DAQ Advice needed

[EdDickens]

Greetz All,

I'm working on a project with the following requirements and need some advice, as I haven't done a lot of DAQ work.

I need to monitor 4 TTL waveforms, looking for dropouts (missed pulses), count the pulses and compare waveform A to B, and C to D. The max frequency for the waveforms will be about 3kHz. Record all waveforms and the time if any waveform drops out of spec, and they want an on-screen o-scope to display all 4 waveforms. These last 2 requirements are not a problem, but I'll also need to monitor 2 currents, and control a power supply with VISA. And they would like to all this with one DAQ card to keep cost down and a laptop so it's portable.

I've been working on it for about a week now using a PXI-6071E since we haven't decided what to purchase for the laptop yet. My impression of what will be needed is this. Counter inputs to count the pulses. Analog In to display the waveforms and monitor the 2 currents. I'm not sure how I'll look for dropouts since the frequency will be varied from ~100-3000Hz.

The counter inputs are a question for me. On any card that has analog inputs, there are a max of 2 counters, as on my 6071E, and on the cards with more that 2 counters, there is no analog.

Now as I was experimenting with the counters, I discovered that I can switch the source selection on the Counter Source(STC).vi from PFI default to any of the 8 PFI lines, and reliably count events on any of the PFI lines. So what's the difference between the counter lines and the PFI lines, they seem to be capable of the same function. And if they are relatively the same, can I do simultaneous readings on 4 of the PFI lines.

So, can this be done on one card for a laptop (pcmcia or USB), and what card would that be. I could also use some help or examples on how handle comparing the waveforms. I have built a 4 channel scope that works on the analog in and should do all that is needed.

We're using LabVIEW 6.0.2 and Win2K & 98.

Thanks in advance.
Ed

[Erin_B.]

Ed,

Unless you are willing to purchase a 660x counter/timer board to perform the event counting on all 4 signals, you may just want to use LabVIEW's analysis VIs to count the number of pulse edges on the 4 signals. The Threshold Peak Detector VI may work for this task. Another option is to purchase 2 DAQPad-6070Es in order to provide a portable solution that has 4 counters.

The counters on your 6071E can use any PFI line as its source or gate, but you can still only count 2 signals at any one time. If you can count the signals at different times, you can programatically swap which PFI line is the counter source.

Overall, I believe that you would probably be better off just performing signal analysis on the acquired waveforms to extract the information
that you need.

Regards,
Erin

[EdDickens]

Thanks Erin,

I'll try the analysis route. Sounds like that would be the best solution for me.

Ed

[Ben]

Hi Ed,

Here's an idea from left field.

An "exclusive-or" gate will only be true when the two input signals are not the same.

A single chip could off-load millions of CPU cycles.

Ben