VISA read timeout error at uneven intervals

[RavensFan]

I don't know which chipset the NI serial device uses, but I would hope that it is guaranteed to work with VISA without issues.

I'd still try to swap that out with some other brand of USB/RS-232 adapter.  See if the problem persists.  Perhaps you can contact NI technical support.  If this is a recently purchased device or you have SSP support, I don't think it would cost you anything to give them a call.

[Alici]

I've connected the stir plate directly by serial connection to a computer and am also using a different serial cord and different computer.  The programs does sometimes run longer this way, twice between 200 to 300 times before I stop getting a response from the stir plate (previous maximum was 180 times), but still does time out.

[RavensFan]

At this point of time, I'd start to suspect the stir plate.

Rereading the message thread and seeing your comment in message #4, "Scilogex (the company that makes the stir plate) has told us that there needs to be at least a 50 ms delay between every two bytes" really leads me to that thought even more that however they implemented RS-232 serial within their firmware is just not very robust.

Do they provide any software to communicate with their plate, and if so is that able to run continuously without problems?

[Alici]

Yes.  There is a program from Scilogex that can run continuously and monitor the stir plate speed without a problem.  Unfortunately, it doesn't have Labview's functionality to connect to other systems so we were hoping to use Labview with the stir plate.  Scilogex told us the stir plate could be used with Labview when we bought it, but the only answer they give us about using Labview now is that "it should work."

[RavensFan]

It might be worth snooping on the communication between that software and the stir plate.  There is some software that could report on communication of a serial port.  (I/O Trace by NI does it, but I'm not sure if it only works with NI software.)  I can't think of the names of any right now.

Or you could use a Y adapter on the serial port and connect to an auxiliary serial port log what is happening.  Perhaps there is something different about the commands of the stir plate software or the timing of their commands that is the difference.