Page 80 - ENGINEERING REVIEW APRIL 2022 DIGITAL MAGAZINE

TECH INNOVATION
#SAFETY CONTROLLERS

INTEGRATED OR SEPARATE?

Safe Control Technology on Smaller Machinery

Safety controllers are becoming increasingly popular as an alternative to relay modules, even on smaller
machinery. The designer can opt for one of two concepts: some designers favour integration of safety into the
automation PLC, but a separate (small) safety controller offers clear benefits.

‘Safety integrated’ or ‘safety separated’:
should machine safety be integrated
into the PLC or implemented separately
using separate hardware and software?
This is the question that every machinery
designer needs to ask today.

Replacing relay modules
The question is especially important in
the case of smaller machinery with a Fig. 1: Developed for
manageable number of safety functions applications with a
manageable number of
and switchgear devices. There is a safety switchgear devices
noticeable trend favouring replacing – the parametrisable
multiple safety relay modules with one compact safety controller
small safety controller or with a PLC with Protect Select.
integrated safety functions.
There is good reasoning behind this
trend. In the first instance, machinery machinery productivity. With a safety- application as it can be realised in wide-
is becoming increasingly complex. It focused control system, machinery ranging areas through parametrisation
features additional and differentiated builders can create the prerequisite and programming.
safety functions, in some cases offering for bringing only part of a machine
interaction with the operator. Examples to a halt in the event of irregularities. Integrated or separate?
include setup with touch mode or Additionally, safety functions can be To return to the original question: should
troubleshooting. This does, however, linked together, which can also lead to the machinery builder accomplish these
presuppose that these options can be increased productivity and avoidance of benefits with an integrated or separated
mapped and monitored in the safety- unscheduled downtime. The enhanced solution for the safety of machinery?
focused control system. Additionally, the diagnosis options when compared to At first glance, there is more than one
requirements on the safety of machinery safety relay modules enable more rapid argument in favour of integration – the
are becoming increasingly stringent, localisation of fault causes in the event of fact, for example, that modern PLCs cover
partly due to growing awareness of malfunctions. safety of machinery tasks and that users
hazards and partly due to increasing With traditional relay modules, the can save on costs as well as space in the
differentiation of general and machinery- effort required for wiring, documentation control cabinet. Plus, it’s for good reason
specific standards. and validation of the module solution that integration has become a popular
becomes disproportionately large concept in automation and digitisation.
Productivity and availability when the safety functions reach a In theory at least, integrated solutions
Equally important is the fact certain complexity. With safety control promise robust coordination of functions
that differentiated, needs-based systems, the wiring effort is reduced. and simple infrastructure with reduced
implementation of safety requirements The configuration is also simpler and hardware effort.
can also enhance user operability and enables better adaptation to the individual In practice, there are clear benefits of a

78 | APRIL 2022