Non-contact thermometers – emissivity

Introduction

When working with non-contact thermometers the key term is emissivity ε. It

is defined as “the relative power of a surface to emit heat by radiation; the ratio of the

radiant energy emitted by a surface to that emitted by a blackbody at the same temperature”

[1]. The user needs to be aware that a non-contact thermometer is not measuring

temperature but radiated energy. In order to show temperature, the emissivity of the

measured object has to be known and correctly set on the thermometer. The purpose of this

experiment is to estimate emissivity of different surfaces and to estimate the error caused by

the wrong setting of emissivity (or fixed – some IR thermometers don’t allow to change

emissivity).

Tasks:

1. With contact thermocouple and

IR thermometer with fixed

emissivity 0.95 determine

emissivity of different surfaces.

2. Calculate absolute and relative

error of temperature reading

caused by the different

emissivity of the object.

3. Make a thermo graphic image

of the Al heat sink with the

thermocamera.

Used instruments:

Fixtures with resistors on a heatsink, Peltier element

IR thermometer with fixed emissivity 0,95

Multimeter Axiomet AX-18B with surface thermocouple probe

Thermocamera FLIR i50

Power supply 18210

Procedure description – gauge factor

The radiation of a black body is described by the Planck’s law as shown in Fig. 1 [3].

It relates the spectral radiance of a black body (the quantity of radiation) with its temperature

and wavelength of the radiation.

A blackbody emits total radiant power WB into a surrounding hemisphere given by [4]

4

BW T (1)

Where σ is Stefan-Boltzman constant and T is temperature in Kelvin.

Any other body can be characterized by a dimensionless parameter - emissivity

/ BW W (2)

Fig. 1 – Black body radiation [3]

It is the fraction of black body power emitted in the surrounding hemisphere.

Emissivity depends on the surface of the body and on its temperature. By definition it is 1 for

a black body.

The black body is an idealized concept. Real objects do not absorb all incident energy,

some part is reflected. They behave like gray bodies. Theirs emissivity is ε<1.

In order to correctly measure temperature

with an IR thermometer, the emissivity of the

measured object has to be known.

The method used here consist in measuring

the real object temperature with a contact

thermometer (thermocouple in this case).

The used IR thermometer has a fixed setting

of emissivity 0.95. Therefore its reading is correct only for this emissivity. The IR

thermometer measures the radiated energy 4

0,95 0,95IRW T (3)

Where T0,95 is the temperature shown on the IR thermometer with fixed emissivity

0,95.

The object radiated energy is a function of its temperature Tobj. 4

. . .obj obj objW T (4)

In order to determine object emissivity εobj. the object temperature Tobj. is measured with a

contact thermometer.

Then the object emissivity εobj. can be calculated as [5] 4

0,954 4

. . 0,95 0,95 . 0,95 4

.

obj obj obj

obj

TT T

T (5)

The temperatures have to be substituted in Kelvin!

Conclusions

In conclusions state the precision of thermocouple measurement from multi-meter

manual, discus the effect of accuracy on emissivity calculation. Also find the accuracy of

reading of the IR thermometer.

References

[1] Emissivity, online on <http://www.merriam-webster.com/dictionary/emissivity>,

accessed on 11.3.2013

[2] Emissivity Coefficients of some common Materials, online on <

http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html>, accessed on

11.3.2013

[3] Planck's law, online on < https://en.wikipedia.org/wiki/Planck's_law>, accessed on

11.3.2013

[4] Chandos, R. J., Chandos R.E. : Radiometric Properties of Isothermal Diffuse Wall

Cavity Sources, online on < http://www.electro-

optical.com/pdf/chandosemissivitypaper.pdf>, accessed on 11.3.2013

[5] A Review of the Physics for Emissivity Correction of Infrared Temperature

Measurements, online on < http://www.apogeeinstruments.co.uk/content/SI-

emissivitycorrection.pdf>, accessed on 11.3.2013

material Emissivity

Al – not oxidized 0,12 – 0,18

Fe - shiny 0,32 – 0,42

Cu 0,1 – 0,35

Graphite, coal 0,65 – 0,97

Ideal black body 1

Non-contact thermometers – IR

thermometer and camera

Introduction

Non-contact thermometers can be used to measure very high temperatures

impossible to be measured in a different way. However the user needs to be aware that a

non-contact thermometer is not measuring temperature but radiated energy. It is not a

simple point and measure device. Precautions need to be taken with IR thermometers. The

purpose of this task is to show their basic properties that need to be considered in order to get

a correct reading. The same rules apply for a thermo camera.

Tasks:

1. With the contact probe of IR thermometer

determine emissivity of the black, white

and silver surfaces on the test plate.

2. Measure the temperature distribution on

the plate for 2 given configurations of

heat sources (sources 1,2 or 3). Plot in a

surface plot. On each colored surfaces, set

the correct emissivity.

3. Take an image of the test plate with the

thermocamera

Used instruments:

Heated plate with Peltier elements

IR thermometer Fluke 576 + PC with software IRGraph

Thermocamera FLIR i50

Power supply Diametral P230R51D

Procedure description

The IR thermometer measures a sum of energies. The energy as seen by the IR

thermometer is composed of emitted energy (function of object temperature), reflected

energy, transmitted energy (energy passing through the object) and absorbed energy (not

shown in Fig. 2 – the energy absorbed between the object and IR thermometer – for small

distances, this can be neglected).

The emitted energy is a function of temperature as given by Planck’s law. In order to

measure the radiation of a body correctly emissivity has to be known. One possibility how

to measure emissivity was shown in the previous experiment.

When the IR thermometer has a possibility to adjust the emissivity, like the one used

here also the following procedure can be used.

1] Measure the object temperature with a contact probe of the IR thermometer.

This usually is a thermocouple, type K in our case.

2] Measure the temperature with the IR thermometer in the same spot, adjust the

emissivity on the IR thermometer until both temperature readings are the same.

Fig. 2 – IR thermometer measures a sum of

energies [1]

The infrared thermometer is not measuring in a single point. Its active area is a cone

with specified D: S ratio like the one shown in Fig. 3.

The further the object is apart, the bigger is the cone. The cone has to be filled

completely with the measured object in order to obtain a correct reading – Fig. 4. When the

object is not filling the whole cone, the IR thermometer measures partially the radiation of the

background and therefore the reading will be false.

For the used IR thermometer Fluke 576, the optical chart is shown in Fig. 7

Due to the used optics, the smallest spot

diameter is 19 mm for a distance of 1150 mm.

For this experiment, set the distance

1150 mm between the IR thermometer and

heated plate.

With the IR thermometer measure the

temperature in the center of each square on the

heated plate. Plot the result in a surface plot and

make a make an image of the plate with a

thermocamera.

During all experiment, consider that you are measuring a sum of radiation. The effects

of different emissivity can be significant. In Fig. 6 there is an object (a garden door) with

same temperature on its surface. There are metallic and wooded parts. As they have different

emissivity they seem to have different temperature. They also reflect differently the ambient

radiation. An example of how the reflected energy affects the result is shown in Fig. 7. This

picture was obtained on a mirror surface. The reflection is visible and masks completely the

real temperature of the object.

Fig. 3 – IR thermometer measures in a cone [2] Fig. 4 – Correct use of a IR thermometer [1]

Fig. 5 – IR thermometer measures a sum of

energies [1]

Conclusions

Assess the influence of different emissivity of the surfaces on the reading, when the

emissivity would not be set to a correct value. From the IR thermometer manual read the

accuracy of reading for both the IR and thermocouple. From response time in the manual

calculate time constant of the IR thermometer.

