Turbine flowmeter structure_Turbine flowmeter installation requirements

　　The structure of turbine flowmeter

　　The principle diagram of the turbine flowmeter is shown in Figure 3-1. A turbine is placed in the center of the pipeline, supported by bearings at both ends. When the fluid passes through the pipeline, it impacts the turbine blades, generating a driving torque on the turbine, causing the turbine to overcome the friction torque and fluid resistance torque and rotate. Within a certain flow range, for a certain fluid medium viscosity, the turbine's rotational angular velocity is proportional to the fluid flow rate. Therefore, the fluid flow rate can be obtained through the turbine's rotational angular velocity, and the fluid flow through the pipeline can be calculated.

　　The speed of the turbine is detected by the sensor coil installed outside the casing. When the turbine blades cut the magnetic lines of force generated by the magnets in the casing, it will cause the magnetic flux in the sensor coil to change. The sensor coil sends the detected magnetic flux periodic change signal to the preamplifier, which amplifies and shapes the signal to generate a pulse signal proportional to the flow rate, which is sent to the unit conversion and flow accumulation circuit to obtain and display the cumulative flow value; at the same time, the pulse signal is also sent to the frequency current conversion circuit to convert the pulse signal into an analog current, thereby indicating the instantaneous flow value.

　　The fluid flows in from the inlet of the casing. A pair of sleeve bearings are fixed on the central axis of the tube through a bracket, and the turbine is installed on the bearing. Radial rectifiers are installed on the brackets upstream and downstream of the turbine to guide the fluid to prevent the fluid from spinning and changing the angle of action on the turbine blades. A sensor coil is installed on the outside of the casing above the turbine to receive the magnetic flux change signal.

　　The main components are introduced below

　　(1) Turbine

　　The turbine is made of magnetic stainless steel and equipped with spiral blades. The number of blades varies according to the diameter, ranging from 2 to 24. In order to make the turbine respond well to the flow rate, the mass is required to be as small as possible. The general requirements for the turbine blade structural parameters are: blade inclination angle 10°-15° (gas), 30°-45° (liquid); blade overlap P is 1-1.2; the gap between the blade and the inner shell is 0.5-1mm.

　　(2) Bearings

　　The turbine bearings generally use sliding fit carbide bearings, which are required to have good wear resistance.

　　When the fluid passes through the turbine, it will generate an axial thrust on the turbine, which will increase the friction torque of the bearing and accelerate the wear of the bearing. In order to eliminate the axial force, hydraulic balance measures need to be taken in the structure. The principle of this method is shown in Figure 3-3. Since the diameter DH at the turbine is slightly smaller than the diameter Ds at the front and rear brackets, the flow is intercepted and expanded in the turbine section, the flow velocity is reduced, and the static pressure of the fluid increases by P. This static pressure P will play a role in offsetting part of the axial thrust.

　　(3) Preamplifier

　　The preamplifier consists of two parts: a magneto-electric induction converter and an amplifying and shaping circuit.

　　The magnetoelectric converter in China generally adopts the reluctance type, which is composed of a magnet and an externally wound induction coil. When the fluid passes through the impeller to rotate, the magnetic resistance is the smallest when the blade is directly under the magnet, and the magnetic resistance is the largest when the gap between the two blades is under the magnet. The turbine rotates, constantly changing the magnetic flux of the magnetic circuit, causing a changing induced potential in the coil, which is sent to the amplification and shaping circuit and becomes a pulse signal.　　

　　(4) Signal reception and display

　　The signal receiver and display consists of a coefficient corrector, adder and frequency-to-electricity converter, etc. Its function is to convert the pulse signal sent from the preamplifier into cumulative flow and instantaneous flow and display them.

　　Turbine flowmeter installation requirements

　　Flowmeter is an indispensable instrument for measuring the flow of liquid and gas. You must have seen many different types of flowmeters. The correct installation method is very important for the flowmeter. Today, the editor will take you to see what are the common installation requirements of turbine flowmeters?

　　When installing the turbine flowmeter, you should keep it away from external electric and magnetic fields. If necessary, effective shielding measures should be taken to avoid external interference. The turbine flowmeter can be installed horizontally or vertically. When installed vertically, the fluid direction must be upward. The liquid should fill the pipe without bubbles. When installing, the liquid flow direction should be consistent with the direction of the arrow indicating the flow direction on the sensor housing. When installing, the pipe must be full of fluid to ensure accurate measurement.

　　The upstream end of the flow meter should have a straight pipe section of at least 10 times the nominal diameter, and the downstream end should have a straight pipe section of no less than 5 times the nominal diameter. The inner wall should be smooth and clean, without defects such as dents, scale and peeling.

　　The sensor's pipe axis should be aligned with the adjacent pipe axis, and the gasket used for connection and sealing should not penetrate deep into the pipe cavity. The straight pipe section requirements under different conditions are shown in the figure below. At the same time, bubbles should be avoided in the pipe during installation, otherwise it will affect the measurement accuracy.