I've done the following test, and my conclusions regarding the problem is given as well.
- After changing my input terminal configuration of the VI to NRSE I found that one of the ai channels (ai8) was actually producing the correct frequency. The other channels produced no readings that were just fluctuations around 0.
- So I connected all of the 16 microphones, one by one, to this particular channel to check whether they gave the correct frequency readings. This did show that all the microphones were working. (when I did this test, I had disconnected all the channels except that channel I was testing on)
- Then using a function generator, I checked each and every ai channel separately and was surprised to find that all the channels did actually give the right signals. So, I came to the conclusion that the individual channels are working (when I did this test, I had disconnected all the channels except the channel I was testing on)
- However, when I connected one microphone to one of the channels, with all the channels left unconnected, it did not produce a signal, except the channel that was already shown to be working (ai8).
-Then I connected all the microphones up again and to my surprise I found that the previous ai channel (ai8) that was reading the correct signals, now did NOT. However, I found that another channel (ai4) was now giving the right frequency readings, which was very strange.
- I disconnected one of the microphones that was connected to a channel that wasn't reading any signals and then I connected the function generator to that channel. The channel which the function generator was connected, and the channel (ai4) now both gave input signals.
So after all this, I've come to the conclusion that the microphones are working, the individual channels are working. The reason why I was obtaining 50 Hz was because somehow the input terminal configuration setting to RSE caused it to display the mains voltage on my VI.
But I can't figure out why all the microphones when connected together isn't working. And also, why is one channel working, and why does the channel that does work keep changing (i.e. in my test from ai8 to ai4). I'm afraid I don't know much about circuitry or how the devices were setup initially.
Any further suggestions will be very much appreciated.
Thank you.