How do I find out the time delay due to multiple data readings?

[JohnGalt]

I am writing a program to take multiple readings from several instruments, and the timing of each of these reads is very important. I am almost certain that this many readings will lead to some kind of delay in the readings and results. How do I a) find out if there is any time delay and b) calculate the time delay so that I can compensate for it? I am writing through a serial ports, with a few A/D reads. I doubt that the A/D will make much of a differencee, but yo nw=ever know with computers...


Thank you

[Megan B.]

Hi John Galt,

Would it work for you to simply use the Get Date/Time in Seconds VI?  You could call this while performing your I/O to get a current timestamp.  You could then subtract this time stamp from later time stamps to determine the elapsed time.

Please post if you have other questions about this or if I am not fully understanding the setup.

By the way--I love your user name 🙂

Megan B.
Applications Engineer

National Instruments

[Dynamik]

Hi JohnGalt,

I don't necessarily have an answer, but hope you don't mind a question for clarification?  It sounds like you're working with with command-based instruments.  Do you send a string like "ReadVolts?", whereupon the instrument makes the measurement and sends it back?  If so, then the "read" seems to consist of three key moments: the moment the read-commmand is sent from the PC to the [external] device, the moment the device makes the measurement, and the moment the program reads the measurement from an input buffer.  If it were me, I'd be most interested in the moment the instrument makes the measurement - but knowing that may require an instrument-specific answer...

Cheers

[JohnGalt]

Yes, that is exactly what I needed, to get the time that the device reads at. I have several of them running at once though, so I need to get a time for all of them. I suppose an average for the group would be good, but I would like all of them to make certain.

And yes, I liked the screenname too.

[johnsold]

If you are using GPIB and all the instruments support it, the GET command (Group Execute Trigger, or something like that) will cause all the instruments on the bus to perform the preset command (e.g., ReadData) simultaneously. The data can then be retrieved over any amount of time provided that all instruments have been read before the next reading.

Lynn