Serial communications has virtually revolutionised the way we install and
operate drives. Modern fieldbus protocols and Ethernet connectivity now
enable a drive to be placed at the centre of a control scheme, where its
communications capabilities and inbuilt intelligence can be used to
greatest effect. Mark Whiteman reports
Ten years ago, serial communication systems were being taken up only by
visionary and so called 'early adopters'. In the past ten years however,
serial communications has grown enormously and moved into the mainstream
as systems designers and consultants have become more aware of its
significant advantages. Many of the early protocols are still going
strong, though some have been enhanced and their capabilities expanded as
a result of strategic business areas adopting them to meet their own
specific needs.
Lonworks is an excellent example. This was originally used solely for
monitoring purposes but it has since been enhanced as users demanded more
of the protocol, and it is now extensively used for control and
diagnostics. Profibus networks are widely used for drive control
applications across a wide spectrum of industry, but particularly in the
food and beverage sector. Profibus offers the advantage that it can now
store a complete set of drives parameters and then, should a drive fail,
the system will upload the parameters to the replacement unit, greatly
simplifying re-commissioning and reducing machine downtime.
Fieldbus connectivity has led to the elimination of digital input and
output terminals, bringing greater compactness, as terminations are a
major factor in physical drive dimensions. It has also allowed more
intelligence to be built into the drive, including
PLC functionality, which is now a standard feature of many drives.
Serial communications has also heralded the return of 'decentralised'
drives installations. Early drives - oil filled and IP55 protected - were
usually sited alongside the driven portion of the manufacturing line.
Then smaller IP21 drives became available and these were arrayed in
control cubicles in control rooms, with the result that control and power
cabling was extensive, running all around a factory or building.
Frequently, poor installation standards, particularly with regard to
screening and earth connections, compromised drive reliability.
Serial Communications has reversed the trend, and drives are once again
being sited next to the driven plant - sometimes on the motors
themselves. So, out go the rows of panels and miles of motor cables and
control wiring, and in comes the two-wire fieldbus cable to be 'daisy
chained' from drive to drive right across the installation.
A more recent development is the use of Ethernet networks for monitoring
and control, bringing drives into the overall control strategy via local
area networks. This technology enables remote monitoring and
interrogation of drives via the internet, without having to install a
separate modem. Other advantages, such as continuous energy monitoring,
are enhanced by Ethernet connection. Modern drives continually monitor
control centre for analysis can lead to valuable energy savings.
Curiously, in the mid 1990s, many of the drives coming from the Far East
were not equipped with a communication port; neither was it offered as an
option. It was the European manufacturers who led the field in the
provision of communications within drives, frequently offering their own
proprietary protocols to interface with their wider range of control
equipment. Today, the adoption of serial communication is almost
universal, and this is particularly true in the HVAC market, where
virtually every new installation is controlled by a building management
system, communicating with, and controlling the drives from a central
location. Closer control of HVAC drives has in turn led to improved
comfort control and reduced e