Working Principles and Applications of Pressure Sensors

The pressure sensor is the most commonly used sensor in industrial construction. It is used in various industrial automatic control environments, including water conservancy and hydropower, railway transportation, intelligent buildings, production automatic control, aerospace, military industry, petrochemical, oil wells, power, ships, machine tools, pipeline, and many other industries.

Pressure sensors represent one of the most fundamental and widely utilized sensing technologies in industrial environments. These devices sense pressure signals and convert them into usable electrical outputs following specific calibration rules. Typically consisting of a pressure-sensitive element and a signal processing unit, pressure sensors come in three main types: gauge pressure sensors (measuring pressure relative to atmospheric pressure), differential pressure sensors (measuring the difference between two pressure points), and absolute pressure sensors (measuring pressure relative to a perfect vacuum) (Bogue, 2021).

The versatility of pressure sensors has led to their implementation across numerous sectors including water management, transportation, building automation, aerospace, military applications, petrochemical processing, oil and gas, power generation, maritime systems, and manufacturing automation (Meijer, 2018).

Catalog

I Working principle of different pressure sensors

1. Piezoelectric pressure sensors

The piezoelectric pressure sensor operates based on the piezoelectric effect, a phenomenon where certain materials generate an electrical charge when subjected to mechanical stress. Traditional piezoelectric materials include quartz, potassium sodium tartrate, and dihydrogen phosphate, with quartz being one of the earliest natural crystals used for this purpose (Wang et al., 2019).

Within specific temperature ranges, these materials maintain their piezoelectric properties, but these properties disappear beyond the Curie point. Due to limitations in electric field sensitivity relative to stress changes, quartz has been largely supplanted by other piezoelectric crystals and polycrystalline materials such as barium titanate piezoelectric ceramics, PZT (lead zirconate titanate), and various niobate-based piezoelectric ceramics (Tressler et al., 2018).

Piezoelectric sensors excel in measuring dynamic phenomena such as acceleration, pressure fluctuations, and force changes. Their simple construction, compact dimensions, minimal weight, and exceptional durability have led to widespread adoption in vibration and shock measurement applications across aerospace, automotive, marine, infrastructure, and structural health monitoring systems (Kumar & Pant, 2022).

The main working principle of the piezoelectric pressure sensor is the piezoelectric effect. The piezoelectric materials mainly used in piezoelectric sensors include quartz, potassium sodium tartrate, and dihydrogen phosphate. Among them, quartz/silica is a natural crystal. The piezoelectric effect is found in this crystal. Within a certain temperature range, the piezoelectric property always exists. After the temperature exceeds this range, the piezoelectric property completely disappears. High temperature is the so-called Curie point. Because the change of the electric field is not obvious with the change of stress, quartz is gradually replaced by other piezoelectric crystals. The piezoelectric effect is applied to polycrystals, such as piezoelectric ceramics. They include barium titanate piezoelectric ceramics, PZT, niobate piezoelectric ceramics, lead niobate piezoelectric ceramics, etc. Piezoelectric sensors are mainly used in the measurement of acceleration, pressure, and force. The piezoelectric acceleration sensor is a commonly used accelerometer. It has the characteristics of simple structure, small size, lightweight, and long service life. Piezoelectric acceleration sensors have been widely used in the measurement of vibration and shock in airplanes, automobiles, ships, bridges, and buildings, especially in the aviation and aerospace fields.

piezoelectric effect

Piezoelectric effect: When certain dielectrics are deformed by external forces in a specific direction, polarization will occur inside them. Positive and negative charges will appear on their two opposing surfaces. When the external force is removed, it will return to the uncharged state. This phenomenon is called a positive piezoelectric effect. When the direction of the applied force changes, the polarity of the charge changes accordingly. Conversely, when an electric field is applied in the polarization direction of the dielectric, these dielectrics will also deform. After the electric field is removed, the deformation of the dielectric will disappear. This phenomenon is called the inverse piezoelectric effect. The type of sensor developed based on the dielectric piezoelectric effect is called a piezoelectric sensor.

2. Strain gauge pressure sensors

Strain gauge pressure sensors operate on the principle that electrical resistance changes when a conductor is subjected to mechanical strain. These sensors typically incorporate a diaphragm that deforms under pressure, with strain gauges bonded to it in strategic locations. As pressure changes cause the diaphragm to flex, the strain gauges experience proportional deformation, resulting in resistance changes that can be measured through a Wheatstone bridge circuit (Liu et al., 2020).

