AK-CC 750A
RS8HP102 © Danfoss 2018-09
81
Alarm thermostat
The function is used for sounding the alarm before the product
temperature at the refrigeration site becomes critical.
You can set alarm limits and time delays for high and low tempera-
tures. Alarm will be given if the set limit is exceeded, but not until
the time delay has expired.
There will be no alarms when refrigeration has been stopped due
to cleaning of the appliance or if the main switch is set in pos. OFF.
The alarm sensor may be chosen independently of the sensor used
for the thermostat function.
Alarm sensor
The alarm sensor may be selected as either S3 or S4, or a
weighted value of both of them.
The setting is performed as a percentage value of S4.
The weighting need not be the same as for the thermostat
function. In other words, the thermostat may regulate accord-
ing to S4 and the alarm thermostat may give alarm according
to S3.
Alarm limits
Different alarm limits can be set for the individual sections. The
alarm limits are set as absolute values in °C.
If thermostat bands are used, separate limits can be set for each
thermostat band. The alarm limits are not affected if there is an
external reference displacement via a voltage signal.
During night operation the value for upper limit will raise with
the same value as night operation is raised with (a negative
night setback will not change the limit value).
Time delay
Three time delays are set for alarms:
- For too low temperature
- For too high temperature during normal regulation
- For too high temperature during cooling down
• after activation of internal or external start/stop
• during a defrost
• after a power failure
• after appliance cleaning.
The time delay will apply until the actual air temperature has
dropped below the “upper alarm limit”..
Example
N:
Thermostat cut-in value
OUT:
Thermostat cut-out value
Lim:
Alarm limit for high temperature and low temperature
S:
Alarm ceases
Curve 1:
Cooling stage
(1): Time delay has been exceeded. . Alarm be
comes active.
Curve 2:
Normal regulation where the temperature
becomes too high
(2): Time delay has been exceeded. . Alarm be
comes active.
Curve 3:
Temperature becomes too low
(3): Time delay has been exceeded. . Alarm be
comes active.
If regulation is carried out with two thermostat bands there will be
a set of alarm limits for each band. Time delays will be common to
the two bands.
Product sensor with alarm function
An extra temperature sensor may be connected to each section.
The sensor will function independently of the other functions.
Alarm limits and time delays can be set, as for the alarm thermo-
stat.
Frost alarm
If the thermostat is controlled according to the S3 temperature
or a weighting of S3/S4, there could be a risk (on the refrigeration
shelves) that the evaporator’s S4 discharge temperature may be-
come so cold that the products at the back of the shelves become
exposed to unintended frost temperatures.
To prevent this, the controller has a built-in frost
alarm. If the S4 temperature falls below a set frost
limit an alarm will be given so that the cause of the
cold outlet temperature can be found and corrected.
Temperature alarms
