Voltage Drop in PXIe-4309 During Multi-Channel Measurements for Strain Gauges

Updated Dec 9, 2024

Reported In

Hardware

  • PXIe-4309

Issue Details

Why does a voltage drop occur when measuring multiple channels for strain gauges with the PXIe-4309 as the sample rate increases, but not when measuring a single channel?

Solution

The PXIe-4309 is equipped with an anti-aliasing filter and a multiplexer (MUX) for channel groups.

Strain gauges need to charge the input capacitance of the amplifiers as the inputs switch. For example, refer to the source impedance errors page in the specification document. Considering that strain gauges are generally greater than 120 ohms, this is likely the cause. The PXIe-4309 is optimized/guaranteed to work at ≤ 50 ohms and ≤ 10 S/s.

 

fig11.png

Additional Information

The anti-aliasing filter reduces voltage when measuring high-frequency components. However, this phenomenon also occurs in single-channel measurements, so it is not the cause in this case.

fig12.png

When you use LabVIEW for the measurement, you can disable the filter by use of AI.DigFltr.Enable in DAQmx Channel property.

fig13.png 

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