Danfoss ADAP-KOOL AK-PC 783, Design Manual, Page: 109 / 128

AK-PC 783 Capacity controller RS8GN202 © Danfoss 11-2013 109
Pump monitoring
The controller monitors pump operation via the "Flowswitch"
safety input. The signal can originate, for instance, from a pressure
difference pressure switch or a flow switch.
Here too, set an alarm delay time that applies during startup and
on pump changeover.
The delay time is to ensure that on startup/pump changeover, no
error is signalled for a pump before CO2 flow has been estab-
lished.
The special case of operating time equalisation
If the pumps are running with automatic operating time equalisa-
tion, the controller can perform a changeover of the pumps in a
case where there is no flow.
Depending on whether pump changeover neutralises the alarm
situation or not, the following occurs:
1) Pump changeover neutralises the alarm situation before the
alarm delay expires.
If pump changeover neutralises the alarm situation, the non-
faulty pump, now in operation, will run until the normal cycle
time has expired. After that, there is changeover again to the
"faulty pump", as it is assumed to have been repaired. At the
same time, the alarm situation is reset (the alarm is acknowl-
edged).
If the faulty pump has not been repaired, this will still trigger
an alarm and still result in changeover to the pump that is not
faulty. This is repeated until conditions are returned to normal.
2) Pump changeover does
not
neutralise the alarm situation
before the alarm delay expires.
If the alarm, on the other hand, is active after pump changeover,
the controller will also emit an alarm for the second pump. At
the same time, both pump outputs are activated in an attempt
to create enough flow for the alarm situation to be neutralised.
From now on, the controller will have both pump outputs
activated until the normal cycle time has expired, after which
the alarm situation is reset and pump changeover to one pump
is performed again.
Separate alarm priorities can be set for drop out of one pump and
for drop out of both pumps. See the Alarms and Messages section.
Alarm handling
Pump alarms are suppressed/acknowledged when normal pump
changeover is performed after the cycle time has expired.
Pump alarms can also be suppressed by setting pump selection
to the "faulty" pump - if the flow switch is OK, the alarm will be
acknowledged/suppressed as a result.