York YCAL0014E Series, Installation Operation & Maintenance

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JOHNSON CONTROLS
81
FORM 150.62-NM8 (1020)
2
SECTION 2 - UNIT CONTROLS
00065VIP
INTRODUCTION
The YORK Millennium MicroComputer Control Center
is a microprocessor 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. IPU II & I/O Boards
2. Transformer
3. Display
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
maintain 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
deactivate the unit.
IPU II AND I/O BOARDS
The IPU and I/O Boards are assembled to function
as a single microprocessor controller requiring no
additional hardware. The IPU II board contains a
coldfire microprocessor and is the controller and decision
maker in the control panel. The I/O Board handles all
of the chiller I/O (Inputs and Outputs). System inputs
from pressure transducers and temperature sensors are
connected to the I/O Board. The I/O Board contains a
processor capable of reading the inputs and controlling
the outputs. It communicates through the transition
header with the IPU II microprocessor.
The I/O Board circuitry multiplexes the analog inputs,
digitizes them, and constantly scans them to keep watch
on the chiller operating conditions. The input values are
transmitted serially to the IPU II microprocessor board.
From this information, the IPU II then issues commands
to the I/O Board relay outputs to control contactors,
solenoids, etc. for Chilled Liquid Temperature Control
and to react to safety conditions. The I/O Board converts
logic signals to operate relay outputs to 115VAC levels
used by motor contactors, fan contactors, solenoid
valves, etc. to control system operation. The low voltage
side of all relay coils on the I/O Board are powered by
+12V.