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3.1.3 Closed-Loop Control
The closed-loop controller (a control system with a feed-back sig-
nal from a transmitter) is programmed for operation of centrifugal
pumps and takes their influence on the hydraulic system into ac-
count.
Fig. 8
PMU 2000
PFU 2000
P
The only control parameter to be set to adapt the controller to the
system conditions is "system time" (display 204), instead of PID
parameters as is the case with conventional closed-loop control-
lers.
•
Operation with PFU 2000 RAM / PMU 2000 Settings:
With the settings in the start/stop menu (displays 300 and 301)
and with the function selector in the PFU 2000 within the range
from 0% to 100%, the closed-loop controller is operating.
•
Operation with PFU 2000 EPROM Settings:
With the function selector in the PFU 2000 within the range
from 0% to 100%, the closed-loop controller is operating.
Fig. 9
Function Selector in the PFU 2000
Setpoint
0%
100%
STOP
MAX
For further information, see section
3.2.5 Setpoint Influences.
GRUNDFOS BUS
P
3.1.4 Cascade Control
Cascade control ensures automatic matching of the performance
to the system demand by cutting in/out the required number of
pumps.The controller will operate the system with as few pumps
as possible.
The frequency of starts and stops is limited by the setting of mini-
mum and medium switching sequences.
The pumps are cut in if the actual value remains below the set-
point.
With the "control function" (display 214) set to "normal", the
switching-off levels for the cascade-controlled pumps are calcu-
lated as follows:
Operation with PFU 2000 RAM / PMU 2000 Settings:
The actual switching-off level is the lower value of H
lated with PFU 2000 RAM / PMU settings and PFU 2000 EPROM
settings.
The H
is calculated as:
stop
On/off band
H
=
-------------------------------------- -
stop
Operation with PFU 2000 EPROM Settings:
The H
is calculated as:
stop
H
0
H
=
-----------------------------------------
stop
H
:
The pressure at which a pump is cut out.
stop
n:
Number of pumps in operation.
H
:
Pump head at zero flow.
0
The default setting of H
settings is the highest value of:
setpoint max. + 10% of setpoint or
setpoint max. + 5% of transmitter measuring range.
H
:
Pre-pressure.
p
H
:
Actual setpoint.
set
On/off-band: The pressure above the setpoint.
If H
+ H
is higher than "max. limit" (display 228), the value for
0
p
"max. limit" is used instead of H
For further information, see sections
3.2.9 Minimum Switching Sequence,
3.2.10 Medium Switching Sequence and
3.2.17 Minimum Pump Speed Limit.
calcu-
stop
–
+
H
set
n
+
H
–
H
p
set
+
H
set
n
+
1
with PFU 2000 EPROM
0
+ H
.
0
p
9
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