Help with PCI-6221 DAQ

[vikg]

Hi,

We have a PCI-6221 DAQ (with only 2 counters on board). We need to generate 2 variable duty cycle 60 Hz PWM signals and at the same time count the number of pulses on two other lines (up to 100 pulses/sec)  without missing any.

Is there any way we could do this without buying more hardware? If not, what's the least expensive solution without resorting to purchasing another DAQ? (e.g. are there inexpensive hardware counters that we can buy that could do the same thing as a DAQ?). If we have to buy another DAQ (for example the PCI-6601), are there any problems/conflicts if we were to use two DAQs with the same PC?

Thanks a lot,

Vic

[devchander]

If we have to buy another DAQ (for example the PCI-6601), are there any problems/conflicts if we were to use two DAQs with the same PC?

No, you will not have any confilcts in such a setup

Plus, there is a little amibuity in the first part of your post.

Are you using the 2 analog output channels on board your PCI 6221 to generate the 60 Hz PWM signals and then counting them using 2 counter ??

hope this question answers your query!

regards

Dev

[vikg]

Hi Dev,

Sorry for the ambiguity but thanks for the response! We're trying to drive two motors with 2 PWM signals, and then we also need to count the pulses on two different lines (coming from reed sensors on the motor). Since the motors have a variable response, we can't predict how much they're going to move, which is why we need accurate counting of the pulses from our reed sensor.

Unfortunately, the PCI-6221 only offers us 2 counters, and we're wondering if there's some cool h/w or s/w solution to our problem without resorting to buying a new DAQ. We tried counting using the digital lines  but we'd always come up 0-5% short on the number of pulses.

thanks again,

Vic

[devchander]

PCI 6221 also has 8 clocked DIO lines( corelated DIO) did you try using these DIO lines to count the number of pulses??

[vikg]

Hi Dev,

How would I go about using the clocked/correlated DIO lines for counting pulses? Is there something special I have to do in LabVIEW? I have already tried counting pulses with a software timed loop using regular DIO and looking for digital transitions. With this method, unfortunately, we lose like 1% of the pulses (with the input pulses coming in at ~50Hz) and even more if we're, say, moving the mouse around or switching windows while the VI is running.

Thanks,

Vic

[devchander]

Hi Vic,

Go to LabVIEW examples and search for 'correlated'

I am sure that the relevant example will show up in the search.

also, this link should be a good place to begin

http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=E4C68BB4D82A126DE034080020E74861&p_...

Just for info, also read this

http://digital.ni.com/public.nsf/allkb/839CCB3E986542EB8625707C004E9F01

Regards

Dev

Message Edited by devchander on 07-18-2006 12:22 AM