What could cause a VI to change its behaviour depending on if it was run in isolation or as a part of a larger program?

[Chris_Kav]

I have tried to collect a list of frequencies used from an Agilent 4294A impedance analyser. I have managed to collect the data but there are a number of additional null/zero values at the start of the list of frequencies. This only occurs if I use the VI within a program. If the VI is run in isolation it works perfectly. Does anyone have any ideas what could cause this behaviour?

Thanks in advance

Chris. 

[Albert.Geven]

How is the instrument connected, what is the program doin,at what speed, is there a memory issue?
Just afew needed answers before I can start to think.....

[Chris_Kav]

Hi

The instrument is connected over a LAN interface. The program is designed to alter settings on the device, trigger a reading and return the data to the screen and save the data to a file. It does this in a linear fashion. At the point the problem occurs the instruments only instruction is to collect the data. The problem doesn’t occur with other modules.

I have a work around where I compare the number of entries in the list with the other lists of electrical data. But I would rather not have to take this step as it will slow the program down and it may cause analysis problems if the frequencies don’t correspond to the correct electrical data point.

Chris 

[Albert.Geven]

Stil to little information to give a good hint.

[johnsold · Accepted solution]

When running a VI as a top level, stand-alone VI you usually have a User Interface which is often managed by an Event Structure.  When running as a subVI, the front panel may not be open (which makes the event structure unresponsive) or some functions of the UI (such as Stop) may have different behavior. Also any file paths which are derived from the VI's path may differ.

As Albert has said, please give us more information.  Posting the VIs would be best.

Lynn