A pressure sensor is a device that senses pressure signals and converts them into usable electrical output signals according to a certain rule. Pressure sensors typically consist of a pressure-sensitive element and a signal processing unit. Based on different types of pressure being measured, pressure sensors can be classified into gauge pressure sensors, differential pressure sensors, and absolute pressure sensors. Pressure sensors are one of the most commonly used sensors in industrial practice, widely applied in various industrial automation environments, including water conservancy and hydropower, railway transportation, intelligent buildings, production automation, aerospace, military, petrochemicals, oil wells, power, shipbuilding, machine tools, pipelines, and many other industries.
A pressure sensor is a sensor that converts physical quantities into electrical signals, primarily used to measure pressure and weight. Pressure sensors possess characteristics such as wide application range, high accuracy and stability, fast response time, low power consumption and high efficiency, high temperature and corrosion resistance, multiple operating principles, customizability and reliability, and ease of integration and use. Pressure sensors are widely used in industrial control, automotive manufacturing, medical, and environmental fields.
The main piezoelectric materials used in piezoelectric sensors include quartz, sodium potassium tartrate, and ammonium dihydrogen phosphate. Quartz (silicon dioxide) is a natural crystal, and the piezoelectric effect was discovered in this crystal. Within a certain temperature range, the piezoelectric property persists, but it completely disappears above this range (this high temperature is known as the "Curie point"). Because the electric field changes only slightly with stress (meaning the piezoelectric coefficient is relatively low), quartz has gradually been replaced by other piezoelectric crystals. Sodium potassium tartrate has a high piezoelectric sensitivity and coefficient, but it can only be used in environments with low room temperature and low humidity. Ammonium dihydrogen phosphate is a synthetic crystal that can withstand high temperatures and relatively high humidity, and therefore has been widely used.
Heavy-duty pressure sensors are a type of sensor, but they are rarely heard of. They are typically used in transportation applications to maintain the performance of heavy-duty equipment by monitoring the pressure, hydraulic force, flow rate, and level of critical systems such as pneumatics, light-duty hydraulics, brake pressure, oil pressure, transmission systems, and truck/trailer air brakes. A heavy-duty pressure sensor is a pressure measuring device with a housing, a metal pressure interface, and a high-level signal output. Many sensors have a cylindrical shape with a circular metal or plastic housing, a pressure interface at one end, and a cable or connector at the other. These heavy-duty pressure sensors are often used in extreme temperature and electromagnetic interference environments. Customers in the industrial and transportation sectors use pressure sensors in control systems to measure and monitor the pressure of fluids such as coolant or lubricating oil. They can also detect pressure spikes and identify system blockages, allowing for immediate solutions. Heavy-duty pressure sensors are constantly evolving. To be used in more complex control systems, design engineers must improve sensor accuracy while reducing costs for practical application.
The principle of pressure sensors
The principle of a pressure sensor is that a strain gauge inside the sensor measures the strain of the object being measured, and then outputs an electrical signal through a cable. This signal is transmitted to a data acquisition system for processing, ultimately yielding the pressure value of the object. A strain gauge is a sensor that converts strain into a change in resistance, measuring the deformation of the object and thus calculating the pressure.
Industrial Control: Pressure sensors have a wide range of applications in industry, primarily for pressure measurement during production and processing. For example, they can be used to measure the pressure of liquids or gases and are commonly used in pharmaceuticals, chemicals, food, and beverage industries. Furthermore, pressure sensors can also be used to measure the weight and pressure of machinery to aid in its maintenance and upkeep.
Automotive Manufacturing: Pressure sensors are also widely used in the automotive industry. For example, they can be used to measure tire pressure to help drivers maintain the correct tire pressure. Furthermore, they can be used to measure engine pressure and oil pressure to help drivers monitor the vehicle's condition.
Medical Applications: Pressure sensors also have wide applications in the medical field. For example, they can be used to measure blood pressure, assisting doctors in diagnosing and treating conditions such as hypertension and hypotension. Furthermore, pressure sensors can be used to measure the pressure of ventilators, helping doctors and nurses monitor patients' breathing.
Environmental applications: Pressure sensors can also be used for environmental monitoring. For example, they can be used to measure parameters such as atmospheric pressure, ocean depth, and soil pressure. This data can be used in research in fields such as meteorology, oceanography, and soil science.