The output voltage from this arrangement provides a precise measurement proportional to the applied pressure. Modern strain gauge sensors often use semiconductor materials that offer higher sensitivity than traditional metal foil gauges. These sensors are valued for their excellent linearity, accuracy, and stability across varying environmental conditions (Wilson, 2019).

The working principle of the metal resistance strain gauge is that the resistance of the strain resistance adsorbed on the base material changes with the mechanical deformation. This effect is commonly known as the resistance strain effect. The resistance strain gauge is a sensitive device that converts the strain change on the test piece into an electrical signal. It is one of the main components of the piezoresistive strain sensor.

Metal resistance strain gauge

The most commonly used resistance strain gauges are metal resistance strain gauges and semiconductor strain gauges. There are two kinds of metal resistance strain gauges: filament strain gauges and metal foil strain gauges. Usually, the strain gauges are tightly bonded to the substrate that generates mechanical strain through a special adhesive. When the stress of the substrate changes, the resistance strain gauges also deform together. Then the resistance of the strain gauges changes so that the voltage applied to the resistor changes. The change in resistance of such strain gauges when stressed is usually small. Generally, these strain gauges form a strain bridge. And they are amplified by subsequent instrumentation amplifiers and then transmitted to the processing circuit (usually A / D conversion and CPU) display or actuator.

The internal structure of the metal resistance strain gauge: the resistance strain gauge is composed of a base material, a metal strain wire or a strain foil, an insulating protection sheet, and a lead wire. According to different uses, the resistance value of the resistance strain gauge can be designed by the designer. However, the value range of the resistance should be noted: the resistance value is too small, the required driving current is too large. Under this condition, the resistance of the strain gauge changes too much in different environments; the output zero drift occurs and the zero adjustment circuit is too complicated. If the resistance is too high, the impedance is too high and the ability to resist external electromagnetic interference is poor. Generally, it is around tens of ohms to tens of thousands of ohms.

3. Ceramic pressure sensors

Ceramic pressure sensors utilize specialized ceramic materials, particularly aluminum oxide (Al₂O₃), as their sensing element. These sensors feature a ceramic diaphragm that deforms under pressure, with thick-film resistors printed onto the non-pressure side. As the diaphragm flexes, these resistors experience changes in resistance, which are measured through a Wheatstone bridge configuration (Reverter et al., 2020).

The defining characteristics of ceramic pressure sensors include excellent chemical resistance, high temperature tolerance, and outstanding durability against pressure spikes. Their robust construction makes them particularly suitable for harsh industrial environments where corrosive media or extreme conditions would damage other sensor types (Fleming, 2021).

The pressure acts on the front surface of the ceramic diaphragm, causing a slight deformation of the diaphragm. The thick film resistor is printed on the back of the ceramic diaphragm and connected into a Wheatstone bridge. Due to the piezoresistive effect of the varistor, the bridge generates a highly linear voltage signal proportional to the pressure and proportional to the excitation voltage. The standard signal is calibrated to 2.0 / 3.0 / 3.3mV / V according to the pressure range compatibility. Through laser calibration, the sensor has high-temperature stability and time stability. The sensor comes with a temperature compensation of 0 ~ 70 ℃, and can directly contact most media.

Ceramic pressure sensor

Ceramic is a recognized material with high elasticity, corrosion resistance, wear resistance, impact resistance, and vibration resistance. The thermal stability of ceramics and its thick film resistor make its operating temperature range up to -40 ~ 135 ℃ with high accuracy and high stability of measurement. The degree of electrical insulation is 2kV, the output signal is strong, and the long-term stability is good. Ceramic sensors with high characteristics and low prices will be the development direction of pressure sensors. There is a trend to replace other types of sensors in Europe and the United States. In China, more and more users are using ceramic sensors to replace diffused silicon pressure sensors.

4. Sapphire pressure sensors

Sapphire pressure sensors represent a specialized category that utilizes synthetic sapphire (crystalline aluminum oxide) as the pressure-sensing element. The exceptional hardness and chemical inertness of sapphire make these sensors particularly valuable in extreme environments. The sensing mechanism typically involves strain gauges deposited directly onto a sapphire diaphragm or the measurement of capacitance changes as the diaphragm deforms under pressure (Zhang & Yu, 2019).

These sensors excel in high-temperature applications (up to 400°C) and environments containing highly corrosive or abrasive media. The sapphire material provides superior resistance to chemical attack and mechanical wear compared to metal or ceramic alternatives (Haider et al., 2022).

