USB-6008 unable to detect mVolt

[john007777]

Hi NI,

 I'm doing an academic project to prototype 'dc motor control using ultrasonic sensor and NI USB 6008  DAQ card.Minimum ultrasonic sensor out put voltage (ultrasonic sensor is Max Sonar EZ-1) what I measure using multimeter is 105mV,but Lab view showing 0.111677 V instead until a distance of 8 inches,then it changes accordingly in terms of volt with a difference of 0.01021V. Can you please advise me how can I able to display the actual mil volt?

I'm using Ai07 to input the analog voltage to DAQ. 

[Aaron_W.]

John,

Look at this forum:

http://forums.ni.com/t5/Multifunction-DAQ/NI-USB-6008-Voltage-Offset-using-RSE-and-Diff-Measurement/...

Depending on your circuit's input impedance it could be because of the low input impedance of the USB-6008.

[johnsold]

John,

You images do not show up. Insert them using the "tree" button in the toolbar at the top of the text window where you post your message.

Depending on your settings you may be seeing the resolution of the USB-6008.  The nominal resolution for the +/-10 V range, single ended is 9.77 mv which is quite close to the 10.2 mV you observe.

As Aaron W. pointed out, the USB-6008 has a non-standard input circuit with low input impedance and a 1.4 V offset. That can also affect your accuracy if the source impedance is high.

Lynn