Siemens SIMATIC 505 - Operator Safety Switch Shutoff

Overview
1-5
Where the operator is exposed to the machinery , such as in loading
or unloading a machine tool, or where the machine cycles
automatically, consideration should be given to the use of an
electromechanical override or other redundant means,
independent of the PLC, for starting and interrupting the cycle.
If provision for changing programs while the equipment is in
operation is required, consideration should be given to the use of
locks or other means of assuring that such changes can be made
only by authorized personnel.
These recommendations are intended as safeguards against the
failure of critical components and the effects of such failure or the
inadvertent errors that may be introduced if programs are changed
while the equipment is in operation.*
Siemens recommends providing a means of disconnecting power
from the output loads when the 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 hard-wired
relay contact placed to interrupt power to the output load. It is not
sufficient to rely solely on the PLC system for this function. (See
Figure 1-1.)
User-supplied
critical loads which
cause injury
Loads which could
not cause injury
TurboPlastic
module
outputs
Relay contacts or limit switch.
Open when operator must
reach into machine.
Output points from programmable controller
Figure 1-1 Operator Safety Switch Shutof f
*This section is reproduced by permission of the National Electrical Manufacturers Associa -
tion from NEMA ICS 3–304, PLC Standard.
WARNING
!