References

[1] Fluke 576 Precision Infrared Thermometer – Users Manual, online on <

http://www.myflukestore.com/crm_uploads/fe_576_users_manual.pdf>, accessed on

11.3.2013

[2] $15 Infrared Thermometer, online on <

http://forums.anandtech.com/showthread.php?t=2049940>, accessed on 11.3.2013

Fig. 6 – Effects of different emissivity Fig. 7 – Mirror image on reflective surface

Emissitivy Submitted by:

Task: Date: 16.1.2014

It is important to wait for steady state. Check with the IR thermometer that the temperature is constant at 1 point.

black painted Al heatsink - current 3A black painted Al heatsink - current 5A Peltier element - current 0,5A

thermocouple (°C) 39,6 thermocouple (°C) 55,1 thermocouple (°C) 60,6 20,8

IR thermometer (°C)39,2

IR thermometer (°C)56,8

IR thermometer (°C)60,9 16,7

emissivity (-) 0,95 emissivity (-) 0,97 emissivity (-) 0,95 0,8981

absolute error (°C) -0,4 absolute error (°C) 1,7 absolute error (°C) 0,3

relative error (%) -1 relative error (%) 3 relative error (%) 0

original shiny Al heatsink - current 3A original shiny Al heatsink - current 5A Heatsink thermal image:thermocouple (°C) 39,8 thermocouple (°C) 53,2

IR thermometer (°C) 24,3 IR thermometer (°C) 26,8

emissivity (-) 0,78 emissivity (-) 0,68

absolute error (°C) -15,5 absolute error (°C) -26,4

relative error (%) -64 relative error (%) -99

Resistor with heatsink - current 2A Human skin

thermocouple (°C) 94,0 thermocouple (°C) 38,4

IR thermometer (°C) 105,0 IR thermometer (°C) 35,7

emissivity (-) 1,07 emissivity (-) 0,92

absolute error (°C) 11,0 absolute error (°C) -2,7

relative error (%) 10 relative error (%) -8

Used instruments:

Conclusions:

1. With contact thermocouple and IR thermometer with fixed emissivity 0,95 determine emissivity of

different surfaces

2. Calculate absolute and relative error of temperature reading caused by the different emissivity of the

object

In conclusions state the precision of thermocouple measurement from multimeter manual, discus the effect of accuracy on emissivity calculation. Also

find the accuracy of reading of the IR thermometer.

3. Make a thermographic image of the Al heatsink with the thermocamera

4

0,95

. 0,95 4

.

obj

obj

T

Tε ε= ⋅

page 1/1

Czech Technical University in PragueFaculty of Mechanical Engineering

Department of Instrumentation and Control Engineering

Technická 4

166 07, Prague 6

Czech republic

Certificate Of CalibrationCertificate No: 1

Model name: IR-101

Manufacturer: Europe supplies Ltd.

Description: Portable IR thermometer

Temperature range: -20°C to 300°C

Serial No: Z2-02001372/000

Calibration date: 17.10.2013

Calibration due: 17.10.2014

Calibration interval: 1 year

Test report

Set value Reading Absolute error Relative error Specification

°C °C °C %

40 44 4 9,09 ±2°C nebo ±2 % (platí větší hodnota)

80 84 4 4,76 ±2°C nebo ±2 % (platí větší hodnota)

Reference standards used

Serial No Manufacturer Model Name Description Calibrated

130209108 Thermoworks IR-500

PORTABLE IR

CALIBRATOR

(BLACKBODY TARGET) 11.7.2013

Laboratory Enviroment:

Temperature: 22 °C

Humidity: 62%

Pressure: 745 torr

Distance of IR

thermometer to

calibrator 30 mm

Calibrated by: Martin Novak Date: 16.1.2014

Non-contact thermometers - IR thermometer and camera Submitted by:

Task: Date:

2. Measure the temperature distribution on the plate for 2 given configurations of heat sources (sources 1,2 or 3). Plot in a surface plot. On each colored surfaces, set the correct emissivity.

3. Take an image of the test plate with the thermocamera

It is important to wait for steady state. Check with the IR thermometer that the temperature is constant at 1 point.

Temperature distribution on the test plate - configuration 1 Emmissitity:Y/X 1 2 3 4 5 6 7 8 black 0,96

1 24,2 24,4 25,1 25,9 26,2 25,7 25,3 25,0 white 0,96

2 24,3 24,5 25,6 27,2 27,4 26,5 25,6 25,0 silver 0,96

3 24,3 24,6 26,2 29,9 33,4 28,0 26,0 25,1

4 24,2 24,7 26,1 29,3 33,9 28,8 26,2 25,2

5 24,1 24,5 25,3 26,6 27,7 26,6 25,6 24,9

Temperature distribution on the test plate - configuration 2

Y/X 1 2 3 4 5 6 7 8 Used instruments:1 24,4 24,4 24,6 24,7 25,1 25,6 26,2 26,8

2 24,8 24,8 25,9 25,0 25,2 26,2 27,5 28,3

3 25,6 26,3 26,6 25,9 25,3 26,5 30,3 32,0

4 26,0 27,7 30,5 26,5 25,9 27,3 30,4 33,5

5 25,7 26,6 27,2 26,2 25,8 26,6 28,1 29,0

Charts:place charts on separate sheet

Conclusions:

1. With the contact probe of IR thermometer determine emissivity of the black, white and silver surfaces on

the test plate.

Assess the influence of different emissivity of the surfaces on the reading, when the emissivity would not be set

to a correct value. From the IR thermometer manual read the accuracy of reading for both the IR and

thermocouple. From response time in the manual calculate time constant of the IR thermometer.

Non-contact thermometers - IR thermometer and camera charts:

Thermocamera image: Thermocamera image:

1

2

3

4

51 2 3 4 5 6 7 8

y (-)

temperature (°C)

x (-)

Temperature distribution - configuration 1

20,0-25,0 25,0-30,0 30,0-35,0

1

2

3

4

51 2 3 4 5 6 7 8

y (-)

temperature (°C)

x (-)

Temperature distribution - configuration 2

25,0-30,0 30,0-35,0

Force – gauge factor

Introduction

One of the basic tasks in mechanical engineering is to measure force or torque.

Strain gauges are used almost solely for this purpose. There are two kinds of strain gauges.

Wire (or foil) strain gauges and semiconductor strain gauges. Wire strain gauges have lower

sensitivity but have better linearity and are not so strongly dependent on temperature like

semiconductor strain gauges. Only foil strain gauges will be used in this task. As the

resistance change with the applied force is very small, a bridge has to be used.

Tasks:

1. Determine Gauge factor K of a

foil strain gauge. Repeat the

experiment 3 times, calculate

average Gauge factor.

2. Measure and plot dependence of

bar bend on applied force y = f (G)

and bridge output voltage on

applied force V =g (G).

3. Test temperature influence – as the

last DEMO.

Used instruments:

Fixture with bar + strain gauges – ¼ bridge configuration

Geometric Quantities Measurement System – INTRONIX – NX 3030 + position

sensor (LVDT-probe ± 0,5 mm – accuracy 1 %),

Digital Precision Measuring Amplifier – SCOUT 55 + strain gauge quarter bridge

with the compensating gauge strain RK = RM = 120 Ω

The loading system with 6 pcs metal discs (0,63 kg ± 1% each)

Resistive decade Rc = 567 k Ω + R, where R … 0-100 kΩ, (1%).

Procedure description – gauge factor

Resistive strain gauges change electrical resistance R with applied strain. Strain is the

relative elongation ε = Δl/l. The basic resistance R for a strain gauge without load is typically

120 Ω.

R lK

R l

(1) Where K is so called “gauge factor” (“the deformation

sensitivity” – the main gauge strain parameter).

The experiment is shown in Fig. 2. The fixture is arranged so as to apply a constant

bending torque M0 between supports. The relative elongation of bar surface filaments can be

calculated as

2

0

0 4

r

yh

EW

M

l

l

(2) Where y is the bar deflection, E is Young's modulus and h,

b, r are bar dimensions.

Fig. 1 - Strain gauge bridge

Equation (2) is valid for a rectangular

bar as

,6

2

0

bhW (r >>y) (3)

8

12

0rM

EJy (4)

3

12

h bJ (5)

A shunt resistor Rc is connected in

parallel to the strain gauge – Fig. 1,

the change of resistance ΔR is

(parallel combination of resistance)

0

2

0

0

00

RR

R

RR

RRRR

cc

c

(6)

As the value of Rc is known, by substituting into (1) the gauge factor K is 2

0

0 4c

R rK

R R yh

where R0 = 120 Ω (7)

The procedure is the following (repeat this experiment 3 times):

1) Apply a known load - all 6 disks = 6x 0,63 kg, measure the bar deflection on

the – INTRONIX – NX 3030 system and the bridge output voltage from the SCOUT 55

system. Don't forget to note the initial bar deflection when the beam is unloaded. Use

this as a reference (ZERO) value.

2) Remove the disks and achieve the same bridge output voltage by connecting a

parallel resistor (decade) to the stain gauge - shunt resistor Rc.

