I am running some devices using a USB-485/4 adapter. The program (Labview 2012, Windows 7) reads and/or writes the devices once per second.
On two occasiions, the communication seems to stop; the values being read are wrong, but there is no error. For instance, and oven that is holding at 100C and reading that on the Yokogawa controller in it, Labview is reporting to be at 74C.
When I stop the program and try to restart, the program can't find the COM ports. Using NI DaqMax, I see that the COM ports assigned to the USB-485 have changed -- i.e., they used to be COM11, 12, 13, 14 and became COM7, 8, 9, 10. Resetting the COM port target in the Labview software the programs then ran fine again.
Later, rebooting the computer reset the device back to the original COM port assignments. This has now repeated a few days later.
What is happening?