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Using USB Based DAQ Devices on a Bus-Powered Hub

Updated Jul 28, 2025

Reported In

Hardware

  • USB-TC01
  • cDAQ-9179
  • USB-6509

Software

  • LabVIEW

Driver

  • NI-DAQmx
  • NI-VISA

Other

  • GPIB USB for Keithley SMU
  • 3rd Party RS45 Device
  • OptoSigma Serial Controller Device

Issue Details

  • I would like to use a USB Hub with a multidrop bus to connect a USB DAQ device to my computer. Are there any specifications that I need to follow to ensure it's success?
  • Are there any limitations or concerns to be aware of when using a bus-powered USB Hub to connect multiple DAQ devices?
  • Will a DAQ device work with a bus-powered USB hub with different upstream and downstream port configurations?
  • Can I connect a USB Hub to my PXI(e) controller to expand the number of USB devices available? Is there any overhead or bandwidth limitation that I should be aware of?

Solution

NI recommends against using USB hubs, as the specifications all vary with each manufacturer. There are power and throughput limitations for each bus that are unknown. Even if the device appears to be functioning, the hub could lose data packets, which is out of the device's control. 

 

Power Limitations

There are two kinds of USB hubs: bus-powered hubs and self-powered hubs. Bus-powered hubs receive all of their operational power from the USB bus, while self-powered hubs receive their operational power from an external power supply. 

Data acquisition devices (DAQs) can be used with bus-powered hubs, but in most cases this will require a power supply to power the hub's downstream ports. The power available to USB devices connected to a bus-powered hub decreases as more devices are connected. This decreased power level can become insufficient to power and operate some of NI's USB devices. In this case, the operating system will report an error, saying that there is insufficient power to run the device. 

A functional supply can be selected as specified by the hub's vendor. This requires that the device support a self-powered configuration where an external supply can be provided.

 

Bandwidth Limitations

A USB hub shares it's maximum bandwidth across each connected device. Even if a connected device is asleep or inactive, some of the bandwidth will still be reserved for that device.

 

For example:

Consider a USB hub using USB 2.0 (with a maximum data transfer rate of 30-40Mbps). If there are two peripheral devices connected to this hub and actively transferring data, each device may only transfer at a rate of 15Mbps. If one of the devices is asleep, the remaining device still does not have access to the full 30Mbps.

 

Therefore, it is important to consider if your USB hub is capable of achieving your desired data throughput while other devices are connected. 

Additional Information

  • Try to have minimal differences in USB version (ex. a USB 2.0 device should not be connected to USB 1.0 port).
  • USB ports on peripherals such as keyboards or monitors are usually bus-powered. In this case, a separate, self powered hub is required.
  • Ports on the back of the computer are typically self-powered. 

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