TC-01 communication in one program disrupts serial communication in another

[jcarmody]

I added a TC-01 read in one program that causes another program to lose communication with a serial device (Keithley 6487 Picoammeter).  Both programs are written in LabVIEW.  The TC-01 is a USB device and the serial device is connected using a USB-serial converter.  Can you suggest something fundamental that I've missed that could cause this phenomenon?

Thank you.

[Sam_Sharp]

USB Arbitration / USB Host issues? How many USB ports do you have / are you using any hubs? What is the chipset of the USB-serial converter - some of them are notoriously unreliable (e.g. I've had one cause bluescreens...it's not unreasonable that it might cause problems with other devices).

You could try connecting one to a different USB port as it might be on a different controller (e.g. some motherboards have the USB controller on the southbridge and then there is an additional 3rd party controller for additional ports).

It could also be a power issue - perhaps you could try a powered hub (although hubs usually make things worse, not better).

[Bob_Schor]

What is a "TC-01 read"?  Are you talking about the NI USB-TC01 Thermocouple Measurement Device?  Does it appear (in MAX) as a VISA device?  I assume your other serial device (which, I gather, is also plugged into a USB port via the USB/Serial converter) also appears as a VISA device.  Is there some code you could show us?  [I'll spare you my "rant" about attaching code, not pictures ...].

I'm also confused by how adding a read "in one program" causes "another program to lose communication with a serial device".  Now that I re-read your Post, it sounds more like plugging in the TC-01 clobbers the earlier program, is that right?  Or does running the TC-01 program render the second program non-operational?  What is the sequence that causes the problem?  What can you do to clear it?  [Does a log off help?  A reboot?]

Are you plugging these two USB devices into the same USB controller?  Using a Hub?  Does either (or both) get power from the USB line, and could that cause a problem?  Might this be a "hardware issue"?  [We Software Guys almost always blame the Hardware ...].

Bob Schor

[Hooovahh]

Yeah my only suggestion would be as others have said, port selection.  If they are both plugged in directly to the motherboard then that probably isn't it, but I'd try a few port combinations maybe with a hub.  If you are on a shared hub can you slow down the DAQ rate of the TC01?  Temperature is probably slow anyway and a single point once a second is probably sufficient.

Oh and also not all USB-232 adapters are the same.  I've had some inconsistency issues with some that are plugged into hubs when using some of the cheaper ones.