Siemens Simatic S7 Series Manual page 51

Analog Output Example. Analog.outputs.from.a.PLC.are.often.supplied.directly.or.
through.signal.converters.or.transmitters.to.control.valves,.
instruments,.electronic.drives.or.other.control.devices.which.
respond.to.analog.signals.
For.example,.analog.outputs.from.the.PLC.could.be.used.to.
control.the.flow.of.fluid.in.a.process.by.controlling.AC.drives..
Rather.than.simply.turning.the.AC.drives.on.or.off,.which.could.
be.accomplished.by.discrete.outputs,.analog.signals.can.be.
used.to.control.the.output.of.the.AC.drives...This.would.allow.
the.speed.of.the.pumps.to.be.varied.dynamically.in.response.to.
changes.in.process.requirements.
AC Drives
PLC
To Pump 1
Central
Signal from
Analog Processing Analog
Level Transmitter
Input Unit Outputs
(CPU)
To Pump 2
Process
Level
Transmitter
Storage
Tank
Pump 1
Pump 2
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