[2025 Control Systems] GDS (Gas Detection System) shall not use a bus architecture
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GDS (Gas Detection Systems) generally do not allow a bus configuration; this restriction also applies to the connection between the field controllers (with 485 interfaces) and the central control cabinet. The core requirements for GDS are extremely high reliability and fast response times, and the bus-based communication method is inherently incompatible with these requirements, which is the main reason why it is explicitly prohibited by relevant standards.
I. Core reasons for banning bus-based architectures 1. Risk to communication reliability: Bus communication (such as 485) relies on a \"shared channel\", with all devices using the same line. Once there is a line failure (such as a broken wire or short circuit) or an abnormality in a certain node, the entire bus network becomes disabled; data from all gas detectors cannot be uploaded, and the security monitoring function is lost.
2. The response speed does not meet the requirements; data transmission via bus communication involves queuing, and communication delays occur when there are many connected devices. GDS requires that, when the gas concentration exceeds the limit, an alarm signal must be transmitted to the control center within milliseconds or seconds; bus delays may result in missing the optimal time for emergency response.
3. Non-compliance with safety standards: Domestic standards such as the \"Design Code for Detection and Alarm of Flammable and Toxic Gases in Petrochemical Industries\" (GB 50493) specify that a point-to-point, independent signal transmission method should be used between the detection units of a GDS and its alarm controller; the use of bus systems is prohibited.
II. Approved alternative connection methods: To meet the security requirements of GDS, the signal transmission from the on-site gas detectors to the control center must be carried out using the following independent methods: 1. Analog signals – A separate cable is drawn for each detector, transmitting 4-20mA analog signals to the GDS controller or I/O module in the control center; these signals are independent of one another and do not affect each other.
2. Digital signals: For scenarios where only an alarm function is required, the detector can output passive digital signals (such as relay contacts); point-to-point wiring is used to directly trigger the central control system for an alarm.
3. Dedicated digital links: Some high-end GDS devices support point-to-point digital signal transmission (such as the “point-to-point” mode based on RS485, without bus sharing), but they must strictly meet the requirements for “dedicated links” as specified in the standards, and they also need to undergo authoritative certification.
III. The use of a bus system in GDS detectors is considered a serious safety hazard. 1. Requirements based on laws and regulations