Using Higher Sample Rate on PXI Temperature Modules

Updated Feb 20, 2019

Reported In

Hardware

  • PXIe-4353
  • NI-9213

Issue Details

I noticed that my cDAQ temperature input module, such as the NI-9213, is able to sample at rates faster than specified in the datasheet. However, if I do this on PXI temperature input modules, such as the PXIe-4353, I get error 4730001: Requested value is not a supported value for this property. The property value may be invalid because it conflicts with another property. Why can't my PXI module sample as fast as my cDAQ module?

Solution

This behavior is only due to slight differences in how the DAQmx driver assigns sample rates. The driver doesn't prevent clock speeds that are out of spec in the cDAQ line, although it does prevent these speeds on the PXI platform.

Be aware that, even though the cDAQ task allows you to choose a higher sample rate, you are not actually obtaining a higher resolution signal. The limitation mentioned in the specifications sheet is still correct - any faster sample rate will just cause the same data point to be sampled multiple times.

Additional Information

If your goal is to sample both a temperature input module and another, higher-speed card at the same rate, you will have to make separate tasks for each, use a slower sample rate for the temperature module, synchronize the tasks, then interpolate the data from the temperature module inside LabVIEW.

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