Anemometer measurement technology and a guide to selecting an anemometer
Anemometer probe selection
The flow velocity measurement range of 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 accurate measurement from 0 to 5m/s; the wheel probe of the anemometer is ideal for measuring flow rates from 5 to 40m/s; and the pitot tube is used to obtain the best results in the high-speed range. result. An additional criterion for the correct selection of the flow velocity probe of an anemometer is the temperature. Usually the operating temperature of the thermal sensor of an anemometer is about +-70C. The wheel probe of the special anemometer can reach 350C. Pitot tube is used above +350C.
Thermal probe for anemometer
The working principle of the thermal probe of the anemometer is based on the cold impact airflow 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 a thermal probe in turbulent flow, airflow from all directions hits the thermal element simultaneously, affecting 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 wheel probe. The above phenomena can be observed during pipeline measurement. Depending on the design of how pipe turbulence is managed, it can occur even at low speeds. Therefore, the anemometer measurement process should be carried out on the straight part of the pipe. The starting point of the straight line part should be at least 10×D (D=pipe diameter, unit: CM) in front of the measuring point; the end point should be at least 4×D after the measuring point. There must be no obstruction in the fluid section. (edges, overhangs, objects, etc.)
Rotary probe for anemometer
The working principle of the anemometer's wheel probe is based on converting rotation into electrical signals. First, through a proximity induction start, the rotation of the wheel is "counted" and a pulse series is generated, which is then converted and processed by the detector. Get the speed value. The large-diameter probe (60mm, 100mm) of the anemometer is suitable for measuring turbulent flows with medium and small flow rates (such as at the pipe outlet). The small-diameter probe of the anemometer is more suitable for measuring airflow where the cross-section of the pipe is more than 100 times larger than the cross-section of the exploration head.
Positioning of anemometer in air flow
The correct adjustment position of the anemometer's wheel probe is when the air flow direction is parallel to the wheel axis. When the probe is gently rotated in the air flow, the indication value will change accordingly. When the reading reaches the maximum value, the probe is in the correct measuring position. When measuring in a pipeline, the distance from the starting point of the straight part of the pipeline to the measurement point should be greater than 0XD. The impact of turbulent flow on the thermal probe and pitot tube of the anemometer is relatively small.
