1. Circuit Description
Components
C-Bus:
A smart building automation network (by Clipsal/Schneider Electric) that communicates lighting, HVAC, and control logic digitally.PIR Sensor (Motion Detector):
Detects occupancy and provides a switched output or logic signal when motion is sensed.Push Button:
Provides manual control (override ON/OFF) for the same circuit or control group.Relay Output (1–2–3):
The diagram shows a simple relay contact (often volt-free/dry contact) connected between terminals 1–2–3, representing a connection point to the controlled device (e.g., HVAC ON/OFF input).
2. How It Works
Normal Operation
The PIR sensor detects motion and sends a signal via C-Bus to activate the relay coil.
The relay then closes the contact between terminals (e.g., 1 and 2), signaling the HVAC system or another load to turn ON.
Manual Override
The push button allows a user to manually operate the relay circuit—turning the HVAC ON or OFF regardless of occupancy detection.
When pressed, it sends a C-Bus command to the PIR input group, effectively simulating a motion event or toggling the same output relay.
Integration to HVAC (Example: Fujitsu VRF)
The relay contact connects to the external input terminals on the indoor unit control board.
When the contact closes (from either PIR motion or manual button press), the system receives an ON command.
When the contact opens (no motion, timed out, or manual off), the system turns OFF.
3. Application Example
| Mode | Input Source | Result |
|---|---|---|
| Auto (PIR) | Motion detected | Unit turns ON |
| Auto (PIR) | No motion for set time | Unit turns OFF |
| Manual (Push Button) | Button pressed | Unit toggles ON/OFF |
| C-Bus Logic | Schedules, groups, or scenes | Can override local input or coordinate with lighting |
This allows the air conditioning unit to be automatically controlled by occupancy and scheduling while retaining manual user override.
4. Why This Is Useful
Energy Efficiency: Ensures the unit operates only when a room is occupied.
Integration: Allows coordination with lighting or BMS control.
Flexibility: Manual override available for occupants.
System Compatibility: The relay output provides a volt-free contact, safe for most VRF or split-system external input terminals.
5. Example Connection Summary (for Fujitsu VRF)
| Function | Connection Point | Notes |
|---|---|---|
| Common (COM) | Terminal 1 | Shared return line |
| External Input Signal | Terminal 2 | Closed = ON signal |
| Ground / Unused | Terminal 3 | Depending on system model |
Ensure dry contacts are used (no voltage applied), and confirm input function settings in the indoor PCB DIP switch configuration.
