s7 program safety

seee

Member
Join Date
Dec 2010
Location
singapor
Posts
112
hello dear friends.

i am curious to know that what safety precedure i should consider
when i write plc program.
i mean that for example if i press emergency stop button on the
machine what should happen in plc program. should all outputs be turned off?
should the hydraulic motor be turned off and it should be
independent of plc program?
please tell also about electrical wiring of emergency stop and
power on the machine.

best regards.
 
Use safety relays. Have the relay cut power to actuators or to plc outputs. For example have the safety relay cut 24V control voltage inside cabinet or/and power supply.
Dont cut the power from PLC itself, let it remain functioning.
I usually create somekinda "permissive" bit from emergency stop state. If permissive is 0, then shut down everything that you want in PLC, let nothing to be controlled manually or automatically.

Controlling safety from standard PLC alone gets you no official safety level. Unless you have special safety PLC.
 
You have to do a hazard analysis of the machine. We can't tell you what exactly you should do.

Typically, with safety PLCs you want the outputs to turn off to put the machine in a safe state. Remember, if an output were to fail, you would want it to fail in the safe state not the hazardous state.

There are exceptions to this (most notably in the process industry). For example, if one of your outputs controlled a cooling pump, you would not want to shut down everything.
 

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