How does a differential Pressure Transmitter work?

In a contained system, pressure can be defined as a value against absolute or atmospheric pressure, and can also be quantified as the differential value between the applied forces of 2 distinct points. As such, a differential pressure (DP) transmitter is an instrument used for measuring the differential value between two distinct points in a vessel or a pipe.

Numerous industries rely heavily on differential pressure transmitters for the purpose of level sensing in condensers and for the acquisition of quantitative data relating to process performance. Additionally, these transmitters are also used to monitor components throughout a network to record changes that happen over time due to the build-up of contaminants and particulates. In this blog, we will discuss the various pressure principles, elements of differential pressure transmitters, and how these transmitters work.

Principles of Pressure

Pressure is derived as a result of force applied to a particular unit of area. When it comes to apparatuses carrying gasses and fluids, the area to be taken into consideration would be the inside of a tank, pipe, sealed housing, or vessel. Pressure is quantifiable and is measured in pascals, bars, torrs, standard atmosphere (atm), and pounds per square inch (psi). However, bar and psi are the most commonly used pressure measurements in fluid- and gas-related industries. 1 bar is equal to the atmospheric pressure at sea level, and a pound per square inch is the force of one pound on an area of one square inch. Most likely, these are the units of measurement in your work that you will come across, as bar and pounds are the most commonly used. Additionally, almost every pressure measurement device manufacturer calibrates such equipment to these measurement units.

How a Differential Pressure Transmitter Works

A DP transmitter, also known as a Delta-P transmitter, is an electrical device or pressure-measuring gauge that utilizes two elements for measuring the difference in pressure of a sealed container.

A DP transmitter usually has a primary element, a secondary element, and electronic housing. The primary element produces a difference in pressure when flow increases in the pipe, and includes parts like flow nozzles, orifice plates, pitot tubes, laminar flow elements, venturi tubes, and wedge elements. The secondary element measures the pressure difference that is produced by the primary element with as much accuracy as possible.

The primary element is also referred to as the high side, whereas the secondary element is known as the low side. It is very crucial to note that the low side and the high side are not always on the respective low- and high-pressure sides of the pipe.

One highly-adopted way of measuring flow with the help of a DP transmitter is for the primary element to introduce a constriction in the pipe. Using the capabilities of a restrictive element on the primary side creates high and low pressure; therefore, when there is an increase in flow, there is also an increase in the drop of pressure. As a result, the secondary element measures the pressure difference which is created by the primary element.

Next, the measurements are sent to the electronic housing where signal processing is carried out. With the help of Bernoulli’s equation, which states that the pressure drop across the constriction is directly proportional to the square of the flow rate, DP is then converted into flow units.


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