Turbine flowmeter working principle

- Nov 16, 2017 -

1 turbine works Turbine flow meter turbine, bearings, preamplifier, display instrument. Turbine flow meter schematic diagram shown in Figure 3-1. Place a turbine in the center of the pipe, supported by bearings at both ends. As the fluid passes through the duct, it impinges on the turbine blades to generate a driving torque to the turbine, causing the turbine to rotate against the friction torque and fluid resistance torque. In a certain range of flow rate, for a certain fluid medium viscosity, turbine rotational angular velocity and fluid flow rate is proportional to. Thus, the fluid flow rate can be obtained from the rotational angular velocity of the turbine, so that the fluid flow through the pipe can be calculated.

The speed of the turbine is sensed by a sensor coil mounted outside the housing. When the turbine blades cut the magnetic flux generated by the permanent magnets in the housing, the magnetic flux in the sensing coil changes. The sensor coil sends the signal of the detected period change of the flux to the preamplifier to amplify and shape the signal to generate a pulse signal proportional to the flow rate and then sent to the unit conversion and flow accumulation circuit to obtain and display the cumulative flow value; At the same time also pulse signal into the frequency current conversion circuit, the pulse signal is converted to analog current, and then indicate the instantaneous flow value. Turbine flowmeter overall principle box shown in Figure 3-2. Measured fluid impact turbine blades, the turbine rotation, the turbine speed changes with the flow rate, that is, flow rate, the turbine speed is also large, and then through the magnetoelectric conversion device to convert the turbine speed to the corresponding frequency electrical pulse, the Preamplifier amplifier, into the display instrument for counting and display, according to the number of pulses per unit time and the cumulative number of pulses can be obtained instantaneous flow and cumulative flow. The working principle of the turbine transmitter is that when the fluid flows along the axis of the pipeline and impacts the turbine blades, a force proportional to the product of the flow qv, the flow velocity V and the fluid density ρ acts on the blades to push the turbine to rotate. While the turbine is rotating, the blade periodically cuts the lines of magnetic force generated by the electromagnets and changes the magnetic flux of the coils. According to the principle of electromagnetic induction, a pulsating potential signal is induced in the coil. The frequency of the pulsation signal is proportional to the flow rate of the fluid to be measured, that is, qv is the volume of the fluid, and N is the pulsation generated by the transmitter Total; ξ is the flow coefficient. ξ is an important characteristic parameter of the turbine transmitter. Different instruments have different ξ, which varies with the wearing condition of the instrument for a long time. The meaning is that when the unit volume flow passes through the transmitter, the output pulse number of the transmitter . Turbo transmitter output pulse signal, amplified by the amplifier in front, into the display instrument, you can achieve flow measurement.

2. Turbine flow meter construction fluid flows into the enclosure from the inlet. A pair of sleeve bearings are fixed to the central axis of the tube by the bracket, and the turbine is mounted on the bearing. Radial-shaped baffles are mounted on the brackets upstream and downstream of the turbine to direct the fluid in order to prevent the fluid from spinning and changing the angle of action on the turbine blades. A sensor coil is mounted on the outside of the turbine housing to receive the flux change signal.

The following describes the main components.

(1) The turbine turbine is made of magnetically permeable stainless steel with helical blades. The number of leaves varies according to the diameter, ranging from 2 to 24 tablets. In order for the turbine to have a good response to the flow rate, the required mass is as small as possible. The general requirements for turbine blade structure parameters are: Blade inclination 10 ° -15 ° (gas), 30 ° -45 ° (liquid); Blade overlap P is 1-1.2; Gap between blade and inner shell is 0 .5-1mm.

(2) bearings Turbine bearings generally use sliding with carbide bearings, wear resistance requirements. As the fluid passes through the turbine, an axial thrust force is generated on the turbine to increase the friction torque of the uranium bearing and accelerate the wear of the uranium bearing. In order to eliminate the axial force, hydraulic balance measures must be taken on the structure. The principle of this method is shown in the figure 3-3. Because the diameter of the turbine is slightly smaller than the diameter Ds of the front and rear brackets, the flow at the turbine section increases and the flow rate decreases so that the hydrostatic pressure increases by ΔP. This ΔP static pressure will counteract part of the axial thrust .

(3) Preamplifier The preamplifier consists of a magneto-inductive converter and an amplifying and shaping circuit. The schematic diagram is shown in Figure 3-4. Magnetoelectric converter Magnetoresistance generally used in the country, which consists of permanent magnet and the external winding induction coil. When the fluid through the satirical wheel rotation, the permanent magnet below the permanent magnet when the magnetoresistive minimum, the two vanes in the magnet below the gap when the maximum reluctance, turbo trip to continue to change the magnetic flux of the magnetic circuit, so that changes in the coil The induction potential, into the amplification shaping circuit, into a pulse signal. The output pulse frequency and the flow through the flow meter is proportional to the proportional coefficient K K = f / qv Where f - turbo meter output pulse frequency; qv - the flow through the flow meter. This scale factor is also known as the meter factor of the turbine flow meter.

(4) signal reception and display signal reception and display coefficient correction, adders and frequency converters, etc. Its role is to convert the pulse signal sent from the preamplifier into a cumulative flow and instantaneous flow and display.

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