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To Calibrate or Not to Calibrate a fieldbus transmitter?
To Calibrate or Not to To Calibrate or Not to Calibrate a fieldbus Calibrate a fieldbus transmitter?transmitter?Dale Perry Pressure Marketing Manager Rosemount
[File Name or Event]Emerson Confidential27-Jun-01, Slide 2
IntroductionIntroductionIntroductionl Digital Transmitters are here
– Wireless– Fieldbus– Same architecture as Smart-HART transmitter but
without the A/D component
l Traditional methods of calculating accuracy apply although most vendors don’t explicitly explain it
l Calibrating Digital Transmitters is easy
[File Name or Event]Emerson Confidential27-Jun-01, Slide 3
AgendaAgendaAgendal Digital Transmitter Theory of Operationl Accuracy Typesl Performing the calibrationl New at the Foundation
[File Name or Event]Emerson Confidential27-Jun-01, Slide 4
Basic Block Diagram of fieldbus TransmitterBasic Block Diagram of fieldbus TransmitterBasic Block Diagram of fieldbus Transmitter
Ff Electronics
Sensor TransducerSensorCorrection
& A/D
Sensor
AI
Function Block
Resource
Function Block
[File Name or Event]Emerson Confidential27-Jun-01, Slide 5
Sensor Correction is Called the Characterize/Verify (C/V) ProcessSensor Correction is Called the Sensor Correction is Called the Characterize/Verify (C/V) ProcessCharacterize/Verify (C/V) Process
SensorCorrection
SensorCharacteristic
Data
CHARACTERIZESet Temperature
Apply pressuresStore Data
Set TemperatureApply PressuresStore Data
…….
VERIFYSet Temperature
Apply pressuresCompare Characterize data
Set TemperatureApply pressuresCompare Characterize data
……….
[File Name or Event]Emerson Confidential27-Jun-01, Slide 6
A/D Converts a Measured Variable to a digital valueA/D Converts a Measured Variable to a digital A/D Converts a Measured Variable to a digital valuevaluel Converts an Analog signal
– infinite number of valuesl To a digital value
– Discrete Number of valuesl Number of digital values determine sensor resolution
Pressure
Infinite Values
UpperRange
Limit
LowerRangeLimit
A/D Pressure
Discrete number of
Values
12.435 PSI
[File Name or Event]Emerson Confidential27-Jun-01, Slide 7
A/D is a Generic TermA/D is a Generic TermA/D is a Generic Term
LH
C1 C2
C3 C4 C/D
Capacitance to Digital
Micro
V/D
Voltage to Digital
Micro
[File Name or Event]Emerson Confidential27-Jun-01, Slide 8
Output of Sensor Transducer Block is Channeled to an AI BlockOutput of Sensor Transducer Block is Output of Sensor Transducer Block is Channeled to an AI BlockChanneled to an AI Block
Ff Electronics
Sensor Transducer
SensorCorrection
& A/D
Sensor
AI
Resource
[File Name or Event]Emerson Confidential27-Jun-01, Slide 9
AgendaAgendaAgendal Digital Transmitter Theory of Operationl Accuracy
– Rangedown – Accuracy Types– Calculating Accuracy– Total Probable Error
l Performing the calibration
[File Name or Event]Emerson Confidential27-Jun-01, Slide 10
Knowing When to Calibrate Requires a lot of InformationKnowing When to Calibrate Requires a lot Knowing When to Calibrate Requires a lot of Informationof Informationl Accuracy
– Reference Accuracy• Linearity, Hysteresis, Repeatability• Accuracy type
– Accuracy at rangedownl Total Probable Error
– Accuracy, Temperature effect, Static Pressure effectl Long Term Stabilityl Accuracy Tolerancesl Test Equipment
[File Name or Event]Emerson Confidential27-Jun-01, Slide 11
Accuracy is Typically Stated in One of Three CategoriesAccuracy is Typically Stated in One of Accuracy is Typically Stated in One of Three CategoriesThree Categories
Accuracy wholly dependent on Full Scale Value
Error is significant at low end
Inexpensive transmitters
Accuracy dependent on Range
Error gets smaller at Rangedown
Standard Rosemount accuracy
Standard high end units
Accuracy dependent on Reading
Reading gets smaller, Error gets smaller.