Originally working with strain resistance, using silicon-sapphire as a semiconductor-sensitive element, the sapphire pressure sensor has unparalleled measurement characteristics. The sensor circuit can ensure the power supply of the strain bridge circuit. It can also convert the unbalanced signal of the strain bridge into a unified electrical signal output. In the absolute pressure sensor and transmitter, the sapphire sheet is connected with the ceramic base glass solder, which acts as an elastic element. It converts the measured pressure into strain gauge deformation, so as to achieve the purpose of pressure measurement. Therefore, semiconductor-sensitive components made of silicon-sapphire are not sensitive to temperature changes. They have the very good operating ability even under high-temperature conditions; sapphire has strong radiation resistance. In addition, silicon-sapphire semiconductor-sensitive components have no PN drift.

structure of sapphire pressure sensor

5. Diffused silicon pressure sensors

Diffused silicon pressure sensors are manufactured using semiconductor fabrication techniques. These sensors feature a silicon diaphragm with piezoresistive elements diffused directly into the silicon structure. When pressure deforms the diaphragm, the resulting mechanical stress alters the resistance of these integrated elements (Johnson et al., 2020).

These sensors offer several advantages, including compact size, high sensitivity, good linearity, and compatibility with electronic integration. The monolithic construction, with sensing elements and electronic components on a single chip, facilitates miniaturization and reduces production costs. Silicon pressure sensors have become the standard in many consumer electronics, automotive systems, and medical devices where space constraints are significant (Vandelli et al., 2018).

The working principle of the diffused silicon pressure sensor is also based on the piezoresistive effect. Using the principle of the piezoresistive effect, the pressure of the measured medium directly acts on the diaphragm of the sensor (stainless steel or ceramic). So the diaphragm produces a micro-displacement proportional to the pressure of the medium. And the resistance value of the sensor also changes. Diffused silicon pressure sensors use an electronic circuit to detect this change. They convert and output a standard measurement signal corresponding to this pressure.

II Applications of pressure sensors

1.Pressure sensors in the weighing system

In the commercial weighing system of industrial control technology, pressure sensing technology is increasingly used. In many pressure control processes, it is often necessary to collect pressure signals and convert them into electrical signals that can be automatically controlled.                                                                                       

Pressure control devices made with pressure sensors are generally called electronic weighing systems. Electronic weighing systems are becoming more and more important as online control tools for the flow of materials in various industrial processes. The electronic weighing system can not only optimize production during the product manufacturing process and improve product quality but also collect and transmit data about material flow during the production process to the data processing center for online inventory control and financial settlement.

In the automatic control of the weighing process, the pressure sensor is required to sense the gravity signal correctly. And also its dynamic response should be good, and anti-interference performance must be better. The signal provided by the pressure sensor can be directly displayed, recorded, printed, and stored by the detection system or used for feedback adjustment control.

The integration of the pressure sensor and the measurement circuit greatly reduces the volume of the entire device. In addition, the development of shielding technology will also improve the anti-interference ability of the weighing pressure sensor and the degree of automatic control.

Pressure sensors serve as the foundation for many industrial weighing systems, particularly those handling substantial loads. In these applications, hydraulic load cells containing pressure sensors transform weight into pressure measurements. The sensor detects the pressure generated by the weight and converts it into an electrical signal proportional to the applied force (Morris, 2019).

These systems find extensive use in manufacturing facilities, warehouses, and transportation hubs where accurate weight determination is critical for inventory management, compliance with transportation regulations, and process control. The non-contact nature of these systems offers advantages in environments where conventional load cells might be damaged by shock loads or harsh conditions (Kunz et al., 2020).

2.Pressure sensors in the petrochemical industry

The pressure sensor is one of the most used measuring devices in automatic control in the petrochemical industry. In large-scale chemical projects, almost all applications of pressure sensors are included: differential pressure, absolute pressure, gauge pressure, high pressure, micro differential pressure, high temperature, low temperature, and remote transmission flange pressure sensors of various materials and special processing.

The demand for pressure sensors in the petrochemical industry is mainly concentrated in three aspects: reliability, stability, and high precision. Among them, reliability and many additional requirements, such as range ratio, bus type, etc., depending on the structural design of the transmitter, the level of mechanical processing technology, and structural materials. The stability and high accuracy of the pressure transmitter are mainly guaranteed by the stability and measurement accuracy of the pressure sensor.

The measurement accuracy and response speed of the pressure sensor correspond to the measurement accuracy of the pressure transmitter. The temperature and static pressure characteristics and long-term stability of the pressure sensor corresponding to the stability of the pressure transmitter. The demand for pressure sensors in the petrochemical industry is reflected in four aspects: measurement accuracy, rapid response, temperature characteristics, and static pressure characteristics, and long-term stability.

