Download - Specification Fund

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Phase I - SpecificationRMT Sales Training - 05 /98

PHASE I

Agenda:Agenda:• Interpretation of transmitter specification

• Physical• Functional• Performance• Dynamic performance

• Types of error• Performance measurement

Fundamentals of Process ControlFundamentals of Process Control

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Sensor interchangeability error

ORStatic pressure effect

ERROR !

Ambient temperature effect

Reference accuracy

4 SOURCES OF ERROR4 SOURCES OF ERROR

Drift over time(stability)

- we need to review Performance Requirements

What Transmitter ???What Transmitter ???

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Physical SpecificationsPhysical Specifications

– Materials of Construction:Materials of Construction:• Housing materials, Process flange materials, Paints, bolts, etc.

– Process/Electrical Connection:Process/Electrical Connection:• Dimensions, thread types, and center-to-center dimensions of the

process connections.– Weight:Weight:

• Lists the weight of the instrument.– Product Specific Physical Specifications:Product Specific Physical Specifications:

• Example: Type of fill fluid, LCD options, Transient protector option, etc.

Describe the Physical Make-Up of the Transmitter.Describe the Physical Make-Up of the Transmitter.

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Functional SpecificationsFunctional Specifications

Range LimitsRange Limits• Upper Range Limit (URL)

» The highest quantity that a device can be adjusted to measure• Lower Range Limit (LRL)

» The lowest quantity that a device can be adjusted to measure• Upper Range Value (URV)

» 20 mA operating point (100% reading)• Lower Range Value (LRV)

» 4 mA operating point (0% reading) SpanSpan

• URV - LRV

Describes the Environment within which the transmitter Describes the Environment within which the transmitter can operator & still meet its Performance Specification.can operator & still meet its Performance Specification.

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Example of Range limits & Spans:Example of Range limits & Spans:

0- 100 psi + 100 psi

LRL URL

A Differential Pressure Transmitter

Sensor Limits

TransmitterCalibrated / Ranged:

4 mALRV

20 mAURV

30 psi 80 psi

CalibratedSpan =50 psi

0%Reading

100%Reading

Turndown ?

URL / Cal. Span = 100 / 50 2:1

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Rangeability / TurndownRangeability / Turndown• Allowable range of spans through which errors are of an acceptable value

» Min. Span up to Span = URL» Ex) Turndown = 10:1 & URL = 500 psi

Min. Span = URL / 10 = 50 psi

OutputsOutputs• The type of signal representing the process variable that is delivered by the transmitter

» Eg. 4-20 mA, 3-15 psi, Digital

ServiceService• Describes the process that be measured. Eg. Liquid, gas, vapor


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Hazardous LocationHazardous Location• Describes the types of hazardous location that the

transmitter is certified for use within. Eg. Class 1, Div 1and 2, Groups B,C

• Approvals


Hazardous Area Risk of FIRE & EXPLOSIONZone 0 HighZone 1 IntermediateZone 2 Occasional

Weather proof Level of IINGRESS PPROTECTIONIP65 / 66 1st digits 6 represent Dust Tight.IP67 / 68 2nd digits represent level of protection

against water. The higher the value thethe better the level of protection.

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Danger of FIRE and EXPLOSION in HAZARDOUS AREAS

Zone Safety approach Letter Code Authority

Intrinsically Safe0 Electronics safe

Flameproof1 Explosion retained

Flame quenched

Non Incendive2 No arcs,sparks or

hot surfaces


I

E

N

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5

6

CENELEC(Europe)

FM(USA)

CSA(Canada)

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Functional SpecificationFunctional Specification

– SST Certification Tag Provided• Explosion Proof

• E5 (FM)• E8 (CENELEC / CESI)

• Intrinsic Safety• I1 (BASEEFA / CENELEC)

• Non-Incendive• N1 (BASEEFA / CENELEC)

• Non-Incendive + Intrinsic Safety• I5 (FM)

• Explosion Proof + Intrinsic Safety• C6 (CSA)• K5 (FM)• K8 ( FM + CSA)• K6 (CSA = CENELEC)

Examples of Approvals for TransmittersExamples of Approvals for Transmitters

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Normal Operating Range

mA

Hardware Alarm

Process Variable Out of Range

21.753.8

2020.8

43.9

Failure Mode AlarmFailure Mode Alarm• If self-diagnosis detects a gross transmitter failure, the

analog signal will be driven to low output /high output to alert the user

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Power SupplyPower Supply

• Describes the power that is required to operate the transmitter which will coincide with the output selected.

Load limitationLoad limitation

• The maximum load that can be present in the loop for the transmitter to operate over its full output range for a given power supply.

