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3 - HARDWARE DESCRIPTION
3.1 - General
Fig. 1 - Control board
3.3 - Light emitting diodes on boards
All boards continuously check and indicate the proper
operation of their electronic circuits. A light emitting diode
(LED) lights on each board when it is operating properly.
• The red LED flashing for a 2 second period on the NRCP-
BASE board indicates correct operation. A different rate
indicates a board or a software failure.
• On dual-circuit units or units equipped with optional
board, the green LED flashes continuously on all boards to
show that the board is communicating correctly over its
internal bus. If the LED is not flashing, this indicates a SIO
bus wiring problem.
3.4 - The sensors
Pressure sensors
Two types of electronic sensors (low and high pressure) are
used to measure the suction and discharge pressure in each
circuit.
Thermistor
The outdoor temperature sensor is mounted below the control
box.
Solenoid valves
A solenoid valve must be mounted on the liquid line of each
circuit, in order to permit pumpdown of the circuit during
shutdown and at restart.
Alarm LED
An LED, mounted on the front of the control box, displays the
unit alarms.
Alarm reset button
A push button, mounted on the front of the control box, permits
resetting of all active unit alarms.
Legend
1 Master NRCP basic board
2 Red LED, status of the board
3 Green LED, communication bus SIO
4 Slave NRCP basic board
5 Remote master board customer control connection contacts
6 Remote slave board customer control connection contacts
7 Master board customer connection relay outputs
8 Slave board customer connection relay outputs
The control system consists of an NRCP-BASE board for
single-circuit units and two NRCP-BASE boards (a master and
a slave board) for dual-circuit units. All boards communicate via
an internal SIO bus. The NRCP-BASE boards continuously
manage the information received from the various pressure and
temperature probes. The NRCP-BASE master board incorpor-
ates the program that controls the unit.
3.2 - Electrical supply to boards
All boards are supplied from a common 24 V a.c. supply
referred to earth. In the event of a power supply interrupt, the
unit restarts automatically without the need for an external
command. However, any faults active when the supply is
interrupted are saved and may in certain cases prevent a circuit
or unit from restarting.
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