32
The table below shows the suggested controller settings:
* T
i
= 100 seconds (factory setting).
1. Heating systems are systems in which an increase in pump
performance will result in a
rise
in temperature at the sensor.
2. Cooling systems are systems in which an increase in pump
performance will result in a
drop
in temperature at the sensor.
L
1
= Distance in [m] between pump and sensor.
L
2
= Distance in [m] between heat exchanger and sensor.
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.
As some systems, such as temperature controls, are slow-
reacting, it may be difficult to observe that the motor is
unstable.
2. Set the gain (K
p
) to half the value 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
.
17.7.3 External setpoint (3.3)
The input for external setpoint signal (terminal 53) can be set to
the following types:
•
Active
•
Not active
.
If
Active
is selected, the actual setpoint is influenced by the signal
connected to the external setpoint input. See section
20
.2
External setpoint
.
System/application
K
p
T
i
Heating
system
1)
Cooling
system
2)
0.2
0.5
SP, SP-G, SP-NE: 0.5
0.5
0.2
0.5
SP, SP-G, SP-NE: 0.5
0.5
0.2
0.5
–2.5
100
0.5
–0.5
10 + 5L
2
0.5
10 + 5L
2
0.5
–0.5
30 + 5L
2
*
0.5
0.5*
0.5
L
1
< 5 m: 0.5*
L
1
> 5 m: 3*
L
1
> 10 m: 5*
CUE
p
CUE
p
CUE
Q
CUE
L
t
L
2
CUE
Δ
t
L
2
CUE
t
L
2
CUE
CUE
Δ
p
Δ
p
L
1
CUE
Grundfos.bk Page 32 Friday, July 30, 2010 10:10 PM
Grundf
os CU
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