Load cell signal chain

Hello,

I design a signal chain for a weight system.

I have up to 8 load cells on my system (0.55 mV/V at 5000Kg)

I want to be able to read each cell independently.

I have some questions concerning that:

1 - Sensor supply:

I know lower is the suppllower is the thermic disturbance of the load cell. So I want to supply my load cell with 5V.

Other benefit is that 5V is a common value for the ADC reference.

But it give me a poor signal sensitivity: 5V=> 1kg -> 0.55µV

Do you know a good documentation about the thermic disturbance? may be I can choose a bigger supply without problem and it will increase the sensitivity.

2 - 8 Channels:

Lot af ADC have integrated MUX, but not more than 3 (sometime 4) channels and for sur never 8 (differential).

That leads to the use of severals ADC. I prefere to have a reduced ADC and amplifier number.

That's why I want to use a multiplexer like ADG5409 (4:1) coupled with a converter like AD7731 or Ad7190.

( for example: 1 ADG5409 manage the  4 first differential inputs to the channel 1 of AD7190 and a second ADG5409 leads the 4 last differential signals to the channel 2 of the same AD7190.)

My question is: Is it a good idee to use a multiplexer for this function? (in therme of noise, signal disturbance,...)

I see the multiplexer add a Ron resitor (~100Ohm or less) but that is not a problem for me because I have a High impedane input after that (Amplificator AD621 or AD7190 directly). So for me the multiplexer will not perturb my signal. Do I think right this way?

What are the points I should take into consderations?

Thanks in advance for your help

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  • Hello Yohann,

    It is recommended to use the ADG5409 with a minimum of 9V as the supply.

    Is there a reason you chose the ADG5409, other than low resistance? These are latchup proof parts and hence are more robust to electrical stresses. Do you see this happening to these parts?

    You could consider the ADG1407, which is a 8:1 differential configuration part. This is also a low on resistance part, but does not have the latch-up proof construction of the ADG54xx series.

    If latchup proof is what you are looking for and the on resistance is not critical because of the high impedance load, then you could consider the newly released ADG5207, which is also 8:1 differential, but is designed for low charge injection and has a higher on resistance.

    Regards,

    Sean

Reply
  • Hello Yohann,

    It is recommended to use the ADG5409 with a minimum of 9V as the supply.

    Is there a reason you chose the ADG5409, other than low resistance? These are latchup proof parts and hence are more robust to electrical stresses. Do you see this happening to these parts?

    You could consider the ADG1407, which is a 8:1 differential configuration part. This is also a low on resistance part, but does not have the latch-up proof construction of the ADG54xx series.

    If latchup proof is what you are looking for and the on resistance is not critical because of the high impedance load, then you could consider the newly released ADG5207, which is also 8:1 differential, but is designed for low charge injection and has a higher on resistance.

    Regards,

    Sean

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