2019/9/19 10:31:44

Choice of caliber

The choice of the diameter of the electromagnetic flowmeter is not necessarily the same as the diameter of the pipe, and should be determined by the flow rate and flow rate. However, as the chemical raw materials and intermediate liquid of Salt Lake, the viscosity is large and the flow rate is low (generally 2.0 to 4.0 m/s). The electromagnetic flowmeter is used on such a pipe, and the diameter of the sensor is the same as the diameter of the pipe. If the flow rate is lower than 1.0m/s, an electromagnetic flowmeter of appropriate flow rate can be selected to ensure measurement accuracy and relatively reduce investment.

Selection of flow rate and range

Basically, they are anti-corrosion plastic pipes, and considering the lining of the flow meter, the flow rate is generally controlled at 2m/s. For some materials that are easy to crystallize (such as sodium carbonate solution, compounding liquid: crystallized mainly boron and magnesium double salt), the flow rate is increased to 3.0 to 4.0 m/s by taking measures. The flow rate will increase the flow noise, and the vibration of the pipeline will affect the measurement accuracy. Under the condition that the electromagnetic flowmeter is installed, the shock absorber should be installed before and after. The full scale of the meter is greater than the expected maximum flow value, which is typically 1.2 times the estimated maximum flow. The normal measurement flow is greater than 50% of the full scale of the meter to ensure a certain measurement accuracy.

Vortex flowmeter working principle

The working principle of the vortex flowmeter is to arrange a vortex generator in the fluid, so that the vortex is alternately generated on both sides of the body, and the vortex column is asymmetrically arranged downstream of the vortex generator to generate a certain frequency, by the formula f= St*v/(1-1.27d/D)*d, (St is the Strauhal number, which is a dimensionless number, related to the vortex generator and Reynolds number; v is the flow velocity; d is the incident head width; D is the nominal diameter) to get the flow rate.

In general, the vortex flowmeter output signal (frequency) is not affected by changes in fluid properties and composition, which means that the meter factor is only related to the shape and size of the vortex generator and the Reynolds number. Its advantages are: simple and firm structure, convenient installation and maintenance; suitable for a variety of fluids, liquid, gas, steam and some mixed phases are applicable; high precision, generally up to ± 1% R; flow range is wide, up to 10 : 1 or 20:1 or more; low head loss; no zero drift; relatively cheap price; disadvantage: not suitable for low Reynolds number Re <20000, limited use of high viscosity, low flow rate, small diameter The requirements for the environment are high, and places with vibration should be eliminated as much as possible, and the upstream side needs to have a long straight pipe section; the meter factor is lower, and the larger the diameter, the lower the diameter. The signal resolution is reduced, so the aperture should not be too large, generally used in DN15~DN300mm.

The working principle of the impeller type flowmeter is that the impeller is placed in the fluid to be measured, and is rotated by the impact of the fluid flow, and the flow rate is reflected by the speed of the impeller rotation. Typical impeller flow meters are water meters and turbine flow meters, which may be of mechanical transmission output or electrical pulse output. Generally, the water meter output of the mechanical transmission has low accuracy and the error is about ±2%, but the structure is simple and the cost is low. The domestic production has been mass-produced, standardized, generalized and serialized. The accuracy of the turbine flowmeter for electrical pulse signal output is high, with a typical error of ±0.2% to 0.5%.

Differential pressure flowmeter (variable pressure drop flowmeter)

The differential pressure flowmeter consists of a primary device and a secondary device. The primary device is called a flow measuring element and is installed in the pipe of the fluid to be measured, generating a pressure difference proportional to the flow rate (flow rate) for the secondary device to display the flow rate. The secondary device is called a display instrument. It receives the differential pressure signal generated by the measuring component and converts it to the corresponding flow for display. The primary device of the differential pressure flow meter is often a throttling device or a dynamic pressure measuring device (piteron, constant velocity tube, etc.). The secondary device is equipped with various mechanical, electronic and combined differential pressure gauges with flow display instruments. The differential pressure sensitive components of the differential pressure gauge are mostly elastic components. Since the differential pressure and the flow rate are in a square root relationship, the flow display instrument is equipped with an open square device to linearize the flow scale. Most meters also have a flow accumulator to display cumulative flow for economic accounting. This method of measuring flow using differential pressure has a long history and is relatively mature. Generally, countries all over the world use it in more important occasions, accounting for about 70% of various flow measurement methods. The flow measurement of the main steam, feed water, condensate, etc. of the power plant is based on this meter.