NI9232 IEPE Module nonlinear measurement deviation

[apmlengineer]

We are troubleshooting the following issue: The behavior of the acceleration signal of subject module behaves strange. All 3 channels show the same behavior. When connecting an IEPE signal simulator (verified calibration master) and simulating a signal (in the range of +/- 100 m/s^2, signal frequency = 80Hz, sensitivity= 500mV/g) for calibration of the measurement chain. The measured signal is correct until 10 m/s^2 (no deviation). At 20 m/s^2 We observe a deviation of 7 m/s^2,  as of 30 m/s^2 We observe a constant deviation of 5 m/s^2.

Does anybody have an explanation for this type of behavior? What could we do to identify the root-cause or eliminate the deviation besides exchanging the hardware?

Thanks!

[santo_13]

Please confirm if my understanding is correct,

• Sensitivity 500mV/g = ~ 50.97mV/m/s^2
• Range +/- 100m/s^2 => +/- 5.097 V range
  • But NI9232 has only one range +/-31.5Vpk typical
• At 10m/s2 - no deviation
  • 509.7mV sine = GOOD
• At 20m/s2 - 7m/s2 deviation
  • 1.02V sine = 356mV deviation
• At 30m/s2 - 5m/s2 deviation
  • 1.53V sine = 254mV deviation

As per specifications,

Uncalibrated measurement accuracy is +/- (1.5% of reading + 0.59% of range) = +/- ( 1.5% of 1.02V + 0.59% of 31.5V) = +/- 0.200V

[Henrik_Volkers]

What did you use as the verified IEPE simulator?

Here is a link to a calibration guidline : DKD-R_3-2_2019_en.pdf   with two simulators proposed. (I build my own down to DC and can set the bias... different story)

I would check the IEPE voltage during calibration.  (DMM in AC mode or if you want to sample it: Use a 9V battery in series to bring it down into +-10V range 😉 )

Oh... 4 mA current and BIAS voltage checked? 

How did you measure the amplitude? Sine fit, tone detection vi, RMS or?