The commonly used spring tube pressure gauge on boilers is mainly composed of spring bent pipes, connecting rods, sector gears, small gears, central shafts, pointers, dials and other components.

When the spring bend tube is subjected to the pressure of the medium, its cross-section tends to become circular, forcing the spring bend tube to gradually straighten, thereby causing the free end of the spring bend tube to lift upwards. The higher the pressure, the greater the upward tilt. This action is transmitted through a lever, sector gear, and small gear to deflect the pointer by an angle, indicating the pressure level on the dial. When the pressure of the measured medium decreases, the spring tube should return to its original state and the pointer should retract to the corresponding scale.

The accuracy level of a spring tube pressure gauge is expressed as the percentage of allowable error to the pressure gauge range, generally divided into seven levels: 0.5, 1, 1.5, 2, 2.5, 3, and 4 (levels 3 and 4 are not used on boilers). The smaller the value, the higher the accuracy.

Electric contact pressure instrument

Another commonly used type on fuel (gas) boilers is the electric contact pressure gauge. An electric contact pressure gauge is composed of a set of high and low power limiting contact devices installed on a regular spring tube pressure gauge. It can not only measure the pressure changes of the medium at any time, but also keep the measured medium within a certain range and automatically issue alarm signals. Electric contact pressure gauges can also be equipped with electrical circuits such as relays and contactors to obtain automatic control signals. Through the control mechanism, the pressure of the measured medium is automatically maintained within the range of the given upper and lower limits.

capacitive pressure sensor

Capacitive pressure sensors use elastic elements to sense pressure, convert the displacement of the elastic elements into changes in capacitance, and output electrical signals reflecting pressure changes. Usually, three methods are used to change the electrical capacity: changing the gap, cross-sectional area, and dielectric. There are two types of structures: single ended and differential. The variation in total capacitance of the differential type is twice as large as that of the single ended type. Provide the working principle and main technical performance of capacitive pressure sensors. Capacitive pressure sensors have advantages such as high sensitivity, fast response, resistance to shock and vibration, and simple structure.

Diaphragm type pressure sensor

The pressure of the measured medium enters the inner cavity of the diaphragm box from the joint, and the free end of the diaphragm box is compressed and displaced. The gear of the movement is driven to rotate by the connecting rod mechanism, and the pointer indicates the measured pressure value on the dial. Used for small pressure measurement on equipment such as boiler ventilation and gas pipelines, the membrane box pressure gauge can be installed and indicated on site.

pressure thermometer

The pressure type thermometer uses a spring tube as the pressure sensitive element, and the inner cavity of the temperature bulb, capillary tube, and spring tube forms a closed and easy to seal structure, which is filled with working substance. When the temperature bulb is heated, the internal working substance increases in pressure due to the temperature rise. The changed pressure is transmitted through the capillary tube to the spring tube, causing deformation of the spring tube. Then, with the help of the transmission system connected to the non fixed end of the spring tube, the pointer is driven to deflect a certain angle, and the temperature value of the measured medium is indicated on the dial.

The working substance inside the temperature chamber of a pressure thermometer can be liquid, gas, or vapor. If gas is used, nitrogen with stable chemical properties is usually chosen. The temperature measurement range is between 100-500 ° C.

Pressure thermometers can be used for both temperature measurement and temperature control, achieving automatic power on or off of temperature control circuits.

Strain type pressure sensor

A resistance strain gauge is a sensitive device that converts strain changes on the measured component into an electrical signal. It is one of the main components of a piezoresistive strain sensor. The most commonly used types of resistance strain gauges are metal resistance strain gauges and semiconductor strain gauges. There are two types of metal resistance strain gauges: wire strain gauges and metal foil strain gauges. Usually, strain gauges are tightly adhered to a mechanically strained substrate using a special adhesive. When the substrate undergoes stress changes, the resistance strain gauges also deform, causing a change in the resistance value of the strain gauges and a change in the voltage applied to the resistance.

The resistance change of this strain gauge when subjected to force is usually small. Generally, this strain gauge forms a strain bridge and is amplified by subsequent instrumentation amplifiers before being transmitted to processing circuits (usually A/D conversion and CPU) for display or execution.