a   两线制超声波液位计其供电（DC24V)与信号输出 （DC4-20mA)共用一个回路，为标准的变送器形式，不足之处是发射功率弱，不适合有较大波动的液面液位测量，当液位有较大挥发时，测量效果也不理想。
A the power supply (DC24V) and signal output (dc4-20ma) of two-wire ultrasonic liquid level meter share a common loop, which is a standard transmitter form. The disadvantage is that the transmitting power is weak, which is not suitable for liquid level measurement with large fluctuation. When the liquid level has large volatilization, the measurement effect is not ideal.
b   三线制超声波液位计，其供电24VDC与信号输出4- 20mADC各使用两条线，电源负级和信号负级共用。其优势是发射功率较大，适用于多种条件的液位和料位进行测量，效果较好。
B three wire ultrasonic liquid level meter, its power supply 24VDC and signal output 4-20madc use two wires respectively, the negative power level and signal level share the same. Its advantage is that the transmitting power is large, which can be used to measure the liquid level and material level under various conditions.
c   四线制超声波液位计，其供电220VAC与信号输出4- 20mADC各使用两条线，电源负级和信号负级分开。其优势是发射功率较大，适用于现场安装，独立供电。
C four wire ultrasonic liquid level meter, its power supply 220VAC and signal output 4-20madc use two wires respectively, the power negative stage and signal negative stage are separated. It has the advantage of high transmitting power, suitable for field installation and independent power supply.