IAEA Technical Meeting 29 September 2004

1
IAEA Technical Meeting29 September 2004

• Accurate and Stable Temperature Measurement in
  the Process Industry
• Moore Industries
• John Emmett CEng MIEE

2
Moore Industries

• Manufacturer of Process Interface Components
  and Systems
• Temperature Transmitters
• Trip Amplifiers
• Signal Isolators
• Data Communications and Intelligent I/O
• Plus much more

3
Topics

• Accuracy considerations for measurement
• Thermowell design / selection
• Sensor selection
• Lead wires
• Latest Temperature Transmitter Developments
• On-line health monitoring using HART
• Standard Field Device Diagnostics
• Device Specific Diagnostics
• Safety Related Accuracy Issues
• Extending proof test intervals
• Application Example

Rob Stockham Mark - Comments I can use please!
4
Typical Temperature Transmitter Assembly
5
Topics

• Accuracy considerations for measurement
• Thermowell design / selection
• Sensor selection
• Lead wires
• Latest Temperature Transmitter Developments

Rob Stockham Mark - Comments I can use please!
6
Types of Thermowells
(A) Tapered, (B) Straight, (C) Stepped, (S)
Sanitary
(A) Tapered 249 Sec Response
(C) Stepped 179 Sec Response
Tapered Threads 1/2, 3/4, 1 NPT
Tapered Threads 1/2, 3/4, 1 NPT
0.25
2.5
0.25
0.50 .26
0.25
.625
1.75
U length
1.75
U length
T (Lagging)
T (Lagging)
(B) Straight 285 Sec Response
(S) Sanitary Tri-Clover Well 149 Sec Response
Tapered Threads 1/2, 3/4, 1 NPT
0.25
Cap Diameter
0.25
0.75 0.26
0.50 0.26
Rob Stockham Mark - Comments I can use please!
U length
1.75
T (Lagging)
U length
3
7
Thermowell Selection Issues

• Where to break into the process?
• Process connections
• Mechanical considerations
• (Wake Frequency Calcs)
• Construction and material
• Response time required
• NACE

Rob Stockham Mark - Comments I can use please!
8
Topics

• Accuracy considerations for measurement
• Thermowell design / selection
• Sensor selection
• Lead wires
• Latest Temperature Transmitter Developments

Rob Stockham Mark - Comments I can use please!
9
RTD or Thermocouple

Pro Con

• RTD
• Better Stability
• Better accuracy
• More Linear
• Narrow temperature spans
• Max Temp(450 ?C)

• T/C
• High Temperatures
• (up to 2300 ?C)
• More Rugged
• Faster response time
• (Without a Well)
• Non-linear
• Extensive Drift
• Poor accuracy
• High Maintenance
• Become Grounded

Rob Stockham Mark - Comments I can use please!
10
RTD Sensor Elements
Least Expensive Fastest Response Not used in Low
or High Temperatures
More Expensive Very Rugged Best for heavy
vibration Best for Cycling Applications Best for
Low High Temps
Rob Stockham Mark - Comments I can use please!
Moore Industries Proprietary Design Wound the
entire length.. 7.5 Meters
11
What is a Class A RTD?

• Class A Elements are
• Temperature Cycled for 1000 hours
• _at_ 0 600ºC (ageing process)
• Class A Elements, after ageing will maintain
  
• accuracy for 5yrs
• Each Element is Tested twice
• for best accuracy, before assembly
• Only (.06) Elements, are used in our
• Calibrated Temperature Assemblies

Rob Stockham Mark - Comments I can use please!
12
Topics

• Accuracy considerations for measurement
• Thermowell design / selection
• Sensor selection
• Lead wires
• Latest Temperature Transmitter Developments

Rob Stockham Mark - Comments I can use please!
13
Lead Wires - Sources of Error

• Terminal block corrosion
• Connectors also create corrosion
• Extension Wire Splices
• Different Manufacturing tolerance of wires
• Loose connections
• Lead length differences
• Changing lead wire gauges

