Slc 504
1746-NI4 Analog card
Honey well AL111 model 41EN,2T,30A
0-10 Volts dc with a range of 0 to 30,000 lbs

I need to convert counts to newtons.

Which program is better and why and is there a better way to do it.
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Thanks .......

Do you need lbs? If not then convert directly to newtons.

How can I be sure that my load cell is working properly?

WE use a checkweigh process. No weight asnd we get zero. Add 10 lbs and do we see that weight etc. I realize this may not be feasable on all systems. I have worked on some tonnage systems were a parallel calibrated source was used.

You must have a way to apply a known load and know what that load is. Calibration labs use NIST certified weights. Put a 10 kg weight on and expect to see 10 kg (98 Newtons.) If you don't have a calibrated weight then stand on the load cell (if its safe to do so) just as a ball park check.

I'm a little concerned however - If I undersand your posts here and on the other forum, there was some existing software already in the PLC that was making the conversion. Is this something that used to work but doesn't work now? If so then it is very unlikely that the problem has anything to do with PLC code but is a problem with either the load cell or with the load cell instrumentation.


A little more info might be just the ticket we need to help you solve the problem.
1) Did this work properly at some time in the past?
2) How is the load applied to the load cell?
3) What sort of apparatus is it? Press? Scale? Test stand?
4) What do you have to test the load cell output?
5) Any auxilary signals that can be used for a ball park check on the load cell, such as hydraulic pressure or air pressure, or component count?

Is there a pressure gage on your hydraulics? Multiply the pressure of your hydraulic oil by the area of your hydraulic cylinder. (Cylinder area is cylinder bore * cylinder bore * 3.14 / 4)

This will give you the force applied by the piston in whatever units you are using for the calculation (eg, if you use PSI and inches, you get pounds of force.)

Make sure you are getting the pressure of the oil at the cylinder, depending on your hydraulic system this could be different from the pressure at your pump - so look at the hydraulic diagrams and determine if what you are reading is actually cylinder pressure.


This will give you a ball park value for checking the function and linearity of the load cell but I wouldn't recommend using it to calibrate the load cell.



Depending on the machine design you may want to use a tare value to zero the load cell automatically every time you know the cylinder hydraulic pressure is unloaded and at piston is at its home position. This will keep the tare up to date as preload tension changes. You can also use a range check on the tare value to flag maintenance if the preload is out of range.