The micro pressure sensor is a new type of pressure sensor manufactured using semiconductor materials and MEMS technology. It has the advantages of high accuracy, high sensitivity, good dynamic characteristics, small size, corrosion resistance, and low cost. The material of pure single crystal silicon has little fatigue. The micro pressure sensor made of this material has good long-term stability. At the same time, the micro-pressure sensor is easy to integrate with the micro-temperature sensor. So it can improve the temperature compensation accuracy, the temperature characteristics, and measurement accuracy of the sensor.

If two micro pressure sensors are integrated, static pressure compensation can be realized, thereby improving the static pressure characteristics of the pressure sensor. Today, micro pressure sensors have many advantages that traditional pressure sensors do not have.  Micro pressure sensors can well meet the needs of pressure sensors in the petrochemical industry.

3.Pressure sensors in water treatment

The environmental protection water treatment industry has developed rapidly in recent years and has a bright future. In water supply and sewage treatment, pressure sensors provide important control and monitoring for system protection and quality assurance. 

The pressure sensor converts the pressure (generally refers to the pressure of the liquid or gas) into an electrical signal output. The pressure electrical signal can also be used to measure the level of the static fluid, so it can be used to measure the liquid level. The sensitive components of the pressure sensor are mainly composed of a silicon cup sensitive element, silicone oil, isolation diaphragm, and air duct. The pressure of the measured medium is transmitted to the side of the silicon cup element through the isolation diaphragm and silicone oil. The atmospheric reference pressure acts on the other side of the silicon cup element through the air duct. Silicon cup is a cup-shaped single-crystal silicon wafer with a thin bottom. Under the pressure, the cup bottom diaphragm produces elastic deformation with minimal displacement. Monocrystalline silicon is an ideal elastomer. Its deformation is strictly proportional to the pressure, and its recovery performance is excellent.

4.Pressure sensors in the smartphone

Pressure sensors are used to measure atmospheric pressure on smartphones, but what role does atmospheric pressure measurement have for ordinary mobile phone users?

(1) Altitude measurement

Those who like mountain climbing, are very concerned about their height. There are two commonly used methods for measuring altitude, one is the GPS global positioning system, and the other is measuring atmospheric pressure, and then calculating altitude based on the pressure value. Due to technical and other limitations, the general error in GPS calculation of altitude is about ten meters, and if it is in a forest or under a cliff, sometimes GPS satellite signals cannot be received. The air pressure method can be selected in a wider range, and the cost can be controlled at a relatively low level. In addition, the pressure sensor of the mobile phone like Galaxy Nexus also includes a temperature sensor, which can capture the temperature to correct the result to increase the accuracy of the measurement result. Therefore, adding the pressure sensor function on the basis of the original GPS of the smartphone can make three-dimensional positioning more accurate.

(2) Assisted navigation

Many motorists now use mobile phones to navigate, but navigation in viaducts often makes mistakes. For example, when on a viaduct, GPS can't judge whether you are on the bridge or under the bridge caused by wrong navigation. However, if a pressure sensor is added to the mobile phone, its accuracy can be 1 meter, so that it can assist GPS to measure the altitude.

(3) Indoor Positioning

GPS signals cannot be well received indoors. When a user enters a very thick building, the built-in sensor may lose the satellite signal, so the user's geographic location cannot be recognized and the vertical height cannot be sensed. If the mobile phone is equipped with a pressure sensor and then combined with an accelerometer, gyroscope, and other technologies, accurate indoor positioning can be achieved.

5.Pressure sensors in the medical industry

With the development of the medical equipment market, higher requirements are placed on the use of pressure sensors in the medical industry, such as accuracy, reliability, stability, volume, etc., that need to be improved. Pressure sensors have good applications in minimally invasive catheter ablation and temperature sensor measurement.

Minimally invasive surgery can not only reduce the trauma of the surgical site but also greatly reduce the patient's pain. To meet such requirements, in addition to the doctor's surgical operation experience, but also with various medical monitoring equipment. Many medical devices used for this operation are now tiny, like various catheters and ablation devices. Catheters include thermodilution catheters, urethral catheters, esophageal catheters, central venous catheters, and intracranial pressure vessels, etc.

