Johnson Controls YORK Tempo YLAA Series, Installation Operation & Maintenance

Page: 125 / 192

FORM 150.72-NM1 (1020)
125
JOHNSON CONTROLS
7
SECTION 7 – UNIT CONTROLS
YORK
MILLENNIUM
CONTROL CENTER
The YORK 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 and 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.
INTRODUCTION 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 115
VAC 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.
Keypad commands are actuated upon by the
microprocessor to change setpoints, cutouts, scheduling,
operating requirements, and to provide displays. The
keypad and display are connected to the I/O board.
LD13283