Multiple load cells

Hello,

I have platform with 4 load cells. Each has amplifier and gives 4-20mA signal(4mA-15kN , 20mA-135kN). Two wires are used for connection.

I have analog module Lenze EPM-S403 with 4 inputs 4-20mA and load cells are connected to them. +24V goes to load cell and comes to input and - goes directly to input

What is the best way to make PLC get the best reading for total load of platform. I looked everywhere but usually a 0-10V load cells were used in examples.

Thanks

The same principals will apply for the 4-20mA as for the 0-10V load cell. You may have to change a couple things, but the only difference is that you are scaling a 4-20mA instead of a 0-10V.

Another option to consider would be using a weight indicator and trimming board for the load cells, though I have never tried this with 4-20mA load cells. Can we get the information off of the load cell?

Just scale each 4-20 ma input to match the load cell scaling, then the sum of scaled inputs is your total weight. This is how I did it recently and it passed the qualification test and received a certification.

That is an oversimplification, as I put logic in for a tare,calibration, and other functions, but the basic principle is sound. Seems like you are dealing with a lot of weight there, if I understand the kN load cell properties?

Yes it is a platform which carries 12000kg.

We tried to do the calibration of inputs with no load and half a load but when we put full load we have difference of almost 1000kg between measured and actual load.

nikoldije said:

Yes it is a platform which carries 12000kg.

We tried to do the calibration of inputs with no load and half a load but when we put full load we have difference of almost 1000kg between measured and actual load.

Click to expand...

With no load on the platform is there more than 4 ma from the transmitters? If I understand your load cell/transmitter specifications, the minimum for each load cell is 15 kN to go above 4 ma?

Correct. Load cells are under upper frame that is very heavy, so even with no load on platform its own weight is pressing load cells.

You have to set the load of the platform without weight to your zero. It is likely that each load cell will be outputting a different signal as well, though it is important that each load cell be rated for the total load of the platform to prevent damage to the load cell.