According to GB 50493 (Design Standard for Combustible and Toxic Gas Detection and Alarm Systems) and general industrial safety design practices, GDS detection units must use independent point-to-point wiring when transmitting signals to the alarm controller.
Bus (multi-drop shared line) communication is not permitted for safety-critical gas detection functions.
The core purpose of a GDS is real-time gas concentration monitoring and rapid alarm response, where communication reliability must be extremely high. A bus network cannot meet these safety requirements.
Why Bus Communication Is Not Allowed
1. Single-Point Failure Risk
Bus communication (such as shared RS485) places multiple detectors on a common cable.
If the cable is disconnected, shorted, or a single device malfunctions, the fault can propagate along the entire bus, causing loss of signals from all detectors on that line.
This leads to complete monitoring failure, which is unacceptable in safety-critical applications.
2. Alarm Response Delay
Bus communication relies on polling or time-slot transmission.
When multiple detectors share the same channel, data transmission may be queued, causing communication latency.
However, GDS alarms must be transmitted within seconds or even milliseconds to allow immediate emergency actions.
Any delay may lead to failure in timely hazard mitigation.
3. Non-Compliance with Safety Standards
Standards such as GB 50493 clearly specify that:
The signal transmission between gas detectors and the alarm controller must be independent
Shared bus structures are prohibited in GDS alarm linkage loops
This prevents failure expansion and ensures system dependability.
Recommended Signal Transmission Methods
To meet reliability and regulatory requirements, the gas detector should be connected to the control panel using independent signal circuits.
| Transmission Method | Allowed | Description |
|---|---|---|
| 4–20 mA Analog (Point-to-Point) | ✅ Recommended | Each detector uses a dedicated cable; stable, interference-resistant, widely used |
| Relay/Contact (Dry Contact Output) | ✅ | Suitable for simple alarm trigger applications |
| Digital Communication (Point-to-Point Only) | ⚠ Conditional | Only allowed when not shared; each detector must have its own dedicated link |
| RS485 Bus with Multiple Devices in Series | ❌ Not Allowed | Violates GDS safety design principles and standards |
Typical Correct Wiring Architecture
Detector A → Dedicated Cable → GDS Controller
Detector B → Dedicated Cable → GDS Controller
Detector C → Dedicated Cable → GDS Controller
( No multi-drop / daisy-chain / shared bus wiring allowed )
Summary
The gas detection system requires high reliability and immediate alarm response, so shared bus communication is not suitable.
To ensure system safety and compliance, each detector must transmit signals independently to the controller using 4–20 mA, relay output, or point-to-point digital links.