Type and characteristics of flow meter (1) Posted by : admin / Posted on : Oct 19， 2019

There are many classification methods for flow meters. The following is a list of the types of flow instruments commonly used in industrial production processes and their main performance characteristics, and a brief introduction.
Differential pressure type
Differential pressure measurement technology is currently the most widely used flow measurement method, which can measure the flow rate of single-phase fluid and high-temperature and high-pressure fluid under various working conditions. In the 1970s, this technology once accounted for 80% of the market. The differential pressure type flowmeter generally consists of two parts: a throttle device and a transmitter. Throttle device, common orifice plate, nozzle, Pitot tube, constant velocity tube, etc. The function of the throttling device is to contract the fluid flowing through and to make a difference upstream and downstream. Among various throttling devices, the orifice plate is most commonly used because of its simple structure and convenient installation. However, it has strict requirements on the processing size. As long as it is processed and installed according to the specifications and requirements, after the inspection is passed, the flow measurement can be performed within the uncertainty range, and the solid liquid test is not required.
All throttling devices have an unrecoverable pressure loss, and the largest pressure loss is the sharp edge orifice plate, which is 25%-40% of the maximum price difference of the instrument. The pressure loss of the Pitot tube is small and negligible, but it is very sensitive to changes in the fluid profile.
2. Variable area type
A typical representative of this type of flow meter is a rotameter. Its outstanding advantage is that when directly measuring in situ, no external power supply is required. Rotor flowmeters are divided into two categories: glass rotor flowmeter and metal tube rotor flowmeter according to their manufacture and materials. The glass rotor flowmeter has a simple structure, the rotor position is clearly visible, easy to read, and is mostly used for normal temperature, normal pressure, transparent and corrosive media, such as air, gas, argon and the like. The metal tube rotameter generally has a magnetic connection indicator for high temperature and high voltage applications, and can transmit standard signals and recorders to measure the cumulative flow.
There is a vertical variable area flowmeter with a loaded spring cone on the market. It has no condensation chamber and buffer chamber. The measurement range is 100:1 and it is a linear output, which is most suitable for steam measurement.
3. Oscillation type
The vortex flowmeter is a typical representative of an oscillating flow meter. It places a non-streamlined object in the direction of fluid advancement, and the fluid forms two columns of regular asymmetric vortex columns behind the object. The frequency of the vortex column is proportional to the flow rate.
This measuring method is characterized by no moving parts in the pipe, repeatability of reading, good reliability, long service life, wide linear measuring range, almost no influence of temperature, pressure, density, viscosity, etc., and low pressure loss. High precision (about 0.5% - 1%). Its working temperature can reach above 300 °C, and the working pressure can reach more than 30 MPa. However, fluid flow rate distribution and pulsating flow can affect measurement accuracy.
Different media can use different vortex sensing technology, vibrating disc or piezoelectric crystal for steam, thermal or ultrasonic for air, almost all sensing techniques for water, like orifice, vortex The flow coefficient of a street flow meter is also determined by a set of dimensions.
turbine flowmeter