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AD620 causes unwanted jumps/spikes in ADC data

Question asked by mostafanfs on Feb 21, 2018
Latest reply on Feb 23, 2018 by Alexxx

I have connected a Figaro Figaro KE-25 Oxygen Sensor with two outputs to a AD620 as an IA and then there is a ADS1232 24Bit converter in which I only use 16 Bit of converted data. 

Sensor output is in 0 ~ 60 mV range (normally 11.0mV) for Oxygen Concentration between 0 ~ 100 % 

I have checked my AD620 configuration with Analog Diamond Plot Tool:

Instrumentation Amplifier Diamond Plot Tool | Analog Devices 

I just needed to connect a +3.0V voltage to the sensor negative output (i.e. AD620 negative input) to make AD620 to work inside operation range. Actually that tool came in very handy !!

 

Everything is fine there is just one problem. I have been logging the ADC output data using LabVIEW on a chart. 

With AD620 connected to the input of ADS1232 there are some jumps in data every once in a while. Even though the sensor output has not changed not even 0.1mV !!

But when I connect the sensor output directly to the ADS1232 (not having amplifying) there are much less jumps in data.

 

Please take a look at the pictures to see what I'm talking about. 

I'm not sure where these spikes are coming from. 

Do you guys have any idea? 

I'm reading ADS1232 using a ATMEGA8 AVR. Do you think it has something to do with these spikes? 

I mean is it really a software problem or there is actually a hardware/noise/bad IA config problem? 

How can I be sure that which part is responsible for these jumps? 

Maybe the ADC converter is causing all this. I have had this problem with another pressure sensor too. It used the same hardware. 

 

ADC data with AD620 as IA

 

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