Compensating Cable Substitution

Measure it?

1) The resistance of thermocouple extension wire is much higher than the corresponding gauge copper wire.  Tables showing T/C wire resistances can be found using our friend, Google. 2)  It is absolutely forbidden to substitute copper cable for thermocouple extension wire.  This is an axiom of physics. 3). Many analog inputs have a limit to how much wire resistance the input can tolerate. 4). The need for long run copper cabling for thermocouple measurement was addressed some 50 years ago with the use of '2 wire loop powered temperature transmitters'.   The thermocouple connects locally to the transmitter 'out at the process' and the transmitter sends a 4-20mA current signal back to the receiver (DCS, PLC, controller, recorder, indicator) over copper wire.   The technique is suitable for very long distances.    Our friend Google will gladly amplify on this subject for you. 5). The chemical symbol for copper is Cu, not Co.

The iPhone is hopelessly out of its league trying to edit posts. The gargantuan paragraph above displayed perfectly as separate, itemized sections (paragraphs), but the layout changed radically when submitted. The iPhone cannot navigate in the edit window. Technology is only great when it works.

I had the same problem with Opera, Bud, I have to use Firefox (Internet Exploder also works) when I make posts, else paragraphs get merged - also the toolbar for inserting images, bullets/numbers, special characters e.g. β does not appear and you cannot insert.

1. A thermocouple cable is used to connect a thermocouple if you want accuracy.
2. That means for Chromel Alumel [NiCr-NiAl] thermocouple you use NiCr and NiAl leads of the same alloy as the thermocouple.
3. Compensating cable uses cheaper materials which around ambient temperatures have the same e.m.f. versus temperature as the thermocouple alloys. Much away from normal room temperatures you get errors.
4. If you use copper cable you will get a temperature error equal to the difference of temperature between the terminals at which you connect to the thermocouple leads and that of the terminals on the measuring instrument. This error is usually too much to accept, especially since it is variable and difficult to know.
   

Look at website www.tc.co.uk and get the free guide. Read it, learn it and think about it.

Website www.omega.co.uk also has useful free manuals, some down-loadable.