Types and Working Principles of Pressure Transducers

Pressure transducers are widely used, and there are various types of pressure transducers on the market. But what types are most common use in the actual applications? Here we would like to share the types of pressure transducers most used on the market.

Strain gauge pressure transducer

Resistance strain gauge is one of the main components of piezoresistive strain transducer. The resistance strain gauge is pasted on the specific surface of the elastic element, when the physical quantities such as force, torque, velocity, acceleration and flow act on the elastic element, it will lead to the stress and strain of the element change, and then the resistance of the resistance strain gauge will also change. The change of resistance is output in the form of electrical signal after being processed by the circuit, which is the working principle of the resistance strain gauge transducer.


The most widely used resistance strain gauges are metal resistance strain gauges and semiconductor strain gauges. There are 2 types of metal resistance strain gauges: wire strain gauges and metal foil strain gauges. Generally, the strain gauge is tightly bonded to the matrix generating mechanical strain through a special adhesive. When the stress on the matrix changes, the resistance strain gauge will also deform together, changing the resistance of the strain gauge, thus changing the voltage applied to the resistance. The resistance value change produced by this strain gauge under stress is usually small. Generally, this strain gauge forms a strain bridge, which is amplified by a subsequent instrument amplifier, and then transmitted to the processing circuit (usually A/D conversion and CPU) display or actuator.


Ceramic pressure transducer

The ceramic pressure transducer is based on piezoresistive effect. The corrosion resistant ceramic pressure sensor has no liquid transmission. The pressure directly acts on the front surface of the ceramic membrane, causing slight deformation of the membrane. The thick film resistor is printed on the back of the ceramic membrane and connected to form a Wheatstone bridge. Due to the piezoresistive effect of the varistor, the bridge generates a highly linear voltage signal proportional to the pressure and also proportional to the excitation voltage. The standard signal is calibrated as 2.0/3.0/3.3 mV/V according to different pressure ranges, which can be compatible with the strain gauge sensor. Ceramic is a recognized material with high elasticity, corrosion resistance, abrasion resistance, impact resistance and vibration resistance. The thermal stability of ceramics and its thick film resistance can make its working temperature range as wide as - 40~135 ℃, and they also have high measurement accuracy and stability. The electrical insulation degree is 2kV, the output signal is strong, and the long-term stability is good.

Diffused silicon pressure transducer

The working principle of the diffused silicon pressure transducer is also based on the piezoresistive effect. Using the piezoresistive effect principle, the pressure of the measured medium directly acts on the diaphragm (stainless steel or ceramic) of the transducer, making the diaphragm produce micro displacement proportional to the medium pressure, making the resistance value of the sensor change. The electronic circuit is used to detect this change, and convert and output a standard measurement signal corresponding to this pressure.

The sensitivity factor of silicon strain resistance is 50~100 times higher than that of metal strain gauge, so the sensitivity of corresponding sensor is very high. Generally, the range output is about 100mv. Therefore, there is no special requirement for the interface circuit and it is convenient to use.

Because the sensing, sensitivity conversion and detection of the transducer are realized by the same element, there is no intermediate conversion link, and the repeatability and hysteresis error are small. Due to the high rigidity and small deformation of single crystal silicon, good linearity can be ensured.

As the working single deformation is as low as the microstrain magnitude, the maximum displacement of the elastic chip is in the submicron magnitude, so there is no wear, fatigue, aging, and the service life is up to 1 × 103 pressure cycling, stable performance and high reliability.

Capacitive pressure transducer

Capacitive pressure transducer is a pressure transducer that uses capacitive sensing elements to convert the measured pressure into electrical output with a certain relationship. It is characterized by low input force and dwarf energy, high dynamic response, small natural effects and good environmental adaptability.

It generally uses a round metal film or a metal plated film as an electrode of the capacitor. When the film feels pressure and deforms, the capacitance formed between the film and the fixed electrode changes. Through the measuring circuit, an electrical signal that has a certain relationship with the voltage can be output. Capacitive pressure sensor belongs to the pole distance change capacitive sensor, which can be divided into single capacitive pressure transducer and differential capacitive pressure transducer.

Inductive pressure sensor

Inductive pressure sensor is an instrument that measures pressure with the change of inductance of inductive coil.

There are 2 types of structures: air gap type and differential transformer type. The working principle of the air gap type is that the measured pressure acts on the membrane to cause displacement, causing the magnetic resistance of the differential inductance coil to change. At this time, the air gap between the membrane and the magnetic core increases at one side, while the other side decreases, and the inductance decreases at the same time. The other side increases, thus forming an electric differential change. An AC voltage corresponding to the measured pressure is output through the bridge composed of inductors. It has the advantages of small size and simple structure, and is suitable for the environment with vibration or impact

The working principle of the differential transformer type is that the side pressure acts on the spring tube_ L. Make it produce displacement in direct proportion to the pressure, drive the iron core connected at the end of the spring tube to move at the same time, make the two symmetrical and reverse serial secondary windings of the differential transformer lose balance, and output a voltage in direct proportion to the measured pressure. It can also output standard current signal and electric unit combination instrument to form an automatic control system.

Sapphire pressure transducer

Based on the working principle of strain resistance, the silicon sapphire is used as the semiconductor sensing element, which has unparalleled metrological characteristics. Therefore, the semiconductor sensor made of silicon sapphire is insensitive to temperature changes and has good working characteristics even under high temperature conditions; Sapphire has strong radiation resistance; In addition, the silicon sapphire semiconductor sensor has no p-n drift.

Sapphire system is composed of single crystal insulator elements, which will not cause hysteresis, fatigue and creep; Sapphire is stronger and harder than silicon, and is not afraid of deformation; Sapphire has very good elasticity and insulation characteristics (within 1000 ℃). Therefore, semiconductor sensing elements made of silicon sapphire are insensitive to temperature changes and have good operating characteristics even under high temperature conditions; Sapphire has strong radiation resistance; In addition, the silicon sapphire semiconductor sensor has no p-n drift. Therefore, the manufacturing process is fundamentally simplified, the repeatability is improved, and the high yield is ensured.

The pressure transducers and transmitters made of silicon sapphire semiconductor sensing elements can work normally under the worst working conditions with high reliability, good accuracy, minimal temperature error and high cost performance. The gauge pressure sensor and transmitter are composed of two diaphragms: titanium alloy measuring diaphragm and titanium alloy receiving diaphragm. A sapphire wafer printed with a heteroepitaxial strain sensitive bridge circuit is welded to a titanium alloy measuring diaphragm. The measured pressure is transmitted to the receiving diaphragm (the receiving diaphragm is firmly connected with the measuring diaphragm with a pull rod). Under the effect of pressure, the titanium alloy receiving diaphragm will deform. After the deformation is sensed by the silicon sapphire sensor, its bridge output will change, and the change amplitude is proportional to the measured pressure.