synchronizing a pulse generator and a A/D read

[TeBlues]

4-8-08

I have a requirement to measure an analog feedback during a 1%, 2% and 20 % duty cycle. I need to sample the signal during the 35 usec that the duty cycle is low.

I’m using a NI-9172 chasse with a NI-9401 in slot 5 to create the different duty cycles. I have 3 NI-9221s in slots 1, 2, and 3. 1 channel of the 9221 in slot 3 is the one I’m trying to synchronize with the duty cycle pulse A NI-9211 in slot 4, and NI-9485 in 6, 7 and a NI-9481 in slot 8.

I tried triggering the read task with the output of the counter generating the duty cycle pulses but every time my vi gets to this steep I get a resource unavailable error. I have tried the DAQmx connect vi but I loose my duty cycle when I connect it to anything else.

I have tried hardwire jumpers to other inputs and many other things. Dose anybody have any ideas how I can synchronize these two signals.

Thanks

[Nick_F1]

Hi TeBlues,

Are you using more than 2 counter for the synchronization?  There are only 2 counters available for the cDAQ chassis.  If you are using 3 different counters, then the third one will get that error.  If you are using a finite pulse train, then you are taking up 2 counters to create a finite pulse train.  If you try to create another pulse after that, all the counters are being used, so you will get a resource reserved error.

One thing that you can do is to use one counter to generate a continuous pulse train and then use the other variable duty cycle pulse that you created to gate the counter.  Then you can use the output of that counter as the sample clock for your analog input.  That way, you will only be acquiring when the sample clock is going and that is determined by the counter output that you created.