according to the flow meter structure principle classification
According to the actual situation of current flowmeter products, based on the structure principle of flowmeter, can be summed up in the following categories:
1. Volumetric flowmeter
The volumetric flowmeter is equivalent to a standard volumetric container, which continuously measures the flow medium. The larger the flow, the more the number of measures, the higher the output frequency. The principle of volumetric flowmeter is simple and suitable for measuring fluids with high viscosity and low Reynolds number. According to the shape of the rotary body, the current production of the product: suitable for measuring liquid flow of elliptical gear flowmeter, waist wheel flowmeter (roots flowmeter), rotary piston and scraper-type flowmeter;
2. Impeller type flowmeter
The working principle of the impeller flowmeter is to place the impeller in the measured fluid, which is rotated by the impact of fluid flow and the speed of rotation of the impeller to reflect the size of the flow. Typical impeller flowmeter is a water meter and turbine flowmeter, the structure can be mechanical transmission output or electric pulse output type. General mechanical transmission output of the water meter low accuracy, error about ±2%, but simple structure, low cost, domestic production has been produced, and standardization, generalization and serialization. The turbine flowmeter with electric pulse signal output is of high accuracy, and the general error is ±0. 2% 10. 5%.
3. Differential pressure flowmeter (pressure reducing type flowmeter)
The differential pressure flowmeter consists of a times and two units. A device is called a flow measuring element, which is installed in the pipeline of the measured fluid, producing a pressure difference proportional to the flow rate (velocity), for a two-time device to display the flow. Two times the device is called the display meter. It receives the differential pressure signal produced by the measuring element and converts it to the corresponding flow for display. The primary device of differential pressure flowmeter is usually a throttling device or a dynamic pressure measuring device (pitot-pitot, mean-speed tube, etc.). Two-time device for a variety of mechanical, electronic, combined differential pressure gauges with flow display meter. The differential pressure sensitive elements of the differential gauge are more elastic elements. Because of the differential pressure and the flow of square root relationship, so the flow display instrument is equipped with a square device to make the flow scale linearization. Most instruments also have a flow-metering device to show cumulative flow for economic accounting. This method uses differential pressure to measure the flow of a long history, relatively mature, the world is generally used in more important occasions, accounting for a variety of flow measurement methods of 70%. This meter is used in the flow measurement of main steam, water supply and condensate of power plant.
4. Variable area type flowmeter (constant pressure drop type flowmeter)
The float in the small cone runner is moved by the force of the fluid flowing from the bottom up. The captive is stationary when the force is balanced with the "display weight" of the float (the weight of the float itself minus the buoyancy of the fluid it is subjected to). The height of the float still can be measured as the size of the flow. Because the flow area of the flowmeter varies with the float height, and the pressure difference between the upper and lower parts of the float stability is equal, so this type flowmeter is called variable area flowmeter or equal pressure drop type flowmeter. The typical instrument of the flowmeter is the rotor (float) flowmeter.
5. Momentum Flowmeter
Flowmeter called Momentum flowmeter is used to measure the flow of fluid to reflect the amount of momentum. Because the momentum p of the flow fluid is proportional to the density of the fluid and the square of the velocity V, i.e. P v2, when the flow section is determined, V is proportional to the volume flow Q, so P Q2. The proportional coefficient is a, then q=a, the measured p can reflect the flow Q. This type of flowmeter, most of the use of detection elements to convert momentum to pressure, displacement or force, etc., and then measure the flow. The typical instrument of this flowmeter is the target-type and rotating-vane-plate flowmeter.