4-12
prepared by filling an insulated container (of sufficient
size to completely immerse bulb) with ice cubes or
chipped ice, then filling voids between ice with water, and
agitating until mixture reaches 0
_
C (32
_
F) as shown by a
laboratory thermometer.
When the temperature at the element sensing bulb
has stabilized at 0
_
C (32
_
F), as indicated by stable stylus
indication, compare temperature indicated by stylus with
temperature shown by a laboratory thermometer. If the
two readings do not agree, the recording thermometer
should be rezeroed. (Refer to paragraph d.)
d. Rezeroing the Recording Thermometer
1. Be certain that the element bulb temperature
has stabilized at 0
_
C (32
_
F). Note the amount of
temperature difference between the test meter or
thermometer reading and the stylus indicated
temperature.
If the difference noted between the known element
temperature and indicated temperature is within
acceptable limits (0.3 of 0
_
C = 1/2
_
of 32
_
F), do not
attempt to rezero. If more than 0.3
_
C (1/2
_
F) in
variation, carefully note the number of degrees.
2. If recording thermometer is found to require
rezeroing:
(a)
Loosen set screw, item 3, Figure 4-16 and
zero thermometer by turning pinion shaft, item 4.
Lengthening pinion shaft (counterclockwise) raises
stylus indicated temperature reading: shortening shaft
(clockwise) lowers stylus reading. Then retighten set
screw.
(b) Reset control at 0
_
C (32
_
F), start the
refrigeration unit and repeat accuracy check. After
temperature stabilization, recording thermometer
should be within 0.3
_
C (1/2
_
F) limits.
e. Replacing Recording Thermometer Element
(Bulb and Capillary)
The
element
is
mercury-filled
and
the
temperature-pressure of the element controls the stylus
which moves across the chart in response to temperature
changes as sensed by the bulb located in the evaporator
supply air.
The element flange contains three O-rings. Care
should be taken to install the new element flange without
damaging the O-rings. It is possible for a mercury leak to
develop at the flange if O-ring damage occurs.
The stylus will continue to fall (container
temperature will actually be higher) if a leak develops in
the flange, capillary or bulb.
To replace the recording thermometer element
:
1. Turn unit OFF and disconnect power source.
2. Remove upper back panel. Remove bulb clamps
securing bulb to unit.
3. Remove two flange screws from recording
thermometer and feed capillary and element through the
unit.
4. Push replacement bulb end and capillary
through the unit.
5. Fill slots with silastic (RTV432, Dow Corning).
6. Attach bulb clamps tightly to bulb.
7. Connect element flange to recorder making sure
hub of flange faces out to fit into the hole in instrument
case (recording thermometer).
8. Rezero the recorder. (Refer to sections 4.18.a.
through 4.18.d.)
9. Install inlet air grille and upper panel. Start unit
and check recorder calibration.
CAUTION
Capillary tubing may be bent, but never sharper
than 1/2” radius: extra care should be taken
when bending adjacent to welds. The sensing
bulb should never be bent, as this will affect
calibration.
4.19 RECORDING THERMOMETER
(SAGINOMIYA)
NOTE
Do not overtighten chart nut after replacing
chart.
a. Battery
1. Open door and remove chart nut and platen.
2. Push voltage indicator test switch, item 2,
Figure 4-17. Replace battery if voltage indicator points to
the red or white zone.
b. Calibration
1. Install new chart on platen.
2. Place recorder bulb in ice bath (0
¦
0.2
_
C = 32
¦
0.35
_
F). (Remove rear upper panel to remove bulb.)
Leave bulb immersed in ice bath for
10 minutes.
3. After 10 minutes, rotate the chart by hand and
check the stylus indicated temperature. Do not touch
stylus during the checkout procedure.
4. If adjustment is required, loosen setscrew
(cross-recessed head). Using a 7 mm wrench, rotate the
adjustment screw clockwise to set the stylus 1 to 2
_
C (1.8
to 3.6
_
F) higher than desired temperature.
5. Rotate the adjustment screw counterclockwise
to set the stylus about 0.5
_
C (0.9
_
F) higher than set
temperature. Rotate the chart by hand. The indicated
temperature should be 0
_
C (32
_
F).
NOTES
1.) One full turn with the adjustment screw
changes
the
indicated
temperature
by
approximately 5
_
C (9
_
F).
2.) Overtightening of setscrew may change set
temperature.
3.) Calibration should only be done when bulb
temperature is decreasing.
4.) DO NOT move stylus by hand.
Downloaded from