Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question dated 2020-08-08

Elastic, capacitive, ceramic, silicon crystal resonant, etc

Liquid-column pressure gauge, spring-type pressure gauge, piston-type pressure gauge, electrical pressure gauge

1. Liquid-column pressure gauge: A liquid-column pressure gauge measures pressure by converting the pressure to be measured into a height of a liquid column, based on the principles of statics. Such instruments include U-tube manometers, single-tube manometers, inclined-tube manometers, etc. Commonly used pressure-indicating liquids include alcohol, water, carbon tetrachloride, and mercury. The advantages of such instruments are their simple structure, rapid response, and high measurement accuracy ； The disadvantage is that it is limited by the density of the liquid, resulting in a narrow pressure measurement range; the liquid column is not easy to stay stable during sharp pressure fluctuations, and there are strict requirements regarding the installation location and orientation. It is generally used only for measuring low pressures and vacuum levels, and is mostly employed in laboratories. 2. Elastic pressure gauge: An elastic pressure gauge operates on the principle of deformation of elastic elements under stress; it converts the pressure to be measured into a displacement of these elements in order to measure the pressure. Common types include Bourdon tube pressure gauges, diaphragm pressure gauges, and diaphragm (or bellows) type pressure gauges. These types of pressure measuring instruments have a simple structure, are durable and robust, inexpensive, reliable in operation, and offer a wide measurement range. They are suitable for use in various production environments with low, medium, or high pressures, and they represent the most widely used category of pressure measuring instruments in industry. However, the measurement accuracy of elastic pressure gauges is not very high, and most of them use mechanical pointers for output, being primarily used for on-site indication in production areas. When long-distance signal transmission is required, additional devices must be installed. 3. Pressure sensors and pressure transmitters: Pressure sensors and pressure transmitters utilize certain physical properties of materials; through various conversion elements, they transform the pressure to be measured into various electrical signals, and pressure is indirectly measured based on changes in these signals. Depending on the type of transducing element, pressure sensors and pressure transmitters can be classified into resistive, capacitive, strain gauge, inductive, piezoelectric, Hall effect, and other types. The greatest advantage of such pressure measuring instruments is that their output signals can be transmitted over long distances easily, allowing them to be used seamlessly with various display, recording, and control devices – thereby facilitating centralized monitoring and control of pressure. It is widely used in production process automation systems.

Instruments for measuring pressure can be divided into four major categories based on their conversion principles: 1) Column-type manometers； 2) Spring pressure gauge ； 3) Electrical pressure gauge ； 4) Piston pressure gauge.

Instruments for measuring pressure can be divided into four major categories based on their conversion principles: 1) Column-type manometers； 2) Spring pressure gauge ； 3) Electrical pressure gauge ； 4) Piston pressure gauge.

Instruments for measuring pressure can be divided into four major categories based on their conversion principles: 1) Column-type manometers； 2) Spring pressure gauge ； 3) Electrical pressure gauge ； 4) Piston pressure gauge.

Liquid-column pressure gauges, spring-type pressure gauges, sensor-type ones. Sensors are further divided into resistive, capacitive, strain-gauge, piezoelectric, etc

Pressure measuring instruments can be roughly divided into four categories: (1) Manometric pressure gauges, which utilize the principles of hydrostatics to convert the applied pressure into a height of a liquid column for measurement. ⑵ An elastic pressure gauge converts the pressure to be measured into a deformation displacement of an elastic element for measurement. ⑶ An electrical pressure gauge is a instrument that converts the pressure to be measured into an electrical signal using mechanical and electrical components for measurement. ⑷ A piston pressure gauge operates on the principle of hydraulic pressure transmission; it converts the pressure to be measured into the mass of the weight applied to the piston in order to carry out the measurement.

1) Liquid column manometer； 2) Spring pressure gauge ； 3) Electrical pressure gauge ； 4) Piston pressure gauge.

Pressure measuring instruments can be roughly divided into four categories: (1) Manometric pressure gauges, which utilize the principles of hydrostatics to convert the applied pressure into a height of a liquid column for measurement. ⑵ An elastic pressure gauge converts the pressure to be measured into a deformation displacement of an elastic element for measurement. ⑶ An electrical pressure gauge is a instrument that converts the pressure to be measured into an electrical signal using mechanical and electrical components for measurement. ⑷ A piston pressure gauge operates on the principle of hydraulic pressure transmission; it converts the pressure to be measured into the mass of the weight applied to the piston in order to carry out the measurement.