NI‑9230 Returns Unexpected Low Readings with Third-Party Accelerometer

Issue Details

I am performing data acquisition using an NI‑9230 module together with a third‑party accelerometer. I have enabled IEPE excitation and selected AC coupling in the NI MAX DAQmx Task. However, the measured signal amplitude is unexpectedly low, and it remains almost unchanged even when I vary the vibration frequency input.

How do I get the NI-9230 to give the correct amplitude from my accelerometer?

Solution

Check the sensor datasheet and confirm whether the sensor is a MEMS-based sensor or an IEPE sensor. If the NI‑9230 shows unexpectedly low readings when using a third‑party accelerometer, it is likely because the sensor is non‑IEPE and requires external excitation power. 

MEMS-based sensor operates differently from IEPE sensors. IEPE sensors can be powered directly by the NI-9230 using the built‑in 4mA excitation current when IEPE mode is enabled in the task configuration. However, MEMS-based sensors do not use IEPE excitation and instead require their own external DC excitation voltage.

To resolve this issue, first disable IEPE excitation in the DAQmx task. Then verify the sensor configuration and provide the required external excitation voltage to the MEMS-based sensor according to its datasheet. Refer to the sensor's wiring diagram for correct connections. Example is as below, where the sensor includes a dedicated excitation wire (red wire) for the external voltage supply.

After supplying the proper excitation voltage, the MEMS sensor should operate normally and produce expected amplitude readings.

Additional Information

If a MEMS-based accelerometer is connected while IEPE mode is enabled, the sensor does not receive the proper operating power. As a result, the NI‑9230 only detects a small and unstable output signal, which leads to the low readings observed during measurement.