Calibration Using Temperature Offset; Defrost Timer - Fisher Scientific Isotemp Plus 13-986-142A Manual

C
ONTROLS
Caution
DECREASING the offset value
INCREASES the temperature at which
the system controls. If the offset is
inadvertently set too low, the chamber
temperature can rise above freezing
when attempting to control at 0.0°C..
18
Calibration Using Temperature
Offset
In the event the freezer needs to be calibrated, a simple
routine is available to adjust the display and control point
to a referenced standard. To set a temperature offset
while in the Control Mode (mode LED off), simply press
and hold the Menu keypad. The display will flash oS fol-
lowed by the last temperature offset value. The factory
setting is 0.0. To change the offset value, press the
Increase or Decrease keypad to the value which when
algebraically added to the last displayed temperature, will
agree with the reference temperature. Next, press the
Menu keypad twice to cycle past the hold-off (Ho) menu
and back to the normal display mode. The Mode LED
turns off.
For Example:
The display indicates -4°C but a reference thermometer in
the freezer chamber indicates -6°C. The operator press-
es the Menu KEY twice and changes the offset (oS) dis-
play value from 0.0 to -2.0. The Menu key is pressed
repeatedly until the Mode LED turns off. Now the display
indicates a chamber temperature of -6.0°C (approx.) and
the controller begins to cool to the desired temperature of
4.0°C. Allow an additional 30 to 40 minutes for the freez-
er to again stabilize. If the display is still inaccurate,
repeat the calibration procedure.

Defrost Timer

All freezers come equipped with a 24 hour defrost timer.
The timer will trigger a defrost cycle 4 times per 24 hours.
When a defrost cycle begins, the display will alternately
flash dfSt and the current chamber temperature. The
defrost cycle typically lasts for 30 minutes or so,
depending on the last freezer temperature. When a
defrost cycle begins, the High Alarm is disabled for a peri-
od of 40 minutes. This is to provide enough time for the
defrost cycle to occur and for the freezer temperature to
drop below the high alarm set point after the defrost peri-
od has ended.