The working principle and structure of the turbine flowmeter
Published on：2014-12-26 10:17:35 Hits：
1. Works turbine flowmeter
Turbine flowmeter principle diagram shown in Figure 3-1. A turbine placed in the center of the pipe, both ends supported by bearings. When the fluid through the pipe, the impact of turbine blades, the turbine generates driving torque, the turbine torque to overcome the friction and resistance torque generated by the rotating fluid. In a certain flow range, the viscosity of the fluid medium to a certain rotational angular velocity is proportional to the flow rate of the fluid turbine. Thereby, fluid flow rate can be obtained by the rotational angular velocity of the turbine, which can be obtained by calculating the fluid flow conduit.
Detected by the rotational speed of the turbine is mounted outside the case of the sensing coil. When the turbine blades cutting magnetic field lines generated by the housing when the permanent magnet, it will cause changes in the sensing coil flux. Sensing coil detects the change in magnetic flux periodic signal into the preamplifier, the signal amplification, shaping, produce and velocity is proportional to the pulse signal into the unit converter circuit and flow totalizer get and display the cumulative flow value; while the pulse signal into the frequency of the current will conversion circuit to convert the pulse signal into an analog current amount, thereby indicating the instantaneous flow rate value.
Turbine flowmeter with the overall principles of the box shown in Figure 3-2.
2. Construction turbine flowmeter
Fluid flows from the inlet housing. By a pair of sleeve bearing bracket fixed to the tube central axis, a turbine mounted on bearings. Upstream and downstream of the turbine is equipped with the bracket radiate rectifying plate, to act as guides for the fluid, in order to avoid effect of changes of spin fluid turbine blade angle. In the top of the turbine housing is equipped with an external sensor coil, the magnetic flux change signal is received.
Here are the main components.
Turbine by permeable stainless steel, fitted with helical blades. According to changes in the number of blades of different diameters, ranging from 2-24 pieces. In order to have a good turbine flow velocity response, quality requirements as small as possible.
General requirements for the structural parameters of the turbine blades: blade angle of 10 ° -15 ° (gas), 30 ° -45 ° (liquid); P blade overlap 1-1.2; the gap between the blades and the inner shell is 0 .5-1mm.
Bearing turbines generally use a sliding fit carbide bearings require good wear resistance.
Since the fluid an axial thrust generated by the turbine when the turbine will make uranium bearing friction torque is increased, acceleration uranium bearing wear, in order to eliminate the axial force, hydraulic balance measures to be taken in the structure, principle this method is shown in Figure 3-3. Since the turbine at slightly less than the diameter DH before and after the stent diameter Ds, therefore, in the turbine section enlarged cross-sectional flow, reduce the flow rate, the fluid static pressure rise P, the static pressure P will act to offset part of the axial thrust.
Figure 3-3 Schematic diagram of the water balance
Preamplifier by magnetic induction with the converter amplification shaping circuit composed of two parts, is shown in Figure 3-4.
Magnetic transducer commonly used domestic reluctance, which by the permanent magnet and induction coil winding external components. When the fluid by making satirical wheel rotating blades magnetoresistive minimum, two blades at the bottom of the magnet gap magnetoresistive largest turbine trip turn in permanent magnet directly below, constantly changing magnetic circuit of the magnetic flux generated in the coil changes the EMF, into the amplification shaping circuit, a pulse signal.
Frequency proportional to the flow through the meter output pulses in a proportion coefficient K is
K = (3-1)
Where f-- turbine flowmeter output pulse frequency;
qv-- flow through the meter.
The scaling factor is also known as the meter factor turbine flowmeter.
Figure 3-4 turbine flowmeter preamp schematics
(4) signal reception and display
Coefficient of signal reception and display calibration, an adder and an electrical converter frequency, etc., whose role is to transform from the pulse signal sent from the preamplifier into a cumulative flow and the instantaneous flow rate and displayed.
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