7
3.5 - Pressure transducers
Two types of electronic sensors (high and low pressure) are used
to measure various pressures in each circuit. These electronic
sensors deliver 0 to 5 VDC. The sensors are connected to the
SIOB/CIOB board.
■
Discharge pressure sensors (high pressure type)
These sensors measure the discharge pressure in each circuit.
It is used to control condensing pressure or high pressure load
shedding. Discharge pressure sensors are mounted on the
discharge line piping of each circuit.
■
Suction pressure sensors (low pressure type)
These sensors measure the suction pressure in each circuit.
They are used for EXV control. Suction pressure sensors are
located on the suction piping of each circuit.
■
Oil pressure sensors (high pressure type)
These sensors measure the oil pressure of each compressor.
Oil pressure sensors are located at the oil port of the
compressor. The economizer pressure is subtracted from this
value to arrive at the differential oil pressure.
■
Economizer pressure sensors (high pressure type)
These sensors measure the intermediary pressure between
suction and discharge pressure sensors. They are used for
EXV economizer control. The sensors are mounted on the
plate exchanger on the economizer side.
3.6 - Temperature sensors
Temperature sensors constantly measure the temperature of
various components of the unit, ensuring the correct operation of
the system.
■
Evaporator entering and leaving water temperature sensors
The evaporator entering and leaving water temperature
sensors are installed in the entering and leaving side water
box. They are used for capacity control and safety purposes.
■
Condenser entering and leaving water temperature sensors
These sensors measure the entering and leaving water
temperatures on the condenser side.
■
Suction gas temperature sensor
This sensor is used to control the suction gas temperature.
It is located at the suction line of each compressor.
■
Discharge gas temperature sensor
This sensor is used to control the discharge gas temperature,
and permits control of the discharge superheat temperature.
It is located at the discharge line of the compressor.
■
Motor temperature sensor
This sensor is used to control the motor temperature of each
compressor.
■
Oil temperature sensor
This sensor is used to control the oil temperature of each
compressor.
■
Temperature setpoint reset sensor
This 4-20 mA sensor can be installed remotely from the unit.
It is used to reset the setpoint on the unit.
■
Master/slave water sensor (optional)
The water temperature sensor is used for master/slave
assembly control.
3.7 - Actuators
■
Evaporator pumps
The controller can regulate one or two evaporator pumps and
takes care of the automatic changeover between these pumps
(see also section 6.4).
■
Condenser pump
The controller can regulate one condenser pump.
■
Electronic expansion valve
The electronic expansion valve (EXV) is used to adjust the
refrigerant flow to changes in the operating conditions of the
machine. To adjust the refrigerant flow, a piston moves
constantly up or down to vary the cross-section of the
refrigerant path. This piston is driven by an electronically
controlled linear stepper motor. The high degree of accuracy
with which the piston is positioned provides precise control of
the refrigerant flow.
■
Water flow switch
The water flow switch configuration allows for the automatic
control of the minimum water flow setpoint of the water flow
switch. The configuration depends on the unit size and is made
automatically at the start-up. If the measured water flow rate
in the water loop is lower than the configured flow rate, the
alarm condition shuts off the unit.
3 - HARDWARE DESCRIPTION
