Working principles of different anemometers
1. Thermal probe of anemometer
A thermal probe is based on the cold shock airflow carrying away the heat from the heating element. With the help of an adjustment switch, the temperature is kept constant, and the current and flow rate are proportional to each other. When using a thermal sensitive probe in turbulence, airflow from all directions simultaneously impacts the thermal element, which can affect the accuracy of the measurement results.
When measuring in turbulence, the reading of the thermal anemometer velocity sensor is often higher than that of the impeller probe. The above phenomenon can be observed during pipeline measurement. According to different designs for managing turbulent flow in pipelines, it may even occur at low speeds. Therefore, the anemometer measurement process should be carried out in the straight section of the pipeline. The starting point of the straight section should be at least 10 × D (D=pipe diameter, in CM) outside the measurement point; The endpoint should be at least 4 × D behind the measurement point. The fluid cross-section must not have any obstruction. (Sharp edges, heavy suspension, objects, etc.)
2. Blade type probe of anemometer
The working principle of the impeller probe of the anemometer is based on converting the rotation into an electrical signal. First, it passes through a proximity sensing head to "count" the rotation of the impeller and generate a pulse series. Then, it is converted and processed by the detector to obtain the speed value. The large-diameter probe (60mm, 100mm) of the anemometer is suitable for measuring turbulent flow with medium to low velocities (such as at pipeline outlets). The small-diameter probe of the anemometer is more suitable for measuring airflow in pipelines with a cross-sectional area greater than 100 times that of the exploration head.
3. Bi tube probe of anemometer
By using a pitot tube, the dynamic pressure characteristics of the fluid can be measured, and according to the following formula, the velocity of the fluid can be calculated. 1) In the formula, Pd represents the dynamic pressure of the fluid, Pa;
W - fluid velocity, m/s;
R - Fluid density, N/m3;
G - gravitational acceleration, m/s2.
This is the principle of measuring wind speed using a pitot tube.
