NI 9361 (FPGA) Frequency Measurement Returns Last Value Instead of Returning Zero

Updated Jun 15, 2018

Reported In

Hardware

  • NI-9361

Software

  • LabVIEW FPGA Module

Issue Details

I am using a NI 9361 in a CompactRIO (FPGA mode). I have configured the Measurement Mode to be Period. I am reading the signal correctly until I expect the value to be zero. When this occurs, I observe that the channel appears to return a previous value. Why is this occurring and how can I fix it?

Solution

The Maximum Measurable Period is the setting responsible for this behavior. This feature makes the counter return a measurement value of zero when the input signal period is slower than this value. When the value is set to zero, the feature is disabled, which keeps the counter measuring until a valid measurement is detected, the counter overflows, or the user stops the counter.

To fix the behavior you are observing, set the Maximum Measurable Period to a the desired period you wish to receive updated signals. You can set this value in the Module Properties.

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