Differential Pressure (DP, Diff, Delta P) Measurement Guide

Differential PressureA guide to differential pressure measurement including explanations, applications and choice of products for measuring pressure with an differential pressure.

Differential pressure is the difference in pressure between two separate points.

A differential pressure can be measured between two points on independent systems or between two different points on the same system.

Products for measuring differential pressure

4-20mA dp transmitters

4-20mA dp transmittersDifferential pressure transmitters with a 4 to 20mA current loop output signal for measuring pressure drops of liquids or gases.

Voltage output dp transducers

Voltage output dp transducersAmplified voltage output differential pressure transducers for dp measurement with 3 wire 0-5, 1-5, 0-10, 1-10 volt outputs.

Digital dp sensors

Digital dp sensorsDifferential pressure sensors with digital interfaces for RS485, RS232 or USB communications with a computer

Air dp sensors

Air dp sensorsAir differential pressure sensors for monitoring and controlling air pressures across filters, through ventilation control vanes, in laminar air flow cabinets and between clean room partition walls.

Wet/Wet dp sensors

Wet/Wet dp sensorsWet Wet differential pressure transducers and transmitters which are compatible with liquid media on both pressure connections.

Intrinsically safe dp sensors

Intrinsically safe dp sensorsIntrinsically safe differential pressure sensors with EEx certification for use in potentially explosive atmospheres with an intrinsically safe zone barrier.

Rangeable dp sensors

Rangeable dp sensorsRangeable differential pressure sensors with output signals that can be adjusted by the user to elevate or suppress the zero position and turn down the full range span.

Low range dp sensors

Low range dp sensorsLow range differential pressure sensors for measuring very small pressure differences.

High accuracy dp sensors

High accuracy dp sensorsHigh accuracy differential pressure sensors for measuring with a high degree of accuracy and resolution to obtain precise dp readings.

Applications involving differential pressure

The main use for a differential pressure sensor is to measure the difference in fluid or gas pressure across a restriction in a pipe. The flow can then be determined by converting the differential pressure reading with bernoulli’s equation. Since flow is proportional to the square root of the differential pressure in a closed pipe it is sometimes preferred to use a square root output signal from the differential pressure sensor to simplify the conversion to a flow measurement.

Other applications for measuring differential pressure are as follows:

Hydrostatic level measurement of a tank’s content, where the gas at the top of the tank is not vented. The difference in pressure between the bottom and the top is measured to determine the true hydrostatic pressure.

Leakage monitoring by measuring the difference in pressure between a controlled reference pressure and the component under test pressurised to the same pressure.

Airspeed using a Pitot tube which provides two air channels, one for measuring the total air pressure facing the airflow and the other for the static pressure measured perpendicular to the air-flow. The difference between the two channels provides the air velocity pressure. This method is used on aircraft to measure air speed and in wind tunnels to simulate air velocity for testing the aerodynamics of an object.

Help Guides for differential pressure

Articles with more information on differential pressure measurement products & applications.

Questions & Answers on differential pressure

Differential vs Gauge

When do you need to measure differential pressure instead of gauge pressure?

You would you use a differential when you need to measure pressure between 2 connection points, and when the reference pressure (negative side) is not the same as atmospheric pressure.

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