Multifunction DAQ

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different voltage in measurement.



I am intending to measure a quadrant photodiode output voltage by a PCI 6040E connected to a BNC2110. I have just found that the voltage in test panel (by NI max or Labview) is a little higher than that I measured by a voltmeter. I have some questions:


1. Does this DAQ hardware has a offset? can I change it to zero? or it is such kind of amplification of voltage?

2- Quadrant photodiode has connected to a power supply with a ground. Which is better in my case, the floating or ground measurement? I have just tried both, but there is no different between amounts of measured signal.  In case of ground, Do I need to connect the ground of power supply to some places like BNC 2110, or computer?


Thank you,


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Hi Faeghe,

You can perform a Self-Calibration from Measurement and Automation Explorer. This will -probably- correct for temperature influences in the measured signal. If the signal is still different from the multimeter and you are sure that the multimeter is correct, a calibration of your DAQ device might be needed (

When it comes to grounding: if the signal source is grounded as in your case, your DAQ device should have a differential or single-ended non-referenced input configuration to avoid ground loops. Connecting a ground wire from the photodiode to the BNC connector is not needed. Have a look at:


Does this help you?


With kind regards,


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