Procedure description – dependence on bend

Apply gradually 0 to 6 disks to the beam and measure the bar deflection and bridge

output voltage. Then gradually remove the disks, measure again in order to determine if there

is any hysteresis.

Conclusions

Calculate sensitivity for dependence of bar bend on applied force y = f (G) and bridge

output voltage on applied force V =g (G). Assess the influence of temperature and the

importance of temperature compensation.

Fig. 2 – Gauge factor experiment

Force – ¼ and ½ bridge

Introduction

¼ bridge uses one sensor. In order to increase sensitivity 2 sensors can be used

in a ½ bridge configuration. As it was seen from the previous experiment, there is a high

dependence on temperature for a strain gauge. It is primarily working as a thermometer and

only when we correctly compensate for temperature changes, it is measuring strain.

Therefore, a temperature compensation strain gauge has to be used at all times. It is the

same strain gauge type, on a same temperature, but not loaded with the measured strain. For a

½ bridge 2 temperature compensating strain gauges have to be used.

Tasks:

1. Determine sensitivity of ¼ and

½ strain gauge bridge

configuration.

2. Compare sensitivities for

compressive and tensile stress

– compare sensitivities in the

I. and III. quadrant. Interpolate

with a straight line with the

linear regression method

Used instruments:

2x fixture with strain gauge half bridge, R0 = 120Ω ± 0,35 ‰, K – factor 2,08 ± 1%,

type 10/120 LY 11 for the steel

Precision Measuring Amplifier – SPIDER (acc. class 0,1)

PC with software for SPIDER amplifier

Procedure description

The condition of bridge balance is

3241 RRRR (8)

When the bridge is balanced, the output voltage Uv = 0

¼ bridge has 1 measuring strain gauge + 1 compensating in the neighboring branch

½ bridge has 2 measuring strain gauges + 2 compensating strain gauges

Theoretically it has a double sensitivity compared to ¼ bridge, the compensating

gauges have to be placed:

- In opposite branch – if the measuring gauges measure the same stress (tensile –

tensile, or compressive – compressive)

- In neighboring branches – if the measuring gauges measure opposite stress

(compressive – tensile)

Full bridge has 4 measuring strain gauges; two have to measure tension, two

compressions. It is self temperature compensating and has theoretically 4 times

sensitivity compared to ¼ bridge.

On the SPIDER unit, the strain gauge bridges are connected to channel 4 and channel 5.

Fig. 3 – ¼ and ½ bridge configurations with temperature

compensation

4th-channel = ½ bridge (in reality it is a full bridge, only 2 strain gauges are active

in this task), configuration name is TEN55 in the software

5th-channel = ¼ bridge (in reality it is a full bridge, only 1 strain gauge is active in

this task), configuration name is TEN55 in the software

The procedure is the following:

Change deflection with step 1 mm from – 5 mm to + 5 mm and measure bridge

output voltage Uv for both ¼ and ½ bridge.

If non-zero value appears for deflection 0 try the RESET button in the software.

DON´T SET the deflection BY MEANS of the MICROMETRICAL SCREW

ALONE!! It is not a motion screw. Instead, bend lightly the beam with a thermally non-

conductive material (pen, pencil, …) , move the micrometrical screw to the desired position

and then release the beam.

Conclusions

Compare sensitivity of ¼ and ½ bridge configurations, compare sensitivities in the I.

and III. quadrant.

Torque

Introduction

Strain gauges can also be used to measure torque. They have to be placed in a

special configuration on the object – placed under a 45° angle. Typically only full bridges are

used in order to obtain the highest possible sensitivity and to assure temperature

compensation.

Tasks:

1. Calibrate the torque sensor -

measure and plot

dependence of bridge output

voltage on applied torque

V = f(T). Use load force in

range m = (0 – 1000) g. 2. Brake the motor and with

the calibration curve

measure the torque.

Used instruments:

Fixture for torsion load with DC motor, strain gauges (full bridge) and brake

Power supply Diametral P230R51D

Digital voltmeter Agilent 34461A

Procedure description

Calibration

1) Make sure, the DC motor is unplugged from the 12 V power supply

2) Screw on the lever-arm

3) Turn on the power supply and voltmeter

4) Hook different weights on the lever arm, from weight and lever-arm length

calculate torque. The calibration curve is the dependence of bridge output voltage

on applied torque

5) UNSCREW THE LEVER-AMR

Torque

1) MAKE SURE THE LEVER-AMR IS UNSCREWED

2) Connect the DC motor to the 12 V power supply, the motor will start to turn

3) By tightening the nut on the brake, brake the motor to 3 different values of torque.

With the previously obtained calibration curve determine the torque.

Conclusions

Discuss the advantages/disadvantages of a torque sensor with rings and brushes. Find,

describe and reference one industrial sensor for measuring torque on a static (non-rotating)

shaft and one on a rotating shaft. Make a table with sensor parameters. Compare prices.

Fig. 4 – Arrangement of the torque experiment

Force - gauge factor Submitted by:

Task: Date:

2. Measure and plot dependence of bar bend on applied force y = f (G) and bridge output voltage on applied force V =g (G).

3. Test temperature influence – as the last DEMO

Gauge factor

No. FU load [

N]

y deflection

[mm]

RC = R +

567 kW

K [ - ] Kawg [ - ]

1 37,1 0,21 657 2,0596

2 37,1 0,21 652 2,0754

3 37,1 0,21 657 2,0596

dependence of bar bend on applied force y = f (G) and bridge output voltage on applied force V =g (G).

Number of used 0,63

kg discs

Applied

force G (N) ↑ ↓ ↑ ↓ Charts:loading unloading loading unloadin

gplace charts on separate sheet

0

0,000

0 0 0 0,007 0,007 0,007

1 6,180 0,008 0,008 0,008 0,041 0,041 0,041 Sensitivities:2 12,361 0,0015 0,015 0,00825 0,076 0,076 0,076

3 18,541 0,023 0,023 0,023 0,112 0,112 0,112 0,001227 (V/N)

4 24,721 0,03 0,031 0,0305 0,148 0,148 0,148

5 30,902 0,038 0,038 0,038 0,182 0,18 0,181

6 37,082 0,046 0,045 0,0455 0,217 0,217 0,217

0,0056632 (mm/N)

Conclusions: Assess the influence of temperature and the importance of temperature compensation.

average average

1.Measure and plot dependence of strain = f(T) and bridge output voltage V0 = g(T) as a

function of torsion load T on a steel tube.

2,06

Bridge output V [V] y deflection [mm]

2

0

04

c

R rK

R R yh=

+

=∆

∆=

G

Vc

F

=∆

∆=

G

ycy

Force - gauge factor - charts:

0

0,005

0,01

0,015

0,02

0,025

0,03

0,035

0,04

0,045

0,05

0,000 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000

V (

V)

G (N)

Bridge output voltage V as function of applied force G

0

0,05

0,1

0,15

0,2

0,25

0,000 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000

y (

mm

)

G (N)

Bar bend y as function of applied force G

Force - 1/4 and 1/2 bridge Submitted by:

Task: Date: ########

-5 -4 -3 -2 -1 0 1 2 3 4 5

¼ - bridge -0,48 -0,39 -0,3 -0,21 -0,12 0 0,08 0,16 0,23 0,31 0,39

½- bridge -0,98 -0,78 -0,63 -0,43 -0,24 0 0,16 0,32 0,48 0,64 0,79

Sensitivities: I. Quadrant III. Quadrant

0,078 (V/mm) 0,096 (V/mm)

0,158 (V/mm) 0,196 (V/mm)

Charts: place charts on separate sheet

Conclusions:Compare sensitivity of ¼ and ½ bridge configurations, compare sensitivities in the I. and III. quadrant.

1.Measure and plot dependence of strain = f(T) and bridge output voltage

V0 = g(T) as a function of torsion load T on a steel tube.

