Siemens Simatic S7 Series Manual page 46

Adding a Limit Switch.
Access Door
Open
Access Door
Closed
The.application.can.be.further.expanded.by.adding.a.limit.
switch..The.limit.switch.could.be.used.in.this.application.for.a.
variety.of.functions..For.example,.the.limit.switch.could.be.used.
to.stop.the.motor.or.prevent.the.motor.from.being.started..
In.this.example,.the.limit.switch.is.associated.with.an.access.
door.to.the.motor.or.its.associated.equipment..The.limit.switch.
is.connected.to.input.I0.3.and.controls.a.normally.open.contact.
in.the.program..If.the.access.door.is.open,.limit.switch.LS.is.
open.and.normally.open.contact.I0.3.is.also.open..This.prevents.
the.motor.from.starting.
Start (NO) Input
Points
Network 1
I0.0
I0.0 I0.1 I0.2
Stop (NC)
I0.1
Q0.0
OL
I0.2
Network 2
Q0.0
LS1
I0.3
Network 3
Q0.0
When.the.access.door.is.closed,.limit.switch.LS.is.closed.and.
normally.open.contact.I0.3.is.also.closed..This.allows.the.motor.
to.start.when.the.Start.pushbutton.is.pressed..
Start (NO) Input
Points
Network 1
I0.0
I0.0 I0.1 I0.2
Stop (NC)
I0.1
Q0.0
OL
I0.2
Network 2
Q0.0
LS1
I0.3
Network 3
Q0.0
CPU Program
Output
Points
I0.3
Q0.0
Q0.1
Q0.2
CPU Program
Output
Points
I0.3
Q0.0
Q0.1
Q0.2
45
Q0.0
Motor
Starter
Motor
With I0.3 Contact Open,
Motor will not Start
RUN Indicator
Q0.1
STOP Indicator
Q0.2
Q0.0
Motor
Starter
Motor
With I0.3 Contact Closed,
Motor can be Started
RUN Indicator
Q0.1
STOP Indicator
Q0.2
Motor is
Stopped
Motor is
Stopped