Commonly used in calibration equipment
Very accurate at low end
% Full Scale% Full Scale
10:1 100:1
% Full Scale% Calibrated Span
10:1 100:1
% Full Scale% of Reading
10:1 100:1
[File Name or Event]Emerson Confidential27-Jun-01, Slide 12
Reference Accuracy Includes Linearity, Hysteresis, and RepeatabilityReference Accuracy Includes Linearity, Reference Accuracy Includes Linearity, Hysteresis, and RepeatabilityHysteresis, and Repeatability
Sensor Output
Pressure
Pressure Range
Linearity
Upper Range Limit
Lower Range Limit + Hysteresis+ Repeatability
Accuracy
[File Name or Event]Emerson Confidential27-Jun-01, Slide 13
Calculating the Rangedown is Simple Calculating the Rangedown is Simple Calculating the Rangedown is Simple l HART/Analog
– Sensor Rangedown is the Ratio between the sensor Upper Range Limit and the calibrated Span
l Digital Transmitters– Sensor Rangedown is the Ratio between the
sensor Upper Range Limit and the calibrated Range
Upper Range LimitCalibrated Span = RangeDown
Upper Range LimitCalibrated Range = RangeDown
[File Name or Event]Emerson Confidential27-Jun-01, Slide 14
Calculating the Rangedown is Simple Calculating the Rangedown is Simple Calculating the Rangedown is Simple l Sensor Rangedown is the Ratio between the sensor
Upper Range Limit and the calibrated Span
3051S Range 2
250 InH202.5 InH20
= 100
Example Rangedown
100:1
Upper Range LimitCalibrated Span = RangeDown
2.49 bar0.5 bar
= 4.98 4.98:1
Span= 0.5bar
[File Name or Event]Emerson Confidential27-Jun-01, Slide 15
Accuracy Statements are Typically Only up to 10:1 Calibrated RangeAccuracy Statements are Typically Only up Accuracy Statements are Typically Only up to 10:1 Calibrated Rangeto 10:1 Calibrated RangeTypical Accuracy Statement:± 0.055 % of span. For Spans less than 10:1 ± [ 0.015+0.005%( )]% of spanURL
Span
See full range but accuracy Depends on last calibration
+250 in H200.62 bar
-250 in H200.62 bar
0
1:110:1± 0.055 % of span
25 in H2062 mbar
0
[File Name or Event]Emerson Confidential27-Jun-01, Slide 16
Three areas need to be investigated to determine Total PerformanceThree areas need to be investigated to Three areas need to be investigated to determine Total Performancedetermine Total Performance
l Total (Installed) Performance– Accuracy of measurement at installed conditions
• Reference Accuracy• Temperature Effects• Line Pressure Effects
l Long Term Stability– Accuracy of measurement over time
l Dynamic Performance– How fast the measurement tracks process changes
[File Name or Event]Emerson Confidential27-Jun-01, Slide 17
Installed Performance can be Calculated by Using the Total Probable Error Equation.Installed Performance can be Calculated by Installed Performance can be Calculated by Using the Total Probable Error Equation.Using the Total Probable Error Equation.
Accuracy at Calibrated Range
2
Installation effectsOn Accuracy
2 2
[File Name or Event]Emerson Confidential27-Jun-01, Slide 18
Example: Total Probable Error Example: Total Probable Error Example: Total Probable Error
l Accuracy = ± 0.1% of spanl Total temperature effects = ± 0.5% of spanl LP effects = ± 0.3% of spanl Calibrated span is 5 psig
What is TPE in psig, given:
TPE = 0.12 + 0.52 + 0.32 = ± 0.59% of span
TPE = 0.0059 x 5 psig = ± 0.03 psig
[File Name or Event]Emerson Confidential27-Jun-01, Slide 19
Determine Calibration Frequency needed to Maintain Required AccuracyDetermine Calibration Frequency needed to Determine Calibration Frequency needed to Maintain Required AccuracyMaintain Required Accuracy
Time
Accuracy
Published Accuracy
Total Probable Error
Maximum Error
Long Term StabilityLo
ng Term
Stability
[File Name or Event]Emerson Confidential27-Jun-01, Slide 20
AgendaAgendaAgenda
l Digital Transmitter Theory of Operationl Accuracyl Performing the calibrationl New at the Foundation
[File Name or Event]Emerson Confidential27-Jun-01, Slide 21
Digital Transmitters Require One CalibrationDigital Transmitters Require One Digital Transmitters Require One CalibrationCalibration
Ff Electronics
Sensor Transducer
SensorCorrection
& A/D
Sensor
Resource
230 inH20
AI
[File Name or Event]Emerson Confidential27-Jun-01, Slide 22
Calibration ProcessCalibration ProcessCalibration Processl Select Accurate Test Equipment
– ANSI Suggest that Calibration Equipment be at least Four times More Accurate than the Device
l Calibrate at Temperaturel Perform Zero Transmitter (optional)l Perform Lower Sensor Trim
– Should be at or below typical lower end of operational range
l Perform Upper Sensor Trim– Should be at or above typical upper end of operational
range
[File Name or Event]Emerson Confidential27-Jun-01, Slide 23
Sensor Zero TrimSensor Zero TrimSensor Zero Triml Zeros out small linear offsets due to
mounting or static pressure effect.
