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Hi engineer team,

I was looking on the ADXL1002 datasheet and I was wondering about something : is that significant and accurate to measure a voltage difference which is less than 2mV or 1mV with the ADXL1002 ? We know that the sensitivity is 40mV/g, and the ADXL1002 is made for a huge range +/-50g, so basically the main purpose is not to measure low variation.

I saw as well that the sensitivity due to the temperature is 5% of 40mV/g. So I assume than measuring an acceleration which is lower than 5% of 1g (which means 2mV) is not really accurate.

I am currently asking this cause we are reflecting about which ADC we are gonna use, and I am wondering if a 12bit ADC with a 4V VREF is enough (which allow us to have a resolution of 0.97mV).

Florent

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• Hi Mark,

• The limits of the capability of the ADXL1002 as a vibration sensor impact the choice of the ADC because if the accuracy limit is 2mV, then it is pointless to select an ADC which got a resolution of ,less than 2mV (aka AD4000) and a 12 bit ADC is enough.
• The ADXL1002 is a 11khz bandwidth accelerometer, so i guess you selected 5Khz as it is an average value, am I  right ?
• Ok I got your calculations,exepted this one :  Quantization noise = q/sqrt(12). Where does the 12 come from ?

Your thinking make sens to me now, and I understand that the ADC noise has to be smaller than the sensor noise.

So according to your calculation, the total noise of the ADXL1002 is 0.0886mV. So does it means there will always gonna be this amount of voltage which is garbage ? So this is pretty much the limit of the ADC so ? I mean that we cannot measure a voltage of less than 0.0886mV otherwise this won't make sense ?

Thanks for your help, much appreciated  !

• Hi Mark,

• The limits of the capability of the ADXL1002 as a vibration sensor impact the choice of the ADC because if the accuracy limit is 2mV, then it is pointless to select an ADC which got a resolution of ,less than 2mV (aka AD4000) and a 12 bit ADC is enough.
• The ADXL1002 is a 11khz bandwidth accelerometer, so i guess you selected 5Khz as it is an average value, am I  right ?
• Ok I got your calculations,exepted this one :  Quantization noise = q/sqrt(12). Where does the 12 come from ?

Your thinking make sens to me now, and I understand that the ADC noise has to be smaller than the sensor noise.

So according to your calculation, the total noise of the ADXL1002 is 0.0886mV. So does it means there will always gonna be this amount of voltage which is garbage ? So this is pretty much the limit of the ADC so ? I mean that we cannot measure a voltage of less than 0.0886mV otherwise this won't make sense ?

Thanks for your help, much appreciated  !

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