Siemens SIMATIC TI525 - Safety Considerations

PRE-INSTALLATION
2-4
Hardware and Installation User Manual
2.2 SAFETY CONSIDERATIONS
Pre-installation planning and site preparation must include consideration of
hazards
to personnel during a system failure. The equipment connected to the
TI525/TI535 PLC should include interlocks and safety switches to prevent
operation during a system failure. Although the specific steps depend on the
application, the general precautions include the following:
 Provide a means for disconnecting power—independent of the
PLC—from the output loads when a machine is not operating, or when
it is necessary for the operator to reach into the machine. Power must be
removed by a non-semiconductor switch or a physically-wired relay
contact, placed to interrupt power to the output. It is not sufficient to
rely solely on the PLC for this function. Figure 2-1 illustrates an
operator
safety switch.
Output
Module
Relay contacts or limit switches
open when operator must
reach into machine.
User-supplied
critical loads
which could
cause injury
Loads which
could not
cause injury
Output points from
the programmable controller
Figure 2-1 Operator Safety Switch
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