[File Name or Event]Emerson Confidential27-Jun-01, Slide 24
Sensor Trim (Lower & Upper)Sensor Trim (Lower & Upper)Sensor Trim (Lower & Upper)
l Sensor Trim is a two-point sensor calibration where two end-point pressures are applied, and all output is linearized between them.
l Lower Sensor Trim is an offset– Shifts entire sensor characterization
curve up or down.l Upper Sensor Trim changes the
slope of the sensor characterization curve.– Pivots on the low trim point.
l Note: Always perform the low trim first!
[File Name or Event]Emerson Confidential27-Jun-01, Slide 25
Sensor Trim (Lower & Upper)Sensor Trim (Lower & Upper)Sensor Trim (Lower & Upper)
Actual
Your test equipment/ideal
Start 150
0
Pressure Input
1500
Reading
Pressure Input
Low Trim
150
0
1500
Reading
Pressure Input
High Trim
150
0
1500
Reading
[File Name or Event]Emerson Confidential27-Jun-01, Slide 26
Calibration DocumentationCalibration DocumentationCalibration Documentationl Last Calibration history stored in transmitterl Maintenance system
– As Found– As Left– Calibration History
[File Name or Event]Emerson Confidential27-Jun-01, Slide 27
AgendaAgendaAgenda
l Digital Transmitter Theory of Operationl Accuracyl Performing the calibrationl What’s New for Calibration
[File Name or Event]Emerson Confidential27-Jun-01, Slide 28
New for Calibration of Ff SensorsNew for Calibration of Ff SensorsNew for Calibration of Ff Sensorsl Transducer Block Standardizationl Human Centered Design User Interfaces
[File Name or Event]Emerson Confidential27-Jun-01, Slide 29
New at the FoundationNew at the FoundationNew at the Foundationl Sensor Transducer Block Standardization
– Easier to make Ff calibrators.
FF-903 – Pressure
FF-904 – Temperature
FF-906 - Positioner
[File Name or Event]Emerson Confidential27-Jun-01, Slide 30
Traditional Technology Driven User InterfaceTraditional Technology Driven User InterfaceTraditional Technology Driven User Interfacel Blockl Model Parameter
[File Name or Event]Emerson Confidential27-Jun-01, Slide 31
Human Centered Design User InterfacesHuman Centered Design User InterfacesHuman Centered Design User Interfacesl Task Based
[File Name or Event]Emerson Confidential27-Jun-01, Slide 32
Human Centered DesignAll Calibration Information AccessibleHuman Centered DesignHuman Centered DesignAll Calibration Information AccessibleAll Calibration Information Accessible
[File Name or Event]Emerson Confidential27-Jun-01, Slide 33
SummarySummarySummaryl Digital transmitters do not have an analog output that has
any correlation to the sensor inputl Digital transmitters use the Calibrated Range when
determining rangedownl Look carefully at the reference accuracy statementl Total Probable Error should be used when determining
calibration frequencyl The simulator used for calibration should be at least four
times better than the accuracy of the transmitterl Human Centered Design User Interfaces makes
calibration of Ff sensors easy.
[File Name or Event]Emerson Confidential27-Jun-01, Slide 35
Where To Get More InformationWhere To Get More InformationWhere To Get More Informationl American National Standard ANSI/CSL Z540.3-
2006– Calibration Laboratories and Measuring and Test
Equipment
l PlantWeb University– http://plantweb.emersonprocess.com/university
l Emerson Process Management Education Services– http://www.emersonprocess.com/education/