YORK INTERNATIONAL
64
FORM 150.62-NM7 (103)
UNIT CONTROLS
YORK MILLENNIUM CONTROL CENTER
The YORK MicroComputer Control Center is a mi cro -
pro ces sor based control system de signed to provide
the entire control for the liquid chiller. The con trol logic
em bed ded in the mi cro pro ces sor based con trol sys tem
will pro vide con trol for the chilled liquid temperatures, as
well as se quenc ing, sys tem safe ties, displaying sta tus,
and dai ly schedules. The MicroComputer Con trol Cen ter
con sists of four basic com po nents, 1) mi cro pro ces sor
board, 2) transformer, 3) display and 4) keypad. The
key pad al lows programming and ac cess ing setpoints,
pres sures, temperatures, cut outs, daily sched ule, op-
tions, and fault in for ma tion.
Remote cycling, demand limiting and chilled liq uid tem-
per a ture reset can be ac com plished by fi eld supplied
contacts.
Compressor start ing/stopping and loading/unloading
de ci sions are per formed by the Mi cro pro ces sor to
main tain leav ing or return chilled liquid temperature.
These de ci sions are a function of tem per a ture devia-
tion from setpoint.
A Master ON/Off switch is available to activate or de ac -
ti vate the unit.
INTRODUCTION MICROPROCESSOR BOARD
The Microprocessor Board is the controller and de-
ci sion maker in the control panel. System in puts such
as pres sure transducers and temperature sensors are
con nect ed directly to the Mi cro pro ces sor Board. The
Mi cro pro ces sor Board cir cuit ry multiplexes the analog
in puts, digitizes them, and scans them to keep a con-
stant watch on the chiller op er at ing con di tions. From this
in for ma tion, the Mi cro pro ces sor then issues com mands
to the Relay Out puts to control contactors, so le noids,
etc. for Chilled Liquid Tem per a ture Con trol and to react
to safety con di tions.
Keypad commands are acted upon by the micro to
change setpoints, cutouts, scheduling, op er at ing re-
quire ments, and to provide displays.
The on-board power supply converts 24VAC from the 1T
transformer to a +12VDC and +5VDC regulated sup ply
located on the Mi cro pro ces sor Board. This volt age is
used to operate in te grat ed circuitry on the board. The 40
char ac ter display and unit sensors are sup plied pow er
from the microboard 5VDC supply.
24VAC is rectifi ed and fi ltered to pro vide un reg u lat ed
+30VDC to sup ply the fl ow switch, PWM remote tem-
per a ture reset, and de mand lim it cir cuit ry which is avail-
able to be used with fi eld sup plied contacts.
00065VIP
Unit Controls
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