How to measure anemometer and how to select it
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 rotary probe of the anemometer is ideal for measuring flow rates from 5 to 40m/s; and the pitot tube can be used to obtain the best flow rate in the high-speed range. Best results. 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. It first passes through a proximity sensor to "count" the rotation of the wheel and generates a pulse series, 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.
Anemometer measures air flow velocity in pipes
Practice has proven that the 16mm probe of the anemometer is the most versatile. Its size not only ensures good permeability, but also can withstand flow rates up to 60m/s. As one of the feasible measurement methods, air flow velocity measurement in pipelines, indirect measurement procedures (grid measurement method) are suitable for air measurement.
Measurement of anemometer in air extraction and exhaust
The vent will greatly change the relatively balanced distribution of air flow in the pipe: a high-speed area will be generated on the surface of the free vent, and the remaining parts will be low-speed areas, and a vortex will be generated on the grid. Depending on the different design methods of the grid, the airflow cross section is relatively stable at a certain distance (about 20cm) in front of the grid. In this case, a large anemometer's aperture wheel is usually used for measurement. Because a larger diameter can average unbalanced flow rates and calculate their average value over a larger range.
The anemometer uses a volumetric flow funnel at the air extraction hole to measure:
Even if there is no grid interference at the exhaust point, the air flow path has no direction, and its air flow cross section is extremely uneven. The reason is that the partial vacuum in the pipeline draws the air into the air chamber in a funnel shape. Even in the area very close to the air extraction, there is no position that meets the measurement conditions for measurement operations. Only pipe or funnel measurement methods can provide reproducible measurement results, such as using a grid measurement method with averaging function and using it to determine the volumetric flow rate. In this case, measuring funnels of different sizes can meet the usage requirements. A measuring funnel can be used to generate a fixed section that meets the flow rate measurement conditions at a certain distance in front of the sheet valve. Measure and locate the center of the section and fix the section. Measure and locate the center of the section and fix it. Measure and locate the center of the section and fix it. Here it is. The measured value obtained by the flow rate probe is multiplied by the funnel coefficient to calculate the pumped volumetric flow rate. (e.g. funnel coefficient 20)
