用于差压测量的传感器总是有两个压力端口。压差可以是正的或负的，这取决于传感器的哪个压力端口连接到更高的压力。能够测量正负压差的传感器称为双向压差传感器。只能测量一种压差的设备称为单向。

　　原文：

　　Sensors for differential pressure measurement always have two pressure ports. Differential pressure can be positive or negative, depending on which pressure port of the sensor is connected to the higher pressure. Sensors capable of measuring both positive and negative differential pressures are called bidirectional differential pressure sensors. Devices that can only measure one type of differential pressure are called unidirectional.