Remember Just 1 Ohm of lead imbalance creates
more than 2.5? C error for 2 or 3-Wire RTDs
Rob Stockham Mark - Comments I can use please!
14
3 Wire RTD Measurement Principle
L1
3-Wire
V
RTD
L2

• Good news
• 3 Wire, Compensates for lead length but...
• Only If L1 and L2 are exactly the same
• Bad news
• 3 Wire, does not compensate for L2 lead
  resistance differences

Rob Stockham Mark - Comments I can use please!
15
4- Wire RTD Mesurement
L1
4-Wire RTD
L2
RTD
V
L3
L4

• 4- Wire circuits use a high impedance voltage
  measurement to virtually eliminate current flow
  in the voltage loop.
• As long as RTD corrosion wire resistance is
  lt4000 ohms,
• This is the most accurate measurement possible

Rob Stockham Mark - Comments I can use please!
16
Topics

• Accuracy considerations for measurement
• Thermowell design / selection
• Sensor selection
• Lead wires
• Latest Temperature Transmitter Developments

Rob Stockham Mark - Comments I can use please!
17
Smart HART Temperature Transmitter
Architecture
Micro-Processor
Analog Output HART Modem
Micro-Processor
A/D
4-20mA/HART
RAM
RAM
ROM
ROM
Isolation
EEPROM
Display
Rob Stockham Mark - Comments I can use please!
FRONT END
BACK END
18
Temperature Transmitter Developments

• Latest 24 Bit Resolution, Self calibrating,
  charge balancing, A/D converter chips
• 0.0015 non linearity
• Sensor Matching software
• Total sensor diagnostics
• Correct discrete component selection
• eg precision wire-wound instead of film resistors
• Industrial grade components (-40 to 85oC)
• Intelligent averaging software that maintains
  response times
• Improved analogue output resolution using unique
  duty cycle filter techniques

Rob Stockham Mark - Comments I can use please!
19
High Accuracy with Sensor Matching

Operating Point 80 ºC
Upper Trim Point 85 ºC
?
Standard RTD (or T/C) curve
Exceptional accuracy near the Operating Point
with excellent performance over the rest of the
range
System Calibrated to /- 0.014 ºC NIST Traceable
Calibration
Rob Stockham Mark - Comments I can use please!
20
Title
? C
? C
Measurement Precision for 0 - 120 ? C Span
Typical Sensor Drift Over One Year
THZ TDZ 1000 ? 0.04 RTD Bath /
Sensor trimmed
0.04
0.03
TRY,TDY,TRX .06 RTD Bath /
Sensor Trim
0.05
0.06
TT Software Matched to RTD
Sensor Data
0.06
0.2
THZ, TDZ / 100 ? 0.06 RTD
0.06
0.3
TT / 100 ? 0.06 RTD / calibrator set-up
0.06
0.6
TRY, TDY, TRX, THZ,TDZ T/C Std sensor
/ bath trimmed
1-3
0.8
TT / 100 ? 0.06 RTD
0.07
0.9
TT /100 ? 0.1 RTD
0.5
1.2
Direct Connected 0.1 RTD
0.5
1.1
TT / Std T/C - calibrator set-up
.5-3
1.2
Rob Stockham Mark - Comments I can use please!
TT / Premium T/C
2.2
.5-3
TT / Standard T/C
.5-3
4.4
Direct connected Standard T/C (w Ext Wire)
3-5
5.5
21
Low level Temperature Signals

• Bottom Line - Convert as soon as practically
  possible

MIS
Rob Stockham Mark - Comments I can use please!
22
Topics

• Accuracy considerations for measurement
• Thermowell design / selection
• Sensor selection
• Lead wires
• Latest Temperature Transmitter Developments
• On-line health monitoring using HART
• Standard Field Device Diagnostics
• Device Specific Diagnostics
• Safety Related Accuracy Issues
• Extending proof test intervals
• Application Example

Rob Stockham Mark - Comments I can use please!
23
HART

• H ighway
• A ddressable
• R emote
• T ransducer

Rob Stockham Mark - Comments I can use please!
24
HART Signal
The Familiarity of 4-20 mA Analogue.. With The
Benefits of Digital Technology
Rob Stockham Mark - Comments I can use please!
25
HART History