2. Compare sensitivities for compressive and tensile stress – compare sensitivities in

the I. and III. quadrant. Interpolate with a straight line with the linear regression method

y deflection [mm]

V [V]

=∆

∆=

y

Vc

2/1

=∆

∆=

y

Vc

4/1 =∆

∆=

y

Vc

4/1

=∆

∆=

y

Vc

2/1

Force - 1/4 and 1/2 bridge

-1,2-1

-0,8-0,6-0,4-0,2

00,20,40,60,81

-5 -4 -3 -2 -1 0 1 2 3 4 5

V (

V)

y deflection [mm]

Output voltage of a 1/4 and 1/2 bridge

¼ - bridge ½- bridge

Torque Submitted by:

Tasks: Date:

Charts:

Calibration

lever-

arm

(mm): 150

load Force Torque Voltage

m (g) (N) T (Nm) V (mV)

0 0 0,0 0,636 0,00

200 1,962 0,3 0,903 0,27

400 3,924 0,6 1,165 0,53

600 5,886 0,9 1,417 0,78

800 7,848 1,2 1,675 1,04

1000 9,81 1,5 1,930 1,29

Braking

# Voltage Torque

(-) V (mV) T (Nm)

1

2

3

Závěr:

1.Calibrate the torque sensor - measure and plot dependence of bridge output voltage on

applied torque V = f(T). Use load force in range m = (0 – 1000) g.

2. Brake the motor and with the calibration curve measure the torque.

Discuss the advantages/disadvantages of a torque sensor with rings and brushes. Find,

describe and reference one industrial sensor for measuring torque on a static (non-rotating)

shaft and one on a rotating shaft. Make a table with sensor parameters. Compare prices.

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

0,0 0,5 1,0 1,5 2,0 2,5

V0

(m

V)

T (Nm)

Bridge output voltage V0 as a function of torsional load force F

Position – LVDT

Introduction

The LVDT (Linear Variable Differential Transformer) is a linear displacement position

sensor. It transfers the movement of the transformer core into the output signal. The output signal is a

voltage signal; in your case the used sensor has build in electronics to transfer the voltage to current

output. Sensors with current output have a limit of maximal resistance that can be connected to

sensors output. The ideal load for a current output sensor is resistance zero; the maximal load is

limited by the available voltage for output. When the output loop resistance is increasing, the output

compensates by increasing output voltage so as to keep constant current. When the output is already on

the maximal voltage, the output current starts to drop. The maximal resistance connected to the current

output limits the wiring length between the sensor and gauge.

Tasks:

1. Measure and plot the static

characteristic I = f(x) for load

resistor RZ = 0.

2. For constant position (x = 100

mm) determine the maximum

value of Rz, until which the

output current remains constant

and the sensitivity of the

transducer.

Used instruments:

Fixture with LVDT

DC ampere meter

Decade resistor Rz

Procedure description

The industry standard for current output is 0 – 20 mA or 4 – 20 mA. It is defined by ANSI/ISA–

50.00.01–1975 (R2002) standard and has wide industrial usage. The advantage is that the reading is not

dependent on the wire length between the sensor and gauge. The limitation of wire length is imposed by

the connecting wire resistance and by the maximal load resistance of the transmitter.

Fig. 1 – Inside an LVDT

A typical connection of

such sensor in a controller system

is shown in Fig. 2. In order to

push a constant current through

the loop (dependent only on the

measured variable), the

transmitter is adjusting its output

voltage.

When the output loop

resistance is increasing (e.g. by

changes of temperature, oxidation

etc.), the output compensates by

increasing output voltage so as to

keep constant current. When the

output is already on the maximal

voltage, the output current starts

to drop.

Conclusions

Calculate the maximal allowed length of AWG 36 [1] copper wire between sensor and 250 Ω

load (gauge) when the ANSI/ISA–50.00.01–1975 (R2002) standard [2] defines maximal load resistance

600Ω.

Discuss advantages and disadvantages of sensors with current and voltage output.

References

[1] American wire gauge, online on < https://en.wikipedia.org/wiki/American_wire_gauge>,

accessed on 31.3.2013

[2] ANSI/ISA–50.00.01–1975 (R2002), Compatibility of Analog Signals for Electronic Industrial

Process Instruments, online on <http://www.isa.org>, accessed on 31.3.2013

[3] Understanding 4-20 mA Current Loops, Application note, BAPI, rev. 10/05/06, online on <

http://www.bapihvac.com/CatalogPDFs/I_App_Notes/Understanding_Current_Loops.pdf>,

accessed on 31.3.2013

Fig. 2 – Typical connection of current loop [3]

Position – Resistive sensor

Introduction

Resistive position sensors are simple, robust and reliable. They have a voltage output;

the ideal load resistance is infinity. Practically the load resistance should be as high as possible, so a

digital voltmeter should be used. Otherwise, the linearity of the sensors’ steady state characteristic is

compromised.

Tasks:

1. Measure and plot the static

characteristic V2=f(x) with a

digital and an analog voltmeter.

2. Compute the maximal error in

% for K=1.2 and compare with

measured value of the error

from graph.

3. Compute the value of K so that

maximal error is less than 1 %.

Used instruments:

Fixture with 5k resistive position sensor Vishay SFERNICE 115L 14E 502 W06017, 5 kΩ, 330

mm

Analog DC voltmeter, range 6 V, 1kΩ/V

Digital multimeter, Ri = 10 MΩ

5 V power supply

Procedure description

The output voltage from a resistive sensor can be calculated from the voltage divider

2

2 2

2

2 1 2 1 21

2

L

L L

L L L

L

R R

R R R RV V V

R R R R R R R RR

R R

(1)

2 0R xR 1 0 2 0 0 01R R R R xR x R 0

LRK

R

(2)

After substitution and simplification, output voltage is

2

1

K xV V

x x K

(3)

Fig. 3 – Task schematic diagram

Relative error is

2

21

% 100 1001

x xV x V

V x x K

(4)

The relative error is zero for K -> . The relative error in this case is always negative (we measure

always lower voltage than would correspond to linear dependence.

Maximal relative error is for

0 2 / 3xx

(5)

Conclusions

Find and reference at least two

industrial versions of resistive position

sensors. Make a table with range,

resistance, accuracy and price.

Fig. 4 – Influence of K on output voltage

Position – Repeatability and accuracy

Introduction

Repeatability is the closeness of the agreement between the results of successive

measurements of the same measurand carried out under the same conditions of measurement [4]. These

conditions are called "repeatability conditions". Repeatability conditions include the same measurement

procedure, the same observer, the same measuring instrument used under the same conditions, the same

location, and repetition over a short period of time. Repeatability may be expressed quantitatively in

terms of the dispersion characteristics of the results.

Tasks:

1. Determine repeatability of the x-axis

of a 3D printer. Check repeatability

in two different points; make 10

measurements in every point.

2. Calculate sample mean and standard

deviation of position in both checked

points.

Used instruments:

3D printer + PC

Variable resistance position sensor

VISHAY SFERNICE - 115L 14E 502

W06017 - TRANSDUCER, LINEAR,

350MM RANGE, 5KOHM

Digital Multimeter Agilent 34461A,

6½ Digit

Procedure description

The x-axis of the 3D printer is

equipped with a variable resistance position

sensor. The resistance (position) is evaluated with the Agilent 34461A digital multimeter.

1) Launch the 3D printer controller software 3D COM Terminal with an icon on the desktop

2) Select port COM4 (“Komunikační port”) and open it (“Otevřít”)

3) Align the printer axes with the button “Zarovnat osy”

4) Wait until alignment is finished

5) In the “G-kód” window write command “G3 X1000” and send with button “Odeslat”. This

will move x-axis to position 1000. Wait until the movement is finished; record the resistance

from the multimeter.

6) In the “G-kód” window write command “G3 X2000” and send with button “Odeslat”. This

will move x-axis to position 2000. Wait until the movement is finished; record the resistance

from the multimeter.

7) Repeat steps 5) – 6) nine more times

Fig. 5 – Repeatability and accuracy

Sample mean: Standard deviation

1

1 n

i

i

x xn

2

1

1

1

n

i

i

s x xn

(6)

Conclusions

In conclusions discus whether the 3D printer axis is accurate and repeatable. Discus the obtained

accuracy and repeatability compared to the desired accuracy 0.5 mm.

References

[4] Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results,

Appendix D, online on < http://physics.nist.gov/Pubs/guidelines/appd.1.html>, accessed on

9.11.2013

Position – LVDT Submitted by:

Task: Date:

x [mm] 0 15 30 45 60 75 90 105 120 135 150

RZ=0 Ω I [mA] 19,41 19,24 17,73 16,34 14,85 13,29 11,82 10,34 8,85 7,35 5,71

Sensitivity: -0,1 mA/mm Used instruments:

Charts:

Conclusions:

1. Measure and plot the static characteristic I = f(x) for load resistor RZ = 0.

2. For constant position (x = 100 mm) determine the maximum value of Rz, until

which the output current remains constant and the sensitivity of the transducer.

