Aug 31, 2026Technical Guides

Pressure Measurement in Industrial Processes: Principles, Selection and Application

Learn how pressure measurement supports industrial processes, how pressure reference and operating conditions affect selection, and what to confirm before choosing an instrument.

A pressure value becomes useful when it helps answer a specific process question.

Pressure can be used to monitor equipment, support process control, observe pressure drop, evaluate vessel or pipeline conditions, estimate liquid level under defined conditions, investigate abnormal operation or provide data to a control system.

The measurement therefore starts with a simple question:

What decision is this pressure reading expected to support?

Selecting an instrument is not only about choosing the highest available accuracy or a range that appears large enough. The pressure reference, complete operating range, medium, temperature, process connection, electrical interface, installation and verification method all influence whether the final reading represents the actual process condition.

What should the pressure measurement tell you?

Different pressure measurements support different tasks.

Typical examples include:

displaying local process pressure;

transmitting pressure to a PLC, DCS or monitoring system;

supporting process control;

detecting an abnormal pressure condition;

observing pressure drop across a filter, restriction or process component;

monitoring pumps, compressors, pipelines or vessels;

supporting liquid-level measurement based on hydrostatic pressure;

supporting flow measurement where differential pressure is part of a defined measurement arrangement;

recording pressure during testing or equipment operation;

investigating process or equipment changes.

The same nominal pressure range can therefore lead to different instrument choices depending on the measurement task.

A mechanical pressure gauge, a pressure switch and a continuous pressure transmitter do not solve the same problem. Before selecting a specific device, first define whether the requirement is local indication, switching, continuous transmission, control input, monitoring or another measurement function.

Pressure also should not be interpreted in isolation.

A change in pressure may need to be considered together with flow, temperature, density, valve position, equipment state or other process variables before a useful conclusion can be reached.

Start with the pressure reference

One of the first selection decisions is the pressure reference.

Gauge pressure

Gauge pressure is measured relative to atmospheric pressure.

It is commonly used where the process condition is naturally understood in relation to the surrounding atmosphere, such as many pipelines, pumps and pressurised equipment applications.

Absolute pressure

Absolute pressure is referenced to vacuum.

It is useful when the actual pressure relative to zero pressure matters and atmospheric-pressure variation should not become part of the measurement.

Vacuum processes are one example where the pressure reference requires particular attention.

Differential pressure

Differential pressure measures the difference between two pressure points.

It can be used to observe pressure drop across a filter, restriction or other process equipment.

Where the physical relationship is properly defined, differential pressure can also form part of flow or level measurement arrangements.

Gauge, absolute and differential pressure are not interchangeable simply because their numerical ranges appear similar.

The useful question is:

What is the pressure being compared with?

That reference should be established before the measuring range is selected.

For a more detailed comparison of these reference types and their application logic, see Gauge vs. Absolute vs. Differential Pressure: How to Choose the Right Reference.

Do not select the range from normal pressure alone

Normal operating pressure is only one part of the application.

Before selecting the measuring range, review the complete operating envelope:

normal operating pressure;

minimum pressure;

maximum continuous pressure;

vacuum conditions, if applicable;

start-up conditions;

shutdown conditions;

pressure pulsation;

transient pressure;

surge or pressure shock;

possible overpressure;

duration of abnormal conditions;

frequency of abnormal conditions.

This distinction is important because measuring range and overpressure capability are not the same characteristic.

Selecting a wider measuring range does not automatically make the measurement safer. It can also change the relationship between the normal operating pressure and the instrument's measurement performance.

The appropriate choice therefore requires both sides of the problem to be considered:

How accurately does the normal process need to be measured?

and

What abnormal pressure conditions must the selected configuration withstand?

Specific overpressure limits should always be checked against the actual model and configuration rather than assumed from the nominal measuring range.

For a practical method of separating operating pressure, pressure excursions and overpressure conditions during range selection, see How to Choose the Right Pressure Range for a Pressure Transmitter.

Accuracy is only one part of measurement performance

Accuracy is important, but the highest accuracy specification does not automatically produce the best field measurement.

The complete result can also be influenced by:

measuring range selection;

process and ambient temperature;

pressure reference;

process connection;

installation orientation;

impulse lines or isolation arrangements;

vibration;

pressure pulsation;

electrical noise;

wiring;

control-system scaling;

calibration and verification practices.

It is therefore useful to think of pressure measurement as a measurement chain rather than treating the sensor as an isolated component.

The chain may include:

Process pressure → pressure connection or impulse path → sensing element → transmitter → electrical signal → PLC/DCS input → scaling → display, control or recorded value

A transmitter can produce a stable electrical output while the final process value is still wrong.

For example, the problem may lie in the pressure reference, a blocked pressure path, incorrect zero, wiring, engineering-unit conversion or control-system scaling rather than in the sensing element itself.

