The types of pressure measuring instruments are divided into liquid column type, elastic type and electric measuring type according to the working principle. The pressure gauge can indicate and record the pressure value, and can be equipped with an alarm or control device. The pressure measured by the instrument includes absolute pressure, atmospheric pressure, positive pressure (usually called gauge pressure), negative pressure (usually called vacuum) and differential pressure. The measured engineering technology is mostly gauge pressure.
The international unit of pressure is Pa, and other units include: engineering atmospheric pressure, bar, millimeter water column, millimeter mercury column. Pressure is an important parameter in industrial production. For example, when the pressure of a high-pressure vessel exceeds the rated value, it is unsafe and must be measured and controlled. In some industrial production processes, pressure also directly affects product quality and production efficiency. For example, when producing synthetic ammonia, nitrogen and hydrogen not only need to be synthesized under a certain pressure, but the pressure directly affects the output.
The following is a brief introduction of different types of pressure measuring instrument.
1. U-shaped tube pressure gauge
The measuring range of U-shaped tube pressure gauge is generally 0～±800 mm water column or mm Hg, and the accuracy is level 1. It can measure gauge pressure, vacuum degree, differential pressure and standard differential pressure gauge as calibration flow meter. Its characteristic is that the zero scale is in the middle of the scale plate, there is no need to adjust the zero before use, and the height of the liquid column needs two readings.
2. Elastic pressure gauge
The elastic pressure gauge is generally composed of a joint, a spring tube, a pull rod, a gear transmission mechanism, a pointer, a dial and a housing. When the instrument is working, the pressure of the measured medium enters the inner cavity of the spring tube through the joint, and the free end of the spring tube produces a displacement proportional to the pressure under the action of the internal pressure. The gear transmission mechanism is driven by the post to turn the displacement into a corner and amplify it. The pointer fixed on the central axis of the mechanism is indicated on the dial with graduations.
3. Hall pressure gauge
Hall pressure gauge is a pressure measuring instrument made of Hall effect. When the measured pressure is introduced, the free end of the spring tube is displaced, thereby driving the Hall plate to move, changing the magnetic induction intensity applied to the Hall plate, and converting it into a change in Hall potential according to the Hall effect, achieving a conversion of pressure-displacement-Hall potential.