Labview Program will hang between 33% and 50% of the time.

Question

I have a problem with a Labview program I made. I have two programs that do the same thing. One is in flat sequence form and the other is in state machine form.
As explained in the link below, I would like to make use of a microcontroller to make wiring connections for automating a measurement process. A separate current source and volt meter will be used.
https://forums.ni.com/t5/LabVIEW/Sequence-a-good-idea/td-p/2601333
I have since made some simple test programs which I have attached. The problem is when executing, the labview program will hang, but not every time the program is execute.
For example: Hall 1.2.vi will work properly twice with the third time it is executed it will hang. If you abort and try again, it will again run twice with no problems with the third hanging. This one is in flat sequence format (was in a flat sequence, but merged the windows because I thought that was the cause). From what I can tell, the program will hang when calling Keithley 6517 Single Read.vi. Both connected Keithley devices are connected to the computer via GPIB at 16 and 27. The way I verified if it was this vi causing it or contributing to it was that I removed it and the program never hung. I find it very strange that it will hang exactly on the third attempt every time.
Hall 1.3 simple.vi will work the first time and hang the second time. So it works 50% of the time. This one is in State Machine format. This one will hang at the case titled "Measure 1" which contains the Keithley 6517 Single Read.vi.
I've used the highlight execution button and watched the program run. Oddly, it doesn't hang when using this button. So I tried adding delays/wait in different places to no avail.
What could be causing this? As a side note, I say the program hangs for two reason. The main one is the program doesn't finish running so the run arrow is still black. The second thing is that if you notice at the end of the labview program, I have a block there that turns the current source off which doesn't happen when it hangs. I have to manually turn it off and then hit the abort program button to stop labview.
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Attachments:
Hall 1.2.vi ‏42 KB
Hall 1.3 simple.vi ‏81 KB

Answer 1

altenbach wrote:
SaintsFan wrote:
Also, I've tried placing wait/delays at various places with no improvement of the problem. My next thought is to just remove all the vi calls and have everything in one program.
How did you place the waits?
Why would placing everything in one program fix the problem. That makes no sense! What is your reasoning?
In the case of hall1.3, I placed a wait in the Measurement cases and CS On cases and there was no affect. In the hall 1.2 when the blocks were broken up similar to the state machine cases where each sequence window was identical to the cases, I placed a wait or delay in each window with no effect on the hanging.
My reasoning for placing everything in one program is the same as my reasoning for figuring delays would help, since the time of execution would be altered. If the execution time is faster and if the timing is the problem then I figured that the problem would happen more frequently or even every time.
Somehow I get the feeling this is not the case. The reason being the interval in which it succeeds or hangs is constant. I believe somewhere, a value is getting set. The 6517 Read vi runs fine if I run this vi by itself no matter how many or how fast I run it. Also, the same goes for both 1.2 and 1.3 if I remove the 6517 read vi they run fine no matter how fast or how many times I run them. 
Somehow after the current source is set to operate and triggers labview will hang on a set interval when calling 6517 read vi.
Separately they work, together there is a problem. I tried placing a delay between these two by connecting the error out of the trigger vi to the error in of the delay block and the error out of the delay block to the error in terminal of the 6517 config block. I've also tried delays between other blocks connected the same way. From what I understand, a called vi can't execute until all inputs are present. Is this the correct way to wire the delays?