There are many ways to classify sensors, but there are two common classifications, one is according to the physical quantity to be measured; the other is according to the working principle of the sensor to be divided. According to the physical quantity to be measured by the division of the sensor, common: temperature sensors, humidity sensors, pressure sensors, displacement sensors, flow sensors, liquid level sensors, force sensors, acceleration sensors, torque sensors, etc..

I. Classification of pressure sensors

Pressure sensor is the most widely used a sensor, used in a variety of industrial self-control environment, involving water conservancy and hydropower, railway transportation, intelligent building, production of automatic control, aerospace, military, petrochemical, oil wells, electric power, ships, machine tools, pipelines and many other industries.

Commonly used pressure sensors are strain gauge pressure sensors, ceramic pressure sensors, diffusion silicon pressure sensors, sapphire pressure sensors, piezoelectric pressure sensors. Pressure sensors are classified according to their use mainly for pressure monitoring, pressure measurement and pressure control and conversion to other quantities. The former is passively powered and requires an external power supply. The latter is a sensor that generates its own electrical charge and does not require an external power supply. Depending on the accuracy of the pressure measurement in different fields, they are divided into low and high precision pressure sensors.

Traditional pressure sensors are based on mechanical structure type devices that indicate pressure by the deformation of the elastic element, but this structure is large in size and heavy in mass and does not provide an electrical output. With the development of semiconductor technology, semiconductor pressure sensors have also emerged. They are characterised by their small size, light mass, high accuracy and good temperature characteristics. Especially with the development of MEMS technology, semiconductor sensors are developing towards miniaturisation, and they have low power consumption and high reliability.

Semiconductor piezoresistive type: semiconductor piezoelectric impedance diffusion pressure sensor is formed on the surface of the sheet semiconductor deformation pressure, through the external force (pressure) to deform the sheet and produce piezoelectric impedance effect, so that the change in impedance into an electrical signal.

Electrostatic capacitance type: Electrostatic capacitance type pressure sensors form a capacitance between the fixed pole of glass and the movable pole of silicon, and convert the change in electrostatic capacity generated by deforming the movable pole through external force (pressure) into an electrical signal. (E8Y action principle is the electrostatic capacity method, other models use semiconductor method).

Second, the pressure sensor how to select the type

1, confirm the type of pressure sensor

(1) electromechanical: the internal mechanical structure of the product, after the taut spring, lever, adjusting screws, metal housing and contact module device and pressure sensor, the internal processing circuit does not contain, and are the output is the switch pressure switch form. Generally can be adjusted by the screw or set the threshold value of the action; volume is more massive, but cheaper, less accurate.

(2) electronic: pressure sensors are ceramic or metal measurement isolation diaphragm, isolation diaphragm and the detected material in direct contact, the role of the pressure on the surface of the diaphragm so that the diaphragm small deformation, the sensor can be internal through the deformation of the reed resistance or capacitor principle of sensing the size of the deformation degree, the mechanical, circuit (bridge) equipment output the corresponding switch action or analog signal.

2、Confirm the type of device

Control circuit or power circuit.

3、Confirm the type of measurement pressure

Pressure types are mainly gauge pressure, absolute pressure, differential pressure, etc.

(1) gauge pressure refers to atmospheric pressure as the reference, less than or greater than the atmospheric pressure pressure.

(2) absolute pressure refers to a definite pressure zero as a reference, higher than the definite pressure zero pressure.

(3) differential pressure refers to the difference between the two pressures.

4、Confirm the scale of measurement

Under general conditions, according to the actual measurement pressure for the measurement scale of 80% selected.

5、Confirm the power supply and output signal

Four output signals are available, including relay output, solid state output and analogue output (4 to 20mA or 0 to 10V). (For electronic pressure sensors) where the solid-state output is further divided into single-segment switch and double-segment switch.

6、Confirm the maximum overload of the system

The maximum overload of the system should be less than the overload maintenance limit of the pressure sensor, otherwise it will affect the service life of the product, and even damage the product.

7、Confirm the pressure interface form

Mainly contains: G1/4A (BSP), 1/4NPT, SAE7/16-20UNF, 4×G1/4 (BSP), G3/8, etc.

8、Confirm the compatibility of the measurement medium and the contact material

In some measurement occasions, the measurement medium has corrosive, at this time, you need to choose the material compatible with the measurement medium or special process treatment to ensure that the transmitter is not damaged.

9, confirm the accuracy level

Transmitter measurement error according to the accuracy level of the division, different degrees of accuracy corresponds to different basic error limits (full-scale output percentages indicate); practical applications, based on the control requirements of the measurement error and in line with the principle of applicable economic selection.

10, confirm the working temperature scale

The temperature of the measurement medium should be in the working temperature range of the transmitter, such as the use of over-temperature, will produce a large measurement error and affect the use of life; in the production process of pressure transmitters, will be measured and compensated for the impact of temperature, to ensure that the product is affected by the temperature of the measurement error in the accuracy level required within the scale. In the higher temperature occasions, can consider the selection of high temperature type pressure sensor or take the installation of condenser (device), radiator and other auxiliary cooling methods.

11、Confirm the site working environment and other conditions

Need to understand whether there is vibration and electromagnetic interference, and provide relevant information in the selection, in order to take the corresponding treatment; in the selection, other such as electrical connection should also be considered according to the situation.