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Setra Blog

Jan 5, 2017 7:02:00 AM

What is the difference between Unidirectional vs. Bidirectional Differential Pressure Ranges?

Nowadays, there are many applications that require positive and negative differential pressures between a reference room and a room of concern. Isolation rooms, respirators, ventilation and air exhaust systems, overshooting and shooting a given liquid level inhalation, and exhalation setups, are a few applications where these pressures are monitored. It is important to understand the difference between unidirectional and bidirectional differential pressure transducers to make sure you choose the best unit for your application.

Unidirectional Differential Pressure (Figure 1)


A unidirectional differential pressure transducer contains a diaphragm that can only deflect in the single direction towards the electrode. Figure 1 depicts an example of a unidirectional transducer where pressure exerted on the high port (p1) from the reference room is greater than the pressure from the concern room, deflecting the diaphragm towards the right. Typically this type of a differential pressure transducer is used for single characterization of positively or negatively pressurized applications. Thus for positive pressurized rooms, the low port is set to the room of reference, and the high port set to the area of concern. For negative differential pressure between both rooms, the low port remains set to the area of concern, and the high port remains connected to the room of reference. If the requirements for both rooms differential pressure where to change from positively pressurized to negative pressure, or vice versa, the user must manually flip the transducer. A unidirectional unit is preferable for selection over a bidirectional unit, when accuracy is a main concern; a unidirectional unit provides an increased accuracy reading. Since the unidirectional differential transducer diaphragm deflects up to half the full span of a bidirectional unit it provides for a better accuracy measurement.


Bidirectional Differential Pressure (Figure 2)


A bidirectional differential pressure transducer contains a diaphragm which can deflect symmetrically in two different directions. An advantage of the bidirectional unit is that it allows both negative and positive differential pressure to be monitored. Figure two depicts an example of a bidirectional unit where the pressure exerted on the high port (p1) from the concern room can be greater or lower than the pressure from the reference room, deflecting the diaphragm towards the left or right respectively. In cases in which one pressure input can be higher or lower than the other, a bi-directional differential range should be used.


CLICK HERE to learn how to select a differential pressure transducer.

Topics: General Industrial

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