Working principle of pressure sensor
Pressure sensors are among the most commonly used sensors in industrial practice, widely applied in various industrial automation environments, including water conservancy and hydropower, railway transportation, intelligent buildings, production automation, aerospace, military, petrochemicals, oil wells, power, shipbuilding, machine tools, pipelines, and many other industries. Below is a brief introduction to the principles and applications of some commonly used sensors.
1. Strain Gauge Pressure Sensor Principle and Application
There are many types of mechanical sensors, such as resistance strain gauge pressure sensors, semiconductor strain gauge pressure sensors, piezoresistive pressure sensors, inductive pressure sensors, capacitive pressure sensors, resonant pressure sensors, and capacitive accelerometers. However, the most widely used is the piezoresistive pressure sensor, which has extremely low cost, high accuracy, and good linearity. We will mainly introduce this type of sensor below.
When learning about piezoresistive force sensors, we first need to understand the element called a resistance strain gauge. A resistance strain gauge is a sensitive device that converts strain changes on a measured object into an electrical signal. It is one of the main components of a piezoresistive strain sensor. The most commonly used resistance strain gauges are metal resistance strain gauges and semiconductor strain gauges. Metal resistance strain gauges are further divided into wire strain gauges and metal foil strain gauges. Typically, the strain gauge is tightly bonded to the substrate that generates mechanical strain using a special adhesive. When the substrate is subjected to stress, the resistance strain gauge also deforms, causing a change in its resistance, which in turn changes the voltage across the resistor. The resistance change produced by this type of strain gauge under stress is usually small. Generally, these strain gauges are used to form a strain gauge bridge, which is then amplified by a subsequent instrumentation amplifier before being transmitted to the processing circuit (usually an A/D converter and CPU) for display or execution.
Internal structure of metal resistance strain gauge
Figure 1 shows a schematic diagram of a resistance strain gauge, which consists of a matrix material, a metal strain wire or strain foil, an insulating protective sheet, and lead wires. Depending on the application, the resistance value of the strain gauge can be designed by the designer, but the range of resistance values should be carefully considered: if the resistance is too small, the required driving current will be too large, and the strain gauge's own temperature will be too high due to heat generation. In different environments, the resistance value will vary too much, resulting in significant zero-point drift and an overly complex zero-adjustment circuit. Conversely, if the resistance is too large, the impedance will be too high, leading to poor resistance to external electromagnetic interference. Generally, the resistance is between tens of ohms and tens of kilohms.
Working principle of resistance strain gauge
The working principle of a metal resistance strain gauge is based on the phenomenon that the resistance of a strain gauge adsorbed on a substrate changes with mechanical deformation; this is commonly known as the resistance strain effect. The resistance value of a metallic conductor can be expressed by the following formula:
In the formula: ρ—resistivity of the metallic conductor (Ω·cm²/m)
S — Cross-sectional area of the conductor (cm²)
L — Length of the conductor (m)
Taking a metal wire strain gauge as an example, when the metal wire is subjected to an external force, its length and cross-sectional area change. It's easy to see from the above formula that its resistance value changes accordingly. If the metal wire is stretched under external force, its length increases while its cross-sectional area decreases, thus increasing the resistance value. When the metal wire is compressed under external force, its length decreases while its cross-sectional area increases, thus decreasing the resistance value. By measuring the change in resistance (usually by measuring the voltage across the resistor), the strain condition of the strain gauge wire can be obtained.
2. Principle and Application of Ceramic Pressure Sensors
Corrosion-resistant ceramic pressure sensors do not transmit liquid; pressure acts directly on the front surface of a ceramic diaphragm, causing a slight deformation. Thick-film resistors are printed on the back of the diaphragm, forming a Wheatstone bridge (closed bridge). Due to the piezoresistive effect of the pressure-sensitive resistors, the bridge generates a highly linear voltage signal proportional to both the pressure and the excitation voltage. Standard signals are calibrated to 2.0/3.0/3.3 mV/V, etc., depending on the pressure range, and are compatible with strain gauge sensors. Through laser calibration, the sensor exhibits high temperature and time stability, incorporates temperature compensation from 0 to 70°C, and can directly contact most media.
