York YCUL0045E, Installation Operation & Maintenance

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JOHNSON CONTROLS
56
FORM 150.63-NM8 (1020)
UNIT CONTROLS
SECTION 2 - UNIT CONTROLS
YORK MILLENNIUM CONTROL CENTER
The YORK MicroComputer Control Center is a micro-
processor based control system designed to provide the
entire control for the liquid chiller. The control logic
embedded in the microprocessor based control system
will provide control for the chilled liquid temperatures,
as well as sequencing, system safeties, displaying status,
and daily schedules. The MicroComputer Control Center
consists of four basic components, 1) microprocessor
board, 2) transformer, 3) display and 4) keypad. The
keypad allows programming and accessing setpoints,
pressures, temperatures, cutouts, daily schedule, options,
and fault information.
Remote cycling, demand limiting and chilled liquid
temperature reset can be accomplished by field supplied
contacts.
Compressor starting/stopping and loading/unloading
decisions are performed by the Microprocessor to main-
tain leaving or return chilled liquid temperature. These
decisions are a function of temperature deviation from
setpoint.
A Master ON/Off switch is available to activate or de -
activate the unit.
INTRODUCTION
IPU2 & I/O BOARDS
The IPU2 Board is the controller and decision maker in
the control panel. System inputs such as pressure trans-
ducers and temperature sensors are connected directly
to the I/O Board. The IPU2 Board circuitry multiplexes
the analog inputs, digitizes them, and scans them to keep
a constant watch on the chiller operating conditions.
From this information, the Microprocessor then issues
commands to the Relay Outputs to control contactors,
solenoids, etc. for Chilled Liquid Temperature Control
and to react to safety conditions.
Keypad commands are acted upon by the micro to
change setpoints, cutouts, scheduling, operating require-
ments, and to provide displays.
The on-board power supply converts 24VAC from the
1T transformer to a +12VDC and +5VDC regulated
supply located on the I/O Board. This voltage is used
to operate integrated circuitry on the board. The 40
character display and unit sensors are supplied power
from the I/O Board 5VDC supply.
24VAC is rectified and filtered to provide unregulated
+30VDC to supply the flow switch, PWM remote
temperature reset, and demand limit circuitry which is
available to be used with field supplied contacts.
00065VIP