USB and ground loops

USB was originally designed for desktop use, but it is increasingly used for industrial applications. For USB to survive in those environments, it needs to be made more rugged. It means that ruggedizing USB for ground loops and using better (more protection and better locking) connectors are often needed.

Ruggedize USB connections for tough environments article tells that when you connect a remote device via USB, the greater the distance between the connected devices, the more likely it becomes that communicating devices will be getting their power from different building ground references. When they do, the USB cable’s ground wire can create a ground loop path.

In home/office environments the ground loop problem is rarely an issue, because the connected devices will normally be quite close, usually sharing a wall outlet and a common ground. But industrial installations will be far more complex and you can get considerable noise through ground loop: ground potentials can vary and magnetic flux from motors or other high-power devices can use this ground loop to induce current noise. If you’re lucky the only result will be data transmission errors. More extreme events, like surges and voltage overloads, will burn out integrated circuits and connectors.

Traditionally, to avoid this problem many types of industrial communication standards, like RS-485, use differential signal transmission with no ground connection to avoid potential ground loops minimizing induced noise in the system and potential for data errors. However, with standard USB cables the ground connection cannot be avoided.

Ruggedize USB connections for tough environments article recommends that in industrial environments, computers and connected devices should be protected with USB isolators Isolation allows the lines to float while keeping the local side at the proper ground and signal level.

Technically implementing such USB isolator has some difficulties because it is not easily isolated using discrete digital isolators. Isolating a USB port to eliminate the cable ground connection is inherently difficult because there are no control signals to indicate whether data is being transmitted downstream (to the peripheral) or upstream (to the host). There are several possible approaches to isolating USB. Generally it is a good idea to use ready made USB isolators. And before rushing to buy one, check carefully when technical characteristics of them, for example the USB version and communication speeds they support (some isolators can only support USB 1.1 and lower communication speeds, not the full speed).

You need to think also the electromechanical characteristics of USB interface on industrial environment. The same easy connection and extraction that makes USB so useful in an office environment can be a problem when you take USB off the desktop to industrial applications. Manufacturers have started to address the problem with “high-retention” USB ports (requires more force to dislodge them), ruggedized USB cables, sealed industrial USB connectors and ports with thumbscrews.

10 Comments

  1. Tomi Engdahl says:

    What’s Inside a USB Isolator?
    http://hackaday.com/2014/04/21/whats-inside-a-usb-isolator/

    [Lindsay] decapped a USB isolator to take a look at how the isolation worked. The decapped part is an Analog Devices ADUM4160.

    Reply
  2. Tomi Engdahl says:

    Why you need USB isolation to protect your instrumentation
    https://www.youtube.com/watch?v=I_Rd_UAxi_Y

    In this video Don shows you why you need USB isolation to protect your instrumentation. He gives a quick demo using a computer monitor to demonstrate how an isolator can benefit you.

    Reply
  3. Tomi Engdahl says:

    Do It Yourself Musician #4 – Fix USB Audio Noise with HifimeDIY USB Isolator
    https://www.youtube.com/watch?v=GbNyINuo-Uw

    In this video I use the HifimeDIY USB Isolator to solve a USB ground loop problem in my home recording setup. If you have a high pitched whining noise in your USB audio system, take a look at this video.

    Reply
  4. Tomi Engdahl says:

    Hjelmslund USB Isolators Review Shut up Noise in your speakers
    https://www.youtube.com/watch?v=tP-BQ6N11rk

    In this episode we talk about USB Interferences and how to stop the annoying noises in your speakers. After hours of investigating the problem and trying different approaches to solve it, we ended up with USB Isolators sold by Hjelmslund in Denkmark.

    Reply
  5. Tomi Engdahl says:

    ADUM4160 USB Isolator protection board removing bluetooth audio ground loop noise
    https://www.youtube.com/watch?v=dmTpriukBlE

    This USB isolator I bought from Ebay successfully decoupled the ground loop noise issue I was having in my DIY Bluetooth speaker. Sorry for the shaky video, I only had one hand to hold the camera and this video is just for proof it works. It does it by decoupling the power supply. You can hear the noise in the first 6 seconds of the video and then its completely gone when I install the USB isolator. This USB isolator is very low power at only 1 watt so only the Bluetooth module with low power consumption can run on it.

    1# Gatgets, Der USB Isolator bis 1500V
    https://www.youtube.com/watch?v=j5RGOkXNKxs

    Reply
  6. Tomi Engdahl says:

    Why you need USB isolation to protect your instrumentation
    https://www.youtube.com/watch?v=I_Rd_UAxi_Y

    n this video Don shows you why you need USB isolation to protect your instrumentation. He gives a quick demo using a computer monitor to demonstrate how an isolator can benefit you.

    Reply
  7. Tomi Engdahl says:

    USB Ground Loop Sound Interference Solved
    https://www.youtube.com/watch?v=ItD2GDpqKkA

    Comments:

    Why in the hell don’t equipment manufacturers just put whatever electronics are in this thing into their gear in the first place?!

    That is a very good point. I imagine it would cost pennies to implement the circuitry to stop USB ground hum.

    yep had this problem before and its down to a ground loop issue…i fixed mine by just buying a cheap small ground loop insulator no noise after that.

    Reply
  8. Tomi Engdahl says:

    The USB isolator is a device that will pass USB signal from input to output connector, while providing galvanic isolation between them. USB isolators are used in applications where direct USB connection can create noise (ground loop noise to audio or measurement), direct connection can be unreliable (noise to USB signal) or where isolation is needed to protect USB port or for electrical safety (for example laboratory measurement). USB isolators are the professional tools to avoid and fight ground loops and equalizing currents and to protect against overvoltage.

    Here is my review of Isolator USB to USB Optocoupler Isolation Module Coupled Protection Board ADUM3160 Isolation Voltage 2500V board
    https://www.epanorama.net/blog/2020/05/18/usb-isolator/

    Reply

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