Safety PLC's

As the law changes on machine safety so will thethe check happen and record the results!
design philosophy required to achieve a safeWiring, when designing a circuit I would always
system. I recently attended a training course onwire back each E-Stop to the main panel MCC,
safety PLC's and was initially shocked that wethis was often criticized, for the installation and
were moving away from traditional techniques.wiring costs but at least the technician would have
Over the years I have been involved in designinga starting point when trying to diagnose problem
and commissioning many safety systems, someon a safety circuit. Often though this is not the
good some not so.case and one plant I recently worked on had
So what will the new legislation mean to peopleover 60 E-Stops all wired in series, imagine a
like me, firstly forget the hard wired interlock?broken wire on that circuit. With safety PLC's this
Yes that's right all the knowledge you have justis no longer a problem as remote inputs and out
forget. This took a while to sink in but once youputs can be used ensuring coded pulses prevent
think about it you can start to see the advantagecrossed channels and fault diagnosis can be fed
- fault tolerance, previously we needed to add astraight back to the PLC we are no longer
lot of wiring and quite complex circuits to achieverelaying on aux wiring the safety wire is now the
fault tolerance and in most cases a fault wouldfeedback.
not be detected, it would require on a weeklySo am I sold? Yes I guess I am and with correct
monthly safety check to ensure an out ofimplementation hopefully more robust systems
position device would not reset. How often didcan be implemented, that not only make plants
these checks get carried out?more reliable but protect people. My only concern
By introducing a safety controller we can makenow is convincing a client.