A flowmeter that uses a turbine to measure. It first converts the flow velocity into the rotational speed of the turbine, and then converts the rotational speed into an electrical signal proportional to the flow. This flowmeter is used to detect instantaneous flow and cumulative total 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 housing. When the ferromagnetic turbine blade passes the magnet, the reluctance of the magnetic circuit changes, thus generating an induction 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 converted from frequency to voltage to indicate instantaneous flow. The rotating speed of the impeller is proportional to the flow rate, and the rotating speed of the impeller is proportional to the total flow rate. The output of the turbine flowmeter is FM signal, which not only improves the anti-interference of the detection circuit, but also simplifies the flow detection system. Its range ratio can reach 10: 1, and its accuracy is within 0.2%. The time constant of turbine flowmeter with small inertia and small volume can reach 0.0 1 sec.

In Europe and America, turbine flowmeter is the second legal natural gas flowmeter after orifice flowmeter, which has developed into a multi-variety, full series, multi-specification and mass production scale natural gas flowmeter. The standard specification is also very complete, but there are also some shortcomings: high requirements for the cleanliness of the measuring medium and limited service life. However, according to foreign users, 240 flowmeters have been used for periodic verification for 8~ 15 years, and it is found that the instrument accuracy deviation is still within the specified range. In addition, a gas turbine flowmeter with a high efficiency rectifier and a turbine flow sensor is coupled to form an integrated structure. When the upstream choke is an elbow or has a semi-open stop valve, only a 2D straight pipe section is needed, which is a prominent feature for the narrow installation space in the city.

Turbine flowmeter is the main type of velocity flowmeter. When the measured fluid flows through the sensor of the turbine flowmeter, the impeller is forced to rotate under the action of the fluid, and its rotating speed is proportional to the average flow rate of the pipeline. At the same time, the blade periodically cuts the magnetic field lines generated by the electromagnet, changing the magnetic flux of the coil. According to the principle of electromagnetic induction, a pulsating potential signal, that is, an electric pulse signal, will be induced in the coil, and the frequency of this electric pulse signal is proportional to the flow rate of the measured fluid.

Among all kinds of flowmeters, turbine flowmeter, positive displacement flowmeter and Coriolis mass flowmeter are the three products with the best repeatability and accuracy. Turbine flowmeter has its own characteristics, such as simple structure, few machining parts, light weight, convenient maintenance, large circulation capacity (large flow with the same caliber) and adaptability to high parameters (high temperature, high pressure and low temperature). Up to now, the technical parameters that can be achieved by this kind of flowmeter products are: aperture 4-750mm, pressure 250MPa, temperature -240-700℃. This technical parameter is difficult for the other two flowmeters to achieve.

Turbine flowmeter is widely used in the following measurement objects: petroleum, organic liquid, inorganic liquid, liquefied gas, natural gas, gas and cryogenic fluid. It is widely used in the first and last stations of large crude oil pipelines for trade settlement in foreign transshipment gathering stations of liquefied petroleum gas, refined oil and light crude oil. In Europe and America, turbine flowmeter is the natural gas metering instrument after orifice flowmeter. In the Netherlands alone, more than 2,600 gas turbine flowmeters with various sizes and pressures ranging from 0.8MPa to 6.5MPa have been used in natural gas pipelines, becoming excellent natural gas flowmeters. Although the excellent metering characteristics of turbine flowmeter are favored by people, it gives people the impression that it is composed of moving parts and has a short service life, so it is inevitable to hesitate when choosing it. After unremitting efforts, it should be said that the situation has been greatly improved. As the most common flowmeter, turbine flowmeter has developed to the scale of multi-variety, full series and multi-specification batch production.

It should be pointed out that, in addition to the aforementioned industrial departments, turbine flowmeters are also widely used in some special departments, such as scientific research and experiments, national defense science and technology, measurement departments and so on. The application of these fields just avoids its weakness (not suitable for long-term continuous use) and gives full play to its characteristics (high precision, good repeatability, and can be used under high pressure, high temperature, low temperature and micro-flow conditions). In these fields, most of them are designed according to the special requirements of the tested object. They are special instruments and are not mass-produced.