I want to take loadcell signal in plc. How I can do it?

 

You should use loadcell transducer which can convert the loadcell signals to 0-10 volts analog signal.

 

I don't know which load cell you are using but most manufacturers offer an amplifier that takes the load cell measurement and converts it into an analog signal that you can wire directly into a PLC analog input module.

 

Use a load cell conditioner like ones from horton. They condition the mv signal to one the PLC can use, like 0-10vdc or 4-20ma.

Michael

 

A loadcell is rated by max weight and produces an X mV/V signal. So, say you have a 100 lb load cell which has a 2.0 mV/V range and you apply an excitation voltage of 12VDC to the cell. At 100 lbs, you would get a 24mV signal (2.0 mV x 12VDC x 100% load). At 50 lbs, you would get a 12mV signal (2.0 mV x 12VDC x 50% load).

If you want to hook up one load cell directly to the PLC, you would just need a DC voltage source and a mV input card. Allen Bradley's SLC PLC has a thermocouple/mV card that works just fine. Just make sure that you use shielded (at one end) cable for these signals because they are so weak.

If you want to take multiple load cells into a PLC, you have two options. One is to get a "summer" box that will "sum" all the voltages together (4 load cells at 50lbs each would put out 4x12mV or 48mV) which can go to one channel on the card. The other is to put each load cell on its own PLC channel and add them together in PLC ladder logic.

One final option is to purchase a load cell that is amplified in the sensor itself. Sensotec makes load cells that put out regular analog signals (0-10VDC, 4-20mA, etc). Then you can use a more common PLC analog input card. Makes life a little easier.

Just a note - voltages can vary. You will need some way to calibrate your load cell with a calibrated weight in order to assure accurate measurement.

Hope this helps.

 

Which PLC?

 

Depending on the type off PLC you could use a loadcellinterface in the PLC or är loadcelltransducer/transmitter.

If you use a loadcellinterface in the PLC you get some (in my opinion) usefull options that you often can use in the program. But this is often the most expensive way to build it.

If you use a transmitter you need some more signals for calibration, tara-setting, measurement etc.
But this is often a cheaper equipment to buy compared to the PLC-interface

Good Luck!
Björn