Anemometer measurement technology and its selection guide
The flow velocity measurement range from 0 to 100m/s can be divided into three sections: low speed: 0 to 5m/s; medium speed: 5 to 40m/s; high speed: 40 to 100m/s. The thermal probe of the anemometer is used for measurements from 0 to 5m/s; the rotor probe of the anemometer is ideal for measuring flow rates from 5 to 40m/s; and the use of a pitot tube gives the best results in the high speed range . An additional criterion for the correct selection of an anemometer's flow probe is temperature, usually the temperature of the thermal sensor of an anemometer is about +-70C. The rotor probe of the special anemometer can reach 350C. Pitot tubes are used above +350C.
Thermal probe of anemometer
The working principle of the thermal probe of the anemometer is based on the cold impact airflow to take away the heat on the heating element. With the help of an adjustment switch, to keep the temperature constant, the adjustment current is proportional to the flow rate. When using thermal probes in turbulent flow, airflow from all directions hits the thermal element simultaneously, affecting the accuracy of the measurement results. When measuring in turbulent flow, thermal anemometer flow sensors tend to have higher indications than rotor probes. The above phenomena can be observed during pipeline measurement. Depending on the design that manages the turbulence in the pipe, it can occur even at low speeds. Therefore, the anemometer measurement process should be carried out on the straight section of the pipeline. The starting point of the straight line part should be at least outside the measuring point qian10×D (D=pipe diameter, in CM); the end point should be at least 4×D behind the measuring point. The fluid section must not have any obstructions. (angular, resuspension, object, etc.)
Rotary probe of anemometer
The working principle of the rotating wheel probe of the anemometer is based on converting the rotation into an electrical signal. First, through a proximity sensing head, the rotation of the rotating wheel is "counted" and a pulse series is generated, and then converted by the detector. Get the speed value. The large-diameter probe (60mm, 100mm) of the anemometer is suitable for measuring turbulent flow with medium and small flow velocity (such as at the outlet of the pipe). The small-diameter probe of the anemometer is more suitable for measuring the airflow with the cross-section of the pipeline more than 100 times larger than the cross-section of the expedition head.
The positioning of the anemometer in the air flow
The correct adjustment position of the rotor probe of the anemometer is that the airflow direction is parallel to the rotor axis. When the probe is gently turned in the airflow, the indication changes accordingly. When the reading reaches the maximum value, the probe is in the correct measurement position. When measuring in the pipeline, the distance from the starting point of the straight part of the pipeline to the measurement point should be greater than 0XD, and the influence of turbulence on the thermal probe and pitot tube of the anemometer is relatively small.
The anemometer measures the airflow velocity in the pipeline
Practice has proved that the 16mm probe of the anemometer is the most widely used. Its size not only ensures good permeability, but also can withstand flow rates up to 60m/s. As one of the feasible measurement methods, the measurement of airflow velocity in the pipeline, the indirect measurement procedure (grid measurement method) is suitable for air measurement.
