USB: Adaptable for Industrial Applications
The Universal Serial Bus
(USB) provides a high data rate and Hot Swap connection for
PCs, providing an easy connection to a wide variety of multimedia
and network USB devices. Generally considered to be for home
or office use, USB is finding its way into Industrial applications.
What might USB offer the
industrial environment? With USB, there is a medium bandwidth
non-proprietary port made available on PC's. USB data uses
a multidrop, half-duplex twisted pair, similar in operation
to a two-wire RS-485 system. This differential signaling offers
a reasonable amount of noise immunity for harsh environments.
Power is distributed on the bus as well. Low power peripherals
have no problem operating without an external power supply.
Data rates are high; the
USB bus operates at a maximum of 12 Mbps. This opens many
possibilities for low cost data acquisition equipment without
the burden of proprietary ISA or PCI bus cards competing for
space inside the PC. The multidrop and Hot Swap nature of
the bus allows many USB devices to be mixed and matched on
the same bus. This provides improved configuration flexibility
over traditional serial and parallel ports.
Many Industrial devices
and networks use a direct interface to a PC for programming,
monitoring, data collection, and diagnostics of the Industrial
buss. The use of laptop computers has been a convenient tool
for accessing these networks. With most laptops coming with
USB ports and no serial ports, devices that help connect a
USB port to an Industrial buss have been increasingly popular.
However, USB was not designed
with industrial applications in mind. Distances are very limited;
any bus segment cannot exceed 5 meters, and there is no provision
for signal isolation. These types of limitations are nothing
new to those using PCs in industrial environments but need
to be addressed for many applications.
USB requires extensive operating
system support. The original release of Windows 95 did not
include USB support, but Microsoft added USB support to Windows
95, labeling it OSR2.1 (also called Win 95b). USB support
was included in Windows 98, 2000 and ME Operating Systems.
Most PCs shipping after 1997 are equipped with USB ports and
full USB Support.
Economics of scale have
pushed the PC into widespread use in many industrial applications.
USB is being carried into these environments as well and provides
one more method of connecting the PC to the outside world.
For more information on USB, we recommend
USB
Complete, USB
Hardware and Sofware, and USB
Explained.
|
