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We appreciate your patience as we improve our online experience.
10-29-2020 01:41 PM
I am having trouble saving data at a particular rate. I need the user to be able to choose the rate at which data is saved. This might be 0.1 second, 1 second, 5 seconds, 3 minutes, etc. My test vary from 30 seconds to 16 hours.
I expected the loop rate to be sample rate/samples per channel. Like 1000S/1000Hz = 1 sec. This saves at 0.62 sec. Then when I change the Hz, it still does not match what I expect. Please help.
DAQmx
Chassis9174
9242 Voltage
9246 Current
9213 Thermocouple
9401 DIO/Counter
10-29-2020 01:51 PM
Hi kyle,
what happens when you read voltage, current and thermocouples in their own DAQmx tasks and loops?
Right now you put all of them (from 3 different modules!) into just one task: the slowest module will determine the possible sample rates.
Did you read all the manuals? Which one might be the slowest module?
10-29-2020 02:52 PM
On a side note, you might want to look at your code more closely. There are a lot of weird things going on.
A few small examples (I move the shift registers up slightly to show that they are not connected on the left):
10-29-2020 04:46 PM
GerdW, Yes, I have the same issue if I just sample the voltage. I just try the Basic Power Measurement vi from NI that sample the current and voltage only. The loop speed has the same issue. That just uses the 50kS/s modules. I want to sample slower and it is going too fast. Your point is well taken since the TC module is 75S/s, but does not seem to be an issue with savings at 0.1 sec so I left it in there for now. The values are just the same for in a certain time period.
Altenbach, Noted, the tunnels should have should not have been there and the wire should be connected to the shift registers. For the TC, any channels without a thermocouple give me a large number. I am just filtering that out. Noted on the dbl output. I just created this vi from my large vi that was needing the waveform. I try the high resolution seconds and get the same timing values (at least to a few decimals).
How do you suggest to control the timing of my while loop? Like I would like it to run at some rate I choose whether it be 0.1 sec or 10 sec without getting some buffer error. Note I can take a general DAQmx vi from Labview with just voltage/current and have the same issue. At 1000 hz and 1000 samples per channel, I was expecting this to take 1 sec so maybe there are some clock setting I do not have right....
10-29-2020 06:48 PM
Here is a simple example sampling voltage only. It give me the loop rate shown below. I try placing a wait in the loop of S/CH / Rate (hz). Ie 10,000/1000 = 10 seconds. I get error 200279 when I do this even in the simple attached vi.
S/CH Rate (hz) Loop time
1000 1000 0.62 sec
10000 1000 6.20 sec
Any idea on how I can get data at specific intervals like 1s or 10s without errors? I get error 200279 when I try to place a wait function in the loop.
Thanks
10-30-2020 02:16 AM - edited 10-30-2020 02:23 AM
Hi Kyle,
@kyle_vi wrote:
Here is a simple example sampling voltage only.
S/CH Rate (hz) Loop time
1000 1000 0.62 sec
10000 1000 6.20 sec
Again I repeat my suggestion from message #2: "Did you read all the manuals?" (A common acronym is RTFM! :))
In case you don't have them at hand: here's the manual for your NI9242.
It contains a paragraph on "Data rates", which will be of big interest to you!
(Suddenly all your numbers on iteration times make a lot of sense…)
Btw. DAQmx offers property nodes and using them you can read the real sample rate of your DAQmx task:
On your last VI:
Why did you define "Loop rate" as SGL and ignore the coercion dot?
10-30-2020 02:01 PM - edited 10-30-2020 02:47 PM
I have been trying to create the Sample Clock rate property but it did not have the selection available on the timing property node. I finally find one from another vi on the web and pasted it in. Amazingly the loop rate is now as expected. 1000 hz/1000 samples gives me a loop rate of 1 sec instead of 0.62 sec and 1000 hz/10,000 samples give me a loop rate of 10 sec instead of 6.2 sec.
Now when I drop a timing property node, the selections are available where I can create the sample clock rate myself. Seems to be some bug in Labview that corrected itself when I pasted the Sample Clock Rate property node into my program.
Thanks GerdW, you forced me to spend 30 minutes hunting down a 2018 or less vi with the sample rate node.
10-30-2020 04:00 PM
#skeptical
Whatever it is you're now observing, my $ are on GerdW and the device manual being correct. Perhaps your latest code no longer uses the device in question? Or something, I dunno, but I very much doubt that you've found a way to make a device do something the manual says it can't.
Your hypothesis that you've somehow "healed" a physical device by tracking down an old copy of a property node is highly dubious. In other words, I wouldn't spike the ball just yet, because it's very unlikely that you've actually crossed the goal line.
I don't know what IS going on, but I'll bet it ain't what you've been thinking. You need some more hypotheses. IMO.
-Kevin P