Calibrating Pneumatic Transducer - Pneumatic
control is accomplished by a transformer which
converts a 3-15 psi pneumatic signal regulated
by a thermostat sensing chilled water temper
ature into an electrical signal. The electrical
signal is transmitted to either a Barber-Colman
or Honeywell Electronic Chilled Water Module
to provide chilled water temperature control. The
same transducer is used for both Barber-Colman
(Fig. 5) and Honeywell (Fig. 4).
MOTOR OVERLOAD MODULE - Calibrate as
outlined under the motor overload sections under
Barber-Colman or Honeywell.
CHILLED WATER MODULE - Calibrate the
Chilled Water Module as outlined in Table 6 for
Barber-Colman or Honeywell.
Table 6 - Chilled Water Module
RESISTANCE COIL WIPER
ARM
SEQUENCE PROCEDURE
1. Supply fixed air
signal to trans
ducer (Fig. 6)
Use either air signal from
control thermostat or sep
arate air supply (such as
a medical aspirator) to
introduce 9 psi signal to
transducer diaphragm and
hold.
Coil wiper arm (Fig. 6),
should be in center of re
sistance coil.
2. Preset chilled
water thermostat
set point
Turn thermostat dial (4)
Honeywell (Fig. 4), or (3)
Barber-Colman (Fig. 5) to
center of scale (vertical).
3. Add throttling
range
Turn the throttling range
screw (19) Honeywell, or
(17) Barber-Colman 1/3
of total clockwise travel.
4. Place machine in
manual control
and start the
compressor
Turn switch (8) Honeywell
to MANUAL position.
Place the capacity con
trol switch (15) Barber-
Colman on HOLD.
5. To complete the
electro-pneumatic
chilled water con
trol calibration
Refer to Table 5- Barber-
Colman, perform steps 1
(E thru H), and 3 (A and
B) or refer to Table 4 -
Honeywell, perform steps
1 (D), 2 (B), 3 (A thru D),
and 4 (A and B).
CONTROL AIR
SUPPLY
Fig. 6 - 19DA Transducer Assembly
(For either Honeywell or
Barber-Colman)
Trimming Refrigerant Charge - After the ma
chine has been placed in operation, it may be
necessary to adjust the refrigerant charge to
obtain optimum machine performance.
When a machine full load is available, add the
remaining refrigerant slowly until the difference
between the leaving chilled water temperature and
the cooler temperature reaches design conditions
or becomes a minimum. Shut the machine down
and allow refrigerant to drain to the cooler, mark
the level indicator and maintain that shutdown
refrigerant level.
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