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10 Tips to Remember About USB

10/23/2018

1. Office-grade USB connections are too weak for real-world applications 

One of USB’s great advantages is that it provides a 5 V power supply on a single wire. Connected USB devices can then be powered by the USB cable connection, eliminating the need for an external power supply. In safe office environments, it is very convenient and normally quite harmless. 

Unfortunately, USB was also designed for quick and easy connections/disconnections. That becomes a problem when USB migrates off the desktop and out into the real world. Standard USB connectors do not grip cables firmly enough to withstand the heavy vibration encountered in industrial applications. Over time, the cables can work themselves loose. And, when they do, there may be risk of arcing. In the wrong environment, that can lead to fire or explosion. Loose USB cables can also lead to data loss, software hang-ups and blue screens. 

So, be wise when using USB off the desktop. Deploy devices equipped with high retention USB ports like those built by B+B SmartWorx, which require 3.2 lbs of force to dislodge them. 

2. Not every USB port provides the specified 500 mA 

According to the USB specification, a device should be able to draw up to 5 unit loads from a USB port. (A unit load in USB 2.0 is defined as 100mA.) “Low-power” devices should be able to draw one unit load or less (under 100 mA). “High-power” devices should be able to draw the full 500 mA. Self-powered devices, like printers, typically register as “low-power” devices, requiring only 100 mA. 

Perhaps, because so many USB devices are self-powered, some manufacturers cut corners and build boards that do not provide the full 500 mA to the USB ports. It will usually seem as if the connected device or the connection itself is to blame. You will try swapping out the USB cables, try reinstalling software, get frustrated, and eventually figure out that the connected device was never receiving full power. After wasting all that time on the problem, you may feel like a donkey. 

You will feel better if had installed a powered USB hub or powered USB isolator. Powered USB devices restore the full 500 mA. 

3. Legacy data devices can be USB-enabled 

It is hard to find a computer with a serial port these days. The USB bus has become the standard. But, there is still a huge installed base of legacy serial equipment out there and there are numerous new applications for which the serial communications protocol is still the perfect answer. 

Rather than abandon serial communications prematurely, the wiser and easier move is to deploy USB-to-serial converters. The serial protocol may have been devised long before USB was even on the horizon, but that does not mean that your data communications cannot flow smoothly over both. 

4. USB’s short range can be overcome 

USB has an effective range of about 5 meters (16ft). So, what happens if you want to communicate with a device that is in another building, on the other side of a river, or many miles away? Every communications problem calls for a slightly different solution, be it long-range wireless bridges, fiber optics, copper wire range extension or serial cable. And, eventually, all of those data communications protocols will need to cover the last length of cable that leads to your USB port. 

No worries. You can deploy devices that will convert USB to serial, Wi-Fi, Ethernet, fiber optic or Modbus with no interruption of your data stream. They are easy to use, and if you have questions just call the technical support folks at B+B SmartWorx. 

5. It is not always necessary to buy new cable 

Do not overlook easy opportunities to save money when designing your communications network. You may very well discover that significant savings lie right under your nose, in the form of legacy cabling like coaxial cable and telephone wiring. 

All kinds of possibilities exist. For example, you could convert a USB signal to an Ethernet package and then use a pair of Ethernet extenders to send your data up to 2600 meters (8530 ft) via coaxial cable or up to 1900 meters (6200 ft) over a pair of unused copper wires. That old copper cabling may be worth some money at the recycling center but, it is probably worth a lot more if it stays right where it is. 

6. USB is vulnerable to power surges 

Do not forget that USB uses copper wire and, thus, can transfer power surges from lightning strikes or heavy machinery to places where they can do serious damage. You can prevent that by using USB isolators, which can be standalone devices or incorporated into USB hubs, USB serial converters and other USB devices. 

7. USB is vulnerable to electromagnetic interference 

Standard USB cabling and equipment is not intended for use around magnetic fields. Just being placed in a medical cart, the crowded trunk of an emergency vehicle or a tight panel may be enough to cause data loss and software glitches when electromagnetic interference from other devices (EMI) induces current in the USB cable. Fortunately, both USB devices and USB cable are available with EMI shielding. 

8. USB is vulnerable to ground loops 

Thanks to media converters there is no reason you cannot connect to remote devices via your USB port. But, the farther away that device is, the more likely it becomes that it will be getting its power from a different building ground reference. If that is the case, the USB cable’s ground wire can create a ground loop path. 

The USB specification more or less assumes that connected devices will be grouped closely together, with a computer and its peripherals sharing a wall outlet and a common ground. But, in industrial applications, the connected devices may not even be in the same building, much less sharing a single wall outlet. A process control system might be powered from one source, the front panel might be powered somewhere else, and connecting your PC to the front panel via USB can then create a ground loop with the remote process control system. If you are lucky, the only result will be software hang-ups and blue screens. If you are not, surges and voltage overloads can burn out integrated circuits and connectors. The potential for ground loops can be controlled with USB isolators. 

9. Simplify installations with multi-function devices 

As networks continue to expand, in both complexity and sheer size, it becomes increasingly likely that yours will employ a variety of protocols: USB, Ethernet, Wi-Fi, serial or Modbus. And, the connecting media may vary as well – from USB cable to Cat 5, and from fiber optic to no wire at all. You may find yourself deploying many different kinds of converters as well as many different kinds of hubs and isolators. 

One way to simplify matters is to use equipment that provides multiple functions within the same device. Don’t just install a USB hub, install an isolated USB hub. Don’t just deploy a USBto- serial converter; deploy an isolated USB-to-serial converter. Simplify things. 

10. Initial investment in good equipment pays off later 

As has already been said, the USB specification was intended for use in climate-controlled homes and offices. But, it has proven to be so useful that USB is now used in everything from hospitals to heavy industry. There’ i a good chance that you will want to use USB in difficult environments, and the standard cables and devices that you can pick up at your local office store may not be able to stand up to it. Repair work is expensive, reprogramming is expensive, and down time is usually unacceptable. If you ruggedize your installation with industrial-grade equipment right from the beginning, it is likely that you will recoup the extra investment very quickly.

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