USB-6001 - Analog Input Voltage Quantization

[nnagrodski88]

Hey All,

     I am using a USB-6001 Analog Input to measure the position of a linear motor.  The position is is read by the DAQ as roughly a 0.0 to 7.0 Volt signal.  The USB-6001 has an input ADC resolution of 14-bits and an input range of +/- 10V (20 Volts total range).  This means one-bit corresponds to 1.221 mV.  (20 V / 2^14) = 0.001221.

     Now when I set the AI Voltage settings to have a minimum voltage of zero Volts and a maximum voltage of 10 Volts, will I double the measurement resolution of the DAQ?  (I.e., will one bit correspond to 0.611 mV).  Likewise can I improve this measurement resolution by setting my limits to zero Volts and +7 V, or are there discrete steps for the voltage input limits like there is for the ADC gain settings (See HERE).  

     Below is my AIO Voltage setup.

     Additionally, I noticed the input limits: "Minimum Voltage Value" and "Maximum Voltage Value" can be exceeded.  Why does this behavior occur?  What purpose does the setting serve if it doesn't limit the signal output of the DAQmx Read?

Thanks,

Nicholas

[nnagrodski88]

Bump...

[crossrulz · Accepted solution]

Looking at the specification document, it looks like the USB-6001 only has 1 range (-10V to +10V).  So setting the max and min to anything else will not doing anything for you here.

The maximum and minimum inputs are used for setting the range.  The DAQmx driver will choose the smallest range that can accept your max and min expected voltages.

[SamuRei]

Hey Nicholas,

I'll tackle this from the top down. The first answer is "No. You will not double the measurement resolution of your DAQ by halving the input range in this way". The USB-6001 has a single Input Range which is specified by the +/- 10V range of the device. In this case, the device's SAR uses the full +/- 10V input range. Other cards have multiple Input Range selections which allow for signal amplification to take full advantage of the SAR.

As far as I know, changing these ranges in software effectively limit the graph ranges that you can view, but you likely won’t see an error. Hope this helps!

Best,