Which type of cable for Data Aquisition

[RickyC]

I am currently using a Type "K" Thermocouple wire
(Shielded and Grounded) to test my system. On a 12" length of wire I have acceptable noise. On the line I will be running to my Fixture, 200' , I have unacceptable noise. Do I need some type of line conditioner or am I running the wrong type of wire?

[Chris_Rake]

I believe that you may have posted this in the wrong forum. You may have better luck posting in Sensors or signal condition.

However, in general, the longer the cable length, the more vulnerable you are to noise. There there are several factors that affect this ranging from line impedance to lack of proper shielding. To me, a 200' cable run sounds like a bad idea for thermalcouple measurements. Configurations that use differential and/or twisted pairs with good shielding can be successful at these lengths, but for unshielded 'reference to ground' signals, its bad news.

[RickyC]

Thanks Chris,
Sorry about the wrong forum thing. I have to have the long run of cable, so I will try a thermocouple at the fixture and run regular wire to the thermocouple. I don't know where to find information about line or signal conditioners, I was hoping one or the other might work and that you might sell them. I think over that long of a run I will be picking up quite a lot of noise from the metal building that I am in, no matter what I run. Any ideas or references would be welcome.
Thanks Again,
Ricky Cheatwood

[tnewton]

Two hundred feet is a long way. It must be adequately shielded. Ground the shield at one end only. The signal itself doesn't necessarily need to be grounded, but that depends on your referencing, of course. Differential is best. One of the most common noise sources is power lines- check for n*60Hz frequency content. Also, if you run goes by motors, coils, etc. More distance is best in this case.
The wires you run should be the same for both legs- length, gauge, and material. Each wire junction you create becomes another thermocouple junction; as long as they are equal it will be OK. Make sure they are solidly connected (you'll see an offset here more than noise).