cDAQmx analog input gets slower and slower

[Martin_Kunze]

Hi Kevin,

I know that relays have a bad reputation but sometimes they are the right choice.

I also agrre that this thread is running out of the headline.

We are devlopers and thigs can change very fast.

In this case I changed the VI and the call of the VI.

Letting the VI run in a infinite loop showed up that the program slows down. in the taskmanager I have seen that the memory consumption goes up in this case.

Using a direct VI call didn't show up a slow down of the system but the calls are much more less than before.

Gerd gave the hint with the sample clock. I have corrected this. 🙂

Never the less let me describe the issue in detail again.

I cahe for relays and control them with digital signals.

When I select channel 1 the first relay establishes a connection between the AI inputs and the load on this channel. The AI inputs are now in parrael to the load of channel 1.

Changing to channel to bit close the connection to the 2'nd load and in parallel is the same AI input channel.

We have measured the voltage at the AI inputs and there isn't a voltage of 9.xx V measurable.

The voltage is always as expected and depends on the load for the specific channel.

There is no reason for me why it should not work and why it shows up this behaviour.

This is my cDAQ configuration:

cDAQ-9174, NI 9401, NI 9403, NI 9209 (DSUB)

Is ist possible that other tasks working in parallel with the two digital I/O cards may have an influence?

Regards

Martin

[Kevin_Price]

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I cahe for relays and control them with digital signals.

When I select channel 1 the first relay establishes a connection between the AI inputs and the load on this channel. The AI inputs are now in parrael to the load of channel 1.

Changing to channel to bit close the connection to the 2'nd load and in parallel is the same AI input channel.

---

This previously-unmentioned info is potentially quite relevant!  What measures have you taken to manage the sequence and timing of when you generate the signal to close/open the relays, how long it takes for them to respond, how long the circuit takes to stabilize, and when you take your AI measurements?

-Kevin P

[Martin_Kunze]

Dear Kevin, dear Gerd

I solved the problem.

It was a parallel running task that fetches digital input information from another module un the same chasis.

Stopping this task while performing the measurement solved the problem.

Never the less.

Thank you very much!

Best regards

Martin

[Kevin_Price]

FWIW, I'm still suspicious of your latest self-diagnosis unless you left out some important info.  It doesn't make a lot of sense to me that a digital *input* task on a different module would affect the behavior of your analog input signals.

Just a caution that good troubleshooting includes making a serious effort at a plausible working theory for the observed anomaly.   And then further making an attempt to confirm the theory by turning the anomaly on and off.  There are times this won't yield anything definitive and you just have to shrug your shoulders, hope for the best and move on.

So what's your plausible working theory?  And for that matter, which "problem" was solved?   I was assuming it was the wrong voltage measurements, but was it merely the slow-down problem?

-Kevin P

[Martin_Kunze]

Dear Kevin

et least it turned out that I had a task conflict or race condition.

I used the same resouces twice and killed the task while another VI still uses the resource.

After removing this issue the application works correct.

Since the above mentioned task is a task that fetches input channel signals from the 32 channel digital GPIO card in the same cDAQ chassis that keeps the ADC modul too it was difficult to find the real problem.

Many thanks to all of you again and best regards

Martin