• Originally developed by Rosemount
• Now, all rights transferred to
• HART COMMUNICATION FOUNDATION
• More than 100 Members
• 15,000,000 installed devices
• More than 2/3 Smart Instruments shipping today
  are HART compatible

Rob Stockham Mark - Comments I can use please!
26
HART Transmitter Detail
Rob Stockham Mark - Comments I can use please!
27
On Line HART Monitoring
Temperature Transmitter
4-20mA
On-line Transmitter Health Monitoring increases
measurement confidence
Diagnostic Alarm
Rob Stockham Mark - Comments I can use please!
28
HART Diagnostic Bits
The HART Message - The Field Device Status
Byte The Field Device Status is transmitted with
all messages
Preamble
Start
Addr
Com
Bcnt
Status
Data
Chk
7
6
5
4
3
2
1
0

• Bit 0 Primary Variable out of limits
• Bit 1 Non Primary Variable out of limits
• Bit 2 Analogue Output Saturated
• Bit 3 Analogue Output Fixed
• Bit 4 More Status Available
• Bit 5 Cold Start
• Bit 6 Configuration Changed
• Bit 7 Field Device Malfunction

Rob Stockham Mark - Comments I can use please!
29
On Line HART Monitoring
Temperature Transmitter
4-20mA
Converting HART directly to RS485 Digital removes
D/A and A/D errors
RS485 Modbus Digital Signal
Rob Stockham Mark - Comments I can use please!
30
On Line HART Monitoring
Temperature Transmitter with Dual Sensor Input
4-20mA
Device specific HART alarms can detect failure
of back-up sensor
Back-up sensor fail Alarm
Rob Stockham Mark - Comments I can use please!
31
Topics

• Accuracy considerations for measurement
• Thermowell design / selection
• Sensor selection
• Lead wires
• Latest Temperature Transmitter Developments
• On-line health monitoring using HART
• Standard Field Device Diagnostics
• Device Specific Diagnostics
• Safety Related Accuracy Issues
• Extending proof test intervals
• Application Example

Rob Stockham Mark - Comments I can use please!
32
IEC 61508 Functional Safety

• Over 35 years experience in high reliability
  instrument has built a robust basis for the
  requirements of safety related instrumentation

• Involvement with IEC 61508 and IEC 61511
  seminars, conferences and committees to increase
  our understanding of what is required

Rob Stockham Copy of FSCA in box

• Working with our customers on real safety
  related applications and to provide practical
  solutions

• Investment in tools, training and resources to
  undertake FMEDA work on our products

• Achieved Accredited Certification by SIRA for
  our product development processes to IEC 61508
  Part 1 and Part 2, under the CASS scheme for
  Functional Safety Capability Assessment

33
Safety Related Considerations

• A Dangerous failure is a failure that results
  in an error of more than 2 of span and leaves
  the output within an active scale
• Measurement drift and inaccuracy is an undetected
  dangerous failure and will affect the SIL (Safety
  Integrity Level) calcs

Rob Stockham Mark - Comments I can use please!
34
Partial Stroke Valve Testing
SMART Valve Positioner
4-20mA
On-line Valve monitoring extends proof test
intervals
Valve Stuck Alarm
Rob Stockham Mark - Comments I can use please!
35
Topics

• Accuracy considerations for measurement
• Thermowell design / selection
• Sensor selection
• Lead wires
• Latest Temperature Transmitter Developments
• On-line health monitoring using HART
• Standard Field Device Diagnostics
• Device Specific Diagnostics
• Safety Related Accuracy Issues
• Extending proof test intervals
• Application Example

Rob Stockham Mark - Comments I can use please!
36
Intel Clean Room Application
Main Air Duct
Compressor
TT
Air Distribution Ducts
Rob Stockham Mark - Comments I can use please!
37
Summary
Summary

• Ensure Primary Measurement Principle is Sound
• Sensors, wiring, transmitter matching etc
• Use on line HART monitoring
• To improve measurement confidence
• To give added diagnostic coverage
• Extend calibration intervals

THANK YOU
Rob Stockham Mark - Comments I can use please!