Dynamic pressure conditions require separate attention

Not every pressure measurement is steady.

Pumps, compressors, rapidly operating valves and other process events can create pulsation, surge, shock or transient pressure conditions.

A transmitter selected for stable process monitoring should not automatically be assumed suitable for every fast pressure event.

When dynamic behaviour matters, consider:

how rapidly the pressure changes;

how long the event lasts;

how frequently it occurs;

whether the objective is process monitoring or transient measurement;

whether the installation path changes the observed response;

whether protection or damping is required.

The instrument response and the physical installation should be evaluated together.

This is another reason that “normal operating pressure” alone is not enough information for selection.

The process medium is part of the measurement

The medium should not be reduced to a simple label such as “water”, “air” or “chemical”.

Useful application information can include:

medium type;

concentration;

process temperature;

contamination;

suspended solids;

viscosity;

crystallisation;

deposits;

cleaning method;

corrosion considerations;

compatibility with all wetted parts.

The complete wetted structure matters.

Depending on the design, this can include the sensing diaphragm, pressure interface, seals, process connection and isolation components.

A material that performs well in one application should not automatically be assumed suitable for every fluid or operating condition.

Likewise, selecting a material with a higher alloy designation does not by itself prove compatibility with a particular chemical.

For corrosive, viscous, crystallising, contaminated or otherwise difficult media, the actual medium, concentration, temperature and wetted construction should be reviewed together.

Process connection is part of the measurement system

The process connection is not only a mechanical mounting detail.

It can affect whether the pressure point remains representative, whether material accumulates, whether maintenance is possible and whether the measurement path stays open.

Questions to review include:

What process connection is available?

Is the pressure port likely to block?

Can the medium crystallise or form deposits?

Is the medium viscous or contaminated?

Is direct installation appropriate?

Is process isolation required?

Is sufficient installation and maintenance space available?

Could vibration affect the instrument?

Could pressure pulsation affect the measurement?

Is the selected pressure point representative of the process?

For some applications, isolation arrangements, remote pressure transfer, manifolds or other accessories become part of the measurement solution rather than optional extras.

Their influence on maintenance, response and measurement behaviour should therefore be considered before final selection.

Impulse paths and installation can create measurement errors

When pressure is transferred through impulse lines or similar arrangements, the path between the process and the instrument becomes part of the measurement chain.

Installation conditions can introduce errors even when the transmitter itself is functioning correctly.

Examples include:

trapped gas in liquid-pressure lines;

accumulated liquid in gas-pressure lines;

blocked or leaking impulse lines;

poor pressure-point location;

unsuitable mounting;

excessive vibration;

process deposits;

installation conditions that make zero verification difficult.

The installation should therefore be reviewed during instrument selection, not only after the product has arrived on site.

A measurement system that is difficult to inspect, isolate or verify can also create additional maintenance cost over its working life.

Select the electrical interface around the complete system

The transmitter output must match the receiving system and installation conditions.

Before selecting the electrical interface, review:

available power supply;

required signal type;

cable distance;

electrical noise;

grounding;

PLC or DCS input requirements;

engineering units;

scaling;

local display requirements;

communication requirements;

remote configuration needs;

diagnostic requirements;

expected behaviour during a fault.

A particular output technology should not automatically be described as “better”.

The appropriate interface depends on the complete system.

For example, signal distance, noise environment, available power, receiving hardware and diagnostic requirements can all influence the selection.

Support for a specific protocol, output or diagnostic function should always be confirmed for the exact product and configuration.

Pressure measurement for process control and equipment monitoring

Pressure measurements often become inputs to control, alarms and maintenance decisions.

A stable and timely signal can help show whether a valve or pump adjustment produced the expected process response.

Pressure trends may also help identify changes that deserve investigation, such as increasing pressure drop, abnormal cycling or changing pump conditions.

However, these observations are not automatic diagnoses.

An increasing differential pressure across a process component, for example, indicates that the pressure relationship has changed. Determining why it changed may require additional process information.

Likewise, a pressure sensor used within an alarm or control system is not by itself a complete safety system.

Alarm logic, redundancy, protective action, proof testing and other safety requirements belong to the overall engineering design and, where applicable, the required compliance framework.

Installation, commissioning and verification

After installation, verify the measurement as a complete chain.

Typical checks can include:

correct pressure reference;

correct installation position and orientation;

process connection;

pressure-transfer or impulse path;

zero condition;

measuring range;

engineering units;

electrical output;

PLC/DCS input;

scaling;

local display;

baseline process reading.

Recording a useful baseline can make later troubleshooting easier.

If an unexpected pressure reading appears later, the investigation should not immediately assume that the transmitter has failed.

Possible causes can also include:

actual process changes;

valve position;

blockage;

leakage;

temperature;

pressure-transfer lines;

electrical supply;

wiring;

scaling;

installation conditions.