Calculate the maximal allowed length of AWG 36 [1] copper wire between sensor and 250 Ω load (gauge) when

the ANSI/ISA–50.00.01–1975 (R2002) standard [2] defines maximal load resistance 600Ω. Discuss advantages

and disadvantages of sensors with current and voltage output.

0

5

10

15

20

25

0 15 30 45 60 75 90 105 120 135 150

Ou

tpu

t cu

rren

t (m

A)

angular position α (°)

RZ=0 W

RZ=0 W

Position – Resistive sensor Submitted by:

Task: Date:

Used instruments:

x [°] 0 30 60 90 120 150 180 210 240 270 300 330

V2[V] (digital) 0,001 0,367 0,784 1,199 1,624 2,047 2,473 2,889 3,313 3,739 4,164,6

V2[V] (analog) 0 0,3 0,51 0,69 0,86 1,725 2,05 2,4 2,8 3,25 3,754,4

Charts:

Maximal error: K for error less than 1 %:

Conclusions:

2. Compute the maximal error in % for K=1.2 and compare with

measured value of the error from graph.

Find and reference at least two industrial versions of resistive position sensors. Make a table with range, resistance,

accuracy and price.

3. Compute the value of K so that maximal error is less than 1 %.

1.Measure and plot the static characteristic V2=f(x) with a digital and an analog

voltmeter.

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

0 50 100 150 200 250 300 350

Ou

tpu

t vo

lta

ge

V2

(V

)

α (°)

V2[V] (digital)

V2[V] (analog)

Position – Repeatability and accuracy Submitted by:

Task: Date:

experiment 1 2 3 4 5 6

pos. X100 1,137 1,139 1,14 1,139 1,139 1,14

pos. X500 1,975 1,975 1,973 1,974 1,975 1,975

Sample mean: Used instruments:X100 1,1390

X500 1,9745

Standard deviation:

X100 1,0954E-03

X500 8,3666E-04

Conclusions:

1. Determine repeatability of the x-axis of a 3D printer. Check repeatability in two

different points; make 10 measurements in every point.

In conclusions discus whether the 3D printer axis is accurate and repeatable. Discus the obtained accuracy and

repeatability compared to the desired accuracy 0.5 mm.

2. Calculate sample mean and standard deviation of position in both checked points.

Position – resolver

Introduction

Resolver is an angular position sensor. It is an absolute sensor within one

revolution. The construction is similar to an electrical motor. It has typically one rotor

winding and two stator windings. The rotor winding is powered with AC voltage with

frequency 2 to 2 kHz. The two stator windings are perpendicular to each other; AC voltage is

induced through inductive coupling from the rotor. The dependence of stator voltages on

position is sinusoidal. Both stator windings’ signals are required to use the resolver as

absolute sensor from 0 to 360°.

Task:

1. Measure the RMS voltage

of both stator windings in

dependence on angle

V1=f(α) , V2=g(α).

Measure the angle α by

step of 15° for one whole

revolution.

Used instruments:

Fixture with resolver

Oscilloscope with signal

generator

Procedure description

Resolver is electrical machine. It has one rotor winding two stator windings. The stator

windings are perpendicular to each other. The rotor winding is supplied from sinusoidal

power supply by frequency approximately 10 kHz. This is called reference voltage.

_ max sin( )gen genV V t (1)

The fixture is supplied from the oscilloscope generator in this task. In an industrial

system, the signal has to be provided.

The change of mutual inductance between rotor and stator is sinusoidal with

dependence on angle α. Induced voltages from rotor to both stator windings follow the same

dependence. Because the stator windings are mutually shifted, the induced voltages are

shifted too. As the shift is 90°, when one stator voltage is maximal (the mutual inductance

between this stator winding and rotor winding is maximal), the induced voltage in the second

stator winding is minimal (the mutual inductance between this winding and rotor winding is

minimal).

1 1_ max sin( ) sin( )V V t (2)

2 2_ max sin( ) cos( )V V t (3)

Fig. 1 – Task schematic diagram

To evaluate the actual angle, one has to measure both stator voltages. Moreover the

dependence is sinusoidal. As we desire from many sensors a linear steady state characteristic,

the signal has to be processed.

The electronics is called “Resolver to digital” converter [1]. It samples both stator

voltages with Analog/digital converters and uses a look-up table do convert to position. The

output is then a digital signal.

The recommended procedure for this task is to read both stator voltages from the

oscilloscope as peak-peak voltages and convert them to RMS voltage with the equation

(valid only for sinusoidal voltage)

/ 2 2RMS p pV V (4)

Conclusions

In conclusions compare resolver and selsyn(synchro). Find and reference at least one

“Resolver-to-digital” converter. Find out the frequency of the reference signal and resolution

(positions per revolution).

References

[1] AD2S1220, Variable Resolution, 10-Bit to 16-Bit R/D Converter with Reference

Oscillator, online on < http://www.analog.com/static/imported-

files/data_sheets/AD2S1210.pdf>, accessed on 7.4.2013

Dimensions – Ultrasonic thickness sensor

Introduction

Ultrasonic thickness sensors are basically composed from a transmitter and a

receiver. The transmitter produces a pulse; this is reflected at the object boundary and

detected by the receiver. The time delay between transmission and reception is proportional to

object thickness and speed of sound in the material. Ultrasonic thickness sensors are used in

places where traditional thickness meters, like a caliper cannot be used e.g. wall thickness of a

closed box. The same principle is used also to detect cracks in materials.

Tasks:

1. Measure the thickness of

enclosed steel plates in five

points. Verify thickness by

micrometer in the same

points.

2. Measure the wall thickness

profile of two steel tubes in

step of 10 mm, measured

on tube perimeter. Draw

thickness profile in polar

coordinates.

Used instruments:

Ultrasonic thickness meter DIO 570

Procedure description

It is necessary to lubricate by grease (e.g. INDULONA) the measured elements to

improve contact with the ultrasonic probe.

Measure the plate thickness in 5

indicated points. Verify at the same points

with a micrometer.

For steel tube wall thickness

measurement, place the probe

perpendicularly to the surface.

Wipe clean the ultrasonic probe

carefully after measurement is finished.

Demo: Measure the dimensions of the laboratory with an ultrasonic distance meter and

laser distance meter.

Conclusions

Discuss errors in the measurement of wall tube thickness that impact accuracy.

Propose a solution. Compare the accuracy of the ultrasonic and laser distance meter. Find and

reference one ultrasonic and one laser distance meter, compare theirs accuracies, ranges and

usage.

Fig. 2 – Principle of ultrasonic thickness sensor

Fig. 3 – Points to be measured on steel plates

3D scanner

Introduction

A 3D scanner is used to create 3D models from real world objects. It can easily

be built with a laser beam projector, camera and rotational table. The object to be scanned is

placed on the rotational table. The laser beam projector projects a line on the object. The

camera records the line shape as the object is rotated. From the known angle between laser

and camera, the 3D model of the object can be reconstructed.

Task:

1. Scan a polystyrene head

Used instruments:

Rotational table with

polystyrene head

Web camera + PC

Laser water level

Description of principle

The camera sees the image in

its image plane. The angle Θ between

the laser line projector axis and camera

axis is known. The distance from the

axis of rotation r can be calculated as follows

/ sin( )r x (5)

Where x is the position of the laser point as

seen by the camera.

This procedure is repeated for all vertical

points of the laser line.

Procedure description

1) Launch the program “3DScanner Gui”. Be

patient, the start takes a while. 2) With the button “Configure webcam”

configure the webcam. Select device

winvideo, device ID 1, format

“YUV2_640x480”

3) Launch preview with button “Start preview”

4) Turn on the laser water level

5) Dependent on the current light conditions,

adjust the line detection threshold to get a

clear laser line. The processed image with the

laser line is obtained with the button

“Capture”

6) Turn on the power supply, adjust voltage to set

speed 1 revolution/minute (voltage around

Fig. 4 – Principle of 3D scanner [2]

Fig. 5 – Principle of 3D scanner, image of

head from [5]

4V)

7) Start the 3D image capture with the button “Timer ON”. The 3D image is made from

120 images, captured with period 0.5s. When satisfied with the image, stop the capture

with the “Timer OFF” button and save the image to a file.

