Abstract: the basic knowledge of doppler
flowmeter scale information produced by excellent flow meter, flow meter manufacturer to offer you the quotation.
Doppler flowmeter is fluid velocity data obtained using the doppler frequency shift, and then according to the original velocity, liquid level data to mathematical model to calculate the average velocity of cross section after the cross-sectional area multiplied by the fluid and get traffic flow detection technology (
The basic formula of flow, flow.
More flow meter manufacturers choose model price quote you are welcome to inquire, here is a doppler flowmeter scale knowledge base article for details.
Doppler flowmeter is fluid velocity data obtained using the doppler frequency shift, and then according to the original velocity, liquid level data to mathematical model to calculate the average velocity of cross section after the cross-sectional area multiplied by the fluid and get traffic flow detection technology (
Flow of the basic formula: cross section area of flow Q = average flow velocity V * A)
。
Therefore, doppler flowmeter measurement flow process can be specific to: determination of velocity, average velocity, cross-sectional area calculation, flow calculation.
The latter two are simple geometric/math.
For the velocity measurement, the first thing to explain is the doppler frequency shift.
When there is relative motion between waves and observer, the frequency of the observer receives the waves of the real frequency is different, the received signal frequency and the difference between the frequency of the sound source, known as the doppler frequency shift, its size is determined by the relative velocity between the two, a physical phenomenon known as the doppler effect.
Flow velocity, the probe launched wave in medium following the suspended, solid particles and bubbles, even the unsteady vortex, disrupt, etc. , all can produce deviating from the emission frequency of the reflected wave, produce doppler frequency change, the effect is proportional to the movement velocity of the reflector.
Receiving probe receives the reflected wave of each point through complex signal processing, the precision of dynamic spectrum analysis and calculation, it can be concluded that the flow rate of the fluid in pipe cross-section.
Currently, doppler flowmeter using zui more wave ultrasonic and radar wave, any wave and used as the measurement of wave doppler flowmeter, the flow rate of the used quantitative principle is a principle of doppler frequency shift.
Basically, can think under the principle of all kinds of wave probe (or a little velocity measurement range
Refers to the sound waves or coverage of radar wave velocity measurement, not the entire section)
The precision of the flow velocity, and there is no essential difference between the basic 1 -
About 2%.
And ultrasonic wave and the difference of radar wave in the current application, mainly under the super wave is often used for fluid measurement, which is commonly used in fluid above measure.
Therefore, ultrasound can according to different time to collect and analyze the echo of the doppler shift of the fluid velocity in different depth data.
While radar for installed above the liquid, can only on the surface of the fluid velocity data obtained.
From the installation, radar wave is not installed below the liquid, not only convenient for installation and maintenance, equipment failure rate is lower.
Both ultrasonic doppler flowmeter, and radar doppler flowmeter, the probe itself from the acoustic radar coverage is very limited, the fact cannot be directly measured by the average flow velocity distribution in the cross section of the water.
Therefore, how to obtain limited original velocity through probe data acquisition section average flow velocity is very important.
At present, the average flow velocity gain is usually according to a certain depth or certain depth data according to the mathematical model of velocity calculation of section average flow velocity.
Radar wave flow meter only commonly have the ability to measured surface velocity, therefore, only at the surface velocity calculated average flow velocity.
And
ultrasonic flowmeter because its installation in below the liquid surface, can obtain more depth velocity, multiple velocity calculated average flow velocity can be obtained.
It is not hard to see in the built-in software of flowmeter must have a theoretical model, according to the feature to find the section average flow velocity and cross section shape and water we probe the relationship between the measuring velocity, so as to calculate the mean velocity of cross section.
But in fact, the flow of the movement form is complicated, usually only suitable for use in uniform flow hydraulics model, so whatever the flowmeter, encountered turbulence are couldn't make accurate calculations of flow, reason is the turbulent section average flow velocity (cannot be computed
Unless really can the velocity of each point on cross section has been measured and the weighted average, this theory is made)
。
Even if the same is laminar flow movement form, current also will still have a small perturbation and vortex (
As a result of the existence of particles and sedimentation, unable to form the ideal state of water)
, in this case, the contrast, underwater ultrasonic (
Up to launch)
Can indeed than radar (
Surface velocity)
The calculated flow more accurately.
The reason is that the underwater ultrasonic measurement of flow velocity in different depth into sections, so as to get relatively accurate approximation of the velocity distribution, and the radar only surface velocity measurement, completely unable to measure the actual velocity distribution.
The underwater ultrasonic can be modified according to the measured results measured the relationship between velocity and average flow velocity, so as to get more accurate average flow velocity, while radar can only assume that the current flow, using the theory model to calculate the average flow velocity.
So the difference of both when calculating the flow can be clear at a glance
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