What is the difference between a two-wire ultrasonic level meter and three- or four-wire ultrasonic level meters?

　　Ultrasonic level meterWhat is the difference between two-wire and three- or four-wire types?

　　Two-wire ultrasonic level meter shares a single loop for power supply (DC24V) and signal output (DC4-20mA), making it a standard transmitter configuration. The disadvantage is that the transmit power is weak, making it unsuitable for measuring liquid levels with significant fluctuations. When the liquid has high volatility, measurement performance is also not ideal.

　　Generally, a two-wire ultrasonic level meter cannot have a relay added. If you need high/low level alarms, you must choose a four-wire ultrasonic level meter, because only four-wire models can have a relay added. An ultrasonic level meter without a relay at the factory cannot have a relay output added by the user. If relay output is required on site, you can add a secondary instrument with relay output, and set the relay output through the secondary instrument.

　　Three-wire ultrasonic level meter: the power supply (24VDC) and signal output (4-20mADC) each use two wires, with the power negative and signal negative shared. Its advantage is higher transmit power, making it suitable for measuring liquid level and solid level under various conditions, with better performance. In practice, a three-wire ultrasonic level meter is actually four-wire, and its power supply is also 24VDC.

　　Four-wire ultrasonic level meter uses two wires for power supply (220VAC) and two wires for signal output (4-20mADC), with the power negative and signal negative separated. Its advantage is higher transmit power, suitable for on-site installation with independent power supply.

　　Two-wire means power and output share two wires; three-wire means power and output share the ground wire; four-wire means power and output are separate.