Non-time based analog acquisition rate

[Gene Z.]

I am trying to collect analog data at a rate dictated by digital encoder. Currently my acquisition rate is time-based. How do I change my program to collect data based on a digital pulse.

Thanks.

[Stuart_G]

You still want your acquisition to be time based, but in terms of time from your encoder. All you need to do is use your encoder signal as an external clock. I'm not sure if you are using Trad DAQ or DAQmx but both APIs have examples for how to use external clocks. Essentially you will hookup your encoder signal to one of the PFI lines and then use that line as the source of your clock.

StuartG

[Gene Z.]

Thank you. I knew I just wasn't looking at it the right way.
Next issue, there are 494,676 ticks in the encoder revolution and it takes about 13 seconds to go full circle. So I am trying to record a data point every 0.000026s. My hardware can not acquire data that fast? I keep getting and error that the rate is too fast. If I eliminate the error handler, I still get data. I have a 6602 card and a BNC 2345. Do you know what the maximum acquisition rate for this hardware?

[Salvador_Santolucito]

At that rate your signal is only at about 39 kHz which is well within the range of your DAQ device. That errror you are seeing may be caused by noise or jitter in the lines that can look like extra ticks in the signal.

Also, what is the pulse width of your encoder signal?

Check out the timing specifiations of yoru 6602 board found here:

http://digital.ni.com/manuals.nsf/websearch/DD0DBB6404BC139886256721007CF16D?OpenDocument&node=132100_US

I would also suggest looking in that document for information about the available filters for input signals.

-Sal