Temperature Back to Basics RTDs (Resistance Temperature Detectors)

Introduction Types of sensors Specifications ASTM vs. IEC-60751 RTD needs, findings and calibration ITS-90 Coefficients using of multiple Pt100 0.00385 tables Smart connectors

Types of sensors

RTD Sensor Types Copper Very linear with a very limited range Nickel Most sensitive but least linear Platinum Linear wide range most commonly used

RTD Sensor Types Thin Film Wire Wound Thin Layer of Platinum on a substrate Trimmed to specific resistance Protective coating Wire Wound Coil of wire Ceramic of Glass tube

RTDs , 3, and 4 Wire (leads) Probe Surface Approximately -200 to 850°C

RTDs Platinum .392 ohms/°C 25.5 ohms @ 0°C Copper .427 ohms/°C 100 ohms @ 0°C Copper .427 ohms/°C 9.035 ohms @ 0°C Nickel .672 ohms/°C 120 ohms @ 0°C Nickel .618 ohms/°C 100 ohms @ 0°C

Specifications ASTM 1137 vs. IEC-60751

ASTM 1137 & IEC60751 ASTM 1137 Classifications Class A ±[0.13 + 0.0017|t| ]°C Class B ±[0.25 + 0.0042|t| ]°C IEC60751 Class A ±[0.15 + 0.002|t| ]°C Class B ±[0.30 + 0.005|t| ]°C

ASTM vs. IEC60751 ASTM Class A ±[0.13 + 0.0017|t| ]°C IEC60751 (100°C X .0017) + .13 = 0.3 IEC60751 Class A ±[0.15 + 0.002|t| ]°C (100°C X .002) + .15 = 0.35 Difference @ 100°C = .05°C

RTD Needs, Findings and Calibration

Replace Thermocouples with RTDs Type of RTD Needed 4 wire ASTM 1137 Class A Range -80 to 250°C Flexible for use in chambers Short probe ITS-90 Coefficients

Tolerances ASTM 1137 Class A -80°C ±.226°C -50°C ±.215°C -38°C ±.195°C Example 100 x .0017 + .13 = .3 -80°C ±.226°C -50°C ±.215°C -38°C ±.195°C 0°C ±.13°C 100°C ±.3°C 250°C ±.555°C

Search for Coefficients None found for ITS-90 ranges Found CVD (Callendar-Van Dusen) Found many tables for .00385 alpha

RTDs and the ITS-90 There isn’t a resistance vs. temperature relationship for RTDs in the ITS-90 as there is with ASTM 1137 and IEC 60751 There are no classification tolerances for RTDs in the ITS-90 as there is with ASTM 1137 and IEC 60751

ITS-90 Ranges Used Range 4 -189.8344°C to .01°C Range -80°C to 250°C Desired Range 4 -189.8344°C to .01°C Range 8 .01°C to 419.527°C Characterized RTD Comparison Tested, Cycled, Drift Checked

Verification of RTDs Characterization method used Treat them as PRTs Use ITS-90 range 4 & 8 Check drift of each Increased accuracy Accuracy of ±0.05°C Possible Drawbacks Calculation of coefficients Tolerance condition by checking drift. Update coefficients in read outs Too much time wasted!

Tables to Coefficients Vendor Tables compared to ASTM 1137 ASTM tables and decimal places Increased decimal places by using (RTD Calc) from Minco ITS-90 Range 4 and 8 coefficients created

Coefficient Calculation Example of TableWare TableWare used with permission of Hart Scientific

RTD Coefficients RTPW: 100.003989 Low Range High Range a4 = -2.07528217 E-02 a8 = -2.02549317 E-02 b4 = -1.13772287 E-03 b8 = 2.93451978 E-04 Temperature Range of -80 to 250°C

Testing of the Coefficients Enter coefficients into Hart Scientific 1590 Super Thermometer. Used a decade box that was standardized with the 1590 (1.55ppm) Decade was connected in a 4 wire connection 1590 was switch from reading resistance to temperature via the coefficients Used with permission of Hart Scientific

Testing Data Test Point Reading -80°C -80.001 0°C -.006 100°C 100.004

Verification of RTDs Drawbacks Tolerance Testing Method Less accurate Faster turn around time Universal coefficients Reduce or eliminated programming of coefficients

Verification Setup Hart Scientific 1590 with 2590 mux (Read out) Hart Scientific 5628 PRT (Reference probe) Hart Scientific 7380, 7025, 6050H (Baths) Hart Scientific MetTemp II (Software) Used with permission of Hart Scientific

Where else can this information be used? Smart Connectors that store the coefficients of the probe. Multi and single channel read outs

WHAT IS THE EQUATION ERROR? Generic Digital Read Outs Typical website Specifications Range Resolution Accuracy Probe # of wires Display Dimensions Typical Manual Specifications Range Resolution Accuracy Probe # of wires Display Sensitivity (alpha) .00385, .003916 WHAT IS THE EQUATION ERROR?

Smart connectors Used with permission of Hart Scientific

Digital Read Outs Type of Read out Needed 4 wire Connection Medium to High accuracy RTD/PRT/ Thermistor Be able to use coefficients Data dump or PC connection Used with permission of Hart Scientific

Surface Probe with Smart Connector

Questions? Mike.Imholte@BSCI.com