ADVANTECH’s eAutomation Group has written about the use of the common Universal Serial Bus (USB) in industrial applications.
For industrial automation users, technology is a double-bladed sword. On the one hand, advances in semiconductor and software technology result in smarter and more capable computers and machines, making automation easier and more robust.
At the same time, advances can often force updates before users are ready. For example, changes to industrial standards can mean new hardware is not compatible with existing communications interfaces.
The industrial PC for example, is seeing a change from the current PCI to a new backplane standard in the form of PCI-Express. This is after ISA was abandoned in the mid-1990s. Of course, old standards stay around for some time after they are superseded, and heritage devices may still continue to use them. For example, ISA, by now practically defunct in consumer computers, continues to be used in embedded computers.
Industrial users become concerned with the question of what changes should be made, and what can be done to avoid repetition of such problems in the future. They are
Advantech believes the current solution for the PC’s internal bus is Universal Serial Bus (USB). The internal bus is the electrical pathway used to communicate with the outside world.
Embedded processor boards are becoming increasingly popular. These boards have only USB ports and no extendable bus such as PCI-Express. The reason for the preference for USB is because virtually all industrial computers ship with multiple USB ports, and the interface is on many other industrial devices as well.
USB is high speed, deterministic, robust, and is universally available. With some modifications to secure connections and bridge long distances, USB can meet all of the industrial application criteria.
The universality of the standard is very important, because automation solutions require a projected life of at least a decade or longer. If the standard is practically phased out before this time, the I/O method becomes obsolete and will have to be replaced.
In terms of speed, transmission rates have to be sufficient to meet data and control speeds. This depends on the nature of the application.
Determinism, or time resolution, should be one millisecond or more for most industrial applications.
Most industries have communications distance requirements in the tens of metres ranges, although larger plant floors may require longer runs. The solution should also be able to handle harsher environmental conditions such as vibration, dust and high humidity.
Finally, the I/O technology must be a readily-available standard, both for compatibility and for cost.
Possible contenders include wired approaches such as Ethernet, Firewire and USB, as well as wireless protocols such ash Bluetooth, 802.11x and wireless USB.
Ethernet and USB are the most universal standards, being found on nearly every computer. Both are expected to last for a long time, and should be available for a decade or more. Both are also experiencing decreasing costs because of their universality.
Ethernet is not a single standard; it is a host of communication protocols. There have been various versions for over 30 years, and it is used in all local area networks.  Some versions provide increased speed.
However, standard Ethernet does not offer real-time performance. It does not prevent data collisions between competing nodes and does not offer any Quality of Service (QoS) provisions.
In a deterministic setting, where a machine must service an interrupt without delay when an internal clock ticks, Ethernet will fail. Given enough traffic, the micro-second level response times of the network will balloon out to milliseconds and that can render Ethernet unreliable for real-time industrial applications.
Although there are versions of Ethernet protocols which offer real-time performance, the same selection problems apply – until a single standard emerges, there is a chance of early adopters picking the wrong version.
USB, currently in version 2.0, has data rates of 480 megabit per second. This speed is generally suited for most industrial applications. It is also deterministic, with response times in the millisecond. There are also versions of the interface for portable devices and another for wireless connections.
However, USB is limited to a five-metre cable run. However, this can be stretched to 100m over CAT5 cabling and with the use of a distance extender.
The USB connector is designed for hot swapping and easy insertion and removal. There is no active latch such as those found in other types of connectors. This means USB can be unplugged accidentally, or vibrated loose, resulting in communication failure.
Solutions to this practical problem exist. For example, a screw lockable clamp has been developed by Advantech for USB type A and type B connectors. The removable clamp attaches to a kit mounted on I/O and hub modules, enabling the cable to be held securely against accidental disconnect and ongoing vibration.
For industrial users, the advent of a PC bus architecture change presents both a challenge and an opportunity. New architecture typically brings better performance and enables new applications, but the central role of the bus means any change will be a major undertaking.
By moving the I/O off of the bus and out of the PC, the problem can be averted and industrial users will then be able to take advantage of the improved performance of the new bus.
However, the communication channel over which the I/O runs has to be carefully chosen, with such characteristics as universality, data rate, determinism, robustness, and distance being important in the selection.
While no bus today natively meets all of these criteria, simple and inexpensive modifications to USB will allow it to satisfy all of the needs of automation and industrial applications.

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