Verification intervals should reflect the process criticality, operating exposure, site procedures and quality requirements rather than relying on one universal calibration interval for every application.

What is the economic value of pressure measurement?

The economic value of pressure measurement does not come simply from installing another sensor.

It comes from whether the measurement improves a useful operational decision.

Depending on the process, pressure information may help with:

process control;

earlier investigation of deviations;

equipment monitoring;

reduced manual observation;

production or test records;

troubleshooting;

maintenance planning.

But the benefit is not automatic.

A poorly selected range can reduce the usefulness of the signal. A blocked pressure path can produce a plausible but incorrect value. An alarm without a defined response can add information without improving the process.

The economic evaluation should therefore consider the complete measurement arrangement:

instrument + installation + verification + maintenance + data use + decision process

Pressure measurement can also contribute to energy analysis of pumps, compressors and fluid systems, but pressure alone cannot establish efficiency.

Flow, operating time, equipment characteristics, control strategy and system losses may also be required.

Pressure should therefore be treated as one input to the analysis rather than as an automatic source of energy savings.

When a standard pressure configuration may not be enough

Some applications require additional review before a standard instrument configuration is selected.

Examples include:

high-temperature media;

corrosive or chemically aggressive media;

strong pressure pulsation;

transient pressure or pressure shock;

vacuum service;

clogging or crystallising media;

viscous media;

hygienic processes;

hazardous areas;

downhole applications;

unusual process connections;

special materials;

special output or communication requirements.

These conditions do not automatically mean that pressure measurement cannot be used.

They mean that the instrument and installation should be reviewed against the actual application rather than selected from a basic range and output alone.

Where a certification or regulatory requirement applies, the exact product configuration and corresponding documentation must also be confirmed.

What information should you provide before selecting a pressure transmitter?

A useful pressure inquiry should normally include more than:

“0–10 bar, 4–20 mA.”

Where possible, provide:

measurement task;

gauge, absolute or differential pressure requirement;

normal operating pressure;

minimum pressure;

maximum continuous pressure;

vacuum conditions, if applicable;

transient, pulsating or surge pressure;

duration and frequency of abnormal pressure conditions;

medium;

concentration, where relevant;

process temperature;

ambient conditions;

process connection;

required wetted materials, if specified;

power supply;

required output;

cable or connector requirement;

installation method;

hazardous-area or other compliance requirements;

required quantity;

any unusual operating conditions.

This information makes it much easier to determine whether a standard configuration is suitable or whether the application requires additional engineering review.

Frequently Asked Questions About Pressure Measurement

What is the difference between gauge, absolute and differential pressure?

The difference is the reference point.

Gauge pressure is referenced to atmospheric pressure, absolute pressure is referenced to vacuum, and differential pressure compares two pressure points.

The correct choice depends on what the measurement needs to represent.

Why is normal operating pressure not enough to select the measuring range?

Because start-up, shutdown, pulsation, pressure shock, vacuum and other abnormal conditions can expose the instrument to pressures outside the normal operating value.

The complete operating envelope should therefore be reviewed.

Does choosing a larger range make a pressure transmitter safer?

Not necessarily.

Measuring range and overpressure capability describe different characteristics.

A wider range can also change the relationship between normal operating pressure and measurement performance.

Both the measurement requirement and the overload requirement should be evaluated separately.

Why is the highest accuracy not always the best selection?

Because the final field result also depends on range selection, temperature, pressure reference, installation, pressure-transfer path, wiring, scaling and verification.

Instrument accuracy is only one part of the complete measurement chain.

Why can a pressure reading be stable but still be wrong?

A stable electrical signal does not prove that the complete measurement is correct.

Possible causes include an incorrect pressure reference, blocked or leaking pressure paths, trapped gas or liquid, incorrect zero or range, temperature effects, wiring, scaling or installation problems.

Can differential pressure be used for flow or level measurement?

Differential pressure can form part of flow or level measurement when the relationship between pressure and the desired variable is properly defined.

The complete measurement arrangement and process assumptions still need to be considered.

When should an application be reviewed instead of selecting a standard model directly?

Application review becomes particularly useful for unusual temperature, corrosion, pulsation, vacuum, clogging, hazardous areas, special materials, unusual connections, dynamic pressure conditions or other non-standard requirements.

Next step

A useful pressure measurement starts with the measurement task and actual operating conditions, not with a single catalogue specification.

Define:

what needs to be measured → what pressure reference is required → what the complete operating envelope looks like → what medium contacts the instrument → how the instrument connects to the process → how the signal reaches the control system → how the result will be verified

For a HRT pressure application review, provide the pressure conditions, medium, temperature, process connection, output, installation requirements and any special operating or compliance requirements.

The objective is to determine whether a standard configuration is suitable or whether the measurement arrangement should be adapted to the actual process.