A pressure sensor is a device that detects pressure and converts it into an electrical, optical or otherwise measurable signal. Pressure is a physical quantity describing force distributed over an area, and depending on context it can refer to absolute pressure, gauge pressure, differential pressure or related pressure measurements. A pressure sensor normally contains a sensing element that deforms or otherwise changes its physical or electrical characteristics when subjected to pressure.
Common technologies include piezoresistive, capacitive, piezoelectric and optical sensing structures. Modern pressure sensors often integrate the sensing element with amplification, temperature compensation and analogue-to-digital conversion, producing an analogue voltage, current or digital data output. Pressure sensing is used in vehicles, industrial machinery, medical devices, weather instruments, pumps, process-control systems, aircraft, consumer products and scientific equipment because pressure provides information about forces, fluid conditions, altitude, flow and system state.
Pressure sensors often operate by measuring mechanical deformation caused by pressure. A thin diaphragm can deflect when pressure is applied to one side or when a pressure difference exists across it. The deformation can then be converted into an electrical signal. In a piezoresistive pressure sensor, resistive elements are arranged so that mechanical strain changes their resistance. A bridge circuit can detect the resulting imbalance and produce a voltage related to pressure.
Semiconductor manufacturing makes it possible to create extremely small diaphragms and piezoresistive structures, allowing compact pressure sensors with high sensitivity. The mechanical structure, material properties, electrical circuit and calibration together determine the sensor's response. Because the diaphragm must deform predictably while surviving the expected pressure range, mechanical design is as important as the electronic measurement circuitry.
Capacitive pressure sensors detect pressure-induced changes in capacitance. A flexible diaphragm can form one plate of a capacitor, while pressure changes its position relative to another electrode. Because capacitance depends on geometry and separation, diaphragm movement produces an electrical change that can be measured by suitable electronics. Capacitive techniques can provide high sensitivity and can be implemented using microelectromechanical systems, commonly known as MEMS.
MEMS pressure sensors can integrate mechanical structures and semiconductor electronics on a small scale, making them suitable for portable devices, automotive systems, industrial instruments and other applications requiring compact measurement. Capacitive sensors can nevertheless be influenced by parasitic capacitance, electrical interference, mechanical stress and temperature, so the complete design must compensate for relevant environmental effects.
Piezoelectric pressure sensors use materials that generate electrical charge when mechanically stressed. When pressure produces deformation in a piezoelectric element, an electrical signal appears that corresponds to the applied mechanical stress. These sensors can respond rapidly to changing pressure and are particularly useful for dynamic measurements such as combustion events, vibration-related pressure fluctuations, shock waves and acoustic phenomena.
A limitation is that piezoelectric sensors are generally less suited to measuring a truly static pressure indefinitely because the generated charge can leak through the measurement system over time. They are therefore especially valuable when changes in pressure or transient events are important. The measurement electronics must also have suitable impedance and conditioning characteristics so that the small generated signal can be measured without excessive loss or distortion.
Pressure sensors are classified according to the pressure reference used. An absolute pressure sensor measures pressure relative to a near-vacuum reference. A gauge pressure sensor measures pressure relative to the surrounding atmospheric pressure, making it useful for applications such as tyre pressure or hydraulic pressure. A differential pressure sensor measures the difference between two pressure inputs and is useful for determining pressure drops across filters, pipes, valves and other components.
A sealed-gauge sensor uses a fixed reference pressure within the package rather than an actively vented atmospheric reference. These distinctions matter because the same physical pressure can produce different readings depending on the reference. Confusing absolute and gauge pressure is a common source of measurement errors, particularly when atmospheric pressure varies significantly.
Pressure sensors are widely used for control and monitoring. In engines and industrial systems, pressure measurements can indicate fluid or gas conditions and help control pumps, valves and combustion processes. Differential pressure measurements can be used to estimate fluid flow when combined with suitable system geometry and fluid properties, or to monitor filter blockage and ventilation performance.
Barometric pressure sensors can estimate altitude because atmospheric pressure changes with elevation, and they are consequently used in weather instruments, aircraft systems and mobile devices. Medical equipment uses pressure sensors for applications such as respiratory monitoring and blood-pressure measurement. Automotive systems use pressure sensing for tyres, fuel systems, manifolds and other subsystems. The pressure measurement is often one input into a larger control or diagnostic system rather than an isolated value.
Pressure-sensor performance depends on characteristics such as measurement range, sensitivity, accuracy, resolution, hysteresis, repeatability, response time, temperature coefficient and long-term stability. Mechanical overload can permanently deform a diaphragm or damage the sensing structure, so sensors have specified pressure limits and sometimes separate burst-pressure ratings. Temperature can affect both mechanical dimensions and electrical characteristics, requiring compensation. Fluid compatibility is also important because the materials exposed to the measured medium must resist corrosion, contamination and chemical attack. Installation can influence readings through vibration, mounting stress, trapped gas or liquid, pressure pulsations and inappropriate tubing. Calibration establishes the relationship between sensor output and known pressure references, but measurement uncertainty remains and must be considered in precision applications.
Pressure sensing should also be distinguished from force sensing because pressure concerns force per unit area, although a pressure sensor necessarily experiences mechanical forces through its sensing structure. A pressure transducer is often used as a near-synonym for a device that converts pressure into another signal, while pressure transmitter can refer to an industrial device that provides a standardised output suitable for control systems.
The broader significance of pressure sensors is that pressure is an indirect indicator of many physical conditions: it can reveal fluid containment, pump operation, airflow, altitude, combustion behaviour and mechanical loading. Modern MEMS fabrication has made pressure sensors small enough for mass-market electronics while industrial and scientific systems continue to use specialised high-temperature, high-pressure and high-precision devices. A pressure sensor therefore combines mechanical measurement, material behaviour and electronic signal processing to turn pressure differences or absolute pressure into useful information for monitoring, control and analysis.
