Memmert CTC 256, Operating Manual

Page: 54 / 68

54
Advanced functions
2. With a calibrated reference instrument, an actual humidity of 88 % rh is measured at nor-
mal operation, with a set setpoint humidity of 90 %rh.
3. Set the compensation correction value in the SETUP for
RH 90
to
-2.0
%rh:
PRINT SETUP
loop
t3
t4 t2
t1
on
off
Mo Tu We Th Fr Sa Su
3
4
2
1
STERI DEFRO
°C °C
rh
mb
%
CO
mb
2
IN 2 OUT IN 1 IN 2 OUT
MIN
AUTO
MAX
rh rh
mb
% % % % %
IN 2 OUT
4. The reference instrument should display 90.0 % rh after the calibration procedure.
With
RH 20
, a further comparison can be programmed at 20 % relative humidity.
If all compensation correction values are set to 0.0 rh , the factory calibration settings are
restored.
7.5 Automatic defrosting system
The integrated automatic defrosting system for the cooling unit ensures the perfect running
of the test chamber at low temperatures and in permanent operation. The time values for the
automatic defrosting system are set in the SETUP submenu under
DEFROST
(see Chapter 7.2
Basic appliance settings (Setup) on page 46 ). If the device is defrosted,
DEFRO
is displayed
(see page 28 ).
For long-term operation with a working temperature below +10 °C, or with a damp chamber
load and/or with the door opened frequently, ice can form on the condenser over time. Heavy
icing may impair the function of the appliance and could damage the cooling system. The
automatic defrosting system can eliminate this formation of ice, at chosen intervals of 3, 6,
12, 24 or 48 hours. The factory setting is every 12 hours.
Because of this automatic defrosting, there is a minor brief increase in the chamber tempera-
ture at regular intervals. If you would like to further reduce this detraction in performance,
you can lengthen the defrosting frequency, e.g. to every 24 hours.
In this case you should check to see if there is a permanent drop in the cooling performance
or a strong fluctuation of the actual value, which may be an indication that the cooling unit is
icing over.
If this is the case, please set the automatic defrosting system one level higher.
If humidity/room temperature are particularly high, it is possible that the factory default for
defrosting, 12 hours, is not sufficient. In this case you should set a more frequent defrosting
interval, e.g. every 6 hours.
The automatic defrosting is disabled with the OFF parameter. When operating at low tem-
peratures this causes the cooling unit to ice over over time.
When operating the chamber with a chamber load which itself emits warmth to the interior,
the automatic defrosting system should be disabled, otherwise one has to be prepared for the
fact that the temperature in the interior will rise considerably during the defrosting cycle. A
defrosting cycle can take up to 10 minutes. During this period the fan is switched off, no cool-
ing takes place and there is no compensation for heat loss.