Conclusions

In conclusions discus the influence of object color on the sensor reading, discuss the

difference between CCD and PSD technology. Made and estimate of precision of this simple

scanner.

References [2] 3D Scanning Basics, online on < http://www.etc.cmu.edu/projects/plastico-

fantastico/?p=295>, accessed on 7.7.2013

[3] Polhemus FastSCAN 3D Laser Scanner, online on <

http://www.youtube.com/watch?v=SyzgBycPxyw>, accessed on 7.4.2013

[4] Make a 3D Laser Scanner, online on < http://www.youtube.com/watch?v=SPywgDBjM1Y>,

accessed on 7.4.2013

[5] Human Head Modeling – 3DS Max, online on < http://www.tutorius.net/2010/03/human-

head-modeling-3ds-max/comment-page-1/>, accessed on 7.4.2013

Fig. 6 – 3D Scanner GUI

Position – resolver Submitted by:

Task: Date:

α [°] V1 p-p [V] V2 p-p [V] V1 RMS [V] V2 RMS [V]

0 0,620 0,500 0,219 0,177

15 0,480 0,640 0,170 0,226

30 0,320 0,740 0,113 0,262

45 0,100 0,800 0,035 0,283 Used instruments:60 0,124 0,800 0,044 0,283

75 0,320 0,740 0,113 0,262

90 0,400 0,540 0,141 0,191

105 0,580 0,460 0,205 0,163 Charts:

120 0,760 0,280 0,269 0,099

135 0,720 0,080 0,255 0,028

150 0,720 0,100 0,255 0,035

165 0,680 0,300 0,240 0,106

180 0,580 0,440 0,205 0,156

195 0,440 0,580 0,156 0,205

210 0,280 0,660 0,099 0,233

225 0,100 0,710 0,035 0,251

240 0,092 0,720 0,033 0,255

255 0,280 0,660 0,099 0,233

270 0,440 0,560 0,156 0,198

285 0,560 0,440 0,198 0,156

300 0,660 0,280 0,233 0,099

315 0,720 0,084 0,255 0,030

330 0,710 0,160 0,251 0,057 Conclusions:345 0,660 0,290 0,233 0,103

360 0,560 0,450 0,198 0,159

1. Measure the RMS voltage of both stator windings in dependence on angle V1=f(α) ,

V2=g(α). Measure the angle α by step of 15° for one whole revolution.

In conclusions compare resolver and selsyn(synchro). Find

and reference at least one “Resolver-to-digital” converter.

Find out the frequency of the reference signal and resolution

(positions per revolution).

( )/ 2 2RMS p pV V

−

= ⋅

0,000

0,050

0,100

0,150

0,200

0,250

0,300

0 100 200 300

Ou

tpu

t v

olt

ag

e (

V)

angular position α (°)

V1 RMS [V]

V2 RMS [V]

Dimensions – Ultrasonic thickness sensor Submitted by:

Task: Date:

Used instruments:

steel plate 1 Charts:

point 1 2 3 4 5

ultrasonic (mm) 5,4 5,3 5,3 5,3 5,3

micrometer (mm) 5,20 5,17 5,23 5,17 5,20

steel plate 2point 1 2 3 4 5

ultrasonic (mm) 4,8 4,8 4,8 4,9 4,9

micrometer (mm) 4,72 4,74 4,75 4,72 4,72

tube 1 - wall thickness

point 1 2 3 4 5 6 7 8 9 10 11 12 13 14

ultrasonic (mm) 3,1 2,9 3,1 3,1 3,6 3,6 3,6 3,6 3,4 3,4 3,3 3,4 3,4 3,3

tube 2 - wall thicknesspoint 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

ultrasonic (mm)

steel box: wall thickness :

Conclusions:

1. Measure the thickness of enclosed steel plates in five points. Verify thickness by

micrometer in the same points.

2. Measure the wall thickness profile of two steel tubes in step of 10 mm, measured

on tube perimeter. Draw thickness profile in polar coordinates.

Discuss errors in the measurement of wall tube thickness that impact accuracy. Propose a solution. Compare the accuracy of the

ultrasonic and laser distance meter. Find and reference one ultrasonic and one laser distance meter, compare theirs accuracies,

ranges and usage.

0

1

2

3

4

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Tube wall thickness profile in mm

3D scanner Submitted by:

Task: Date:

3D image:

Precision estimation: 5 mm

Conclusions:

1. Scan a polystyrene head

In conclusions discus the influence of object color on the sensor reading, discuss the difference between

CCD and PSD technology. Made and estimate of precision of this simple scanner.

Pressure - calibration

Introduction

When calibrating an instrument, readings from two gauges are compared. One

is the calibrated one; the other has to use a definition principle for the calibrated physical

property. In case of pressure the definition is force acting on a known area (used in e.g.

deadweight tester) or equivalent to this - hydrostatic pressure. The reading from the definition

instrument is then taken as “correct”. The calculated deviations are then used to add/subtract a

correction from the meter reading in order to obtain the correct pressure.

Tasks:

1. Draw task´s block diagram

2. Calibrate deformation manometer in 11

points of whole range including zero and

maximal pressure 100 kPa.

3. Plot graph of absolute errors.

Used instruments:

manometer to be calibrated = deformation

manometer with strain gauge transducer,

accuracy class = 0,5

liquid mercury manometer (well type)

control deformation manometer with Bourdon tube – including valve for pressure

setting, accuracy class = 0,6

Procedure description

Many industrial pressure gauges use the deformation principle. Pressure is transduced

into a deformation of a Bourdon element, spring bellows or a diaphragm. Although this

principle is robust and reliable, it is not a definition principle for pressure and all such

gauges need to be calibrated. An example of a diaphragm pressure gauge is shown in Fig. 1.

The position of the diaphragm is measured. Either mechanically like in Fig. 1, or by means of

e.g. strain gauge or capacitive sensors.

The calibration gauge used in this task is a

well type manometer shown in Fig. 2.

Liquid column height h is read from the

scale.

The pressure is then

p g h (1)

Where g is gravitational acceleration and ρ

is density of the used liquid.

Mercury (Hg) is used in our manometer.

Table 1 - Hg density in dependence on temperature

Fig. 1 – Diaphragm pressure gauge

Fig. 2 – Well type manometer

t(°C) 0 10 20 30

p (kg.m3) 13595.1 13570.4 13545.7 13521.2

Fig. 3 – Correct reading Fig. 4 – Avoid parallax error

Conclusions

In conclusion discuss what properties are required for a calibration instrument (from

accuracy and range point of view). Find, describe and reference at least two either industrial

or automotive applications of deformation pressure sensors.

Pressure - verification

Introduction

For instrument verification a more precise instrument is required. Its reading is

compared with the device under test. None of both uses the definition principle so it is

different from calibration. Both instruments need to have approximately the same range; the

more precise instrument needs a higher accuracy. The reading from the more precise

instrument is then taken as “correct”. Verification serves to check whether the meter can be

trusted, usually in multiple points of the scale.

Tasks:

1. Draw task´s block diagram

2. Verify accuracy class of deformation

manometer. Make verification by

comparing pressure with control

manometer in 5 points in the whole range

of pressure - including maximal pressure

(but not zero pressure).

3. Create verification protocol.

Used instruments:

tested deformation manometer (diaphragm,

Tp = 1,5)

Smart pressure difference transducer

Honeywell ST3000, type STD924,

accuracy 0.1%. Variable range, basic range

100" inch H2O, with handheld unit

Honeywell SFC

24 VDC power supply

current supply for 4 - 20 mA current loop

control deformation manometer with Bourdon tube – including valve for pressure

setting, accuracy class = 0,6

Procedure description

The goal is to compare pressure from both meters, the verified one with the more

precise one. The verification protocol will contain calculated values in Pa and absolute

and relative errors. Take the reading from the Smart sensor as the correct ones.

Conclusions

In conclusion state whether the tested deformation manometer has the declared

accuracy class Tp = 1.5 or not. Discuss the difference between calibration and verification.

