7.2. USB Troubleshooting

This section provides USB interface troubleshooting for issues that arise with new installations, existing installations, and intermittent lockups.

New installation

  1. Check that the USB driver is installed properly and that the device is functioning. In Microsoft Windows®, the device status can be checked using Device Manager by right-clicking Lake Shore Model 346 Temperature Controller under Ports (COM & LPT) or Other Devices and then clicking Properties.

  2. Check that the correct com port is being used. In Microsoft Windows®, the com port number can be checked using Device Manager under Ports (COM & LPT).

  3. Check that the correct settings are being used for communication.

  4. Check cable connections and length.

  5. Send the message terminator.

  6. Send the entire message string at one time including the terminator. (Many terminal emulation programs do not.)

  7. Send only one simple command at a time until communication is established.

  8. Be sure to spell commands correctly and use proper syntax.

Existing installation no longer working

  1. Power the instrument off, then on again to see if it is a soft failure.

  2. Power the computer off, then on again to see if communication port is locked up.

  3. Check all cable connections.

  4. Check that the com port assignment has not been changed. In Microsoft Windows®, the com port number can be checked using Device Manager under Ports (COM & LPT).

  5. Check that the USB driver is installed properly and that the device is functioning. In Microsoft Windows®, the device status can be checked using Device Manager by right-clicking Lake Shore Model 346 Temperature Controller under Ports (COM & LPT) or Other Devices and then clicking Properties.

Intermittent lockups

  1. Check cable connections and length.

  2. Increase the delay between all commands to 100 ms to make sure the instrument is not being overloaded. If possible, append *OPC? to the end of a command string It is highly recommended to append the Operation Complete Query (*OPC?) to the end of any given command string. The operation complete query is a SCPI mandated IEEE 488.2 query that will cause the instrument to send a “1” back to the user program when all commands have been processed. This scheme closes the timing loop and provides the proper balance for a user program to maximize command throughput yet not risk overrunning the instrument SCPI buffer. *OPC? can be appended onto a single command or a chained SCPI message.

  3. Ensure that the USB cable is not unplugged and that the Model 346 is not powered down while the com port is open. The USB driver creates a com port when the USB connection is detected, and removes the com port when the USB connection is no longer detected. Removing the com port while in use by software can cause the software to lock up or crash.