In the process of selecting and using the transmitter, the signal output and wiring method must be considered and paid attention to. The two-wire, three-wire, and four-wire systems involved in the transmitter refer to a variety of transmitters with DC current signals output, and the problem of the transmitter’s multi-wire system is fundamentally the difference in working principle and structure, not only the wiring form of the transmitter on the simple surface. The so-called two-wire system means that the power supply and load are connected in series and have a common point, and the signal communication and power supply between the field transmitter and the control room instrument only use two wires, which are both power lines and signal lines. The two-wire transmitter provides a static working current for the transmitter because the signal starting current is 4ma.dc, and the electrical zero point of the instrument is 4ma.dc, which does not coincide with the mechanical zero point, which is conducive to identifying faults such as power failure and wire breakage. Moreover, the two-wire system also facilitates the use of safety barriers, which is conducive to safety and explosion protection.

Due to the popularization and application of 4-20ma.dc (1-5v.dc) signal system, in order to facilitate connection in the application of control system, the unification of signal system is required, for this reason some instruments of non-electric unit combination, such as online analysis, mechanical quantity, electricity and other instruments, can adopt the output of 4-20ma.dc signal system, but due to the complexity of its conversion circuit, large power consumption and other reasons, it is difficult to fully meet the above three conditions, and can not achieve two-wire system, The only way to use the external power supply is to make a four-wire transmitter with an output of 4-20ma.dc.

In order to reduce the volume and weight of the transmitter, improve the anti-interference performance, and reduce the wiring, some instrument factories change the power supply of the transmitter from 220v.ac to low-voltage DC power supply, such as the power supply is taken from the 24V.DC power box, because the low-voltage power supply creates conditions for the negative line sharing, so that there are three-wire transmitter products.

Therefore, due to the different working principles and structures of various transmitters, different products have emerged, which also determines the two-wire, three-wire and four-wire wiring forms of the transmitters. For the user, the transmitter selection should be based on the actual situation of the unit, such as the unification of the signal system, explosion-proof requirements, receiving equipment requirements, investment and other issues to comprehensively consider the selection. If you have any questions about product consultation, product customization, agency, technical inquiry, quotation, etc., please contact Xingyi, 400-600-4496!