0-20mV Loadcell with 2080-TC card Micro850 PLC

[chikhim]

Hi everyone.
I'm trying to read values from a Loadcell with a 2080-TC card.
I know the 2080-TC is a thermocouple card but it reads millivolts that is the signal I need.
I use the TC as type K and with the Type K Thermocouple Reference Table and the formula: Connected Components Workbench software Data Count = (Temp (°C) + 270.0)*10 I know the counts what I need to read in the Input (2700 for 0 mV and 7550 for 20 mV).
The system is like a big pulley, when the load is stable the PLC read a steady value but when the pulley starts moving the value at the input populates from a very low to a very high value constantly.
Does anyone has an idea what would be happening?
As an addition, I'm doing the same with a siemens PLC 1214 with AI1 x TC (6ES7 231-5QA30-0XB0) and it works very well.
As an addition, I used an 0-20 mV calibrator to check the channel and with the calibrator I read 2700 counts with 0 mV and 7750 counts with 20 mV).

 

[Steve Bailey]

What is the frequency of the variation and does it correlate to anything mechanical? Stick/slip in the bearing?

 

[chikhim]

What is the frequency of the variation and does it correlate to anything mechanical? Stick/slip in the bearing?

It changes like every second the value and its not related to any mechanical thing.
I set the channel at 16.7 Hz as data update rate and then a I set it as 10 Hz but it was changing too like every second.

 

[Steve Bailey]

Can you post a graph of the value over time while the actual load remains constant?

 

[chikhim]

Can you post a graph of the value over time while the actual load remains constant?

The load was about 6900 lb (I measured 1.5mV aprox from the load cell and the gain is 4300 Lb per mV). I didn't use a graph software but I recorded a Video with the values of the "load" while the pulley was moving.

I Known the value of the load because I made the same test with the same Loadcell but connected to SIemens PLC with the TC card while the Pulley was moving and the load remains in the 69xx weigh.

For the graph, 23 seconds 23 change of values.

 

[chikhim]

I will use 2080sc-IF4u spectrum card and see if it works as I need.

 

[James Mcquade]

the load cell puts out a linear signal of millivolts.
the thermocouple input interpets the load cell signal as a thermocouple of type j,k... and linearizes the signal.
it may not give you the results you want.
if i an incorrect, someone please correct me.
james

 

[JeffKiper]

If you put your calibrator on the systems do you get the signal oscillation?