Flammable toxic gas detection system 485 communication
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Hello everyone. Our unit’s flammable and toxic gas detection system uses 485 communication. One cabinet contains 90 testing cards. Each card corresponds to a set of testing probes on-site. If one of the tests fails (the circuit is not connected), all the cards inside the cabinet will give irregular error alerts; the display will show that many signals are offline, with flashing lights that change randomly, rather than indicating only the specific card that is faulty. The personnel on site saw that the readings on the meters appeared normal, and since the control room couldn’t determine which meter was faulty, it was not possible to check all the sensors on site (many of them were in the air). This means that whenever there is a problem, it’s necessary to unplug each card inside the cabinet to shut down the system, restart it, and then plug them back in one by one to resolve the issue. What is the cause of this phenomenon? Is it a problem with the 485 communication? What exactly is the problem?
It wasn’t clear how the 485 communication works. 90 cards, each connected to its own probe – it’s probably a point-to-point hard wiring setup, right? So what about 485?
This kind of thing shouldn’t happen! Is the wiring connection correct, or are the interlock settings proper?
The signals from the field probes to the detection cards are analog signals, while the communication between the detection cards and the main controller is via 485 protocol. Is that correct, sir? Check for any issues with the wiring connections and whether the terminal resistors are functioning properly
In my opinion, it’s likely a problem with the RS485 communication. First and foremost, it should be clear that the centralized display units installed in the control room receive analog signals of 4–20mA or 1–5VDC from each field sensor; these signals are sent to the respective display cards. The communication between the centralized display unit and the system is carried out through the communication interface of the centralized display unit itself. RS485 is a type of serial communication interface, and to establish communication with the system, it’s necessary to define the communication protocol in detail, including the specific modes and the meaning of each bit in the data stream. RS485 is a broad concept, and there are differences in its implementation. If not handled properly, serial communication can fail, leading to chaos in the entire system. Since your specific situation isn’t clear, I recommend that you consult with the control system supplier and the manufacturer of the combustible gas detectors, carefully check their requirements regarding communication interface protocols, and configure everything according to their specifications. This should help resolve these issues.
Each test card has its own address; if there is a malfunction with the card, this address may be lost or corrupted, leading to 485 communication issues. When the upper-level software attempts to read data and encounters an issue at a certain address that prevents data retrieval, it restarts the COM port, resulting in a disruption in data flow
It’s a bit similar to the old thermal control system we used here; one connector corresponds to one card, but the signals are connected directly, without using 485 communication. The issue with the original poster’s setup is definitely related to 485 communication; either there is a defect in the hardware itself, or the communication configuration isn’t set up properly. It’s recommended to contact the manufacturer for assistance. I’m providing a method to check whether a probe is in good condition for the original poster’s reference; I’m not sure what brand or type of probe the poster has. The probes here have three wires and are of the chemical combustion type; the resistance between any two of them is 6 ohms. If the resistance between any two wires is not 6 ohms, then the probe is damaged, and it can be replaced and recalibrated. Personal opinion, for reference only.
The personnel on site are certainly not sure; the probe cannot establish a communication link, but it still has the ability to trigger alarms, which means that the communication modules should be independent of each other. The question format should be used for 485 communication. If there are no issues with system setup, then it is a defect on the part of the probe manufacturer.
What brand is it? How is the quality of the probe tested in that way?