If the leads are Alumel / Chromel , not only is the polarity important, but the total length of the harness as well, as it will affect the calibrated reading. Some use trimming resistors for calibration, (the old fasioned wire wound type). Dave -----Original Message----- From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com]On Behalf Of George Goff Sent: Sunday, December 28, 2003 7:28 PM To: vanagon@GERRY.VANAGON.COM Subject: Re: What makes a pyrometer's cable so special?
In a message dated 12/28/03 6:24:38 PM, lalofs@RCN.COM writes: << the type of wire can be important. The thermocouple probe itself is a junction where two different metals meet, typically just melted together in a small bead. It produces a VERY small voltage roughly proportional to temperature. >> Any extension conductors from the thermocouple head to the associated instrumentation/controller are ALL important and must be the same metals as the thermocouple. This can be an expensive proposition considering the noble metals which are needed for certain types of thermocouples. Swapping the leads as sometime happens because of color coding variations, can wreak more havoc than running copper wire to the thermocouple. The potential produced is very small and very nonlinearly proportional to the temperature. George |
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