Principles of metal tube float flow meters

Thread Content

A metal tube float flow meter is a type of variable-area flow measurement instrument commonly used in industrial automation process control. It features a small size, a large detection range, and easy use. It can be used to measure the flow rate of liquids, gases, and vapors, and is particularly suitable for measuring the flow rate of media with low velocities and small flow volumes. Working principle and features of metal tube float flowmeters: They are intelligent in design and available in both local display versions and intelligent remote transmission versions. They feature pointer displays for instantaneous/accumulated flow, LCD displays, upper/lower limit alarm outputs, accumulated pulse outputs, batch control, as well as standard two-wire 4–20mA current output options. It provides users with a very wide range of options for use. Furthermore, this instrument features an advanced microprocessor-based central chip as well as high-quality industrial components. Depending on the structure of the measuring tube, the Chengfeng flow meter’s metal tube float-type flow meter allows for the selection of different types of measuring tubes to meet various user requirements, thereby offering improved convenience in terms of maintenance and cleaning. On this basis, by adding an intelligent metal tube float flow meter indicator, an intelligent metal tube float flow meter can be constructed. Over the years, metal tube float flowmeters have demonstrated various excellent properties and reliability, as well as a good performance-to-price ratio. It is widely favored by the petrochemical, steel, power, metallurgy, light industry, food, pharmaceutical, and water treatment sectors. Structural principle: 1. The HLZ series metal tube float flowmeter consists of two main parts: the measurement tube and the HR-F indicator. The measuring tube includes components such as conical tubes or orifice plates, guides, stoppers, floats, etc., while the indicator consists of elements like magnetic follow-up systems, pointers, dials, and wiring. 2. Working principle: The medium to be measured flows from bottom to top through the measurement tube; this creates a pressure difference between the upper and lower ends of the float, resulting in an upward force. When this upward force exceeds the weight of the float submerged in the fluid, the float rises. As a result, the area of the gap between the float and the tube increases, causing the flow velocity of the fluid in that gap to drop rapidly. The pressure difference between the upper and lower ends of the float decreases, and thus the upward force acting on it also decreases. Once this upward force balances the weight of the float submerged in the fluid, the float stabilizes at a certain position. The height of this position corresponds directly to the flow rate of the medium being measured. The float contains magnetic steel, and as the float moves up and down with the medium, the magnetic field changes accordingly. a. For the in-situ type, rotation occurs as a result of the coupling between the follow-up magnet in the in-situ indicator and the magnet inside the float, which in turn drives the pointer; the scale then indicates the flow rate at that moment. b. For the intelligent type, rotation occurs due to the coupling between the follow-up magnet in the intelligent indicator and the magnet inside the float. It also drives the sensing magnet and pointer; a magnetic sensor converts changes in the magnetic field into electrical signals, which are then processed through A/D conversion, digital filtering, temperature compensation, and microprocessor handling, before being output as D/A signals for display on an LCD screen, thereby showing both the instantaneous flow rate and the cumulative flow volume. Suitable for measuring small-diameter, low-flow rates of gases, liquids, and steam. 2. Magnetic coupling principle ensures leak-free and high-pressure resistance. 3. Heat-resistant, capable of reaching 450°C. 4. Affected by a certain viscosity, it is not suitable for measuring high-viscosity media. 5. When the flow rate exceeds 100 m3/h, the pressure loss is high. 6. It is mostly used in instruments for process control; the desired accuracy is 1%, with a typical value of 1.5%, and the range ratio is 10:1. 7. Both intrinsically safe and flameproof types are available, suitable for hazardous environments. 8. There are various options available, including local pointer type, battery-powered type, two-wire type, and 220V AC powered type. 9. The most suitable installation method is vertical installation with flow from bottom to top. 10. When measuring media at high and low temperatures (below -30 ℃), a jacketed type is preferred. 11. Not suitable for measuring media with large density changes. 12. Not suitable for measuring the flow rate of pulsating media (such as at the outlet of a metering pump). 13. For gases, there is no temperature and pressure compensation in this table, which requires separate consideration. 14. In cases where multiple instruments are installed closely together, or when carbon steel process pipelines pass near the instruments, a distance of more than 100 mm should be maintained from the instruments to avoid magnetic field interference. 15. When measuring the flow rate of media containing a large number of ferromagnetic particles, a magnetic filter should be installed in front of the instrument, and it should be purged regularly. 16. Metal tube float flowmeters do not have high requirements regarding straight pipe sections; generally, 5D in front and 250 mm behind is sufficient. 17. If instruments are to be used in explosion-proof environments, round-shell M4 indicators should be selected. 18. The high and low flow meter alarms are generally of the collector-open OC gate type; an external relay is required for current amplification. A relay output type is also available, with contact ratings of 1A@30VDC or 0.2A@250VAC or 0.1A@125VAC.