"0" value from AI (4-20mA) at the start of a program (needs to restart multiple time to finally work)

[Iforire]

Hi everyone,

I have a recurrent problem on my Labview VIs.

Actually I did two for recording and controling different lab equipment (probes, pumps, ...).

The problem is when I run the program most of the time there are probes that are giving no value "0". I have to restart the program multiple times to finally get the value. Once I have the value, the program can run without any problem for a few hours/days.

For both program, it was the same probes (same brand) on two different DAQ systems (1 from Advantech and 1 from NI). The other equipments that are controlled by the program seems to work (2 AO/AI mass flow controllers, 1 AO agitator, 6 other AO channels, 1 solenoid valve).

So either there is a problem with these particular probes, or I do something wrong when programming the VIs (I think the latter is more probable...).

You will find below the typical program I am using.

Do you see something wrong there?

Would you have any advice for me? Should I modify some parameters?

Thanks a lot!

[GerdW]

Hi lforire,

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@Iforire wrote:

Do you see something wrong there?

Would you have any advice for me?

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• Why do you need to convert an array (of 2 elements) into a cluster of 9 elements to unbundle the first two elements???
• Why don't you use IndexArray when you want to index elements of an array???
• Why don't you clean up your code? (Straight wires…)

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@Iforire wrote:

The problem is when I run the program most of the time there are probes that are giving no value "0". I have to restart the program multiple times to finally get the value. Once I have the value, the program can run without any problem for a few hours/days.

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Which "probes" are you talking about?

(Why do you expect "0" values at AI channels when you start your VI?)

[Iforire]

Hi GerdW,

Thank you for your answer.

And sorry for not being crystal clear.

The image is an example, the full VI is more complex so I simplified it to the maximum so it can be better understood.

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@GerdW  a écrit :

• Why do you need to convert an array (of 2 elements) into a cluster of 9 elements to unbundle the first two elements???
• Why don't you use IndexArray when you want to index elements of an array???
• Why don't you clean up your code? (Straight wires…)

Yes indeed this is silly, in the final VI, I am using IndexArray, but not everywhere, I will modify that.

What do you mean by "clean up the code"? Actually my final VI is a total mess, I really need to improve that and need to learn how to do clean my code. I am gonna look for some tutorial (if you have some, I will be glad if you can share them!)

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Which "probes" are you talking about?

(Why do you expect "0" values at AI channels when you start your VI?)

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Sorry my English is not always good. When I say probes it's the pH and temperature sensors. There are a few others I am using that do the same thing. And they are of the same brand.

Actually, I do not expect to have a "0" value when starting the VI but a real value between 4 and 20mA. 

And something important, when I get "0" when starting the VI, it does not change and stay "0", so I cannot read the sensors values and I need to restart a few times before it can work. 

Thanks

[GerdW]

Hi lforire,

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@Iforire wrote:

What do you mean by "clean up the code"? Actually my final VI is a total mess, I really need to improve that and need to learn how to do clean my code. I am gonna look for some tutorial (if you have some, I will be glad if you can share them!)

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There is a "Style Guide" chapter in the LabVIEW help…

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@Iforire wrote:

Actually, I do not expect to have a "0" value when starting the VI but a real value between 4 and 20mA. 

And something important, when I get "0" when starting the VI, it does not change and stay "0", so I cannot read the sensors values and I need to restart a few times before it can work.

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DAQmxRead will give you a "constant 0" when there is an (upstream?) error. Are there any errors?

(We cannot debug your VI without your hardware, so you need to do that on your own!)

[Kyle97330 · Accepted solution]

As was somewhat mentioned above, you're probably getting an error but the error is hidden so you don't see it.

To give more concrete instructions on what to do:

• In your While loop, add a Boolean "Or" node between the "Stop button" and the "Stop" for the loop. 
  • One input should still be for the stop button, and the other one should be the error wire coming out of the DAQmx read VI.
• At the very end, after the Clear Task VI, add an "error out" control wired up to the error output of the Clear Task VI.
• Run your code again
• This time, if you get zeroes, the code should stop itself right away, and you will see an error code and details in the "error out" control.
  • Take that code and those details and either do a web search or forum search on them, or post them here.

[Iforire]

Thank you Kyle for the suggestion. It gives me multiple errors I need to investigate!