Differential Pressure Sensors Guide: Selection, Installation, and Maintenance

You are standing next to a filter skid that has just been flushed. The impulse lines are purged, the three-valve manifold is seated, and the wiring is connected. If the range, wetted materials, and mounting orientation were not matched to the actual process, the sensor will begin to drift before the line reaches operating pressure. Differential pressure sensors look simple, but they are one of the least forgiving instruments in a process plant. They require two pressure ports, a stable reference, and careful thought about the media on both sides.

The practical rule is straightforward: differential pressure sensors are the most direct way to measure the difference between two points in a fluid system, and they are highly reliable when that difference stays inside the sensor's rated span. The rest of this guide covers what actually matters on the job, from range selection to impulse line layout, so that you avoid the common traps that lead to false readings and unnecessary maintenance.Differential Pressure Sensor for Industrial Process MeasurementA differential pressure sensor measures the difference between two pressures, providing a reliable signal for flow, level, and filter monitoring. It is essential for controlling process conditions in harsh industrial environments.View Product →

How a Differential Pressure Sensor Measures Process Conditions

A differential pressure sensor is a transducer that converts the difference between two applied pressures into a proportional electrical output. The high-pressure port receives the higher pressure, the low-pressure port receives the lower pressure, and the sensor's internal diaphragm displaces by an amount that is linearly related to the difference. A strain element or piezoresistive element converts that displacement into a millivolt signal, which a transmitter then converts into a 4-20 mA signal, HART, or a digital protocol.

Do not confuse a differential pressure sensor with a gauge pressure sensor. A gauge sensor reads the difference between process pressure and atmospheric pressure. A differential sensor reads the difference between two distinct process lines. That distinction is why a differential pressure sensor needs two impulse lines, and why the low-pressure side is often left open to atmosphere when used for gauge-style measurements.

Paku Sensors offers micro differential pressure transmitters that cover low-differential spans from a few hundred pascals up to several bar. For very low ranges, the sensor must be capable of resolving a small pressure difference without being overwhelmed by line static pressure. That capability comes from the membrane material and the way the sensor body isolates the two chambers.

Key Selection Parameters for Differential Pressure Sensors

Selecting a differential pressure sensor is a different task from picking a standard pressure transmitter. You need to define two values at once: the static line pressure that both ports will see, and the differential pressure you intend to measure. If either value is misjudged, the sensor will either saturate at zero or drift beyond its accuracy class.

Range and Overpressure

Choose a range where the normal operating differential pressure sits between 60 and 80 percent of the rated span. This leaves headroom for process surges. Overpressure rating is the maximum static pressure either port can tolerate without damage. A sensor rated for 10 bar DP but only 2 bar overpressure will be ruined if the line is pressurized to 6 bar. Always check the overpressure rating against the highest possible combination of static pressure and DP.

Accuracy and Temperature Effects

Accuracy is usually expressed as a percentage of full scale. For filter monitoring, a 0.25 percent FS sensor is often sufficient. For flow measurement using an orifice plate, use 0.1 percent FS or better. Temperature effects matter because the sensor body expands and the oil fill inside the sensor changes volume. A compensated temperature range of -20 to 80°C is common, but if your process runs hotter or cooler, verify the zero and span temperature coefficients.

Media Compatibility

The wetted parts on the high-pressure side and the low-pressure side may see different media if a barrier fluid is used. Standard materials include 316 stainless steel, ceramic, and PVDF. For aggressive media such as chlorine or sulfuric acid, specify a ceramic diaphragm with a fluoropolymer coating. For sanitary applications, request a flush diaphragm and CIP-compatible materials.

