12-17-2007 09:20 AM
12-17-2007 09:34 AM
12-17-2007 09:34 AM
Not sure if I fully understand your question but did you check out omega.com....they probably have something to suite your application.
12-17-2007 09:38 AM
12-17-2007 10:31 AM
You do not neccessarily have to make your own T/C's from T/C wire. You can buy the thermocouples off the shelf , then use the appropriate matching connectors and thermocuple extension wire to exten dyour lead length. This way, if a T/C fails you simply unplug the bad unit and plug in a new one.
Omega's site has a lot of useful information. Make sure you have the polarities correct, use the proper wire and connectors that match the T/C you use.
12-17-2007 10:43 AM
I agree omega is probably the place to look.
Omega has nice connectors for each thermocouple type, so you can easily make "extension cords" if needed to be used with off-the shelf thermocouples. Since each of the connector terminals must match the metal of each wire, make sure you get the connectors for the correct type.
If you want to make your own thermocouple junction, one easy way is to spot weld the two wires together.
12-17-2007 01:31 PM - edited 12-17-2007 01:36 PM
12-17-2007 02:06 PM
let me add my 2c:
if you already have termocouples, with a junction, and only want to extend the wire all the way to your DAQ instrument, depending on your desired accuracy you have several choices:
1) simply connect the 2 cold side (measurement side) to simple electrical wire (shielded is a little bit better). with this, assuming the room temperature is uniform, you might expect a negative systematic error of a few degrees, on top of the room noise, typically for this kind of connections of 1Deg, for K types.
2) connect to as you call: thermocouple wire. much better quality, you have to be sure that the cold side connect to a wire made of identical material, fitted exactly for each side of the thermocouple. for that, it is common to use special type of non-symmetric connectors, also made of same material for each electrode. as everybody told you, Omega is the best. be aware: you will not avoid systematic error, rather reduce significantly the noise.
3) on top of 2, add a thermo bridge compensator (also Omega), for simulating a cold spot at 0 Deg Celsius
4) instead of 2, connect the thermo bridge to a differential amplifier. (again, yes Omega). i like this best, as you can have a full range of 10V instead of the typical few mV. noise is kept to a minumum because of the proximity of the amplifier to the source (shorter wires), and because the measuring device is totally decoupled. significant reduction of ground loops and general ground problems. of course, the amplified signal can now run in a standard BNC for 10 of meters...
12-18-2007 01:37 AM