wandering signal with electret microphone

[tommyjpuz]

Hi, I'm getting strange results from my electret microphones. When they pick up a noise of a fairly low amplitude, they are fine, but when they pick up a really high amplitude noise, the signal voltage jumps up and takes a while to settle down again. Excuse my lack of technical terminology. For example, a mic which generally sits at about +.75V when idle will jump up to about +.95V for a few seconds after being hit hard. Wondering if this is a wiring problem or something in the card (i don't get the same problem when i look at the mic output using an oscilloscope).

The circuit i am using to power them:
+9V--mic--daq channel--2.2KOhm resistor--ground

[Filipe A.]

Hello;

Some things to double check:

1) Is the board configured as Differential Input mode? If not, change that mode to differential.
2) Is the Mic hooked up accordainly with the board input mode? For differential input, the positive lead of the mic goes to channel X and the negative lead goes to channel X+8.
3)If the sample rate is high, try to increase the interchannel delay to let the instrumentation amplifier settle for a longer period pf time.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments