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How to convert differential to single ended (load cell amplifier)

Category: Hardware
Product Number: AD8426

I am using a 6-axis load cell which has a built in amplifier.  However, the output signal is differential and the analogue inputs on the control unit are single ended (0V to 5V). 

Therefore I need to convert the load cell differential signal to single ended (0V to 5V).

I was wondering if I could use an AD8426 instrumentation amplifier to convert the differential signal to single ended and if so how ?

Details about the load cell are below (M3815C) :

The full scale for each channel is 5V...

I have assumed that: 

  • +SIG can swing from -2.5V to +2.5V (with respect to ground)
  • -SIG can swing from -2.5V to +2.5V (with respect to ground)

My understanding is that +SIG and -SIG are always the same magnitude, just opposite polarities.  In which case the behavior is shown in the animation below...

I used the online tool to simulate the circuit.  Are the following parameters correct ?

  • Vs = +/-12V
  • Gain = 1
  • Vref = 5V
  • Vcm = 0V

https://tools.analog.com/en/diamond/#difL=-5&difR=5&difSl=-5&gain=1&l=0&pr=AD8426&r=0&sl=0&tab=2&ty=1&vn=-12&vp=12&vr=5 

As the output is 10V I was thinking of using a potential divider to scale it down to 5V (the simulation does not allow a gain of less than 1).

Edit Notes

Revised understanding of differential signals (+SIG and -SIG are always the same magnitude, just opposite polarities) and added GIF
[edited by: skyrat at 3:49 PM (GMT -5) on 27 Nov 2024]

Thread Notes

  • Hi  ,

    Good day. Yes, the parameters you had were correct. I recommend using LT6372-0.2, which offers a gain of 0.5 in its configuration. As long as the application's operating range is within the limits, your configuration should work. 

    Thank you.


    Regards,
    Gilbeys

  • Thanks Gilbeys, I am considering using the LT6372-0.2 as it has the 0.5 gain option.

    As there are 6 differential signals to convert to single ended, I will need to use 6 x LT6372-0.2.

    My circuit is shown below, although there are a few things I'm not sure about:

    1. Will 100mA voltage regulators (+12V and -12V) be sufficient to power all 6 amplifiers and the voltage reference (LTC6655-5) ?

    2. Is it ok to share the voltage reference (LTC6655-5) between all 6 amplifiers, or should each amplifier have its own voltage reference ?

  • Also, in the LT6372-0.2 datasheet the typical circuit shows a LTC6655-5 voltage reference.

    However, the LTC6655-5 (and the film capacitors it requires) appear to be difficult to procure.

    Can I use the AD4550 instead ?

  • Hi  ,

    The LT6372-0.2 can draw a supply current of ~ 3 mA and therefore, the 100 mA supply current should be sufficient for the 6 amplifiers. As for the reference, I've checked with the reference current of LT6372-0.2 and the sourcing/sinking current of both the LTC6655-5 and ADR4550 should be sufficient for the amplifier. Thank you.


    Regards,
    Gilbeys