Can I change the resolution of ADC from 16 bits to 12 bits?

[averagejoeb]

Hi,

I am using NI USB-6211 DAQ device. For one of my application I need to use DAQ device to convert the analog input to data samples. Since, I am mimicking the function of a particular MCU, I need to use 12 bits ADC resolution instead of 16 bits resolution which this device has. Is it possible somehow to use this device and get 12 bit resolution? 

Currently I am using DAQExpress and I am not familiar with LabView, but I am open to suggestions related to LabView as well.

Thank you! 

[JensG69]

If you read raw values (that is possible with DAQmx within LabVIEW) you could divide the results by 16 (or shift the results 4 bit right).

Regards, Jens

[averagejoeb]

@JensG69, I tried to use logical shift function in LabView...but all I can see is 0...I am not sure why, if you can help me with that. Also, I don't think dividing raw data (integer values) by 16 will produce the 12 bit data because that's scaling...but 12 bit/16 bit is related to the resolution of the ADC.

Before sending the data to logical shift function, I can see the output properly on waveform graph and I am able to log the data however, when this data is passed on to logical shift function it just gives 0.
I have attached my project. Thanks!

[santo_13]

You cannot change the resolution of ADC from 16-bit to 12-bit, the only option is to discard the resolution of the extra 4 bits at software level.

[averagejoeb]

@Santo_13, that is what I am trying to do here in my project, but can't figure out why it is not working.

[Henrik_Volkers]

OMG shifting 4 bit (and ignore the 4 bits) or dividing by 16 for integer values is the same, and yes, you need to adapt the scale.

Or you AND all unsigned integer value with 0xF0 ....:D

[averagejoeb]

Okay, I did not get what you mean by "adapt the scale"? Can you explain more? 

[santo_13]

Adapt the scale means changing the V/LSB multiplier.

For example, for a +-10V range with 16-bit ADC, each LSB corresponds to 305.176uV

whereas, for the same +-10V range with 12-bit ADC, each LSDB corresponds to 4.883mV

So, the technique has to be read raw values from DAQ at 16bit, discard the lower 4-bits, now scale it with a new LSB value.

[averagejoeb]

Thank you Santhosh for the reply. I am sorry I don't have much experience with LabView. I understand how each LSB corresponds to what value. But I couldn't find how to change this LSB value. Also I am unable to discard last 4 values. 😞

[santo_13 · Accepted solution]

I hope this helps