Example Offset; Open Thermocouple; Over-Temperature Indicator - Fisher Scientific Isotemp 550 Series Instruction Manual

Note
If no keypad activity occurs within 3
seconds, the display will return to the
temperature display mode.
Note
This condition can also be created by
decreasing the setpoint 100 C lower
than the current chamber temperature.
2. While pressing the MODE keypad, place the power
switch in the ON position. The display now shows
the current offset value. The display offset values
are limited to a range of ±30°C.
3. Press and hold the UP arrow keypad to increase or
the Down arrow keypad to decrease the offset
value.
4. Press the MODE keypad again to enter the new off-
set value or wait 3 seconds and the new value will
automatically be entered.
When finished, the temperature display will be updated based
on the offset value entered. For example:

Example Offset

A desired setpoint of 450°C. is entered and the furnace is
allowed 1 hour to stabilize to the setpoint. A reference temper-
ature is then measured inside the chamber to be 455°C. In
order to match the temperature display to the reference ther-
mometer, a display offset of 5 is entered. The temperature
display is then increased by 5°C and the display is in agree-
ment with the reference standard. The control will then cut the
heater ON time down so that the chamber cools by 5°C, thus
matching the desired setpoint.

Open Thermocouple

In the event the thermocouple becomes detached or broken,
the display will indicate so by showing "otc" (open thermocou-
ple). When this condition is encountered, the heaters are held
off. Repair or replace the thermocouple connection as needed
to clear the display.
Over Temperature Indicator
If the temperature in the chamber exceeds the setpoint by
100 C, the display will warn the user by flashing "HIGH" along
with the current chamber temperature. Also, the safety relay
will cut the heater circuit out and de-energize the heater.
Allow the unit to cool and the "HIGH" temperature alarm will
turn off when it falls to within 25°C of the setpoint. The con-
troller will then resume normal heater control.
O
PERATION
9