A pressure transmitter is a device that can detect pressure values and provide remote signal transmission. It is a commonly used sensor in industrial automation process control, used to measure the pressure of gases or liquids and convert this pressure value into a measurable and transmittable electrical signal. These electrical signals are typically standard current or voltage signals, such as 4-20mA current signals or 0-10V/0-5V voltage signals, to facilitate remote transmission, display, recording, or control in industrial automation, process control, monitoring, and measurement systems. It can meet the requirements of centralized detection and control in automated systems and is widely used in industrial production.
A pressure transmitter typically consists of a pressure-sensitive element (such as a strain gauge, capacitive diaphragm, or piezoresistive chip) and a signal processing circuit. When the measured medium acts on the pressure-sensitive element, it causes a physical change in the element (such as a change in resistance, capacitance, or resonant frequency), which is then converted into an electrical signal. The signal processing circuit is responsible for amplifying, linearizing, and temperature-compensating this electrical signal to output a stable and accurate pressure value.
Pressure transmitters come in various structural forms and can be classified according to their working principle as strain gauge, piezoresistive, capacitive, piezoelectric, and frequency-resonant types. The following is a brief introduction to several commonly used pressure transmitters.
Strain gauge pressure transmitters have a wide measurement range, capable of measuring pressures up to several hundred megapascals, and possess excellent dynamic performance, making them suitable for measuring rapidly changing pressures. However, it has relatively obvious temperature drift and time drift. This type of instrument is mostly used for dynamic pressure detection with general requirements. Piezoresistive pressure transmitters are manufactured based on the principle of piezoresistive effect. Its pressure-sensitive element is a diffused resistor made on a semiconductor substrate using integrated circuit technology. When it is subjected to external force, the resistance value of the diffused resistor changes due to the change in resistivity.
The main characteristics of piezoresistive pressure transmitters are their small size and simple structure. The sensitivity coefficient of the diffusion resistor is tens of times that of a metal strain gauge, enabling direct measurement of minute pressure changes. Furthermore, piezoresistive pressure transmitters have excellent dynamic response and low hysteresis, allowing them to measure pulsating pressures at frequencies of several kilohertz and even higher. This is a rapidly developing and widely used type of pressure transmitter.
Capacitive pressure transmitters use differential capacitance as the sensing element and mainly consist of two parts: measurement and conversion/amplification. They primarily utilize a central pressure-sensing diaphragm and two arc-shaped capacitor plates to convert the differential signal into a differential capacitance signal. The central pressure-sensing diaphragm forms capacitances with the two arc-shaped capacitor plates. The differential pressure causes displacement of the central pressure-sensing diaphragm, resulting in unequal spacing between the movable electrode and the two fixed electrodes, forming a differential capacitance. The relative change in the differential capacitance is linearly related to the differential pressure. Because capacitive differential pressure transmitters lack internal lever-based mechanical transmission mechanisms, they feature high precision, high stability, and high reliability, achieving an accuracy class of 0.2. They are currently a widely used type of transmitter in industry.
Piezoelectric pressure transmitters utilize the piezoelectric effect of piezoelectric materials to convert the measured pressure into an electrical signal. They are commonly used sensors for dynamic pressure detection but are unsuitable for measuring slowly changing or static pressures.
Frequency-based pressure transmitters utilize the relationship between the resonant frequency of the sensing element and the pressure, detecting pressure by measuring changes in the frequency signal. These sensors come in various forms, including vibrating cylinders, vibrating wires, diaphragms, and quartz resonators. These instruments are small in size, output a high-frequency signal, have good repeatability, are vibration-resistant, and offer high accuracy, making them suitable for gas measurement.
Pressure transmitters are widely used in various industrial fields, such as petroleum, chemical, metallurgy, power, pharmaceutical, and water treatment, to measure and control the pressure of various fluids, ensuring the stability and safety of processes. They can measure a wide range of pressures, from minute to extremely high, and feature high accuracy, high stability, high reliability, and long lifespan.
Furthermore, based on different measurement principles and application scenarios, pressure transmitters can be classified into several types, such as differential pressure transmitters (used to measure the difference between two pressures), absolute pressure transmitters (used to measure absolute pressure relative to a vacuum), and gauge pressure transmitters (used to measure pressure relative to atmospheric pressure), etc.