Technical data

Chapter 6 – Programming
Siemens Building Technologies, Inc. 53
MV M1 M2
Pressure sensor
to PID input of
variable speed drive
Motor starterVariable
speed drive
Mains voltage
5192Z24en
MV: Motor, speed-controlled by SED2.
M1: Motor, controlled by digital output relay 1 DOUT1.
M2: Motor, controlled by digital output relay 2 DOUT2.
Figure 35. Staging Pumps.
If MV runs at maximum frequency and the PID feedback shows that a higher speed is demanded
in accordance with the staging, the SED2 switches on one of the relay-controlled motors M1 or
M2 (staging). To keep the controlled variable as constant as possible, and to compensate for the
difference in output, the SED2 must decrease to minimum frequency (Figure 36). During the
staging process, PID control is suppressed.
If MV runs in parallel to M1 and M2 at a
minimum frequency, and if the PID feedback
demands an even lower speed, the SED2
switches off one of the relay-controlled motors
M1 or M2 (destaging). In this case, the SED2
must increase the ramp from the minimum to
the maximum frequency. In this phase, PID
control is suppressed.
Motor MV
Motor M1
Motor M2
Motor MV
Motor MV
Motor M1
kW
Demand or Volume Flow
Figure 36. Motor Staging on Output Demand.