Pulse Width Measurement is Incorrect When Measuring Two Pulses at the Same Time

Updated Jul 16, 2020

Reported In

Hardware

  • Counter/Timer Device
  • USB-6210
  • USB-6212
  • USB-6363
  • USB-6366

Software

  • LabVIEW

Issue Details

I am measuring the pulse width of a digital pulse using my USB-type DAQ device. If I measure one pulse signal, the measurement has no problem. However, if I try to measure two pulse signals at the same time using two counters in the DAQ, the measurement values are incorrect as described below. How can I fix this?


     correctly measured values                     incorrectly measured values
 

Solution

This can happen when the two pulses are generated from a single device and when the pulse generating device and the DAQ don't have the common ground.
Grounding the both devices to the same reference can resolve the incorrect measurement problem. In this case, it is to connect the ground terminal of the pulse generator to the DGND terminal of your DAQ device.