USB Connection Keeps Disconnecting

Updated Apr 4, 2019

Reported In

Hardware

  • CompactRIO Chassis
  • PXI Chassis
  • myRIO Student Embedded Device
  • Stratom myRIO X-HUB Adapter

Issue Details

  • I have a USB cDAQ Chassis connected to a USB hub which is plugged into a PXI controller. The cDAQ disconnects randomly after days or weeks of continuous operation. What could be the cause of this issue?
  • I have a myRIO connected to my computer using a 10 m USB cable. Sometimes I cannot connect to my myRIO. What can I do to improve the situation?
  • I want to expand the one USB port on my myRIO using external USB hubs. What should I watch for?

Solution

There are several caveats you can run into when using USB:
  • Respect the maximum specified length for a USB cable of 5 meters for high-speed data rates.
  • If possible use externally-powered USB hubs.
  • Use shielded USB cables to minimize interference from surrounding equipment or cables.
  • Do not use USB extension cables, they often break connections due to signal reflections.
  • Do not use USB signal repeaters, use self-powered USB hubs instead.
  • Do not daisy-chain more than five USB hubs serially.
  • Take into account the bandwidth of your USB port. Depending on how many devices you connect to it you might run into its limit.