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CONTROLS

Controls Deﬁnitions

ANALOG SIGNAL — An analog signal varies in propor-

tion to the monitored source. It quantiﬁes values between

operating limits. (Example: A temperature sensor is an ana-

log device because its resistance changes in proportion to

the temperature, detecting many values.)

DIGITAL SIGNAL — A digital (discrete) signal is a two-

position representation of the value of a monitored source.

(Example: A switch is a digital device because it only

indicates whether a value is above or below a set point or

boundary by generating an on/off, high/low, or open/closed

signal.)

VOLATILE MEMORY — Volatile memory is memory in-

capable of being sustained if power is lost and subsequently

restored.

The memory of the PSIO and LID modules are volatile.

If the battery in a module is removed or damaged, all

programming will be lost.

General Controls Overview — The 23XL hermetic

screw liquid chiller contains a microprocessor-based control

center that monitors and controls all operations of the ma-

chine. The microprocessor control system matches the cool-

ing capacity of the machine to the cooling load while pro-

viding state-of-the-art machine protection. The system controls

cooling capacity within the set point plus the deadband by

sensing the leaving chilled water or brine temperature and

regulating the slide valve via a mechanically linked, hydrau-

lically actuated piston. Movement of the slide valve alters

the point during rotor travel at which compression begins

and reduces the effective length of the compression cavities.

This permits internal gas recirculation and reduces suction

volume. Thus, smooth, stepless capacity regulation is pro-

vided without changing suction pressure. Closing of the slide

valve increases capacity. Opening of the slide valve de-

creases capacity. See Fig. 10. Machine protection is pro-

vided by the processor, which monitors the digital and ana-

log inputs and executes capacity overrides or safety shutdowns,

if required.

PIC System Components — The Product Integrated

Control (PIC) is the machine’s control system. The PIC con-

trols the operation of the machine by monitoring all oper-

ating conditions. The PIC can also diagnose a problem with

the machine. It promptly positions the slide valve to main-

tain leaving chilled water temperature. It can interface with

auxiliary equipment such as pumps and cooling tower fans

so that they turn on only when required. The PIC continu-

ally checks all safeties to prevent any unsafe operating con-

dition. It also regulates the oil heater (Frame 1 and 2 ma-

chines) (while the compressor is off) and the hot gas bypass

valve, (if installed).

The PIC can be interfaced with the Carrier Comfort Net-

work (CCN) if desired. It can communicate with other PIC-

equipped chillers and other CCN devices.

The PIC system consists of 3 modules housed inside three

major components. The component names and the control

voltage contained in each component include the following

(also see Table 2 and Fig. 11-16):

• control center

— all extra low-voltage wiring (24V or less)

• power panel

— 230 or 115 control voltage (per job requirement)

• starter cabinet

— machine power wiring (per job requirement)

Table 2 — Major PIC Components and Locations*

PIC COMPONENT LOCATION

Processor Sensor Input/Output Module

(PSIO)

Control Center

Starter Management Module (SMM) Starter Cabinet

Local Interface Device (LID) Control Center

6-Pack Relay Board Control Center

8-Input Module (Optional) Control Center

Oil Heater Contactor (1C)

(Frame 1 and 2 Machines)

Power Panel

VI Contactor Relay (2C) (Optional) Power Panel

Hot Gas Bypass Relay (3C) (Optional) Power Panel

Control Transformers (T1-T4) Power Panel

Control and Oil Heater Voltage

Selector (S1)

Power Panel

Temperature Sensors

See Fig. 11,12,

and 13

Pressure Transducers

See Fig. 11,12,

and 14

VI — Volumetric Index

*See Fig. 8A, 8B, 9, 11, 12, 13, 14, 15, and 16.

PROCESSOR SENSOR INPUT/OUTPUT MODULE (PSIO)

— The PSIO is the brain of the PIC. This module contains

all of the operating software needed to control the machine.

The 23XL uses 3 pressure transducers and 8 thermistors to

sense pressures and temperatures. These are connected to the

PSIO module. The PSIO also provides outputs to the: slide

valve assembly; oil heater (Frame 1 and 2 machines); hot

gas bypass (optional); motor cooling solenoid; and space alarm

contact. The PSIO communicates with the LID, the SMM,

and the optional 8-input modules for user interface and starter

management.

STARTER MANAGEMENT MODULE (SMM) — This mod-

ule is located within the starter cabinet. This module imple-

ments PSIO commands for starter functions such as start/

stop of the compressor, start/stop of the condenser and chilled

water pumps, start/stop of the tower fan, spare alarm con-

tacts, and the shunt trip. The SMM monitors starter inputs

such as ﬂow switches, line voltage, remote start contact, spare

safety, compressor high discharge pressure, motor current sig-

nal, starter 1M and run contacts, and kW transducer input

(optional). The SMM contains logic to safely shut down the

machine if communications with the PSIO are lost.

Fig. 10 — Slide-Valve Capacity Control

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 103 104

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