Voltage

Lo

ad

At voltage Vs :

At no load min. voltage is 12 V dcThe max. voltage should not exceed 45 V dc

RL is the max. load possible

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Static Pressure LimitsStatic Pressure Limits• Level of static(line) pressure that a transmitter can be

exposed to in which the transmitter will function within specifications

Overpressure LimitsOverpressure Limits• Level to which only one side of a pressure transmitter

can be exposed to without causing damage Proof (burst) pressureProof (burst) pressure

• Pressure to which transmitter can retain fluid without flying parts

Pressure LimitsPressure Limits

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QuizQuiz

1151DP4S

(URL = 150 inH2O, min span = URL/15

Min. Span= _______

Max. Turndown = __________

3051CD3

(Range: 0 -10 to 0 - 1000 inH2O)

Min Span _______

Max. Turndow = __________

Example #2Example #2

10 inH2O

15:1

10 inH2O

100:1

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Performance SpecificationsPerformance Specifications

Quantify Uncertainty of a Measurement as a Function Quantify Uncertainty of a Measurement as a Function of Changing Ambient & Process Conditions.of Changing Ambient & Process Conditions.

Reference AccuracyReference Accuracy• Defines maximum error at reference conditions

» Zero-based:» 14.73 psia, 68 deg F.» May have limits on material types» Includes effects of linearity, repeatability, hysteresis» Typically expressed as a % of calibrated span

• Ways to express reference accuracy:

» % of URL» % of span» % of reading

Commonly used in Transmitters

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Performance SpecificationsPerformance Specifications– Transmitters are factory calibrated at room temperature.– If transmitter operates at a different ambient temperature,

the electronics perform differently. – The change in performance can create an error in the

measurement.This error is the This error is the

Ambient Ambient Temperature EffectTemperature Effect

Zero Temperature EffectsZero Temperature Effects» Expressed as a % of URL per some T from

standard conditions Span Temperature EffectsSpan Temperature Effects

» Expressed as a % of Calibrated Span per some T from standard conditions.

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• The effect on transmitter zero and span due to the application of static (line) pressure

» Applies to differential pressure transmitters only.

» Zero LP Effect: Expressed as % of URL per change in static pressure

» Span LP Effect: Expressed as % of Calibrated Span change in static pressure

Static Pressure EffectsStatic Pressure Effects

Span = 20 psi

At differentLine Pressure

50 psi 30 psi100 psi 80 psi500 psi 480 psi1000 psi 980 psi

Same Flow Rate

However at higher line pressure the sensor is subject to higher stress & therefore may induced error in registering the DP

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Vibration EffectVibration Effect• The effect upon output is solely due to the vibratory

environment to which the transmitter is subjected.

Power Supply EffectPower Supply Effect• If a transmitter is operated at a different voltage in the

field, then it was calibrated with on the bench, then variations in output (for the same input) can occur.


All transmitters will drift over time , All transmitters will drift over time , compounding error in the point measurementcompounding error in the point measurement

StabilityStability•Change in output given a fixed input as a function of TIME.•Determines calibration frequencies.

»Units of uncertainty are dependent on product type.

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RFI/EMI EffectsRFI/EMI Effects• Output change as a result of radio or electromagnetic interference.

Potential sources of interference:» Motors, Radios

Mounting positionMounting position– Difference in output when a transmitter is mounted in a position different to

which it was calibrated.

Load EffectLoad Effect– If the total loop should alter, then the output of the transmitter (for the

same process input) may be effected

LinearityLinearity– Maximum deviation from a Straight Line.


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Repeatability:Repeatability: • Ability to reproduce output reading when same input is

applied under the same conditions, and in the same direction.

Hysteresis:Hysteresis:• The maximum difference in output at any input value,

when the value is approached first with increasing then decreasing input.


Reproducibility:Reproducibility:• The closeness of agreement among repeated measurements

of the output for the same value of the input under the same operating conditions over a period of time, approaching from both directions.

• It includes hysteresis, drift and repeatability.

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• Acc = ±0.1% of URL



Assuming an input of 80 inH2O:Pressure Transmitters URL = 300 inH2OCalibration: 0-200 inH2OWhat is the maximum error (%) at reading ?

• Accuracy = ±0.1% of reading

0.001 x 300 = 0.3 inH2O

(0.3 / 80) x 100% =±0.375%0.001 x 200 = 0.2 inH2O

(0.2 / 80) x 100% =±0.25%

±0.1%

• Accuracy as specified (±0.1% of span)

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What is the maximum LP error (%) of an 1151DP4S (URL = 150 inH2O) at 1500 psi static pressure, calibrated 0 to 100 inH2O, measuring 60 inH2O?

What is the maximum LP error (%) of an 1151GP8S measuring 1000 psig?


Given Zero Error = ±0.25% of URL for 2,000 psi & Span Error correctable to ±0.25% of reading per 1,000 psi

(0.0025 x 150 x 0.75) + (0.0025 x 60 x 1.5) =±0.58 psig

Zero error span error total error

N.A

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What is temperature error (%), expressed in psig, of a 3051CG5 (URL = 2000 psig) , calibrated 0 to 1000 psig in factory at 68°F, measuring 500 psig, at 168 deg F.

