SD24 to sample a resistive bridge with pulsed bridge supply

Hi,

I want to use the SD24 (24 bit ADC in the MSP430AFE2x3) to sample a resistive  
strain gauge bridge (load cell) with 350ohms directly. This is no rocket 
science in case the bridge supply is at a DC reference voltage. But I want to 
save power! The bridge supply is power hungry (2.5V at 350 ohms).
My idea is to pulse the bridge supply e.g. 10 times per second (the load is 
stable) and sample it with the adc24 10 times per second. 
I want to get a load resolution of at least 12 bits.
(bridge sensivity is 2mV/V, in case of a 2.5V supply I have 1uV for the LSB)

I have not worked with the ad24 yet. Will this approach save power? From the 
datasheet I see that the reference needs at least 5ms turn on time. 
But in case I use the ratiometric concept (ADC-reference = bridge supply), I 
do not need the reference at all.
How low can I get the supply current? How long does it take for the AD24 to 
take a sample? (I do not see any timings in the datasheet?)

Or should I go a different way (e.g. sample and hold circuit in front of high 
impedance low power OPV-instrumenation amplifier) and then I use the 12bit 
ADC to sample it. 

Any of your ideas are valuable for me.

Thanks!
Matthias




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Posted by: Matthias Weingart <[email protected]>
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