Selection Of Function For Digital Input; Setting Of Stop Function - Grundfos CRE Installation And Operating Instructions Manual

6.3.7 Selection of function for digital input

The digital input of the pump (terminal 1, fig. 5, 8 or 11) can be
set to different functions.
Select one of the following functions:
• Min. (min. curve),
• Max. (max. curve),
• Ext. fault (external fault),
• Flow switch.
The selected function is activated by closing the contact between
the following terminals:
• 1 and 9 of single-phase pumps (fig. 5).
• 1 and 9 of three-phase pumps, 0.75-7.5 kW (fig. 8).
• 1 and 3 of three-phase pumps, 11-22 kW (fig. 11).
See also section 7.2 Digital input.
Min.:
When the input is activated, the pump is operating according to
the min. curve.
Max.:
When the input is activated, the pump is operating according to
the max. curve.
Ext. fault:
When the input is activated, a timer is started. If the input is
activated for more than 5 seconds, the pump is stopped and a
fault is indicated. If the connection is disconnected for more than
5 seconds, the fault condition will cease and the pump can be
restarted manually by resetting the fault indication.
The typical application will be detection of missing inlet pressure
or water shortage by means of a pressure switch installed on the
suction side of a pump.
Flow switch:
When this function is active, the pump will be stopped when a
connected flow switch detects a low flow.
It is only possible to use this function if the pump is connected to
a pressure sensor.
When the input is activated for more than 5 seconds, the stop
function incorporated in the pump will take over, see section

6.3.8 Setting of stop function.

6.3.8 Setting of stop function
When the stop function is active, the pump will be stopped at very
low flows to avoid unnecessary power consumption.
It is only possible to use this function if the pump is connected to
a pressure sensor, a non-return valve and a diaphragm tank.
The stop function can be set to:
• Active,
• Not active.
There are two possibilities of low-flow detection:
1. By means of the built-in "low-flow detector" which automati-
cally starts functioning if no flow switch is chosen/connected to
the digital input.
16
1. The pump will check the flow regularly by reducing the speed
for a short time, thus checking the change in pressure. If there
is no or a small change in pressure, the pump will detect a low
flow.
2. By means of a flow switch connected to the digital input. When
the input is activated for more than 5 seconds, the stop func-
tion of the pump takes over. Unlike the built-in low-flow detec-
tor, the flow switch measures the minimum flow at which the
pump must stop. The pump will not check the flow regularly by
reducing the speed.
When the pump detects a low flow, the speed will be increased
until the stop pressure (actual setpoint + 0.5 x ΔH) is reached and
the pump stops. When the pressure has fallen to the start
pressure (actual setpoint – 0.5 x ΔH), the pump will restart.
H
Stop pressure
ΔH
Start pressure
Fig. 26 Difference between start and stop pressures (ΔH)
ΔH is factory-set to 5 % of actual setpoint.
ΔH can be set within the range from 5 % to 30 % of actual
setpoint.
The non-return valve must be fitted immediately
Note
before the pump, fig. 27.
Pumps without factory-fitted sensor: If the non-return valve is
fitted between pump and diaphragm tank, the pressure sensor
must be fitted after the non-return valve.
Correctly installed
non-return valve
Pump
Fig. 27 Position of non-return valve in the system
The stop function requires a diaphragm tank of a certain minimum
size. The tank must be installed immediately after the pump and
the precharge pressure must be 0.7 x actual setpoint.
Recommended diaphragm tank size:
Nominal flow of pump
[m³/h]
0-6
7-24
25-40
41-70
71-100
If a diaphragm tank of the above size is installed in the system,
the factory setting of ΔH is the correct setting.
If the tank installed is too small, the pump will start and stop too
often. This can be remedied by increasing ΔH.
Q
Diaphragm tank
Diaphragm tank size
[litres]
8
18
50
120
180