Ceramics are a recognized material with high elasticity, corrosion resistance, wear resistance, and resistance to impact and vibration. The thermal stability of ceramics and their thick-film resistance allow for operating temperatures ranging from -40°C to 135°C, while also providing high measurement accuracy and stability. They exhibit electrical insulation strength >2kV, strong output signal, and good long-term stability. High-performance, low-cost ceramic sensors represent the future direction of pressure sensor development, and in Europe and America, they are trending towards completely replacing other types of sensors. In China, an increasing number of users are also using ceramic sensors to replace diffused silicon pressure sensors.
3. Principle and Application of Diffused Silicon Pressure Sensors
Working principle: The pressure of the measured medium acts directly on the diaphragm of the sensor (stainless steel or ceramic), causing the diaphragm to produce a micro-displacement proportional to the medium pressure. This causes a change in the resistance value of the sensor, which is detected by electronic circuitry and converted into a standard measurement signal corresponding to this pressure.
Schematic diagram
4. Sapphire Pressure Sensor Principle and Application
Utilizing the strain gauge principle and employing silicon-sapphire as the semiconductor sensing element, this method offers unparalleled metrological characteristics. Sapphire is composed of a single-crystal insulating element, thus exhibiting no hysteresis, fatigue, or creep. Sapphire is stronger and harder than silicon, making it resistant to deformation. It possesses excellent elasticity and insulation properties (up to 1000°C), therefore, semiconductor sensing elements made from silicon-sapphire are insensitive to temperature changes and maintain excellent operating characteristics even at high temperatures. Sapphire also exhibits strong radiation resistance. Furthermore, silicon-sapphire semiconductor sensing elements are free from pn drift, fundamentally simplifying the manufacturing process, improving repeatability, and ensuring a high yield.
Pressure sensors and transmitters made with silicon-sapphire semiconductor sensing elements can operate normally under the harshest conditions, offering high reliability, accuracy, minimal temperature error, and cost-effectiveness. The gauge pressure sensor and transmitter consist of a dual-diaphragm design: a titanium alloy measuring diaphragm and a titanium alloy receiving diaphragm. A sapphire wafer printed with a heterogeneous epitaxial strain gauge bridge circuit is soldered onto the titanium alloy measuring diaphragm. The measured pressure is transmitted to the receiving diaphragm (which is securely connected to the measuring diaphragm by a tie rod). Under pressure, the titanium alloy receiving diaphragm deforms; this deformation is sensed by the silicon-sapphire sensing element, causing a change in the bridge output proportional to the measured pressure. The sensor's circuitry ensures power supply to the strain gauge bridge circuit and converts any imbalance signal from the strain gauge bridge into a uniform electrical signal output (0-5V, 4-20mA, or 0-5V). In absolute pressure sensors and transmitters, a sapphire wafer, connected to a ceramic base glass solder, acts as an elastic element, converting the measured pressure into strain gauge deformation, thereby achieving the purpose of pressure measurement.
5. Principle and Application of Piezoelectric Pressure Sensors
Pressure sensor features
Wide pressure range: Pressure sensors are suitable for measuring various pressure ranges, from minute to extremely high pressures. A suitable pressure sensor can be found for different applications and needs.
High accuracy and stability: Pressure sensors provide highly accurate results during measurement and exhibit excellent long-term stability. Their accuracy and stability are indispensable features in many critical applications.
Fast response time: Pressure sensors respond to pressure changes very quickly. They can capture and report pressure changes in real time, thus meeting the requirements for real-time monitoring and control.
Low power consumption and high efficiency: Many pressure sensors are designed with low power consumption to ensure energy efficiency during long-term use. This is a very important feature, especially for devices and systems that rely on battery power.
High temperature and corrosion resistance: Pressure sensors are typically used in harsh environments, such as high temperatures or corrosive media. Therefore, a good pressure sensor must be resistant to high temperatures and corrosion to ensure its reliability and long lifespan.
Multiple operating principles: Pressure sensors can employ various operating principles, such as resistance strain gauge, piezoelectric effect, and resonance principle. This allows them to adapt to different application requirements and provides a wide range of options.
Customizability and reliability: Since different applications have different requirements for pressure sensors, a good pressure sensor should have a certain degree of customizability and be able to maintain reliable performance in various environments.
Easy to integrate and use: A good pressure sensor should be easy to integrate and use to ensure convenience and flexibility in a variety of applications.
