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 their own energy absorption and the ability to feed this data back to the 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 energy consumption.
So despite the early prognostications of a consolidation round a select number of protocols, there are as many different standards today as there were ten years ago. There is no question that serial communication is the modern way forward and as each successive generation of engineers and technicians comes along with more knowledge of computers and programming, bus systems will increasingly become the acknowledged standard in all machine and building management systems and the drives industry will be in the forefront of their development and adoption.
Mark Whiteman is commercial manager, drives division, Danfoss Motion Controls