Recently, when looking at our local electronics’ supermarket, the pile of 32 Gigabytes USB memory sticks, now costing less than $100, caught my attention. It made me ponder, yet again, the ubiquitous USB standard and its industrial usage. There is no doubt that Ethernet is a strong industrial standard used widely around the traps - but USB offers a real alternative. Spend a few minutes considering it as you read the following.
Over 2.5billion USB (Universal Serial Bus) devices were shipped last year and there are more than 6 million installed (according to the USB Implementers Forum). The brilliance of USB (well, USB 2.0) is that it is almost ‘plug and play’ (not ‘plug and pray’, as many jokers referred to the earlier incarnations of industrial networks and PCs). One can see the different USB speed benefits for a 25 GByte high definition movie. It ranges from; USB 1.0 (9.3 hours), to USB 2.0 (1.39 minutes), to USB 3.0 (70 seconds).
USB provides a medium bandwidth, non-proprietary port with multi-drop, half duplex twisted pair operation (similar to RS-485). Because of its differential nature, noise immunity for industrial environments is a positive consequence. Data rates are high and it can connect up to 127 devices. Although it is half the speed (480 Mbit/s) of Gigabit Ethernet (which incidentally, is not used overwhelmingly in industrial applications) it is the USB’s versatility and convenience, rather than its speed, which is magnificent for industrial applications. A data logger can be installed in a few seconds, up to 5m from the PC. It can be simply plugged into the PC to draw the necessary power from the USB connection. It is also easy to add and (hot) swap new modules. Many instrumentation companies are using USB for a range of applications including; data acquisition, digital multimeters (DMMs) and switching modules and sensors - such as proximity detectors. USB is also particularly useful as a power supply (where the DMM uses only 2W, for example).
The great benefit of a USB port is that a hub can be easily added and then onto this several devices attached with minimal software impact (some designers up to 12 devices). With a hub it is possible to cascade up to 5 levels. And another trusty old use is replacing old DOS based floppies with USB data storage, thus providing a new lease of life to old hardware. Although the main standard at present is USB 2.0; USB 1.1 is still around and being used for mice and keyboards. Many industrial users are relieved to find the arrival of a plethora of ‘ruggedized’ USB chip sets. These have wider temperature ranges and there is greater driver support for USB across most operating systems ranging from x86 chips to Linux.
On the negative side, however - the USB lacks a widely used industrial connector (Industrial Ethernet uses industrialised connectors now to replace the horrible RJ-45 connector). Furthermore, the challenges for USB, in an industrial context, include; connector strain relief and the maximum cable length of 5m (although with USB hubs (to 30 m) and extenders (to 500m) the distance is greatly increased). And finally, there is no provision for electrical isolation - a problem for industrial applications, surely.
Despite these detractors, in your next project don’t automatically assume that Ethernet is the name of the game - seriously consider USB.
And to those of you who poo-poo the idea of using USB for industrial purposes, may I be so bold as to quote Samuel Johnson:
“Nothing will ever be attempted if all objections must first be overcome.”
Thanks to Electronics Design, Wikipedia and B&B Electronics for references.
Yours in engineering learning