References

[1] Pressure transmitters lower plant lifecycle costs, online on

<http://www.myflukestore.com/crm_uploads/fe_576_users_manual.pdf >, accessed on

31.3.2013

Fig. 5 – Smart pressure sensor [1]

Humidity

Introduction

Humidity is closely related to pressure and temperature. Absolute humidity is

the mass of water vapor - mh20 - present in the air water vapor mixture [2]. Relative humidity

is the ratio of the partial pressure of water vapor in an air-water mixture to the saturated vapor

pressure of water at a prescribed temperature [3]. Relative humidity is usually expressed in

per cent and abbreviated by φ or RH.

Tasks:

1. Measure transient response of

electronic hygrometers, determine time

constant.

2. Measure the air humidity in the lab

with a psychrometer

Used instruments:

Climatic chamber

Kir Sensirion Sensirion EKH-4 with sensors SHT21 (0 – 100 % RH ; ±2.0 %) ,

SHT71 (0 – 100 % RH ; ±3.0 %) , SHT21 (0 – 100 % RH ; ±1.8 %)

PC + software EHK viewer

aspiration psychrometer with mercury thermometers, aspiration psychrometer with

thermistor temperature transducers

Procedure description – electronic hygrometers

One of the principles used in electronic hygrometers is based on changes of capacity

or resistance of a dielectric material. The dielectric is Al2O3. The dielectric is placed between

one porous and one non-porous electros. The humidity from the air can enter into the

dielectric material through the porous electrode and will cause changes of capacity/resistance.

This change is evaluated. In our case the build-in electronic communicates through I2C bus.

Steps – electronic hygrometers

1) If not done so by the previous group – pull out the sensor from the climatic chamber.

2) Turn on the power supply for the EHK-4 it, on the PC start EHK4 viewer.

3) On the power supply for the ultrasonic humidifier set voltage 20V, connect the power

supply to the humidifier, and turn on the fan (voltage 9,2V).

4) Wait 3 minutes to reach steady state. In the meantime, use a psychrometer to

measure air humidity in the lab.

5) In menu File -> Log to file select the file where the recorded data will be stored.

On the PC start the data recording with the START button.

6) Insert the sensors into the climatic chamber, measure transient response, remove the

sensors from the climatic chamber and measure the transient response as well. The

recording is stopped with the STOP button.

Conclusions – electronic hygrometers

Explain why the time constant is different for adsorption and desorption.

Fig. 6 – Principle of Al2O3 hygrometer

Procedure description – psychrometer

The principle of psychrometer is

shown in Fig. 7. The instrument is composed

from 2 thermometers. One is called dry

(measures the temperature of the air where

humidity is to be measured), the other is called

wet (measures temperature of air with relative

humidity 100 %). From temperature

difference Δt and dry thermometer reading

tdry, relative humidity RH can be found in a

psychrometric chart or table.

Conclusions – psychrometer

Discuss differences in RH reading from

different psychrometers.

References

[2] Absolute Humidity of Air, online on < http://www.engineeringtoolbox.com/absolute-

humidity-air-d_681.html>, accessed on 31.3.2013

[3] Relative humidity, online on < https://en.wikipedia.org/wiki/Relative_humidity>, accessed on

31.3.2013

Fig. 7 – Principle of psychrometer

Pressure - calibration Submitted by:

Task: Date:

2. Calibrate deformation manometer in 11 points of whole range including zero and maximal pressure 100 kPa.

3. Plot graph of absolute errors.

Block diagram:deformation

manometer

(kPa)

well type

manometer

(mm Hg)

well type

manometer

(kPa)

absolute

error

(kPa)

4,8 37,0 4,9 -0,1

10 77,0 10,2 -0,2

20 151,0 20,1 -0,1

30 226,0 30,0 0,0

40 303,0 40,3 -0,3 Charts:50 379 50,4 -0,4

60 452 60,1 -0,1

70 529 70,3 -0,3

80 604,0 80,3 -0,3

90 680,0 90,4 -0,4

100 755,0 100,3 -0,3

lab. air temperature t(°C) 22,0

lab. barometric pressure(kPa) 96292

Used instruments:

Conclusions:

1. Draw task´s block diagram

In conclusion discuss what properties are required for a calibration instrument (from accuracy and range point

of view). Find, describe and reference at least two either industrial or automotive applications of deformation

pressure sensors.

Laboratory conditions:

-0,4

-0,4

-0,3

-0,3

-0,2

-0,2

-0,1

-0,1

0,0

0 20 40 60 80 100 120

absolute error (kPa)

absolute error (kPa)

Pressure - verification Submitted by:

Task: Date:

3. Create verification protocol.

Verificaton protocol: Block diagram:deformation

manometer

(mm H2O)

deformation

manometer

(kPa)

"Smart"

pressure

reference

(kPa)

absolute

error

(kPa)

relative

error (%)

500 4,9 6,1 -1,2 -24,2

1000 9,8 12,5 -2,7 -27,5

1500 14,7 19,2 -4,5 -30,3

2000 19,6 27,0 -7,4 -37,8

2500 24,5 34,2 -9,6 -39,3 Charts:

lab. air temperature t(°C) 22,0

lab. barometric pressure(kPa) 96292,0

Used instruments:

Conclusions:

1. Draw task´s block diagram

In conclusion state whether the tested deformation manometer has the declared accuracy class Tp = 1.5 or not.

Discuss the difference between calibration and verification.

2. Verify accuracy class of deformation manometer. Make verification by comparing pressure with

control manometer in 5 points in the whole range of pressure - including maximal pressure (but not

zero pressure).

Laboratory conditions:

-45,0

-40,0

-35,0

-30,0

-25,0

-20,0

-15,0

-10,0

-5,0

0,0

0,0 5,0 10,0 15,0 20,0 25,0 30,0

relative error (%)

relative error (%)

Humidity Submitted by:

Tasks: Date:

Measured transient responses: Used instruments:

SHT25 SHT71 SHT75

lab. air temperature t(°C)

lab. barometric pressure(kPa) lab air humidity - measured with psychrometers

Conclusions

Explain why the time constant is different for adsorption and desorption. Discuss differences in RH reading from different psychrometers.

1. Measure transient response of electronic hygrometers, determine time constant.

2. Measure the air humidity in the lab with a psychrometer

time constant - adsorption

Laboratory conditions:time constant - desorption

30

40

50

60

70

80

90

100

15:00:43 15:01:26 15:02:10 15:02:53 15:03:36 15:04:19 15:05:02

RH

(%

)

time

SHT25

SHT71

SHT75

DC tachogenerator

Introduction

DC generator is in many ways similar to a DC motor/generator. Its main parts

are a permanent magnet, coils, commutator and brushes. As the rotor rotates, the coils are

provided with variable magnetic flux and voltage is induced. The induced voltage is AC. The

commutator acts as a mechanical rectifier. The limited number of commutator lamellas limits

the achievable accuracy. The output voltage is a function of rotor speed. As it depends also on

tachogenerator load, a defined load resistor has to be connected to the output.

Task:

1. Measure steady state

characteristic of a DC

tachogenerator with an

unloaded and loaded

output with RL = 25

kΩ. Calculate

sensitivities for both

cases.

2. Hand draw schematic

diagram of the task

Used instruments:

Fixture with DC motor, DC tachogenerator 80V/1000 RPM, optical speed sensor

Power supply Manson ED-613

Voltmeter UNI-T (range 1000 V dc)

Counter TR-525B/D009

Procedure description

Control the DC motor speed by changing the power supply voltage. Read the correct

speed (frequency) from the counter. Repeat experiment twice – first without the load resistor

24 kΩ, then with the load resistor. Calculate sensitivities.

Conclusions

Discuss what happens with the output voltage when the DC tachogenerator is loaded.

Discuss what limits the accuracy of a DC tachogenerator. Find, describe and reference at least

one industrial DC tachogenerator.

Fig. 1 – Schematic diagram of the laboratory set-up

AC tachogenerator

Introduction

The AC tachogenerator is an electrical machine. Its output voltage and

frequency is a function of speed. Both of them can be used to measure speed.

Tasks:

1. Measure amplitude and

output voltage as a

function of speed for the

AC tachogenerator.

2. Hand draw schematic

diagram of the task

Used instruments:

Power supply Diametral

P230R51D

Voltmeter UNI-T

Oscilloscope GW

INSTEK GOS-620FG

Counter Goldstar FC-2015

Tachometer DT-2236

Fixture with DC motor and AC tachogenerator

Procedure description

Control the DC motor speed by changing the power supply voltage (variable part). Do not

change the second power supply voltage. Read the correct speed from the optical tachometer.

