Grundfos CRE Instructions

Constant differential pressure
K
p
T
i
p
0.5 0.5
p
p
p
Δp
L1
0.5
L1 < 5 m: 0.5
L1 > 5 m: 3
L1 > 10 m: 5
L1
Δp
L1: distance in meters between pump and sensor.
Constant
temperature
K
p
T
i
Heating
system
Cooling
system
L2
t
0.5 -0.5 10 + 5L2
L2
t
0.5 -0.5 30 + 5L2
1
In heating systems, an increase in pump performance results in a rise in
temperature at the sensor.
2
In cooling systems, an increase in pump performance results in a drop in
temperature at the sensor.
L2: distance in meters between heat exchanger and sensor.
Constant differential
temperature
K
p
T
i
t
L2
-0.5 10 + 5L2
t
t
t
L2
L2: Distance [m] between heat exchanger and sensor.
Constant flow rate
K
p
T
i
Q
0.5 0.5
Constant pressure
K
p
T
i
p
0.5 0.5
p
0.5 0.5
Constant level
K
p
T
i
L
-20 0
L
20 0
General rules of thumb
If the controller is too slow-reacting, increase the gain.
If the controller is hunting or unstable, dampen the system by
reducing the gain or increasing the integral time.
How to set the PI controller
For most applications, the factory setting of the controller constants
K
p
and T
i
will ensure optimum pump operation. However, in some
applications an adjustment of the controller may be needed.
Proceed as follows:
1. Increase the gain (K
p
) until the motor becomes unstable.
Instability can be seen by observing if the measured value starts
to fluctuate. Furthermore, instability is audible as the motor
starts hunting up and down. Some systems, such as
temperature controls, are slow-reacting, meaning that it may be
several minutes before the motor becomes unstable.
2. Set the gain (K
p
) to half of the value which made the motor
unstable. This is the correct setting of the gain.
3. Reduce the integral time (T
i
) until the motor becomes unstable.
4. Set the integral time (T
i
) to twice the value which made the
motor unstable. This is the correct setting of the integral time.
General rules of thumb:
• If the controller is too slow-reacting, increase K
p
.
• If the controller is hunting or unstable, dampen the system by
reducing K
p
or increasing T
i
.
5.4.3
External setpoint
16
English (US)

Grundfos CRE Specifications

General

Protection Class	IP55
Material	Stainless Steel
Applications	Water supply, pressure boosting, irrigation
Impeller Material	Stainless Steel
Pump Housing Material	Stainless Steel
Connection Size	DN32 to DN200 (depending on model)
Power Supply	3-phase
Control	Integrated frequency converter