Principle analysis of various types of flowmeters
(1) Principles of mechanics: Instruments belonging to such principles have differential pressure and rotor type using Bernoulli's theorem; impulse type and movable tube type using momentum theorem; direct mass type using Newton's second law; The target type of the momentum principle; the turbine type using the angular momentum theorem; the vortex type using the principle of fluid oscillation, the vortex type; the pitot tube type using the total static pressure difference; the volumetric type, the enthalpy, the trough type, and the like.
(2) Electrical principle: The instruments used for such principles are electromagnetic, differential capacitive, inductive, strain resistant, etc.
(3) Acoustic principle: Ultrasonic type, acoustic type (shock wave type), etc. are used for flow measurement using the acoustic principle.
(4) Thermal principle: The heat, direct thermal, indirect calorimetry, etc., which measure the flow using the thermal principle.
(5) Optical principle: laser type, photoelectric type, etc. are instruments belonging to such principles.
(6) Originally based on physical principles: nuclear magnetic resonance, nuclear radiation, etc. are instruments of this type.
(7) Other principles: Marking principle (trace principle, NMR principle), related principles, etc.
Vortex flowmeter verification detection method
Standard table method
The vortex flowmeter is used as a standard device in series with the flowmeter to be inspected, and can be verified by static method or dynamic method. By comparing the readings of the two flow meters, the error of the vortex flowmeter to be tested is obtained.
Standard table flow meter standard device features:
1. Standard table method is suitable for measuring various fluids (including liquids and gases), and also for liquids of various viscosities.
2. The indication value is checked. The flow meter used as the standard meter is installed in series with the flowmeter to be tested in the same closed pipeline system. Generally, there is no time measurement error.
3. As a standard table, the vortex flowmeter can be the same as or different from the flowmeter to be tested.
4. When the flow meter is verified by the standard meter method, the airflow or liquid flow can be not cut off, so it is suitable for online verification, and is also suitable for the measurement standard for the closed pipeline. 5, the standard table method is easy to achieve automation, sealed and safe, does not pollute the environment.
6. Small size, light weight, simple device structure, convenient operation, easy transportation and installation, and low cost.
7. Standard meter flowmeters have low accuracy and poor stability, and often need to be compared regularly or irregularly to monitor their metering performance. The standard table has a shorter verification period.
Turbine Flowmeter Product Introduction
A flow meter that uses a turbine for measurement. It first converts the flow rate to the speed of the turbine and then converts the speed into an electrical signal proportional to the flow. This flow meter is used to detect instantaneous flow and total integrated flow, and its output signal is frequency, which is easy to digitize. In the figure, the induction coil and the permanent magnet are fixed together on the casing. When the ferromagnetic turbine blade passes the magnet, the magnetic resistance of the magnetic circuit changes to generate an induced signal. The signal is amplified and shaped by an amplifier and sent to a counter or frequency meter to display the total integrated flow. At the same time, the pulse frequency is frequency-voltage converted to indicate the instantaneous flow rate. The speed of the impeller is proportional to the flow rate, and the number of revolutions of the impeller is proportional to the total amount flowing. The output of the turbine flow meter is a frequency modulated signal that not only improves the immunity of the detection circuit, but also simplifies the flow detection system. It has a turndown ratio of 10:1 and an accuracy of ±0.2%. Turbine flowmeters with small inertia and small size have a time constant of 0.01 seconds.
Turbine flowmeter is the main type of velocity flowmeter. When the fluid to be measured flows through the turbine flowmeter sensor, under the action of the fluid, the impeller is forced to rotate, and its rotational speed is proportional to the average flow velocity of the pipeline. At the same time, the blade periodicity The magnetic flux generated by the electromagnet is cut and the magnetic flux of the coil is changed. According to the principle of electromagnetic induction, a pulsating potential signal, that is, an electric pulse signal, is generated in the coil, and the frequency of the electric pulsation signal is proportional to the flow rate of the fluid to be measured.