Why PXI-4462 is reading this spikes without the sensor being connected to the Cable or PXI-4462?

[Karthik_Moog]

Hello,

Currently, we are using below mentioned NI Hardware for implementation of Noise Monitoring Test System.

• PXI-1031 (Chassis)

• PXI-4462 (Slot 1)

• PXI-6514 (Slot 2)

• PXI-8108 (Controller)

We are facing a problem with PXI-4462 Card, as we are observing an anomalous behavior, while monitoring the microphone as mentioned below.

1) If we remove the micro phone and cable connecting the Micro Phone to the BNC Connector of PXI-4462 Card, we are observing Spikes in the test data monitoring.

2) If we connect the only cable without Micro Phone to the BNC Connector of PXI-4462 Card, we are still observing the spikes in the test data monitoring.

3) If we connect the microphone to the cable and then to the BNC Connector of PXI-4462 Card, we are not observing the spikes and change in the sound pressure is monitored.

However, the end user\customer is expecting a feature, when the Software application should be smart enough to detect the absence of the Micro phone (Not connecting the Microphone) to the cable. For, this feature, we are calculating the RMS values of the Microphone and comparing the same with the minimum floor limit. This logic had worked for us in the past. Because of the anomalous behavior of the PXI-4462, the RMS value of the data is always higher than the Floor Limit, though the connector had been connected.

Can you please let me know why PXI-4462 is reading this spikes without the sensor being connected to the Cable or PXI-4462?

[Vijay_J]

Hi Karthik,

Can you share the image of the noise signal if you have?

One possible cause i can think of is the High frequency noise source nearby. Have you analyzed the Noise characteristic? You can perform simple FFT to identify the noise source by switching ON and OFF of the nearby lights or machines etc...

One more way is to move the measurement setup out of the current location.

I guess there shall be a better way of identifying the Microphone connectivity rather than comparing the floating signal RMS with the sound pressure threshold level for identification. 

Thanks,

Vijay.