York YCAL0080SC - Manual (Page 58)

YORK INTERNATIONAL 58
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 em-
bedded 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 Cen-
ter consists of four basic components, 1) microproces-
sor board, 2) transformer, 3) display and 4) keypad. The
keypad allows programming and accessing setpoints,
pressures, temperatures, cutouts, daily schedule, op-
tions, and fault information.
Remote cycling, demand limiting and chilled liquid tem-
perature reset can be accomplished by field supplied
contacts.
Compressor starting/stopping and loading/unloading de-
cisions 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 deac-
tivate the unit.
INTRODUCTION MICROPROCESSOR BOARD
The Microprocessor Board is the controller and deci-
sion maker in the control panel. System inputs such as
pressure transducers and temperature sensors are con-
nected directly to the Microprocessor Board. The Mi-
croprocessor Board circuitry multiplexes the analog in-
puts, digitizes them, and scans them to keep a con-
stant watch on the chiller operating conditions. From
this information, the Microprocessor then issues com-
mands to the Relay Outputs to control contactors, so-
lenoids, 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 re-
quirements, 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 Microprocessor Board. This volt-
age is used to operate integrated circuitry on the board.
The 40 character display and unit sensors are supplied
power from the micro board 5VDC supply.
24VAC is rectified and filtered to provide unregulated
+30 VDC to supply the flow switch, PWM remote tem-
perature reset, and demand limit circuitry which is avail-
able to be used with field supplied contacts.
00065VIP
Unit Controls