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7/28/2019 Hashemian Sensors Expo06
http://slidepdf.com/reader/full/hashemian-sensors-expo06 1/36
Standards
Certification
Education & Training
Publishing
Conferences & Exhibits 1
Automation Connections
ISA EXPO 2006
H.M. HashemianPresident Analysis and Measurement Services Corporation
Knoxville, Tennessee USA
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3
H. M. Hashemian
(“Hash”)
• President of AMS, founded in 1977, specializing intesting process instrumentation.
• Fellow of ISA. Author of over 100 publicationsincluding technical papers, books, book chapters, journal articles. Most recent books:
–“Sensor Performance and Reliability ,” published by ISAin 2005
– “Maintenance of Process Instrumentation in Nuclear Power Plants,” published by Spinger -Verlag in 2006
• Latest patent, “Integrated System for Verifying thePerformance and Health of Instruments and
Processes,” awarded July 2005.
• Chairman, project leader or author of ISA, IEC, andIAEA committees writing standards, guidelines, andreports on process instrumentation.
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Process Instrumentation
• Sensors – RTDs
– Thermocouples
– Pressure Sensors
• Process-To-Sensor Interface – Thermowell for Temperature Sensors
– Sensing lines/impulse line for pressure sensors
• Cables and Connectors
– I&C Cables – Other Cables
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RTD Assembly
Seal
Weld to
External Lead
Wires
Insulation
Material
Extension
Leads
Sheath
Typical RTDs
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Air Gap in RTD Thermowell
AMS-DWG RTD062CS
RTD
FILL MATERIAL
THERMOWELL
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RTD Insertion Experiment
RTD
AIR GAP
THERMOWELL
FEELER
GAGE
SPRING
METALPLATES
RTD
CLOSEUP OF
AIR GAP 0
Gap Size (inches)
Response
Time (sec)
6.3
0.006 7.1
0.010 8.0
0.016 8.9
0.022 9.5
0.035 10.5
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RTD Response Time
RTD Response Time as a Function of Test Media
RTD
Response Time (sec)
Water (1 meter/sec) Air (5 meters/sec)
1 2.0 14.4
2 2.7 22.03 3.6 24.0
RTD Response Time With and Without Thermowell
Response Time (sec) in water at 1 meter/sec
RTD No. Well Well #1 Well #2 Well #31 1.7 4.8 5.2 6.0
2 1.8 3.6 4.1 4.6
3 1.9 4.4 4.9 5.9
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RTD Accuracy
Source of Error Estimated Value (ºC)
Bath Stability and Uniformity 0.02
SPRT Accuracy and Drift/Yr. 0.01
Measurement Equipment for SPRT(Accuracy and Drift)
0.01
Measurement Equipment for RTD(Accuracy and Drift)
0.01
Hysteresis 0.03
Repeatability 0.02
Self-Heating 0.01
Fitting Errors 0.01
Combining the Errors
Maximum Error = 0.02 + 0.01 + 0.01 + … = 0.12 ºC
RSS Error = 0.05°C=...+
2
(0.01)+
2
(0.02)
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Examples of Potential Installation Errors
Source of Error Cause
Stem Losses Large temperature gradient between the
two ends of a sensor
EMF Errors Dissimilar metals in the RTD circuit that fall
in a large temperature gradient
Lead-wire Effects Difference in lead-wire resistances in three-
wire RTDs
Insulation Resistance Low element-to-sheath resistance
(shunting error)
Contact Resistance Bad or loose connections in temperature
sensor circuit
Stratification Error Temperature gradient in fluid or gas
streams as a result of incomplete mixing
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Illustration of RTD Stem Loss
Hot Fluid
Cool
Medium
50°C
Hot Fluid320°C
Insulation
AMS-DWG RTD034D
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LCSR Test for Detection of
Cross Connected Thermocouples
JDH120A-01A
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 2 4 6 8 10
R E S P O N S E
LCSR ON CROSS WIRED THERMOCOUPLE
NORMAL LCSR TRANSIENT
TIME (SEC)
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Secondary Junction in Thermocouples
Thermocouple Tag Number
0
2
4
6
8
10
12
1 2 3 4 T
4 C
4 B
5 T
5 C
5 B
6 T
6 C
6 B
7 T
7 C
7 B
8 T
8 C
8 B
9 T
9 C
9 B
1 0 T
1 0 C
1 0 B
1 1
1 2
1 3
R e s p o n s e
T i m e
( s e c
)
DWM139A-02D
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Thermocouple Inhomogeneity Test Results
THERMOCOUPLE
INHOMOGENEITY
AMS-DWG THC014C
CHART SPEED: 6MM/SEC
TEST RESULTS
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Case Study
“Erroneous Data fromThermocouple Results in Fire in
an Industrial Facility”
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Reverse Polarity
T1 = 20C TC = 100
C TH = 600
C
VH = -27.828 mv
VC = 4.249 mv
VI = 1.019 mv
V = - 22.56
T/C Connector
Reversing the leads
at the indicator
makes V positive,
but it is the wrong
thing to do. Why?
DT = 500 C
DT = 80 C
DT = 20 C
Indicator (V)+
-
+ -
- +
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Example of RTD Cabling in a
Nuclear Power Plant AMS-DWG RTD073B
Penetration
Protection Cabinet
150' Cable
in Control Room at ASP
375' Cable
OutsideContainment
Terminal Box
20' Pigtail
Butt Splices
175' Cable
ContainmentInside Pull Box with RTD
-0.2
0.0
0.2
0.4
-50 50 150 250 350
DISTANCE (METERS)
FIELD
PENETRATION
TEST LEAD
WIRES 1 & 2
WIRES 2 & 3
TERMINAL
BOX RTD LOCATION
IN THE FIELD
R E F L E C T I O N
C O E F F I C
I E N T ( R H O )
c
3 2 1
RTD
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Principle of Indenter Operation
InstrumentedAnvilCable
SupportBlock
Applied Force
CSPE Jacket, EPR Insulated Cable
250
150
100
50
0
M o
d u
l u s
( l b / i n
. )200
Hours
0 50 100 150 200 250 300 350
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Potential Sensing Line Problems
• Blockages• Air or Gas
• Freezing
• Improper line-up or seating of isolation and equalizing
valves• Leakage in the sensing lines due to valve problems
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Dynamic Response When
Oil Has Leaked Out of Cell
JPF025A-04AS
80
96
112
R C S F l o w
( % )
FT-445
FT-444“Expected
Response”
125
105
110
115
120
R C S F l o w
( % )
10:30 AM 11:51 AM
FT-425
FT-424
“Expected
Response”
JPF025A-01B
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Related Resources from ISA
Phone: (919) 549-8411
E mail Address: info@isa org
• “Sensor Performance and Reliability ,” H.M.Hashemian, published by ISA, 2005.