How to choose an anemometer
The measurement range of flow velocity from 0 to 100m/s can be divided into three sections: low velocity: 0 to 5m/s; medium velocity: 5 to 40m/s; high velocity: 40 to 100m/s. The thermal probe of the anemometer is used for accurate measurement of 0 to 5m/s; the rotary probe of the anemometer is ideal for measuring the flow velocity of 5 to 40m/s; and the results can be obtained in the high-speed range by using the pitot tube. An additional criterion for the correct selection of the flow rate probe of the anemometer is the temperature. Usually, the temperature of the thermal sensor of the anemometer is about +-70C. The rotor probe of the special anemometer can reach 350C. Pitot tubes are used above +350C.
Thermal probes for anemometers
The working principle of the thermal probe of the anemometer is based on the cold impact air flow taking 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 impinges on the thermal element simultaneously, which can affect the accuracy of the measurement results. When measuring in turbulent flow, the indication value of the thermal anemometer flow sensor is often higher than that of the rotary probe. The above phenomenon can be observed in the pipeline measurement process. Depending on the design of the managed pipe turbulence, it can occur even at low speeds. Therefore, the anemometer measurement process should be carried out on the straight part of the pipeline. The starting point of the straight line should be at least 10×D (D=pipe diameter, in CM) before the measuring point; the end point should be at least 4×D behind the measuring point. The flow section must not be obstructed in any way. (angular, resuspended, objects, etc.)
Rotary Probe for Anemometers
The working principle of the rotating wheel probe of the anemometer is based on converting the rotation into an electrical signal. First, it passes through a proximity sensor to "count" the rotation of the rotating wheel and generate a pulse series, which is 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 rates (such as at the pipe outlet). The small-caliber probe of the anemometer is more suitable for measuring the airflow where the cross-section of the pipe is more than 100 times larger than the cross-section of the probe.
Positioning of anemometers in air flow
The correct adjustment position of the rotor probe of the anemometer is that the airflow direction is parallel to the axis of the rotor. When the probe is turned slightly in the air flow, the indicated value will change accordingly. When the reading reaches a maximum value, it indicates that 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 measuring point should be greater than 0XD, and the influence of turbulent flow on the thermal probe and pitot tube of the anemometer is relatively small.
Anemometer measures the air flow velocity in the pipeline
Practice has proved the use of the 16mm probe of the anemometer. Its size not only ensures good permeability, but also can withstand a flow velocity up to 60m/s. As one of the feasible measurement methods, the airflow velocity measurement in the pipeline is suitable for air measurement by the indirect measurement procedure (grid measurement method).
Anemometer Measurements in Extraction Exhaust
The vent will greatly change the relatively balanced distribution of the airflow in the duct: a high-speed area is generated on the surface of the free vent, and the rest is a low-speed area, and a vortex is generated on the grid. According to the different design methods of the grid, at a certain distance (about 20cm) in front of the grid, the airflow section is relatively stable. In this case, the aperture wheel of a large anemometer is usually used for measurement. Because larger bores are able to average unbalanced flow rates and calculate their average value over a larger range
