Input Gain on a PXI-4462

[Mystik]

Hello,

I'm trying to build a simple VI which acquires data from a microphone, performs a PSD and displays the result, in order to extract calibration information. I'm using an electret microphone powered by a battery box, and I would like to avoid having to use a mic preamp in the signal path by using the gain function inbuilt in PXI-4462. I read elsewhere that to set the gain, I just set the max input limits on the DAQmx Create Channel. However, the magnitude of my measured signal stays the same irrespective if I set the input limits to +/- 10V (0dB gain) or +/- 0.316V (+30dB gain). Am I missing something, or there might be a possible fault in my hardware?

Many thanks,

Ben 

[devchander]

Hi Ben,

Your Hardware is working fine

You have misintepreted the gain concept for NI DSA devices

This is a link gives an explanation for to the DSA gain settings

http://digital.ni.com/public.nsf/allkb/5dbcdb11906354018625676f0083cc32 

this note is given in the end of that document.

NOTE: Remember that the gain will not affect your voltage reading (just like a data acquisition device). The gain is going to affect your input range, your resolution, and thus your performance in using the 16 bits of resolution on the delta-sigma ADC. This means that if you are reading 0.5 V, and you use a gain of 20 dB, your voltage reading is going to be 0.5 V, not 5 V. Internally, the instrument keeps track of the gain, amplifies the signal, converts it to digital, and then divides it down by the gain to get the real voltage, but with the complete use of the resolution.

Hope this answers your query

Regards

Dev

Message Edited by devchander on 01-31-2006 01:56 AM

[Mystik]

Dear Dev,

thanks for your reply. I had missed that note at the end of the document! Now it makes sense 🙂 .

Regards,

Ben