Vogt TUBE-ICE P-118F, Руководство по обслуживанию

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P118F Service Manual
SERVICE OPERATIONS
1/6/09
9-9
Sentronic Oil Pressure Safety Control.
All Sentronics utilize a pressure sensor and an electronic
control module to precisely measure oil pump differential pressure. The main advantage of
Sentronic is the elimination of the traditional capillary tubes, bellows, and pressure connections that
mechanical pressure switches require to measure differential oil pressure. These require careful
handling and are known to be a source of leaks in refrigeration systems.
A second advantage of Sentronic is in the use of a precise electronic clock for the two minute time
out circuit. Traditional mechanical controls use resistance heaters to provide the time to trip in the
event of low oil pressure. 208 volt systems, low ambient temperatures or brown-out type conditions
cause the heater output to be reduced, thus increasing the time out period from two minutes to three
or four minutes when low oil pressure conditions exist. With the electronic clock, the time out will
always be the same.
As a result of the elimination of the capillary tube measuring system and a more precise timing
circuit, Sentronic will improve the overall reliability of the refrigeration system. As in the past, all
new and replacement Copelametic compressors equipped with oil pumps require the use of a
Copeland approved oil pressure safety switch. Failure to use an approved oil pressure safety switch
will be considered as misuse of the compressor, and can adversely affect warranty replacement of
the compressor should a lubrication connected failure occur.
Sentronic Sensor. The same oil pressure sensor is used for all Sentronics. It mounts directly into
the oil pump. The Sentronic sensor measures oil pump differential pressure. It has an internal
contact that opens on low oil pressure and signals the Sentronic electronic control module to begin
time out. The same contact closes when proper oil pressure is present and stops the module time
out. Should oil pressure fall below 7-9 PSID for a period of two minutes, the Sentronic module will
open the control circuit, using its Normally-Closed (N) contact, and shut the compressor off.
Approximate oil pressure can be measured in the field. Oil pumps are furnished with a Schrader
valve mounted on the oil pump discharge port. To measure oil pressure, subtract crankcase pressure
from discharge oil pressure. Tripping of the oil pressure safety switch is a warning that the system
has been without proper lubrication for too long a time. Repeated trips of the oil pressure safety
control are a clear indication that something in the system requires immediate remedial action.
Sentronic Module. The Sentronic has in addition to the (N) contact, used for compressor shutdown,
a Normally Open (N.O.) contact that can be used in an alarm circuit (See Diagram 4A). The Single
Pole Double Throw (S.P.D.T.) contact of Sentronic can be electrically isolated from the control
circuit power supply, and used to control a circuit with a different voltage (See Figure 6). Sentronic
has a timing circuit that actually compares the amount of time with good oil pressure to that with
insufficient oil pressure and has a memory that will shut the compressor down after a period of more
than two minutes if the compressor has a "history" of oil pressure fluctuations with more
unacceptable than acceptable pressures.
Sentronic also has a memory that retains the compressor oil pressure "history" for up to one minute
in the event of a power loss. Sentronic uses a permanent magnet integral with the reset button to
reset its output control relay in the event of a trip. When the reset button is depressed, it
magnetically pulls the Sentronic relay's armature to its original, reset position. Sentronic needs no
voltage present to reset.