW MC watchdog error Safety status 1

21. „Valve error n “ MHP MC No electrical response of valve n

22. „Potentiometer n“ HP MC Potentiometer makes no contact Safety status 2

23. „power supply error“ HP MC,

ÜW

PC /SV_PG + /SV_PGLV Safety status 1

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6 Failure Mode Analysis

6.1.1 Control Unit

The failure mode analysis for the control unit is found in the following table.

No. Failure/error type Detec.. Explanation

F_BE1 Contact error of the contact of

the Pot. und Schalter

yes see 1 and 2

F_BE2 LED defect yes Detection during unit selftest

F_BE3 Incr. transmitter Tex defect ja no reaction of expiration time to

change in IGR. Detection also during

unit selftest.

F_BE4 Line break in databus yes see 3.

F_BE5 Keys defect yes see 4.

F_BE6 Incr. transmitter monitor

defect

yes No reaction of menu bar to change in

IGR. Detection also during unit

selftest.

F_BE7 Display screen defect yes Detection during operation and during

unit selftest.

1. The potentiometer and switch receive a primary voltage that is 90% that of the reference

voltage. In addition, all ADU inputs are connected, via high-impedance resistors, with the

reference voltage. In the case of line break or interruption in the contact, the ADU

measures the primary voltage, which is evaluated as a nonplausible setting and thus as an

error. In this event, the new value is not accepted, the unit continues to operate with the old

value, however, it triggers a HP alarm with error description.

2. During the unit selftest, all settings of the potentiometer and switch are displayed in a

menu item. These settings are to be confirmed by the tester.

3. Only the databus lines MC_D0...MC_D9 are used. During the unit selftest all LEDs are

switched on and off, and the numeric display is activated. Thus, and in connection with

point 2, the entire databus is tested. This must be confirmed by the tester.

4. During the unit selftest all keys must be tested and the response of each checked by the

illumination of the respective LED. In this fashion, a complete check, including the

respective component of the microcomputer necessary for this function, is carried out.

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By means of this test, all errors possibly occuring in the control unit can be detected.

pediatric ventilator stephaniepediatric ventilator stephanie technical manual january 2003 1. ......

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