York YCAL0014SC Unit Controls York Millennium Control Center, Introduction, Microprocessor Board

Unit Controls

UNIT CONTROLS

YORK MILLENNIUM CONTROL CENTER

00065VIP

INTRODUCTION MICROPROCESSOR BOARD

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.

AMaster ON/Off switch is available to activate or deac- tivate the unit.

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.

58 YORK INTERNATIONAL