I'm using the attached lock-in vi to detect a signal modulating at 1kHz from noise. To check the system is working properly I have a function generator inputting the 1kHz reference signal into a BNC-2120 DAQmx board with the other signal being a 1kHz sine wave that is both generated and read by the same DAQ board.
I get values out with a magnitude that rises as the amplitude of the input (non-ref) signal rises so that's good. However I do want some clarification as to how certain parameters affect the signal.
- On decreasing the output filter time constant (TC) the magnitude of the output (R) increases. I just thought the time constant affects the noise level around the output, not the magnitude of the output itself?
- On increasing the order of the low-pass filter (filter rolloff) the magnitude of the output (R) decreases. Again, why should this be?
- I have the reference signal being input to channel 0 of the DAQ and the other signal being input to channel 1 of the DAQ. On the block diagram of the vi the ref is connected to channel 0 but the other signal is connected to a channel = iteration of the lockin loop. This was how the vi came and this is how it works! I tried reconnecting it to channel 1 but this gave me no output at all. So does anybody know why this is connected to the iteration value rather than a numerical constant?
Thanks in advance for any help!
Jenna
