Anemometer measurement technology and selection guide

The anemometer's probe selection range of 0 to 100 m/s flow rate can be divided into three sections: low speed: 0 to 5 m / s; medium speed: 5 to 40 m / s; high speed: 40 to 100 m / s. The anemometer's thermal probe is used for accurate measurement from 0 to 5 m/s; the anemometer's rotary probe measures the flow rate of 5 to 40 m/s; ideally, the pitot tube can be used in the high speed range. result. An additional criterion for properly selecting the anemometer's flow rate probe is temperature. Typically, the anemometer's thermal sensor is used at temperatures up to +-70C. The special anemometer's rotor probe can reach 350C. Pitot tube is used for +350C or above. The thermal probe of the anemometer's thermal probe anemometer works on the basis of the cold impinging airflow to remove heat from the thermal element. With an adjustment switch to keep the temperature constant, the current and flow rate are proportional. When a thermal probe is used in turbulent flow, airflow from all directions simultaneously impacts the thermal element, which can affect the accuracy of the measurement. When measured in turbulent flow, the temperature indicator of the thermal anemometer is often higher than that of the rotary probe. The above phenomenon can be observed during the pipeline measurement process. Depending on the design of the management pipe turbulence, it can occur even at low speeds. Therefore, the anemometer measurement process should be performed in the straight section of the pipe. 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 is at least 4 × D behind the measuring point. The fluid section must not have any obstruction. (Angle, Resuspension, Object, etc.) The working principle of the rotary probe of the anemometer's rotary probe anemometer is based on converting the rotation into an electrical signal, first passing through a proximity induction and counting the rotation of the rotor. And generate a pulse series, and then through the converter conversion process, you can get the speed value. The anemometer's large bore probe (60mm, 100mm) is suitable for measuring turbulence at medium and small flow rates (eg at the pipe outlet). The anemometer's small-caliber probe is more suitable for measuring airflow with a pipe cross-section that is more than 100 times larger than the cross-section of the expedition. Positioning of the anemometer in the air flow The correct adjustment position of the rotary probe of the anemometer is that the airflow is parallel to the axis of the rotor. When you gently rotate the probe in the airflow, the indication changes. When the reading reaches a large value of zui, 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 turbulence on the thermal probe and pitot tube of the anemometer is relatively small. The anemometer's airflow velocity measurement in the pipeline proves that the 16mm probe of the anemometer is widely used. Its size guarantees good permeability and can withstand flow rates up to 60m/s. Airflow velocity measurement in the pipeline is one of the feasible measurement methods, and the indirect measurement procedure (gate measurement method) is applicable to air measurement. VDI12080 provides the following procedures: ● Square section grid, measuring common specifications ● Circular section gate, measuring centroid axis specifications ● Circular section gate, measuring range linear specification Anemometer measuring vent in exhaust air It will greatly change the relatively balanced distribution of airflow in the pipeline: a high-speed zone is generated on the surface of the free vent, and the rest is a low-speed zone, and a vortex is generated on the grid. According to the different design of the grid, the airflow section is relatively stable at a certain distance (about 20cm) in front of the grid. In this case, the measurement is usually carried out using a caliber wheel of a large anemometer. Because larger calibers average the unbalanced flow rates and calculate the average over a larger range. The anemometer is measured in the suction hole using a volumetric flow funnel: even if there is no grid interference at the pumping point, the air flow path has no direction and the airflow section is extremely uneven. The reason is that the partial vacuum in the pipe draws the air out of the air chamber in a funnel shape, even in a region close to the suction, and there is no position that satisfies the measurement condition, and the measurement operation can be performed. If the measurement is performed by the grid measurement method with the average value calculation function, and the volume flow method is used to measure and determine the volume flow rate, etc., only the pipe or funnel measurement method can provide repeatable measurement results. In this case, different sizes of measuring funnels can meet the requirements of use. A measuring funnel can be used to generate a fixed section at a certain distance in front of the flap valve to meet the flow rate measurement condition. The center of the section is measured and fixed, the center of the section is measured and the section is fixed, and the center of the section is measured and fixed. Here. The measured volume obtained by the flow probe is multiplied by the funnel coefficient to calculate the volumetric flow drawn. (eg funnel factor 20)

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