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8.3.8
Precommand input ( )
"Precommand input" helps to enable the first precommand output (of the step
switch) of the rotary step switch. For example, the evaporator pump of the first
refrigeration machine can be switched to enable the flow sensor to acquire the
correct flow temperature.
The precommand output of the aggregate switches on at current priority if run
priority changeover (linear rotary step switch) is enabled.
The precommand input acts on precommand A during normal operation on all
other rotary step switches.
Aggregates can switch on only if there is a precommand and after the
precommand switch-on time is expired if the precommand input is configured.
Notes
The precommand input can be used as a release for the rotary step switch. It is
active also if no precommand is configured. As a result, the aggregates switch
on only if the precommand input issues a release.
Switch-on sequence (current priority aggregate B):
Example
0
1
0
0
1
0
1
0
1
0
0
PcmdRndw
Precommand input
Start condition 1
Precommand output A
Command B
Precommand output B
Start condition 2
Command A
PcmdRnup = Precommand runup time
PcmdRndw = Precommand rundown time
Main menu > Commissioning > Extra configuration > Aggregates > Rotary step switch >
Rotary step switch 1…2 >
Configuration
Operating line
Adjustable values / Comment
Precommand input
---, X1, X2, ...
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Siemens
Switching and monitoring device RMS705B
CE1P3124en
Building Technologies
Aggregates
01.04.2010