Model 916/917______________________________________________________________________________Calibration
3-1
Section 3 - Calibration
Required equipment:
Accurate low temperature remote bulb
thermometer or thermocouple of known accuracy.
3.1 Temperature Display Calibration
Place a measuring device near the probe cover. See Figures 1-4
and 1-5.
1. Allow the unit to stabilize at the operating temperature.
2. Remove the top two screws securing the control panel and
loosen the bottom screws.
3. Carefully remove the control panel.
4. Remove the six screws securing the cover of box attached to
the inside of the control panel. Remove the cover.
5. Adjust R17 until the control panel display matches the inde-
pendent measuring device. Several turns of R17 may be
required to achieve the desired temperature.
6. Reinstall cover to the box and secure.
7. Check the control temperature set point. Set point may have
been altered during the calibration procedure.
3.2 Optional Recorder Calibration
a. Changing the recorder range:
The chart recorder contains eight temperature ranges
and is factory-programmed for the freezer.
1. Press and hold button #3 for one second, then let the pen
move off the chart paper.
2. Press and hold for five seconds either button #1 or button #2.
3. Release the button and the green LED will begin to flash.
Count the number of flashes to determine the present program
setting.
4. To change the program setting, press the left or right arrows to
increase or decrease the count.
5. When the desired program number is flashing, press button #3
to bring the pen arm back onto the chart. Recording will
begin in the new program.
NOTE: Changing ranges may require an offset calibration as
outlined in Section 3.2.b.
Program No.
Range
Program 1
-40°C
to
30°C
Program 2
0°C
to
60°C
Program 3
-100°C to
38°C
Program 4
-5°C
to
50°C
Program 5
0°C
to
100°C
Program 6
-100°C to
-200°C
Program 7
-115°C to
50°C
Program 8
-10°C
to
70°C
b. Calibrating the chart recorder:
The recorder must be in service for 24 hours before per-
forming the following calibration procedure.
1. Place an accurate thermometer in the chamber next to the
recorder probe.
2. Temperature probes for the recorder are located in the left
front corner of the freezer chamber (Figure 1-4).
3. After about three minutes, compare the thermometer reading
with the chart recorder reading.
4. If an adjustment is necessary, press the #1 button to move the
pen to the left or the #2 to move the pen to the right. The but-
ton must be held about five seconds before the pen begins to
move. Release the button when the pen position matches the
thermometer.
NOTE:
The felt-tip pen on the recorder requires periodic
replacement. Usually the ink will appear to fade before
replacement becomes necessary. Additional pen tips
may be purchased from Thermo Forma. Refer to Parts
List, Section 7.
Calibration must be performed when the unit is at
operating temperature.
Figure 3-1, Temperature Control Board, R-17 Location
Table 3-1
Recorder Range Chart