10
3.1.6 Water shortage monitoring
The water shortage monitoring function switches off all
pumps.
Note: If the booster set has been delivered without a water short-
age monitor, it should not be started until a water shortage moni-
tor has been installed. Otherwise, there is a risk of damage to the
pumps.
If the function “fire fight” (display 222) is activated, the water
shortage monitoring function is suppressed.
Operation with PFU 2000 RAM / PMU 2000 settings:
Pre-pressure measuring can be set to “on” or “off” (display 216).
Via an analog signal:
Set “prepress.measuring” to “on” (display 216) if a pressure
transmitter is installed on the suction side of the booster set.
The PFU 2000 analog input 2 measures the pre-pressure. The
water shortage monitoring will be carried out according to the set
“min. prepressure” (display 231).
Via a digital signal:
Set “prepress.measuring” to “off” (display 216).
The signal on the PFU 2000 analog input 2 is evaluated as a dig-
ital signal for water shortage monitoring from a pressure switch,
level switch or an electrode relay.
Operation with PFU 2000 EPROM settings:
The pre-pressure can be measured via the PFU 2000 analog
input 2.
Via an analog signal:
If the signal is lower than 5% of the measuring range for more
than 5 secs., a fault is indicated.
Via a digital signal:
If the switch contact indicates water shortage for more than
5 secs., a fault is indicated.
For further information, see section
3.2.13 PFU 2000 analog input 2 configuration.
3.1.7 On/off mode at low flow
One of the advantages of variable-speed pump systems is the
possibility of maintaining a constant discharge pressure, irrespec-
tive of flow and pre-pressure. To avoid unnecessary energy con-
sumption at low flow, it is possible to operate the system with an
adjustable pressure hysteresis (on/off band).
If only one pump is operating at low speed, changeover to on/off
mode will be attempted by checking whether the flow is low
enough (approx. once per minute).
The boost frequency and the flow rate at which the controller
changes over to on/off mode and back to constant-pressure
mode is influenced by the following control parameters:
• On/off band
When the setting of the on/off band is increased, the change-
over will be carried out at higher flow rates (lower boost fre-
quency at the same flow). If the on/off band is set to zero,
there will be no changeover to on/off mode.
• Medium switching sequence
When this setting is reduced, the changeover will be carried
out at higher flow rates (higher boost frequency allowed).
• Buffer tank capacity
With increased tank capacity, the changeover will be carried
out at higher flow rates (lower boost frequency at the same
flow).
Fig. 11
1. Actual setpoint.
2. Pressure: actual setpoint + on/off band.
3. Operation at normal flow.
4. 3% boost (high flow is registered).
5. 3% boost (low flow is registered), increased test boost and
changeover to on/off mode.
6. Short period of pressure boosting.
7. Long period at zero speed.
8. Further decreased flow caused lower boost frequency in on/off
mode.
9. Increased flow; controller changes back to constant-pressure
mode.
For further information, see sections
3.2.6 On/off band,
3.2.10 Medium switching sequence and
3.2.17 Minimum pump speed limit.
4.
2.
1.
3.
Time
7.
8. 9.
5.
6.
H
Pressure in on/off mode
TM00 7785 1996
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