The bus system is also called RS485, and the branch system is also called 4-20mA model. These two wiring modes have their respective alarm host.
Generally speaking, the vast majority of bus based gas detectors use 4-core shielded wire, 2 power lines and 2 signal lines, and the transmission distance is relatively long, about 1-2km; the three core wire, 2 power lines, 1 signal line, the negative pole of power supply and the signal line are common, and the transmission distance is relatively short, less than 1km.
Advantages and disadvantages of bus system and wire system:
Advantages of bus system:
The signal is unified and the probability of failure is low. The bus control system has no such inconvenient factors. It transmits data in the same form on the data line and enhances the reliability of data. The wiring is simple and the workload is small. The obvious advantages of bus system are less wiring, simple wiring and less cost. Four bus system, two signal lines, two power lines, simple wiring, convenient.
The disadvantages of bus system:
Signal delay. The data are all brushed out one by one, especially when there are a lot of probes. Power supply problem. All probes are centralized power supply through the host. When the number of probes is large, the power supply capacity of the host is insufficient, so local power supply is needed.
The advantages of 4-20mA wire system:
The data synchronization is good and the power supply is unlimited. Compared with the bus system, separate line system, each gas detector communicates with the controller independently, which can timely transmit the field situation to the control part, so that the monitoring personnel can make timely and effective judgment, and the corresponding peripheral control equipment can make the corresponding control action in time and effectively, so as to avoid the occurrence of dangerous accidents
The disadvantages of 3 wire system are as follows:
The wiring is complex. The signal interference is large. There are a lot of wiring, heavy workload, complicated wiring, complex installation and construction, and high installation and material costs.
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