Having trouble processing multiple signals simulataneously: Error -50103

[Simeonsko]

Hi,

I am a complete beginner trying to do some basic measurements using my USB-6001 DAQ and DAQExpress software.

My setup consists of three pressure sensors (analogue input) and two flow meters (frequency signal which I am reading as counter input since I couldn't set it up as frequency input directly)

Everything is connected to the same board on channels AI0, AI1, A2 for the pressure sensors and PFI 0 and PFI1 for the flow meters. I have created separate tasks for each channel and and an individual application to interpret the signal from each task.

This has worked ok so far when I had to measure a constant signal from each channel where I was starting each application, taking the measurement, stopping it and going on to the next one.

I now need to sample time dependent data and was looking for a way to start all applications simultaneously and record the data in a file so they can be compared at the same points in time. This is when I get the message "Error -50103 occurred at NI::DAQmx::Internal::DAQmx Start Task.gvi::6610001".

I looked around the forums and from what I can understand (with practically not experience in this topic) is that the tasks are fighting over the clock/counter signal. I tried combining the inputs in a single application thinking that this way the problem will be solved but I had no success.

I am sorry to be asking the same question again when it has already been discussed in other posts but I am really struggling to solve this and would really appreciate any help.

Thank you for your help

Simeon

[Kevin_Price]

I don't know anything about DAQExpress, but the *main* problem is that the USB-6001 simply isn't a suitable device for your purposes.

It may be fine for your analog measurements, but you need a device offering 2 counters that can each do frequency measurement.   The USB-6001 has 1 counter which cannot do frequency measurement, it can only count edges.

There can sometimes be workarounds where you sample the flowmeter signals as additional analog channels, but it'll depend very much on the way those devices pulse.   I'm guessing they emit short fixed-duration pulses rather than 50% duty cycle square waves, right?   Well, that's bad news for the analog workaround and *probably* make it not worth pursuing.

Do you have any other DAQ hardware available for this?

-Kevin P

[Simeonsko]

Hi,

Thank you for the reply. Unfortunately I don't have any other DAQ hardware that I can use right now 😕

I am not sure exactly what kind of pulse the flow meter outputs but I have already solved that  (I think..) by just counting rising edges and then building an application that calculates frequency from that, which seems to be working ok so far with the steady signal.

You say there may be a way to use the single counter for simultaneous analogue measurements, what would be the workaround in that case? I already tried to read just the analogue channels in a single application with the hope that they will share a counter but that still didn't work. If I manage to get that working it would still be a massive help and much better that nothing.

Many thanks

Simeon

[Kevin_Price]

Counting edges with a counter can be a start, but you only have 1 counter on your device and 2 flowmeter signals to count.  Not enough.  Also, the freq measurement is based on software-queried times which will fluctuate under Windows.  Most of the time you'll probably get a decent approximate value, but you won't get the accuracy, resolution, or repeatability you could get with different hardware.

My other comment wasn't about combining counter and analog in the same task -- that's not possible.  It was about capturing the flowmeter signals as analog channels in the analog task.  But as I said before, it probably won't work out well.

Another idea I should have thought to mention before: consider putting the flowmeter signals through a frequency-to-voltage converter before wiring into the 2 additional analog channels.  Here's one randomish example I found on amazon with many options for freq and voltage ranges (and thus scaling).

-Kevin P

[Simeonsko]

Thanks again for your help.

It looks like the best way would be back to the drawing board in this case or just settle with doing the measurements separately

All the best

Simeon