Offsetting an amplifiers nonzero output to zero?

Other Hardware General Electronics
1

Hi there,

I have some load cells that I am using with a INA125P. Unfortunately, I didn't realize until later that in order to get a high enough gain for the precision of the load cells to be useful, I end up oversaturating the 5V analog input into the Arduino using the INA125p without any load.

I excite the load cells at 10V. I can of course excite them at a lower voltage or lower the gain, but then the load cells end up as junk essentially. What I want to know is, how can I take the output it provides (i.e. let's say at 0g load it outputs 5V and at max load of 2kg it outputs 10V) and offset the 0 load case to zero (such that it is 0V and 5V instead)?

If I do this, will I encounter nonlinearities introduced into the system? The cells are relatively linear, so I wouldn't want to make calibration harder. I know I could theoretically just buy a high bit ADC, but I can't seem to find one with quite the gain I want. I would rather use digi pots to fine tune it better.

Thanks guys!

2


You can use level shfter like this

3

You should be using a 24 bit ADC like the HX711. I know you're saying that you want more gain but every bit of precision of the ADC is like doubling the gain. And of course there's always that point where all you're really going to do is amplify noise and more gain doesn't help.

4

Agreed with Chagrin, and the HX711 has differential input programmable gain Op Amps built-in. It is expressly created for the purpose of taking input from load cells.

5

This site has a trimming circuit possibility:REKLAB manual [McGill Faculty of Medicine - BioMedical Engineering Department]