Does the wire system of the gas alarm have anything to do with the connection to the DCS system?

Combustible gas (poisonous gas) detectors are composed of 2-wire, 3-wire and 4-wire systems. In the 3-wire system, the signal loop and the power supply loop share a negative wire. In the 4-wire system, the signal loop and the power supply loop are mutually exclusive.* * of. When entering DCS, generally only the signal loop is connected to the DCS input card. The power needs to be provided by the power supply system alone. The signal and power can be separated in the terminal cabinet.

Generally, the combustible gas transmitter is matched with its secondary instrument (combustible gas alarm). It needs to provide 220V power supply to the secondary instrument, and then the secondary instrument outputs a two-wire switching or analog signal.； As for the two-wire combustible gas transmitter, it can directly output an analog quantity to the control system. However, this analog quantity is different from the analog signal of the secondary instrument (combustible gas alarm). The analog signal output by the combustible gas transmitter is passive and needs to be powered by the control system, while the analog signal output by the secondary instrument (combustible gas alarm) is active and does not require power supply from the control system. The control system can only receive two-wire or four-wire field instrument signals. For a four-wire instrument, two of them are signal lines and two are power lines. If it is a 24V powered instrument, these four lines can use the same cable. Two cores are connected to the analog input terminals of the control system, and the other two cores are connected to the 24V power output terminals (pay special attention not to reverse the positive and negative poles of 24V). For three-wire combustible gas transmitters, the signal line and the power line share the negative end. Generally, they cannot be directly connected to the control system, but are used in conjunction with the secondary instrument.

Any number of wire systems can be connected to DCS. DCS mainly collects a 2-wire 4~20mA signal. The other wires are used for power supply. If your product is a two-wire system, then the 4~20mA signal is superimposed on the 24V DC voltage. ； If it is a three-wire system, the neutral line is shared, and the other two wires are connected to the positive pole of the signal line and the positive pole of the power supply. ； If it is a four-wire system, there are 2 signal lines and 2 power lines. Also, if your combustible gas alarm uses a bus system or MODUBS protocol, it is generally a four-wire system, with 2 signals and 2 power supplies.

The three-wire system is actually a simplification of the four-wire system, sharing one power cord.

This post was last edited by ddfly on 2009-12-27 21:17 Just separate the power lines and signal lines. The two-wire system has its own power supply voltage, (active and passive). The three-wire system uses a common COM line for power and signal. The four-wire system uses power and signals are completely separated. The signal line goes into the DCS and the power line goes into the distribution cabinet.

There is no problem. In the two-wire system, the power supply and signal feedback are on the same wire. Three-wire system * * Use a negative terminal. This is not a problem for DCS and can be achieved. DCS can power the transmitter alone.

Of course it does matter. This involves DCS terminal arrangement and cabinet-to-cabinet wiring. So it needs to be determined in advance, otherwise the route will have to be changed on site. The problem of power consumption also needs to be determined. Although the DCS card can be connected to the three-wire system for direct power supply, the power of the on-site instrument is too large and exceeds the power supply of the card and cannot be started.