We have several vessels that have scales on them. Recently I was given the "opportunity" to calibrate each of them. Now that I have done this I measured the mv/V output at each of the Digital/Analog transmitters. Each of the scales gets its signal from 3 load cells. Each of the load cells has a different output.

For example; scale D-1's load cell list [email protected]/V
[email protected]/V
[email protected]/V

At 3300 lbs I am reading 6.305mvDC. Does this seem correct? What is the formula for calculating the total output I should be receiving?

Thanks for your help.

 

The load cells are a bridge and the mV/V rating is used to quantify the output. To answer your question you need to know the voltage applied to the input terminals of the load cell. This excitation voltage is normally around 5 or 10 volts. It can be varied for calibration.

With 5VDC applied you could expect a full scale of 15mV at 2000kg. So one would expect more than 6 mV at 3/4 full scale. Working backwards, your full scale would be about 8mV if you have 6 at 3/4 full scale. 3/4 of 3mV should be 2.25 mV so your reading is correct for a excitation voltage of 6.3/2.25 or 2.8 V. That seems a little low but isn't necessarily wrong. Your full scale would be 8.4 mV at 2000kg. If your excitation voltage isn't 2.8 you have a load cell problem. I don't know if this is readable, I'm used to doing these in my head and I had to think a bit about what exactly is done.

Regards,
cww

 

As well as what Kurt said don't forget you have 3 load cells so each one only has a third of the load.

You will have some form of summing block also, usually a resistor network.

Roy

 

Allow me to elaborate on my previous inquiry, and thanks for the good information. The excitation voltage is 5vDC. The load cells are 2k kilograms @ 3mV/V, so 6000 kg=45mv at the display signal input terminals. Yes each system has a summoning box or "junction box".