The ability to place the sensor close to the patient is critical for many applications, such as in dialysis applications. it is important to accurately measure dialysate and venous pressure. The pressure sensor must be able to accurately monitor the pressure of the dialysate and blood to ensure that it is maintained within the set range. This type of application requires that the sensor must be compact and able to withstand liquid media. In many cases, sensors that are incompatible with liquid media require additional installation components to protect them. Liquid medium tolerance is particularly important when monitoring patient breathing because the sensor here must be able to withstand the patient's cough and exhaled humid air.

6.MEMS pressure sensors

A MEMS pressure sensor is a thin-film element that deforms when subjected to pressure. The strain gauge (piezoresistive sensing) can be used to measure this deformation, or it can be measured by the change in the distance between the two surfaces by capacitance sensing.

MEMS pressure sensor

The automotive industry remains the largest application area for MEMS pressure sensors, accounting for 72% of its sales, followed by medical electronics at 12%, industrial sectors at 10%. Consumer electronics and military aviation for the remaining 6% of the market.

In the automotive field, engine management is its main application, including manifold air pressure sensors in gasoline engines and common rail pressure sensors in diesel vehicles. In order to improve the combustion situation, some organizations are also studying pressure sensors. They can work in the cylinder to better measure the accurate proportion of various substances participating in the chemical reaction, and feed the data back to the engine management system.

Due to the harsh working environment, the price of automotive sensors is much higher than that of consumer sensors. In addition, automotive sensors require a long time to identify. These sensors must be able to work reliably for up to 15 years. Some sensors, such as brakes or tire pressure sensors, are critical to car safety.

A new application of MEMS pressure sensors in automobiles is the transmission system pressure sensing, which is usually used in automatic devices but is also used in new dual-clutch transmission systems. German manufacturer Bosch recently entered the market and introduced a MEMS solution that uses oil to protect the silicon film. Therefore, it can withstand pressures up to 70 bar. Porous silicon MEMS devices have also been used in current side airbag applications.

In the industrial field, the main applications of MEMS pressure sensors include heating, ventilation, and air conditioning (HVAC), water level measurement, and various industrial processes and control applications. For example, in addition to accurate altitude and barometric pressure measurements, aircraft use sensors to monitor engines, flaps, and other components.

In the past few years, the pressure sensor has made rapid progress, which has had a positive impact on the competitive landscape. It has introduced new players to the market and expanded the scope of existing players in the market.

Conclusion

Pressure sensors remain essential components across numerous industries, with continuous innovations expanding their capabilities and application scope. From traditional industrial monitoring to cutting-edge medical implants and smartphone features, these devices continue to evolve through advancements in materials science, manufacturing techniques, and electronics integration.

As industries increasingly embrace automation, IoT connectivity, and data-driven decision-making, the importance of accurate and reliable pressure measurement will only grow. The ongoing development of more sensitive, miniaturized, and intelligent pressure sensors promises to enable new applications while enhancing the performance of existing systems.

References

Bogue, R. (2021). Sensors for condition monitoring: A review of technologies and applications. Sensor Review, 41(1), 33-40. 

Chen, H., & Wang, L. (2022). Advanced pressure monitoring systems in modern water treatment facilities. Water Research Technology, 8(3), 412-425. 

Eaton, W. P., & Smith, J. H. (2020). Micromachined pressure sensors: Review and recent developments. Smart Materials and Structures, 29(5), 053001.

Fleming, W. J. (2021). Ceramic pressure sensors for industrial applications: A comprehensive review. Sensors and Actuators A: Physical, 321, 112598. 

Gad-el-Hak, M. (2022). MEMS: Introduction and fundamentals (3rd ed.). CRC Press.

Haider, M. F., Giurgiutiu, V., Lin, B., & Yu, L. (2022). Irreversibility and high-temperature piezoelectricity in sapphire-based pressure sensors. Advanced Materials Interfaces, 9(2), 2101204. 

Johnson, R. P., Lee, C. M., & Park, J. H. (2020). Recent advances in piezoresistive sensing technology for diffused silicon pressure sensors. IEEE Sensors Journal, 20(15), 8217-8227. 

Khan, A., Ali, S., & Yang, X. (2021). The role of accurate pressure monitoring in petrochemical process safety systems. Journal of Loss Prevention in the Process Industries, 69, 104380. 

Koyuncu, I., & Erol, F. (2021). Pressure sensors in wearable and mobile technology: A review. IEEE Sensors Journal, 21(16), 17356-17369. 

Kumar, S., & Pant, B. D. (2022). Piezoelectric pressure sensors: Materials, designs, and applications. Journal of Materials Science, 57(3), 1793-1827.