Advantages and disadvantages of gas detector line system and bus system
The bus system is also called RS485, and the split line system is also called 4-20mA model. At present, the gas detector mainly adopts these two wiring methods, and each has its corresponding alarm host.
Generally speaking, the vast majority of bus system gas detectors use 4-core shielded wires, 2 power lines, and 2 signal lines, and the transmission distance is relatively long, about 1-2Km; Core wire, 2 power lines, 1 signal line, the negative pole of the power supply and the signal line are common, and the transmission distance is relatively short, within 1Km.
Choose the bus system or the split line system, and the details should be confirmed according to the actual working conditions. 1. The number of gas detectors to be connected. If the number of probes is more than 8, it is recommended to choose the bus system. This can reduce wiring difficulty and wiring cost. All probes are connected to the host through one cable, and a maximum of 256 gas detectors can be connected in theory; if the number of gas detectors is less than 8, the split-line system can be selected, and each probe can be connected through a separate The cable is connected to the host. 2. Distance. In actual working conditions, since the installation position of each probe and the distance between the probes vary from far to near, when the distance is relatively long, it is recommended to use the bus system. The general transmission distance of the bus system is 1-2Km, and only one main line is needed Cables are enough, and all probes can be connected to the main line; in addition, the transmission distance of RS485 can be increased by adding repeaters, and the distance is theoretically unlimited. Use split lines for short distances. 3. Signal processing needs. In many cases, the detection data of the gas detector needs to be processed multiple times. 4-20mA is a standard industrial signal, which can be connected to various PLC and DCS systems, but when it is necessary to save data and display data twice, it needs to use RS485 signal.
Here is a summary of the advantages and disadvantages of the bus system and the split line system:
Advantages of bus system
The signal is uniform and the probability of failure is low. The bus control system does not have such inconvenient factors at all, and the data is transmitted in the same form on the data line, which enhances the reliability of the data.
The wiring is simple and the workload is small. The obvious advantage of the bus system is that the amount of wiring is small, the wiring is simple, and the cost is low. Four-bus system, two signal lines, two power lines, simple and convenient wiring.
Disadvantages of bus system
Signal delay. The data is flashed out one by one, especially when there are a lot of probes.
Power problem. All probes are powered centrally by the host. When the number of probes is large, the power supply capacity of the host is insufficient, so local power supply is required.
Advantages of split line
Data synchronization is good. Compared with the bus system, each gas detector in the split-line system communicates with the controller independently, which can transmit the on-site conditions to the control part in a timely manner, so that the monitoring personnel can make timely and effective judgments, and the corresponding peripheral control equipment can be timely Effectively make corresponding control actions to avoid dangerous accidents.
Power without limitation
Disadvantages of split line
Wiring is complicated. The amount of wiring is large, the workload is heavy, the wiring is complicated, the installation and construction are complicated, and the installation and material costs are high.
There is a lot of signal interference.