Measure amplitude and output voltage as a function of speed for the AC tachogenerator from

0 to 5000 RPM.

Conclusions

Discuss linearity of voltage and frequency, calculate the number of pole-pairs of the

AC tachogenerator.

Fig. 2 – Arrangement of the experiment

IRC, Hall sensor, stroboscope

Introduction

The IRC (Incremental encoder) is a precise optical sensor. It has typically a

resolution of several thousand of pulses per one revolution. It is a relative sensor. The Hall

sensor uses the variations of a magnetic field in order to detect position (or speed) of a

ferromagnetic mark. The distance between the ferromagnetic wheel and the sensor is most

important. If not set correctly, the sensor will not output a correct signal.

Tasks:

1. For speed 2000 RPM

record oscilloscope

signals 1 and 2 from IRC.

Reverse direction of

rotation and record once

more. Based on those 2

signal propose an.

2. Record the Hall sensor

output signal frequency

for different distance of

the sensor from the

wheel. State for what

distances the sensor is measuring correctly.

Used instruments:

Power supply Manson EP-613

Voltmeter UNI-T

4 channel oscilloscope GW INSTEK GDS-2104

Multimeter Agilent 34401A (used as a frequency-meter)

Stroboscope TR5555

Fixture with DC motor, IRC, Hall sensor

caliper

Fig. 3 – Arrangement of the experiment

Procedure description

By adjusting the voltage on the power supply set motor speed to 2000 RPM. Use the on the

fixture available DC tachogenerator to set approximately the speed. DC tachogenerator

constant is 2V/1000 RPM.

Use the stroboscope to set the precise speed of 2000 RPM.

1. IRC On channel 1 and 2, visualize output signals 1 and 2 from the IRC for both directions of

rotation. Draw the signal for both cases and propose an algorithm able to distinguish left and

right rotation.

2. Hall sensor Synchronize the oscilloscope from channel 3 (with the TRIG button and the on-screen menu)

to visualize the Hall sensor signal. By adjusting the distance of the Hall sensor (pink sensor)

from the ferromagnetic wheel record the signal frequency with a counter and check with the

oscilloscope is the signal is OK (no pulses are missing).

!!!When adjusting the distance STOP THE MOTOR by

turning of the power supply. !!!

Conclusions

Find, describe and reference at least one industrial Hall sensor for speed. Describe its

application and compare available speed range with inductive speed sensor

Accelerometer

Introduction

A multi axis MEMS (Micro Electro Mechanical System) accelerometer is today a

common component of many devices. It is used to control the rotation of a mobile phone

screen or fires the airbag in a crash. Many accelerometers are based on capacitive sensing and

is the inertial force acting on a mass when acceleration is applied. The movement of the mass

is the measured.

Task:

1. Set 5 different inclination

angles of the

accelerometer platform.

Record acceleration in all

axes, calculate pitch and

yaw

Used instruments:

Development board XTRINSIC-

SENSORS-EVK on a inclined

platform (2 axes)

Arduino UNO + servos

PC + Hyperterminal software

Power supply 5 V

Procedure description:

1) Turn on the PC, with an icon on the

desktop run the software

“Hyperterminál”. In menu Soubor -

> Otevřít open profile „Akcelerometr“ (communication speed is 115200 bps). Open

the serial port with icon „Zavolat“.

2) Turn on the 5 V power supply. Push the reset button on XTRINSIC-SENSORS-EVK

board, a text will be shown in the Hyperterminál window.

3) In the Hyperterminal window enter command „S2“. Send with ENTER. The reading

will start in the window and show acceleration in all axes.

4) The second board– Arduino – controls the servos. With a screwdriver set the variable

resistors do different positions, this sets the position of servos (inclination of the

platform) in two axes. Set 5 different inclinations, record acceleration in all axes.

5) Deduce equations for pitch α and yaw β calculations – use figures 5 to 7

6) Calculate pitch α and yaw β of the platform for all 5 inclinations.

Fig. 4 – Principle of capacitive accelerometer [1]

Fug. 5 – Axes orientation

Conclusions

Discuss why differential capacitive sensing is used and in what application such a

system measuring two axial inclination could be used.

References

[1] Rob O'Reilly, Kieran Harney, Analog Devices Inc., Alex Khenkin Sensors, Sonic

Nirvana: MEMS Accelerometers as Acoustic Pickups in Musical Instruments, online

on < http://www.sensorsmag.com/sensors/acceleration-vibration/sonic-nirvana-mems-

accelerometers-acoustic-pickups-musical-i-5852>, accessed 29.11.2013

[2] Tom Lecklider, Measuring Motion, online on <

http://www.evaluationengineering.com/articles/200609/measuring-motion.php >,

accessed 29.11.2013

Fig. 6 – Platform not inclined Fig . 7 – Inclination in XZ axis - pitch

Fig . 8 – Inclination in YZ axis - yaw Fig . 9 – Accelerometer under a microscope [2]

DC tachogenerator Submitted by:

Task: Date:

Charts:speed (RPM) V (V) - unloaded V (V) - loaded

with 24k

0 0 0

500 45 42

1000 88 81

1500 133 122

2000 177 163

2500 222 203

3000 265 245

3500 308 280

4000 340 325

4500 400 364

5000 443 401

Used instruments: Schematic diagram:

Conclusions:

1. Measure steady state characteristic of a DC tachogenerator with an unloaded and loaded output with RL = 25

kΩ. Calculate sensitivity for both cases.

2. Hand draw schematic diagram of the task

Discuss what happens with the output voltage when the

DC tachogenerator is loaded. Discuss what limits the

accuracy of a DC tachogenerator. Find, describe and

reference at least one industrial DC tachogenerator.

0

100

200

300

400

500

0 1000 2000 3000 4000 5000

ou

tpu

t vo

lta

ge

(V

)

speed (RPM)

Steady state characteristics

V (V) - unloaded V (V) - loaded with 24k

AC tachogenerator Submitted by:

Task: Date:

Charts:speed (RPM) V (V) f (Hz)

0 0 0

1000 38 50

2000 77 105

3000 114 151

4000 153 200

5000 191 250

Used instruments:

Schematic diagram:

Conclusions:Discuss linearity of voltage and frequency, calculate the number of pole-pairs of the AC tachogenerator

1. Measure amplitude and output voltage as a function of speed for a AC tachogenerator

2. Draw schematical diagram of the task

0

50

100

150

200

250

300

0 1000 2000 3000 4000 5000vo

lta

ge

(V

), f

req

ue

ncy

(H

z)

speed (RPM)

Steady state characteristics

V (V) f (Hz)

IRC, Hall sensor, stroboscope Submitted by:

Task: Date:

IRC signal - 2000 RPM - left: IRC signal - 2000 RPM - right:

Hall sensor: Used instruments:distance sensor -

whell (mm)

frequency (Hz)working correctly (yes/no)

1,0 550,0 yes

1,4 550,0 yes

1,8 550,0 yes

2,0 550,0 yes

2,5 - no

3,0 - no

Conclusions:

1. For speed 2000 RPM record osciloscope signals 1 and 2 from IRC. Reverse direction of rotation and record

once more. Based on those 2 signal propose an algorithm to distingush left and right rotation

Find, describe and reference at least one industrial Hall sensor for speed. Describe its application and compare available speed range with

inductive speed sensor

2. Record the Hall sensor output signal frequency for different distance of the sensor from the wheel. State for what

distances the sensor is measuring correctly.

Accelerometer Submitted by:

Tasks: Date:

position

acceleration in X:

(mg)

acceleration in

Y: (mg)

acceleration in

Z: (mg)

pitch α (°) yaw β (°)

1 -101 -150 -980 -5,9 -8,7

2 -252 -150 -958 -14,7 -8,9

3 -300 -235 -900 -18,4 -14,6

4 -95 248 -939 -5,8 14,8

5 23 105 -973 1,4 6,2

Used instruments:

Conclusions:

1. Set 5 different inclination angles of the accelerometer platform. Record acceleration in all axes, calculate

pitch and yaw

Discuss why differential capacitive sensing is used and in what application such a system measuring two

axial inclination could be used.