Component structure of anemometer
Anemometers are based on the fact that a cold impinging airflow carries away the heat from the thermal element, with the help of a regulating switch that keeps the temperature constant, then the regulating current is proportional to the flow rate. When using a thermal probe in turbulent flow, air currents from all directions impact the thermal element at the same time, which can affect the accuracy of the measurement results. When measuring in turbulence, the thermal anemometer flow rate sensor tends to show a higher value than the rotating wheel probe. The above phenomenon can be observed during duct measurements. Depending on the different designs used to manage duct turbulence, they can occur even at low speeds.
Therefore, the anemometer measurement process should be carried out in a straight part of the duct. The starting point of the straight section should be at least 10 x D (D = diameter of the pipe in CM) away from the front of the measurement point; the end point should be at least 4 x D after the measurement point. The fluid cross-section shall not be obscured in any way
Rotating probe of anemometer
The working principle of anemometer's rotating wheel probe is based on the conversion of rotation into electrical signals, first through a proximity inductor, the rotation of the wheel to "count" and produce a pulse series, and then converted by the detector to get the value of the rotational speed.
The large diameter probes (60mm, 100mm) of the anemometers are suitable for measuring turbulent flows (e.g. at the outlet of pipelines) with small or medium flow velocities. The small diameter probes of anemometers are more suitable for measuring airflow where the cross-section of the pipe is more than 100 times the cross-sectional area of the probe.
Positioning of the anemometer in the air stream The correct adjustment position of the anemometer's rotor-type probe is the direction of air flow parallel to the rotor axis. When the probe is gently turned in the air stream, the indicated value changes. When the reading reaches a *large* value, it indicates that the probe is in the correct measuring position. Measured in the pipe, the starting point of the straight part of the pipe to the measurement point should be greater than 0XD, turbulence on the anemometer's thermal probe and Pitot tube of the relatively small impact.
Anemometer in the pipeline air flow velocity measurement practice has proved that the anemometer 16mm probe is the most widely used. Its size ensures good permeability and can withstand flow velocities up to 60 m/s. The measurement of air flow velocity in ducts is one of the feasible measurement methods, and the indirect measurement protocol (grid measurement method) is applicable to air measurement.
