Hello everyone,

Can we use the thermocouple cable for signal about 15 meter distance?

We understood thermocouple cable characteristics are different than normal copper wire.

We are planning to connect servo valves, LVDT's, few pressure transmitters signal (4-20 mA) to thermocouple cable for 15 meters.

take care
G.Rajesh

 

G.Rajesh,

In a pinch (in a temporary emergency situation--of a few hours or a few days duration at most) it might be possible to use T/C extension cable in place of normal twisted, shielded pair wiring for the devices you have mentioned. They are conductors, but they aren't intended for high current flows as they normally only carry millivolt signals at extremely low currents. So, I don't know how they will react (what kind of voltage drop) they will develop when used for other, higher current, higher voltage signals.

Personally, unless it was an emergency I wouldn't recommend it. I know it's been done--in an emergency--but I don't think it worked very well.

And, most of the T/C extension cables I've see were two-conductor, twisted pairs--WITHOUT a shield and shield drain wire. I've seen multi-conductor T/C extension cables with an overall cable shield and drain wire, but the individual T/C pairs were not individually shielded with individual drain wires.

T/C extension wire comes in both solid and stranded configurations, also. I've had very great problems with using solid wire for any industrial process control. It's "brittle" and it's very difficult to crimp a terminal lug on solid wire so that it doesn't vibrate loose or simply fall off. It takes a LOT of effort and a lot of tugging and pulling on every crimp-on terminal lug one tries to put on solid wire to be sure it's firmly connected. And, once it is that wire is usually pinched and if subjected to any kind of strain when terminated, and if subject to any temperature changes and/or vibration the solid conductors usually break much faster than anticipated.

It's just not a good idea to use T/C extension wire for anything other than T/C applications--except in a temporary emergency.

 

Thank you CSA,

Completey agreed with you. Yes we too not fully ready to replace the cable with T/C's extension, just studying the mertis and demerits if any emergency occurs. Thanks again.

Take care
G.rajesh

 

Technically, the 4-20mA circuits will overcome the relatively high resistance of T-C wire (0.5 ohm type J, 1.1 ohm type K per running foot) and regulate the current signal over 15m of wire run.

But, there is the 'safety' issue in that no one expects a shock level voltage on a clearly identifiable thermocouple wire. The 4-20 circuits are not likely to be shock level but the others might.

Poor practice at best.

 

Thank you Carl

We noted your concern.

take care
g.rajesh