Process temperature measurement


Thread Starter


I am trying to install 14 type J thermocouples for temperature measurement at a distance of 1000' from the P.L.C. Which A.B. component
should I use for processing the signal? Should amplifiers be used near the thermocouples and can standard copper wire be used from the amps
to the P.L.C.?

david mertens

Use TC to I (4-20mA) transmitters. The TC signals are mV signals and would be useless after 1000m, the current signals normally have no
problem with 1000 distances if you use the proper wires. Another option would be to use remote IO and place the analog input cards (TC or I if you use the transmitters) in the vincinity of your TC's. This would reduce the cabling from the PLC to the remote IO to only one (bus) cable.

There are many manufacturers of loop powered transmitters that convert a millivolt (thermcouple) signal to 4-20ma. You can bring the transmitter output back into an AB analog input card. 1000' shouldn't be a problem at all with this type of arrangement.

P.S. make sure your cables coming back to the PLC are shielded, and only ground the shield at one end!!

no need to connect any additional device, Just use type JX wire from sensor to PLC with metalic shield and earth all individual shield only at PLC end.