Load Cell Application

Typically, in stand alone meters like this, you need to go through a Set Up Routine. In that routine you indicate High and Low mV readings and corresponding weights.

Find the data sheet for the Load Cell and find the nominal weight range for the Load Cell.
(It would be nice if the maximum load you expect to read is no more than 75% of full load capability.)

Find the corresponding mV, or possibly, mA, for the range.

Find the instruction booklet for the Meter.
(You should take the time to read the entire booklet... it's small!)

It would be nice if the meter is capable of handling the full range from the Load Cell... very nice... in fact, it is required.

Go to the Set Up Routine.

Find the Min & Max Weight function.
Enter the minimum weight for the minimum signal.
Enter the maximum weight for the maximum signal.

There might be other issues that you discover as you read the booklet... handle those as well.

Exit from the set up routine.

Press the TARE button to "zero-out" the reading.

Find a "known" weight (about 75% of nominal maximum).
Put it on the scale and read the display.

Is it close to correct? If so, then try other, various "known" weights.

If not close to correct then read the mV or mA. Do the calculation to see what the mV or mA should be.

If 10 kg should produce 1.0mV then 7.5 kg should produce .75mV. It's just a ratio kinda thing.

If you can't get the meter to display the correct weight when the correct signal occurs... then it might be time to get a new meter.

Load cells as analog inputs????

I agree with the 920 (Rice Lake) idea. Let the
instrument do the logic, and move on.

This is one of those areas where an off-the-shelf
weighing head instrument is far superior to the
PLC solution.

Consider:

1.) Motion. Good scale instruments have frequency
sensitive filters that isolate vibration noise from
actual data. Good luck with a PLC doing that.

2.) Operator interface. Once you're done cobbing
together some arcane analog interface, next you have
to show the operator what the weight is.

3.) Calibration. What happens when the PLC input
card is replaced?

To me, this whole thread falls into the
"just because you can do a thing does not mean you should do a thing"
category.

The real main advantage of using a 920I is that if you have a spare you can replace and calibrate in 15 minutes flat.