p (Pressure)
Time
Time
No/Low Flow
detected
P 22-45
P 22-44
Sleep mode
activated
Boost
activated
P
Boost
P
Set
P
Wake
f
Ref
f
out
(Frequency)
P
System
130BA257.10
t
1
p
System
= p
Wake
Illustration 3.47
If
no flow is detected, the frequency converter will increase
the set point for pressure to ensure a slight over pressure
in the system (boost to be set in 22-45 Setpoint Boost).
The feedback from the pressure transducer is monitored
and when this pressure has dropped with a set percentage
below the normal set point for pressure (P
set
), the motor
will ramp up again and pressure will be controlled for
reaching the set value (P
set
).
FC 103
130BB188.11
External PID
controller
f
Ref
p
Set
p
System
f
Out
Illustration 3.48
2) In systems where the pressure or temperature is
controlled
by an external PI controller, the wake up
conditions can not be based on feedback from the
pressure/temperature transducer as the setpoint is not
known. In the example with a boost system, desired
pressure Pset is not known. Par. 1-00, Configuration mode,
must be set for Open Loop.
Example: Boost system.
130BA258.10
t
1
p
(Pressure)
Time
Time
No/Low Flow
detected
p
System
P
Set
Sleep mode
activated
P
Ref
= P
Wake
(Frequency)
f
Ref
f
Ref /
f
Out
f
Ref
f
Out
f
Wake
f
Out
Illustration 3.49
When low power or low speed is detected the motor is
stopped,
but the reference signal (f
ref
) from the external
controller is still monitored and because of the low
pressure created, the controller will increase the reference
signal to gain pressure. When the reference signal has
reached a set value f
wake
the motor restarts.
The speed is set manually by an external reference signal
(Remote Reference). The settings (parameter group 22-3*)
for tuning of the No Flow function must be set to default.
Parameter Description
VLT
®
Refrigeration Drive Programming Guide
MG16H102 - VLT
®
is a registered Danfoss trademark
133
3 3
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