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Keypad commands are acted upon by the micro to
change setpoints, cut-outs, scheduling, operating
requirements, and to provide displays.
A +12VDC REG supply voltage from the Power Supply
Board is converted to +5V REG by a voltage regulator
located on the Microprocessor Board. This voltage is
used to operate the integrated circuitry on the board.
Four system switches located on the Microprocessor
Board activate and deactivate the individual systems
(compressors).
I/O EXPANSION BOARD
The I/O Expansion Board allows additional analog inputs
to be tied to the Microprocessor Board. Without this
board, the Microprocessor is limited to a specific number
of individual inputs that can be connected without
enlarging of the board. The expansion board is basically
a multiplexer that allows a group of inputs to be connected
to the expansion board and then rout these inputs to the
Microprocessor Board on a single data line. The individual
inputs are multiplexed according to the selection made by
the Microprocessor by means of address lines.
Signals routed through the I/O Expansion Board include
Discharge Temperature, Oil Temperature, and Optional
Mixed Water Temperature.
POWER SUPPLY BOARD
The on-board switching power supply protected by fuse 2
FU converts 24VAC from the 2T transformer to +12V
REG which is supplied to the Microprocessor Board,
Relay Output Board, and the 40 character display to
operate the integrated circuitry.
24VAC is filtered, but not regulated, to provide
unregulated +24VDC to supply the flow switch, PWM
remote temperature reset, PWM remote current reset,
lead / lag select, and remote print circuitry which is
available to be used with user supplied contacts.
24VAC is also filtered and regulated to +24VDC to be
used by the optional BAS Circuit Boards for remote
temperature or remote current reset.
Individual rectifier and filtering circuits are present which
receive the C.T. signals for each phase of motor current
on each compressor. These circuits rectify and filter the
signals to variable DC. A phase rotation circuit for each
compressor is also present to assure that the screw
compressors do not run in the wrong direction. All of these
signals are sent to the I/O Expansion Board which
multiplexes them and then feeds them to the
Microprocessor Board.
YORK INTERNATIONAL
RELAY OUTPUT BOARD
Two Relay Output Boards are required to operate the
chiller. These boards convert 0 - 12VDC logic levels
outputs from the Microprocessor Board to 115VAC levels
used by motor contactors / starters, solenoid valves,
expansion valves, etc. to control system operation. The
common side of all relays on the Relay Output Board is
connected to +12VDC REG.
The open collector outputs of the Microprocessor Board
energize the DC relays or triacs by pulling the other side
of the relay coil to ground. When not energized, both sides
of the relay coils or triacs will be at +12VDC potential.
Triacs are used for load and unload slide valve solenoids
as well as liquid line solenoid or electronic expansion
valves when fitted. Triacs are more suitable than relays
when high frequency switching is required.
CURRENT TRANSFORMER (C.T.)
C.T.s on each of the 3 phases of the power wiring of each
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 to allow it to monitor
motor currents for low current, high current, imbalanced
current, and single phasing.
40 CHARACTER DISPLAY
The 40 Character Display (2 lines of 20 characters) is a
liquid crystal display used for displaying system
parameters and operator messages. The display has a
lighted background for night viewing as well as a special
feature which intensifies the display for viewing in direct
sunlight.
KEYPAD
An operator keypad allows complete control of the
system from a central location. The keypad offers a
multitude of commands available to access displays,
program setpoints, and initiate system commands.
BATTERY BACK-UP
The Microprocessor Board contains a Real Time Clock
integrated circuit chip with an internal battery back-up.
The purpose of the battery back-up is to assure any
programmed values (setpoints, clock, cut-outs, etc.) are
not lost during a power failure regardless of the time
involved in a power outage or shutdown period.
FORM 201.10-NM1
73
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