Hashemian Sensors Expo06

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





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.



4

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







RTD Assembly

Seal

Weld to

External Lead

Wires

Insulation

Material

Extension

Leads

Sheath

Typical RTDs



Air Gap in RTD Thermowell

AMS-DWG RTD062CS

RTD

FILL MATERIAL

THERMOWELL



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



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





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)





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



Illustration of RTD Stem Loss

Hot Fluid

Cool

Medium

50°C

Hot Fluid320°C

Insulation

AMS-DWG RTD034D





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)



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



19

Thermocouple Inhomogeneity Test Results

THERMOCOUPLE

INHOMOGENEITY

AMS-DWG THC014C

CHART SPEED: 6MM/SEC

TEST RESULTS





21

Case Study

“Erroneous Data fromThermocouple Results in Fire in

an Industrial Facility”





23

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)+

-

+ -

- +



24

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





26

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









30

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





32

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









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.

Hashemian Sensors Expo06

Documents