Grundfos CUE Series Installation And Operating Instructions Manual page 25

How to set the PI controller
For most applications, the factory setting of the controller
constants K and T will ensure optimum pump operation.
p i
However, in some applications an adjustment of the controller
may be needed.
Proceed as follows:
1. Increase the gain (K ) until the motor becomes unstable.
p
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 ) to half the value of the value which made the
p
motor unstable. This is the correct setting of the gain.
3. Reduce the integral time (T
unstable.
4. Set the integral time (T ) to twice the value which made the
i
motor unstable. This is the correct setting of the integral time.
General rules of thumb:
• If the controller is too slow-reacting, increase K
• If the controller is hunting or unstable, dampen the system by
reducing K or increasing T
p
10.7.3 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
13.2 External setpoint.
) until the motor becomes
i
.
p
.
i
10.7.4 Signal relays 1 and 2 (3.4 and 3.5)
The CUE has two signal relays. In the display below, select in
which operating situations the signal relay should be activated.
Signal relay 1
• Ready
• Alarm
• Operation
• Pump running
• Not active
• Warning
• Relubricate.
For distinction between alarm and warning, see
Note
section 10.5.3 Fault indications.
10.7.5 Buttons on the CUE (3.6)
The editing buttons (+, –, On/Off, OK) on the control panel can be
set to these values:
• Active
• Not active.
When set to Not active (locked), the editing buttons do not
function. Set the buttons to Not active if the pump should be
controlled via an external control system.
Activate the buttons by pressing the arrow up and arrow down
buttons simultaneously for 3 seconds.
10.7.6 Protocol (3.7)
This display shows the protocol selection for the RS-485 port of
the CUE. The protocol can be set to these values:
• GENIbus
• FC
• FC MC.
If GENIbus is selected, the communication is set according to the
Grundfos GENIbus standard. FC and FC MC is for service
purpose only.
10.7.7 Pump number (3.8)
This display shows the GENIbus number. A number between 1
and 199 can be allocated to the pump. In the case of bus
communication, a number must be allocated to each pump.
The factory setting is "–".
Signal relay 2
• Ready
• Alarm
• Operation
• Pump running
• Not active
• Warning
• Relubricate.
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