What is the minimum amount of error (%) that could be achieved without re-zeroing at temperature?


Example #5Example #5 Given Ambient Temperature Effect per 50°F : ±(0.0125% URL + 0.0625% Span) spans from 1:1 to 10:1 ±(0.025% URL + 0.125% Span) spans from 10:1 to 100:1

(0.000125 x 2000) + (0.000625 x 1000) = ±0.65 psig

0.65 psig x 2 =±1.3 psig

0 psig

100°F

2:1

2:1

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Dynamic Performance Dynamic Performance

Response Time DefinitionsResponse Time Definitions

Time0

}

T63

63.2%

TcTd– Faster Responding Sensor (Tc)

– Faster Update Rate (Td)

– Optimized Software / Processing (Td)

– Minimal Filtering (Tc)

– Total Response Time (T63)Damping

• Transducer response time

• Signal conversion time (eg. A/D modem)

• Micro-processing time

• adding a delay time

Deadtime (Td): The time before output starts to change.

Time Constant (Tc): The time necessary (after deadtime) for output to reach 63.2% of its final value.

Total Response Time (T63): Deadtime (Td) plus one Time Constant (Tc)

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Different Types of ErrorsDifferent Types of Errors

Span-ErrorSpan-Error• Difference between

calibrated and ideal span.

4-20 mA OUTPUT

4-20 mA OUTPUT

4-20 mA OUTPUT

Ideal Span0 to 100 inH2O Input

4-20 mA OUTPUT

4-20 mA OUTPUT

4-20 mA OUTPUT

Ideal Span0 to 100 inH2O Input

Zero-ErrorZero-Error– Fixed offset between

true and measured

value.

Total-ErrorTotal-Error• Zero Error plus Span Error.

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P

F

0 URL

Sensor Curve

Turndown ErrorTurndown Error• Arises when a span less than the Transmitter’s full span is used.

The smaller the calibrated span, the greater the errors over the span.

Different Types of ErrorsDifferent Types of Errors

Turndown Factor 4 : 14095 : 1023

8 : 14095 : 511

4:1

Resolution < 0.1%

Resolution > 0.1%Capacitance to

Digital converter (A/D)

For example:

12 bits Register represent full sensor range

Resolution = 1/4095 < 0.1%

8:1

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Performance MeasurementPerformance Measurement

Total probable error (TPE)Total probable error (TPE) analysis provides a more accurate picture of how a transmitter can be expected to perform under specific conditions or changes in conditions.

The Root Sum Square(RSS)The Root Sum Square(RSS) method determines the TPE by summing the squares of individual error components, and then taking the square root of the total.

Up = (accuracy2 + temp eff2 + (...eff)2)1/2

where Up = total uncertainty (TPE)

Worse Case ErrorWorse Case Error is the sum of individual error components. This error is unlikely to occur, since all the effects may not take place at the same time.

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Total Probable ErrorTotal Probable Error

Given:• Accuracy = +/-0.1% of span• Total Temperature Effects = +/-0.5% of span• LP Effects = +/-0.3% of span• Power Supply Effect = +/- 0.010% of span

What is the TPE in (express in psig) if the calibrated span is 3.61 psig?


(0.12 + 0.52 + 0.32 + 0.012) ½ =±0.59%

0.0059 x 3.61 psig = ±0.02 psig

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TestTest

Select the appropriate term for the following definitions:

(A) Damping (B) Reference Accuracy

(C) Dead-time (D) Time-constant

(E) Response time (F) Repeatability

(G) Stability (H) Span error

(I) Turndown error (J) Zero error

1. An error occurred when the transmitter is used

at a span other than its full span. [ ]

2. Fixed offset between true & measured value. [ ]

3. Time necessary for analog output to reach

63.2% of its final value. [ ]

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TestTest

4. Deviation in measurement for the same input

approaching from one direction. [ ]

5. Electronic delay circuit to increase transmitter’s

response time. [ ]

6. Limits of error at standard reference conditions. [ ]

7. Time before transducer’s output starts to change. [ ]

8. Transmitter’s drift over time. [ ]

9. Dead-time + Time constant. [ ]

10. Drift in transmitter’s calibrated range. [ ]

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Answer SheetAnswer Sheet

Enter the answers for the test given in this module and sent one copy to the RMT A/P Trainer in Singapore . Attention to RMT Trainer at Fax : (65) 7708000 or (65) 7770947 or (65) 7770743E-Mail : [email protected]

RMT Trainer will feedback to you the result & solution

Name: Title:

Company: Date:

Q1 Q6

Q2 Q7

Q3 Q8

Q4 Q9

Q5 Q10

Marks: /10 Marks (%):

Specifications FundamentalSpecifications Fundamental

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