Differential pressure transmitters are capable of measuring the differential pressure between the high pressure and low pressure. The DP transmitters are built around the pressure capsule concept.
A differential pressure capsule is mounted inside a housing. One end of a force bar is connected
to the capsule assembly so that the motion of the capsule can be transmitted to outside the housing.
A sealing mechanism is used where the force bar penetrates the housing and also acts as the pivot point for the force bar.
Provision is made in the housing for high- pressure fluid to be applied on one side of the capsule and low-pressure fluid on the other. Any difference in pressure will cause the capsule to deflect and create motion in the force bar. The top end of the force bar is then connected to a position detector, which via an electronic system will produce a 4 - 20 ma signal that is proportional to the force bar movement.
The DP is used to measure pressure on the LP ( Low-pressure side ) is vented to atmosphere. DP is also used to measure level and flow. The pressure measured will be proportional to the differential pressure of the flowing liquid and pressure of the liquid level kept in stationary.