Integrated safety – space and cost saving technology
04 January 2012
Safety systems are an important and integral part of a modern process plant or manufacturing automation system. Hitherto, safety and automation functions were separated, but there is now a trend to integrate a number of safety functions with the control platform itself. In this article John Inskip describes how safety functionality can be integrated into the variable speed drive platform
Historically, safety systems were monitored using traditional technology such as safety relays and speed monitoring units. These devices ensured that the system was both safe and fully compliant with the prevailing standards. However, this established methodology is now being challenged as a result of technological advances, and traditional safety circuitry is gradually being replaced with a more integrated approach to safety systems implementation.
Take the variable speed drive as an example. With safety functionality implemented within a variable speed drive, external safety devices can be wired directly to it, rather than having to be routed via safety relays and separate safety controllers. This is further enhanced where industrial communications networks such as Profibus and ProfiNet are employed, as the safety functions can be transmitted via the bus as opposed to being hard-wired back to the drive.
Safety integrated technology has some major benefits in terms of cost savings and reduced downtime, as well as having a positive impact on installation and panel build costs. These savings can be made by both the end user and equipment manufacturer alike.
Take the example of a robot cell where an operator may need to carry out a cleaning cycle or a set-up procedure. The cell is likely to comprise several safety zones - some inactive and others active. Safety integrated technology will enable active zones to remain active while being safely monitored. For our operator working in the inactive zone, internal safety functions will prevent the robot encroaching upon this area of work, ensuring that he or she is safe at all times when carrying out maintenance and set-ups. This type of configuration enable production to continue with reduced downtime.
Another advantage of safety integrated technology is the reduction in necessary hardware and wiring. This makes machine modification, extension and modernisation easier to achieve, with less time required for installation and commissioning. And should the regulations governing the safe operation of a machine change, or future modernisation become necessary, the customer is able to respond to these changes more quickly.
This article is based on a presentation given by John Inskip at the MDS 2011 conference. John Inskip is a product specialist with Siemens Drive Technologies
Safety integrated technology in action A good example of a drive with safety functionality built in, is the Siemens Sinamics G120 series inverter. Compact units, such as the G120C, are suitable for installation close to the machines that they control and offer very high energy densities. Each G120C has the integrated Siemens safety technology ‘Safety Integrated’ as standard and the drive is equipped with a double safe input ex-works, enabling control over the ‘Safe Torque Off’ (STO) function without need for external devices.
With the STO function, following an emergency stop activation, timing pulses in the Sinamics G120 power unit are cancelled and the drive coasts to a stop without braking. The emergency stop contacts are directly connected to the G120’s digital inputs without an intervening safety contactor. The result is that there are no worn parts, as the entire function is implemented electronically and, as the drive remains connected to the line supply, full diagnostics capability is retained so that the cause of the stoppage can be immediately analysed.
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