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Load cell signal chain

Question asked by Ahygoon on Aug 16, 2012
Latest reply on Aug 20, 2012 by Ahygoon

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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