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AD7194 Calibration data for 4 bipolar channels

Question asked by ottelo on Aug 18, 2013
Latest reply on Aug 21, 2013 by ChrisD.Rama

Hi there,

 

I want to measure the voltage (-10 - +10 mV) in 4 strain gauge sensors. So I decided to use the AD7194 with up to 8 bipolar channels and fast wakeup time ~ 200us. The fastest measurement period is 4ms, so the uC initated the first measurement @ channel 1 (AIN7 & 8) with Gain 128 and filter 1 = 4.8 kHz, settling time ~ 0.9ms.

 

Before I do a System offset calibration for each channel and save this calibration data on my uC. After this, I do a internal fullscale calibration on channel 1. Because each strain gauge sensor is connected to the same 3V RefV and use the same gain of 128 I assume that this single calibration on a various channel is ok. Because I have only one calibration register for one offset value I send the standard offset value (0x800000) to the adc and use "somehow" the saved offset data on my uC for later calculation.

 

But now I dont know how to calculate the real measurement value in mV or uV with my saved offset values. Or could I use other method to do a good offset calibration? I know I could send the offset data to the offset register before I do the measurement on this channel but for this I have to power down the ADC, send the data to the register, power on the ADC ... 200us and then do the measurement ... power down, change channel, send offset wait 200us... next measurement and so on = lot of time and not good for 4 channels and fast switching timings.

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