Let's talk about the wiring of transmitters: two-wire system, three-wire system, four-wire system, and their applications.
As a long-term frontline instrumentation worker, I often hear terms like two-wire system, three-wire system, and four-wire system. However, if you ask what these systems represent, very few people would know. Today, the technical editor from Shaanxi Huibo Electromechanical will have a good discussion with everyone about the two-wire, three-wire, and four-wire systems for transmitter wiring.
Release time:
2021-11-03
Source:
The two-wire system, three-wire system, and four-wire system that we often talk about actually refer to various transmitters that output signals mimicking direct current. They differ in their operating principles and layouts, rather than just the wiring methods of the transmitters. Next, let's take a look at their definitions.
In fact, the term 'several wire systems' only came about after the birth of the two-wire transmitter. This is a result of the widespread application of electronic amplifiers in appearance, where amplification essentially involves an energy transformation process, which cannot be separated from power supply. Therefore, the first to appear was the four-wire transmitter; that is, two wires are responsible for power supply, while the other two wires are responsible for outputting the transformed and amplified signals (such as voltage, current, etc.). The emergence of the DDZ-Ⅱ type electric unit combination instrument, powered by 220V AC and outputting a signal of 0-10mA DC, has been widely used, and it can still be seen in some factories today.
In the 1970s, China began producing the DDZ-Ⅲ type electric unit combination instrument, adopting the International Electrotechnical Commission (IEC) standard for analog signals used in process control systems. This means that the instrument transmits signals using 4-20mA DC, while the connection signals use 1-5V DC, thus employing a signal system that transmits current and receives voltage.
Using the 4-20mA DC signal, field instruments can achieve a two-wire system. However, due to limitations, the two-wire system is actually only used in pressure and differential pressure transmitters, while temperature transmitters still use the four-wire system. Nowadays, the range of domestic two-wire transmitter products has greatly expanded, and their application fields are increasing. At the same time, most of the transmitters imported from abroad are also of the two-wire type.
Key words:
Transmitter wiring, wiring system, two-wire system
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