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levels outputs from the Microprocessor Board to
115VAC levels used by the contactors, valves, etc.
The common side of all relays on the Relay Output
Board is connected to +12VDC REG. The open collec-
tor outputs of the Microprocessor Board energize the
DC relays or triacs by pulling the other side of the relay
coil to 0VDC. When not energized, both sides of the
relay coils or triacs will be at +12VDC potential.
1.6
CIRCUIT BREAKERS
Three Circuit Breakers are provided for the 115VAC
controls.
CB1 allows removal of control power from System 1
for control system circuitry servicing. Specifically, the
115VAC feed to Relay Output Board 1 which energizes
contactors and solenoids.
CB2 allows removal of control power from System 2
for control system circuitry servicing. Specifically, the
115VAC feed to Relay output Board 2 which energizes
contactors and solenoids.
CB3 allows removal of control power to the Micropro-
cessor Board, Power Supply board, I/O Expansion
Board, and Evaporator Heater.
The Circuit Breakers remove 115VAC
control power only. High voltage cir-
cuitry will still be energized from the
high voltage supply.
Removing 115VAC power to CB3 or
opening CB3, removes power from the
evaporator heaters. This could cause
evaporator freeze-up in low ambient
temperatures.
1.7
CURRENT TRANSFORMERS (C.T.)
C.T.s located internally in the Motor Protector Modules
on each of the 3 phases of the power wiring of each com-
pressor motor send AC signals proportional to motor
current to the Power Supply Board which rectifies and
filters the signals to variable DC Voltage (analog). These
analog levels are then fed to the Microprocessor Board
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via the I/O Expansion Board allowing the microproces-
sor to monitor motor currents for low current, high cur-
rent, unbalanced current, and single phasing.
3 Transformers (2T, 3T, and 4T) are located in the Con-
trol Panel. These transformers convert the 115VAC
Control Power Input to 24VAC to operate the micro-
processor circuitry.
2T: This 75VA transformer supplies the
Microprocessor power supply.
3T: Supplies the I/O Expansion Board voltage
for slide valve control.
4T: Supplies power to the Motor Protector
Modules.
1.9
MOTOR PROTECTION MODULES
A Motor Protection Module for each compressor is lo-
cated in the Control Panel. These modules supply mo-
tor over-temperature protection, 3-phase current pro-
tection, phase imbalance, phase rotation, and a program-
ming and troubleshooting 7-segment display.
The motor over-temperature protection is supplied by
3 temperature sensors imbedded in the motor windings
120 degrees apart. The module monitors these sensors
allowing it to sense a hot winding and shut down the
compressor if motor cooling is inadequate.
The on-board C.T.s provide 3-phase current protection
which look at 3 of the 6 motor legs and send an analog
signal proportional to average motor current to I/O Ex-
pansion board and on to the microprocessor board for
microprocessor low/high current protection and current
display. This allows the micro to monitor current and
shut a system down if low or high motor current is
sensed. This is a non-adjustable protection circuit elec-
tronically sized to a system's motor specifications.
Internally, the on-board 3 C.T.s and internal circuitry
allow the Motor Protection Module to protect against
high motor current as programmed on the Motor Pro-
tector dip switches. These switches are set at the fac-
tory according to motor specifications.
The module also provides phase rotation protection to
assure the screw compressor does not rotate backwards.
FORM 201.18-NM8
9
103
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