Differential Pressure Sensor with Corrosion-Resistant Wetted PartsChoose a sensor with appropriate wetted materials like 316 stainless steel, ceramic, or PVDF for aggressive media. Proper material selection ensures long-term reliability and avoids costly failures.View Product →

Installation Positions and Impulse Line Layout

Installation can destroy a differential pressure sensor more quickly than any process variable. The two impulse lines must arrive at the sensor with the same temperature, the same fluid density, and no trapped gas or condensate. Practical rules that work in the field are:

• Keep impulse lines as short as possible and use a slope of at least 1:10 down toward the sensor for gas service, or up toward the sensor for liquid service.
• Use a three-valve manifold so that both ports can be equalized before zeroing. A two-valve manifold forces the sensor to see full line pressure on one side during startup, which can push the diaphragm against its stops.
• Install a vent valve on each impulse line to remove air in liquid service and condensate in gas service.
• Place the sensor above the impulse lines for liquid service so that any bubbles can rise back into the pipe. Place the sensor below the impulse lines for gas service so that condensate drains away.
• Use a blow-down connection on the low-pressure side if the media can clog the line.

When you mount the sensor, avoid vibration near the manifold. Corrugated diaphragm sensors are sensitive to mechanical shock. The sensor housing is not a structural support; use a proper bracket and keep the manifold aligned with the sensor body.

For projects that involve custom mounting arrangements, our engineering staff can review the impulse line layout and the sensor configuration before you purchase.

Typical Applications of Differential Pressure Sensors

Differential pressure sensors are found in almost every industrial plant, but the dominant uses fall into three categories.

Filter and Strainer Monitoring

Install a differential pressure sensor across any filter or strainer. The difference between the upstream and downstream pressure indicates the pressure drop caused by retained particulate. A clean filter shows a low, stable DP. As the filter loads, the DP rises. When the DP reaches the specified limit, it is time to clean or replace the element. This application relies on a relatively low range, often 0-50 kPa or 0-100 kPa, and the sensor must tolerate the full line static pressure.

Flow Measurement with Primary Elements

Orifice plates, venturi tubes, and pitot tubes all generate a differential pressure that follows Bernoulli's equation. The square root of the DP is proportional to flow rate. This method remains widely used for steam, natural gas, and clean liquids. For this service, the differential pressure sensor needs a pulse or square-root output in the transmitter firmware, and the range must be specified at the maximum expected flow.

Liquid Level Measurement

In an open tank, a differential pressure sensor with the low side open to atmosphere can measure level by placing a leg down to the bottom of the tank. The DP equals the hydrostatic pressure, which is proportional to level. In a closed tank, a dry-leg or wet-leg arrangement is needed. A dry leg requires the secondary impulse line to be filled with gas, and the sensor must be installed above the tank so that condensate does not form a wet leg.Differential Pressure Sensor for Level and Flow ApplicationsIn level measurement, a differential pressure sensor with a dry or wet leg arrangement provides accurate readings. Regular maintenance of impulse lines prevents common faults such as zero drift and blockage.View Product →

Field Maintenance and Common Faults

Differential pressure sensors fail in predictable ways when the impulse lines are not maintained. The most common fault is a slow zero drift caused by a small leak on one port. A second common fault is a blocked low-pressure side, which forces the sensor to read full DP regardless of the actual process. A third fault is condensation in the low-pressure side of a flow measurement installation, creating a wet leg that changes the reference height.

The daily checklist is short: record the zero value at equalized pressure, inspect the impulse lines for leaks, and check the drain valves. If you see a slow upward drift over weeks, look for a partial clog on the low side. If you see a sudden step change, check the manifold equalizing valve and the vent screws. For transmitters with a ceramic diaphragm, do not use an air jet to clean the process connection; the jet can damage the diaphragm.

Most manufacturers, including Paku Sensors, offer a sensor with a replaceable process isolation diaphragm. That feature is valuable when the media is corrosive or when the process must be cleaned regularly. The key to long service life is to know the two pressures in your system, treat the impulse lines with the same care as the sensor itself, and give the sensor time to equalize before you zero it.

When a differential pressure sensor is selected carefully and installed with proper impulse line design, it becomes one of the most stable measurements in the plant. The best way to start is to take the actual static line pressure and the maximum differential pressure that you expect. With those two numbers, you can narrow the field quickly. You can also review our pressure sensor selection guide to compare the technology options side by side. If the process has a corrosive medium, a hazardous area, or a low-flow requirement, request our catalog and check that the specific sensor model has the right overpressure rating and wetted materials before putting it on the line.