Thermocouples + Lightweight Small backlash by deformations + No self heating + Physically defined Zero No calibration for control loops - Characteristic sensitive Small temperature differences to cable bending/stress for high precision necessary - Low Sensitivity 42,8 µv/k for Cu-Constantan Investigation of 32 different thermocouples regarding stability of zero point and characteristics dependence on stress and temperature cycles - different materials Cu/Konstantan, Ni-Cr/Ni-Al, Pt/Rh, - Wire Manufacturer, length and diameters - Connectors - foil and thin film thermocouples Jens Flügge - 17 - Euspen Maastricht 2007
Thermocouple measurement : Design considerations 4 n lines
Thermocouple Selection: Nr. Kanal Material Schenkellänge / Durchmesser 1 00 omega Typ K, Form Y, selbstgeschweißt, gelb / rot 1m, 0,25mm 2 01 omega Typ K, Form Y, selbstgeschweißt, gelb / rot 1m, 0,25mm 3 02 omega Typ J, Form Y, selbstgeschweißt, weiß / rot 1m, 0,25mm 4 03 omega Typ J, Form Y, selbstgeschweißt, weiß / rot 1m, 0,25mm 5 04 omega Typ E, Form Y, selbstgeschweißt, violett / rot 1m, 0,25mm 6 05 omega Typ E, Form Y, selbstgeschweißt, violett / rot 1m, 0,25mm 7 06 omega Typ T, Form Y, selbstgeschweißt, blau / rot 1m, 0,25mm 8 07 omega Typ T, Form Y, selbstgeschweißt, blau / rot 1m, 0,25mm 9 08 omega Typ T, Form Y, selbstgeschweißt, blau / rot 0,5m, 0,25mm 10 09 omega Typ T, Form Y, selbstgeschweißt, blau / rot 2,5m, 0,25mm 11 10 omega Typ T, Form Y, selbstgeschweißt, blau / rot 5,0m, 0,25mm 12 11 omega Typ T, fertig gekauft 1m, 0,25mm 13 12 omega Typ T, fertig gekauft 1m, 0,25mm 14 13 ephy-mess Typ T, Folienthermoelement, geklemmt verlängert mit 1m, 0,25mm 15 14 ephy-mess Typ T, Folienthermoelement, geklemmt verlängert mit 1m, 0,25mm 16 15 Heraeus Hanau Typ K, 32 230 289 1m, 0,5mm 17 16 Heraeus Hanau Typ K, 32 230 285 1m, 0,3mm 18 17 Heraeus Hanau Typ K, 32 220 222 1m, 0,3mm 19 18 Heraeus Hanau Typ K, 32 230 283 1m, 0,2mm 20 19 Heraeus Hanau Typ K, 32 230 225 1m, 0,5mm 21 20 tc-direct Typ K, geschweißt, grün / weiß 1m, 0,2mm 22 21 tc-direct Typ K, geschraubt, grün / weiß 1m, 0,2mm 23 22 tc-direct Typ K, gesteckt, grün / weiß 1m, 0,2mm 24 23 tc-direct Typ J, geschweißt, schwarz / weiß 1m, 0,2mm 25 24 tc-direct Typ J, geschraubt, schwarz / weiß 1m, 0,2mm 26 25 tc-direct Typ J, gesteckt, schwarz / weiß 1m, 0,2mm 27 26 tc-direct Typ N, geschweißt, rosa / weiß 1m, 0,2mm 28 27 tc-direct Typ N, geschraubt, rosa / weiß 1m, 0,2mm 29 28 tc-direct Typ N, gesteckt, rosa / weiß 1m, 0,2mm 30 29 tc-direct Typ T, geschweißt, braun / weiß 1m, 0,2mm 31 30 tc-direct Typ T, geschraubt, braun / weiß 1m, 0,2mm 32 31 tc-direct Typ T, gesteckt, braun / weiß 1m, 0,2mm
Setup:
Result: Measurement over 6 month Kanal 7 Typ T Omega wire 1,0m
Result: Measurement over 6 month Kanal 17 Typ K Heraeus wire 1,0m, 0,3 mm
Result: Measurement over 6 month Kanal 31 Typ T with connector 1,0m
Result: First 10 days Kanal 7 Typ T Omega wire 1,0m
Result: Last 10 days Kanal 7 Typ T Omega wire 1,0m
Result: First 10 days Kanal 17 Typ K Heraeus wire 1,0m, 0,3 mm
Result: Last 10 days Kanal 17 Typ K Heraeus wire 1,0m, 0,3 mm
Result: First 10 days
Result: Last 10 days
Result: Influence of motion induced by a motor Kanal 10 Typ T Omega wire 1,0m
Result: Influence of a motor controller (thermocouple in air) Typ T Omega wire 3,0m
Result: Temperature increase in the oil bath (aprox. 30 C)
Result: Temperature increase along connection wires (to 37 C) Copper and Constantan simultanously heated (10 cm)
Result: Temperature increase along connection wire (to 35.5 C) only Copper wire heated (along 10 cm)
New Amplifier: First measurement 0,00014 0,00012 0,0001 0,00008 0,00006 0,00004 0,00002 0.2 mk K 0-0,00002-0,00004-0,00006-0,00008 0 2000 4000 6000 8000 10000 Stability of measuring a short over one day Measurement cycle: 4 s per channel Developed by Dietmar Drung PTB-Berlin 0.7 nv/sqrt Hz Potential free operation possible. Coupling to data aquisition by optical fiber. Noise decreased by Factor of 3
Result: Temperature increase along connection wires (to 33 C) Gold and Platinum simultanously heated (10 cm)
Result: Temperature increase along connection wire (to 35.5 C) only Gold wire heated (along 10 cm)
Thermocouples: Conclusion and Recommendation The Zero Point of a thermocouple is stable in the sub-mk range over long time No calibration necessary for measurements of small temperature differences or control of thermal gradients Noise levels of 0.25 mk p-p are possible with measurement times of less than 2 s per channel Minimize especially the length of the constantan wire between the measurement points and prevent thermal gradients along the wire as well as extreme bending Don t use thermocouples together with switching power electronics fot precision measurements Place the switching box near to the sensor in a thermally stable environment If the environment is not suited for thermocouples look for stable thermistors Jens Flügge - 17 - Euspen Maastricht 2007