Experience | Comparison of the differences between two-wire and four-wire systems for external-mounted level gauges

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I. Meaning 1. Four-wire system: The four-wire system refers to two wires for the power supply and two wires for the signal. It refers to the two wires for power supply and the two wires for signals. The power supply and the signal operate separately. 2. Two-wire system: A two-wire system is one in which, as opposed to a four-wire system (two power lines and two communication lines), the power line and the signal line are combined into one, with these two wires serving both for communication and power supply. II. Advantages and Disadvantages 1. The two-wire system reduces construction and cable costs, facilitating on-site installation as well as subsequent maintenance. 2. The four-wire system has fewer intermediate links, resulting in higher instrument stability. III. Two-wire and four-wire systems for Dinghua Electronic level gauges: 1. The sonar-type external level gauge uses a four-wire system, with one pair of wires for the 24VDC power supply and another pair for the 4–20mA output ； Two-wire system: The field instrument uses one pair of wires for both the 24VDC power supply and the 4–20mA output; direct current carrier technology is employed, with one carrier module installed in the control room per unit. https://bbs.hcbbs.com/forum.php?mod=image&aid=2132426&size=300x300&key=d001d51581f660a1&nocache=yes&type=fixnone2. Ultrasonic external level switch, four-wire system; powered by 24VDC – one pair of wires for power supply, one pair of wires for relay output ； Two-wire system: The field instrument is powered by 24VDC, and the relay output shares the same wire; direct current carrier technology is used, with one two-wire module installed in each control room. https://bbs.hcbbs.com/forum.php?mod=image&aid=2132425&size=300x300&key=f2749af5b2666c20&nocache=yes&type=fixnone