Thermocouple input ML 1400

[Dcon]

I am getting a unstable reading from 1762-IT4 module...jumping up and down, but only when the heating element is on. Here is what I got, a single type J thermocouple to 1762-IT4 moudle, the thermocouple is connected to a block of metal heated with one 120v element, element is controlled by 4-20ma proportinal SS contactor. I am controlling heat with PID in the ML 1400. Here are the 1762-IT4 settings I have,10hz filter, upscale, degrees F, thermocouple J, scaled for pid.

Any help would be great!!

Thanks

 

[kwm985]

What do you mean exactly by jumping up and down? Sounds like something is going to ground on the device your measuring.

 

[Mickey]

Try adjusting the filter setting. See PDF below.

 

[danw]

1) use an ungrounded thermocouple.
2) don't run the thermocouple extension wire parallel to the wires carrying current to the heater element.

 

[ecoste68]

Looks like you are running the 4-20ma and the heater 120vac cables together in the same conduit. If thats is corret reparate them.

 

[shooter]

when measuring be sure to have the element off, and yes a filter in software is also ossible, however not precise.
And as usual do not ground the sensor anywhere, but the shield of the cable has to be grounded on one point only (next to PLC.

 

[Dcon]

I am just bench testing this set up for now, the wires are separated also. Also tried tho adjust the filter on the module and really didnt help.

 

[Dcon]

I got it figured out. Just used a ungrounded thermocouple and the reading is very steady now.

Thanks to all for the help

 

[Mickey]

I am just bench testing this set up for now, the wires are separated also. Also tried tho adjust the filter on the module and really didnt help.

Is the system grounded properly?

There are other filters see txt below, but this is just a bandage.