Ancillary Circuit Boards - York MILLENNIUM YCAS Installation Operation & Maintenance

ducers and sensors around the chiller are either con-
nected directly to the Microprocessor Board or are con-
nected to the I/O Expansion Board and multiplexed be-
fore being sent to the Microprocessor Board. The Mi-
croprocessor Board circuitry multiplexes all of these
analog inputs, digitizes them, and constantly scans them
to monitor chiller operating conditions. Based on this
information, the Microprocessor issues commands to
the Relay Boards to activate and deactivate contactors,
solenoids, etc. for chilled liquid, operating control, and
safety control.
Commands are sent from the Microprocessor Board to
the I/O Expansion Board to control the slide valves for
chilled liquid control.
Keypad commands are acted upon by the micro to
change setpoints, cutouts, scheduling, operating require-
ments, and to provide displays.
A +12VDC REG supply voltage from the Power Sup-
ply Board is converted to +5V REG by a voltage regu-
lator located on the Microprocessor Board. This volt-
age is used to operate the integrated circuitry on the
board.
System Switches 1 - 4
System Switches for each system are located on the
Microprocessor Board (Section 1.11, Item 5). These
switches allow the operator to selectively turn a given
system on or off as desired.
Internal Clock & Memory Backup Battery
The Microprocessor Board contains a Real Time Clock
integrated circuit chip (Section 1.11, Item 2) with an
internal battery backup. The battery backup assures that
any programmed values (setpoints, clock, cutouts, etc.)
are not lost during a power failure or shutdown period
regardless of the time involved.
The battery is a 10 year lithium type, but life will depend
upon whether the Real Time Clock's internal clock cir-
cuit is energized. With the clock OFF, a rated life of
approximately 10 years can be expected. With the clock
ON, approximately 5 years. The clock is enabled and
disabled using a jumper on the microprocessor board.
If the chiller is shut down or power failure is expected
for extended periods, it may be desirable to disable the
clock to save battery life. The clock can then be reacti-
vated and reprogrammed when the chiller is returned to
service. This will not affect the maintenance of pro-
grammed values and stored data by the backup battery.
While a chiller is operating, the clock must be ON (Sec-
tion 1.11, Item 1) or the internal clock on the micropro-
YORK INTERNATIONAL
cessor will not be active and the micro cannot keep
track of time, although all other functions will operate
normally. Failure to turn the Clock ON could result in
the chiller not starting due to the time "frozen" on the
clock falling outside the Start/Stop time programmed in
the Daily Schedule, see Section 7.3.

1.5 ANCILLARY CIRCUIT BOARDS

Power Supply Board
The on-board switching power supply is fuse protected
and converts 24VAC from the logic transformer 2T to
+12V REG which is supplied to the Microprocessor
Board, Relay Output Boards, and the 40 character dis-
play to operate the integrated circuitry.
24VAC is filtered, but not regulated, to provide unregu-
lated +24VDC to supply the flow switch, PWM remote
temperature reset, PWM remote current reset, lead /
lag select, and remote print circuitry which may be uti-
lized with user supplied contacts.
24VAC is also filtered and regulated to +24VDC to be
used by the optional EMS/BAS Circuit Boards for re-
mote temperature or remote current reset.
Individual rectifier and filtering circuits are present which
receive the Current Transformer 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.
I/O Expansion Board
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.
Relay Output Boards
One Relay Output Board per system operates the mo-
tor contactors / starters, solenoid valves, and heaters
which control system operation.
FORM 201.18-NM2
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