Standards Certification Education & Training Publishing Conferences & Exhibits 1 Automation Connections ISA EXPO 2006 H.M. Hashemian President Analysis and Measurement Services Corporation Knoxville, Tennessee USA

Standards Certification Education & Training Publishing Conferences & Exhibits 2 Problems and Solutions with Temperature and Pressure Measurements in Industrial Processes

3 H. M. Hashemian (“Hash”) President of AMS, founded in 1977, specializing in testing process instrumentation. Fellow of ISA. Author of over 100 publications including technical papers, books, book chapters, journal articles. Most recent books: – “Sensor Performance and Reliability,” published by ISA in 2005 – “Maintenance of Process Instrumentation in Nuclear Power Plants,” published by Spinger-Verlag in 2006 Latest patent, “Integrated System for Verifying the Performance and Health of Instruments and Processes,” awarded July Chairman, project leader or author of ISA, IEC, and IAEA committees writing standards, guidelines, and reports 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

5 Examples of Problems Encountered with RTDs Response Time Breaking Extension Wires Low Insulation Resistance Accuracy Determination Extrapolation Errors Installation Errors

6 RTD Sensing Element Weld Platinum Element Lead Wires Mandrel

7 RTD Assembly Seal Weld to External Lead Wires Insulation Material Extension Leads Sheath Typical RTDs

8 Air Gap in RTD Thermowell AMS-DWG RTD062CS RTD FILL MATERIAL THERMOWELL

9 RTD Insertion Experiment RTD AIR GAP THERMOWELL FEELER GAGE SPRING METAL PLATES RTD CLOSEUP OF AIR GAP 0 Gap Size (inches) Response Time (sec)

10 RTD Response Time RTD Response Time as a Function of Test Media RTD Response Time (sec) Water (1 meter/sec)Air (5 meters/sec) RTD Response Time With and Without Thermowell Response Time (sec) in water at 1 meter/sec RTDNo. WellWell #1Well #2Well #

11 Examples of Expected Response Time vs. Actual Response Time ExpectedMeasured 6 Seconds21 Seconds 4 Seconds12 Seconds 6 Seconds37 Seconds

12 RTD Accuracy

13 Errors in RTD Readings for Extrapolation from 200  C to 350  C

14 Examples of Potential Installation Errors Source of ErrorCause Stem LossesLarge temperature gradient between the two ends of a sensor EMF ErrorsDissimilar metals in the RTD circuit that fall in a large temperature gradient Lead-wire EffectsDifference in lead-wire resistances in three- wire RTDs Insulation ResistanceLow element-to-sheath resistance (shunting error) Contact ResistanceBad or loose connections in temperature sensor circuit Stratification ErrorTemperature gradient in fluid or gas streams as a result of incomplete mixing

15 Illustration of RTD Stem Loss Hot Fluid Cool Medium 50°C Hot Fluid 320°C Insulation AMS-DWG RTD034D

16 Problems with Thermocouples Accuracy Moisture in Sheath Insertion into Thermowell Cross-Connected Wires Secondary Junction Inhomogeneity

17 LCSR Test for Detection of Cross Connected Thermocouples JDH120A-01A RESPONSE LCSR ON CROSS WIRED THERMOCOUPLE NORMAL LCSR TRANSIENT TIME (SEC)

18 Secondary Junction in Thermocouples Thermocouple Tag Number DWM139A-02D

19 Thermocouple Inhomogeneity Test Results THERMOCOUPLE INHOMOGENEITY AMS-DWG THC014C CHART SPEED: 6MM/SEC TEST RESULTS

20 LCSR Results of In-Situ Testing of Thermocouple Inhomogeneties Seconds a) Without Inhomogeneity b) With Inhomogeneity

21 Case Study “Erroneous Data from Thermocouple Results in Fire in an Industrial Facility”

22 Correct Thermocouple Configuration T 1 = 20  CT C = 100  CT H = 600  C V = V H + V C + V I V H = mv V C = mv V I = mv V +V + V =  T = 500  C  T = 80  C  T = 20  C 600  C Connector H C T Indicator (V)

23 Reverse Polarity T 1 = 20  CT C = 100  CT H = 600  C V H = mv V C = mv V I = mv V = T/C Connector Reversing the leads at the indicator makes V positive, but it is the wrong thing to do. Why?  T = 500  C  T = 80  C  T = 20  C Indicator (V)

24 Example of RTD Cabling in a Nuclear Power Plant AMS-DWG RTD073B Penetration Protection Cabinet 150' Cable in Control Roomat ASP 375' Cable Outside Containment Terminal Box 20' Pigtail Butt Splices 175' Cable Containment Inside Pull Box with RTD

25 Results of TDR Test of a Four-Wire RTD with an Open Compensation Lead 1234 RTD ,2 2,3 3,4 Reflection (Rho) Distance (Feet)

26 Principle of Indenter Operation Instrumented Anvil Cable Support Block Applied Force CSPE Jacket, EPR Insulated Cable Modulus (lb/in.) 200 Hours

27 Cable Depot PLANT PIPING CABLE BASKET

28 Examples of Pressure Transmitter Problems Sensing Line Blockages Shared Sensing Lines Mechanical Snubbers Used in Sensing Lines Damping Pots Oil Loss Hydrogen Permeation Problem Nonlinearity in Force-Balance Transmitters Loose Strain Gauge

29 Process to Sensor Connections

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

31 Effect of Sensing Line Blockage on Dynamic Response 1E-7 1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E Frequency (Hz) PSD (in. w.c.^2/Hz) LT-475 LT-474 SG A SLB005A-02A

32 Dynamic Response When Oil Has Leaked Out of Cell JPF025A-04AS RCS Flow (%) FT-445 FT-444 “Expected Response” RCS Flow (%) 10:30 AM11:51 AM FT-425 FT-424 “Expected Response” JPF025A-01B

33 Capacitance Cell Pressure Transmitter Sensing Diaphragm Isolating Diaphragm Oil Fill Glass Insulators Convolution Plate Fill Tubes / Leadwires Ceramic Insert Metallic Capacitance Plates High Pressure Side Low Pressure Side AMS-DWG PXT084LS

34 In-Plant Detection of a Failed Rosemount Transmitter Descriptor Normal Value LT518LT528LT538LT548 Skewness 5 th Moment Variance Ratio Skewness Ratio 5 th Moment Ratio

35 Questions and Discussion

36 Related Resources from ISA Phone: (919) Address: “Sensor Performance and Reliability,” H.M. Hashemian, published by ISA, 2005.