Thermocouples + Lightweight

Small backlash by deformations

+ No self heating + Physically defined Zero

No calibration for control loops

- Characteristic sensitive to cable bending/stress

Small temperature differences 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 - Wire - Connectors - foil and thin film thermocouples

Jens Flügge

Cu/Konstantan, Ni-Cr/Ni-Al, Pt/Rh, … Manufacturer, length and diameters

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Euspen Maastricht 2007

Thermocouple measurement : Design considerations

4√n lines

Thermocouple Selection: Nr. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Kanal 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Michael Voigt, Jens Flügge

Material omega Typ K, Form Y, selbstgeschweißt, gelb / rot omega Typ K, Form Y, selbstgeschweißt, gelb / rot omega Typ J, Form Y, selbstgeschweißt, weiß / rot omega Typ J, Form Y, selbstgeschweißt, weiß / rot omega Typ E, Form Y, selbstgeschweißt, violett / rot omega Typ E, Form Y, selbstgeschweißt, violett / rot omega Typ T, Form Y, selbstgeschweißt, blau / rot omega Typ T, Form Y, selbstgeschweißt, blau / rot omega Typ T, Form Y, selbstgeschweißt, blau / rot omega Typ T, Form Y, selbstgeschweißt, blau / rot omega Typ T, Form Y, selbstgeschweißt, blau / rot omega Typ T, fertig gekauft omega Typ T, fertig gekauft ephy-mess Typ T, Folienthermoelement, geklemmt ephy-mess Typ T, Folienthermoelement, geklemmt Heraeus Hanau Typ K, 32 230 289 Heraeus Hanau Typ K, 32 230 285 Heraeus Hanau Typ K, 32 220 222 Heraeus Hanau Typ K, 32 230 283 Heraeus Hanau Typ K, 32 230 225 tc-direct Typ K, geschweißt, grün / weiß tc-direct Typ K, geschraubt, grün / weiß tc-direct Typ K, gesteckt, grün / weiß tc-direct Typ J, geschweißt, schwarz / weiß tc-direct Typ J, geschraubt, schwarz / weiß tc-direct Typ J, gesteckt, schwarz / weiß tc-direct Typ N, geschweißt, rosa / weiß tc-direct Typ N, geschraubt, rosa / weiß tc-direct Typ N, gesteckt, rosa / weiß tc-direct Typ T, geschweißt, braun / weiß tc-direct Typ T, geschraubt, braun / weiß tc-direct Typ T, gesteckt, braun / weiß

Schenkellänge / Durchmesser 1m, 0,25mm 1m, 0,25mm 1m, 0,25mm 1m, 0,25mm 1m, 0,25mm 1m, 0,25mm 1m, 0,25mm 1m, 0,25mm 0,5m, 0,25mm 2,5m, 0,25mm 5,0m, 0,25mm 1m, 0,25mm 1m, 0,25mm verlängert mit 1m, 0,25mm verlängert mit 1m, 0,25mm 1m, 0,5mm 1m, 0,3mm 1m, 0,3mm 1m, 0,2mm 1m, 0,5mm 1m, 0,2mm 1m, 0,2mm 1m, 0,2mm 1m, 0,2mm 1m, 0,2mm 1m, 0,2mm 1m, 0,2mm 1m, 0,2mm 1m, 0,2mm 1m, 0,2mm 1m, 0,2mm 1m, 0,2mm

Setup:

Michael Voigt, Jens Flügge

Result: Measurement over 6 month

Michael Voigt, Jens Flügge

Kanal 7 Typ T Omega wire 1,0m

Result: Measurement over 6 month

Michael Voigt, Jens Flügge

Kanal 17 Typ K Heraeus wire 1,0m, 0,3 mm

Result: Measurement over 6 month

Michael Voigt, Jens Flügge

Kanal 31 Typ T with connector 1,0m

Result: First 10 days

Michael Voigt, Jens Flügge

Kanal 7 Typ T Omega wire 1,0m

Result: Last 10 days

Michael Voigt, Jens Flügge

Kanal 7 Typ T Omega wire 1,0m

Result: First 10 days

Michael Voigt, Jens Flügge

Kanal 17 Typ K Heraeus wire 1,0m, 0,3 mm

Result: Last 10 days

Michael Voigt, Jens Flügge

Kanal 17 Typ K Heraeus wire 1,0m, 0,3 mm

Result: First 10 days

Michael Voigt, Jens Flügge

Result: Last 10 days

Michael Voigt, Jens Flügge

Result: Influence of motion induced by a motor

Michael Voigt, Jens Flügge

Kanal 10 Typ T Omega wire 1,0m

Result: Influence of a motor controller (thermocouple in air)

Michael Voigt, Jens Flügge

Typ T Omega wire 3,0m

Result: Temperature increase in the oil bath (aprox. 30 C)

Michael Voigt, Jens Flügge

Result: Temperature increase along connection wires (to 37 C)

Michael Voigt, Jens Flügge

Copper and Constantan simultanously heated (10 cm)

Result: Temperature increase along connection wire (to 35.5 C)

Michael Voigt, Jens Flügge

only Copper wire heated (along 10 cm)

New Amplifier: First measurement 0,00014 0,00012 0,0001 0,00008

0,00006 0,00004

0.2 mK

0,00002 0

K-0,00002 -0,00004

Developed by Dietmar Drung PTB-Berlin

-0,00006 -0,00008 0

2000

4000

6000

8000

10000

Stability of measuring a short over one day Measurement cycle: 4 s per channel

Noise decreased by Factor of 3

0.7 nV/Sqrt Hz Potential free operation possible. Coupling to data aquisition by optical fiber.

Result: Temperature increase along connection wires (to 33 C)

Michael Voigt, Jens Flügge

Gold and Platinum simultanously heated (10 cm)

Result: Temperature increase along connection wire (to 35.5 C)

Michael Voigt, Jens Flügge

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 mKp-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

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Euspen Maastricht 2007