1.6 Circuit Breakers; Current Transformers (C.t.) - York Millennium YCAS Series Installation Operation & Maintenance

I/O Expansion Board #1
The I/O Expansion Board provides multiplexing to al-
low additional inputs to be connected to the Micropro-
cessor Board via a single data line. The additional in-
puts are multiplexed according to the selection made
by the Microprocessor through address lines.
Signals routed through the I/O Expansion Board include
Discharge Temperature, Current Transformer outputs
(motor current signals), and Oil Temperature.
Included on the I/O Expansion Board are the outputs for
the slide valve control. This control consists of a Digital
to Analog Converter (DAC) and power transistors to
modulate current through the slide valve solenoids.
I/O Expansion Board # 2
The second I/O Expansion Board is used only on 3 and
4 compressor YCAS chillers. Due to limited output and
input capabilities of the main Microprocessor Board,
an additional Microprocessor is needed to control a third
and fourth compressor.
The second I/O Expansion Board has processing
carpabilities. It's job is to monitor inputs from the third
and fourth compressor, provide safety control, and
shuttle information back to the main Microprocessor
Board. The shuttling of information is done using an
RS-485 communication line to the Microprocessor
Board.
Communication between the Microprocessor Board and
I/O Board #2 takes place approximately once every sec-
ond. The communications transfer is necessary to en-
able the main Microprocessor to display system param-
eters and command the starting, stopping, loading, and
unloading of System 3 and 4 to control chilled liquid
temperature.
The second I/O Expansion Board also controls the out-
puts to a Relay Output Board which activates and
de-activates 115VAC control outputs to System 3 and
4 compressors, solenoids, etc. These outputs are con-
trolled in response to commands issued by the Micro-
processor Board.
Relay Output Boards
One Relay Output Board per system operates the mo-
tor contactors/starters, solenoid valves, and heaters
which control system operation.
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The relay boards are located in the logic section of the
control panel(s). The boards convert 0 - 12VDC logic
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 collector out-
puts of the Microprocessor Board energize the DC re-
lays 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

Circuit Breakers are provided for the 115VAC controls.
• CB1, CB2, and CB3 allows removal of control
power from respective System 1, 2, or 3 for control
system circuitry servicing. Specifically, the 115VAC
feed to Relay Output Board 1 which energizes
contactors and solenoids.
• CB4 allows removal of control power to the Micro-
processor Board, Power Supply Board, I/O Expan-
sion Boards, and Evaporator Heater on 3 System
chillers. On 4 Compressor chillers, CB4 functions
identically to CB1 - CB3 for System 4.
• CB5 allows removal of control power to the Micro-
processor Board, Power Supply Board, I/O Expan-
sion Board, and Evaporator Heater on 4 System
chillers.
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 or
opening CB4 (3 System chillers) or
CB5 (4 System chillers), 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
compressor 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
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.
FORM 201.18-NM4
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