由涡轮、轴承、前置放大器、显示仪表组成。 Turbine flowmeter consists of turbine, bearing, preamplifier and display instrument. The measured fluid impacts the turbine blades, causing the turbine to rotate, and the rotation speed of the turbine changes with the change in flow rate, that is, the flow rate is large, and the rotation speed of the turbine is also large. After the preamplifier is amplified, it is sent to the display instrument for counting and display. The instantaneous flow rate and accumulated flow rate can be obtained according to the number of pulses and the accumulated pulse number in a unit time. 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 rate qv, the velocity V and the fluid density ρ acts on the blades, pushing the turbine to rotate. While the turbine is rotating, the blade periodically cuts the magnetic lines of force generated by the electromagnet, changing the magnetic flux of the coil. According to the principle of electromagnetic induction, a pulsating potential signal will be induced in the coil, and the frequency of this pulsating signal is proportional to the flow rate of the measured fluid. The pulse signal output by the turbine transmitter is amplified by the pre-amplifier and sent to the display instrument to realize the flow measurement.
的选型 2 Selection of turbine flowmeter
(1) It is best to use 316 stainless steel for corrosion prevention in the body of the flowmeter. If it is an explosion-proof area, it must also be the result of explosion-proof. (2) Bearings generally have three specifications of tungsten carbide, polytetrafluoroethylene, and carbon graphite: tungsten carbide has the highest accuracy, which is used as a standard component for industrial control; polytetrafluoroethylene and carbon graphite can be anticorrosive, and it is generally preferred in chemical sites . The life of the bearing is proportional to the inverse square of the flow rate, so the best flow rate is better than 1/3 of the maximum flow rate. (3) The inductive probe detects the motion of the rotating body and converts it into a pulsed digital electrical signal. Its electromagnetic coil voltage output value is close to a sine curve. The frequency range of the pulsed signal changes linearly with the measured flow rate. The typical range is 10 : 1, 25: 1 and 100: 1 specifications. The resistance of the electromagnetic coil is generally less than 2000Ω, and it may be damaged if it is larger than this value.
的测量准确,必须正确地选择安装位置和方法 In order to ensure accurate measurement of the turbine flowmeter , the installation location and method must be selected correctly
1. Requirements for straight pipe sections: The flowmeter must be installed horizontally on the pipeline (the pipeline is inclined within 50), and the axis of the flowmeter should be concentric with the pipeline axis and the flow direction should be the same during installation. The length of the upstream pipe of the flowmeter should be equal to or greater than 2D, and if the installation site permits, it is recommended that the upstream straight section is 20D and the downstream is 5D. 2. Requirements for piping: The inner diameter of the upstream and downstream piping at the installation point of the flowmeter is the same as the internal diameter of the flowmeter. 3. Requirements for the bypass pipe: In order to ensure that the normal use of the medium is not affected during the maintenance of the flow meter, a shut-off valve (cutoff valve) should be installed on the front and rear pipelines of the flow meter, and a bypass pipeline should be set at the same time. The flow control valve should be installed downstream of the flow meter. When the flow meter is used, the shut-off valve installed upstream must be fully opened to avoid the unstable flow of the upstream fluid. 4. Requirements for the external environment: The turbine flowmeter is best installed indoors. When it must be installed outdoors, it must be protected from sun and rain. Lightning protection measures to avoid affecting the service life. 5. Requirements for impurities in the medium: In order to ensure the service life of the flowmeter, a filter should be installed before the straight section of the flowmeter. Installation place: The flow meter should be installed in a place that is easy to maintain, without strong electromagnetic interference and heat radiation. 6. Requirements for installation and welding: The user has another pair of standard flanges welded on the front and rear pipes. Welding with a flow meter is not allowed! Before installing the flowmeter, it is necessary to strictly remove the dirt such as welding slag in the pipeline. It is best to use an equal-diameter pipe (or bypass pipe) instead of the flowmeter to purge the pipeline. To ensure that the flowmeter is not damaged during use