Anemometer measurement technology and selection guide methods!
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/anemometer is used for measurements from 0 to 5m/s; the rotary probe of the anemometer/anemometer is ideal for measuring flow rates from 5 to 40m/s; while the pitot tube can be used at high speeds Get the best results within the range. An additional criterion for the correct selection of flow velocity probes for anemometers/anemometers is temperature. Usually the operating temperature of thermal sensors for anemometers/anemometers is about +-70C. Specially made anemometer/anemometer wheel probe can reach 350C. Pitot tube is used above +350C.
The working principle of the thermal probe of the anemometer/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 flows, thermal anemometers/anemometer flow sensors tend to give higher indications than rotary probes. 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/anemometer measurement process should be carried out on the straight section of the pipe. The starting point of the straight line part should be at least 10×D (D=pipe diameter, in 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.)
The working principle of the anemometer/anemometer's wheel probe is based on converting the rotation into an electrical signal. 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. , the speed value can be obtained. The large-diameter probe (60mm, 100mm) of the anemometer/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/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 explorer head.
The correct adjustment position of the rotary probe of the anemometer/anemometer is that the airflow direction is parallel to the rotor axis. When the probe is gently rotated in the air flow, the indication value will change accordingly. When the reading reaches the maximum value, it indicates that the probe is in the correct measurement 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/anemometer is relatively small.
Practice has proven that the 16mm probe of anemometer/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.
VDI12080 provides the following procedures:
●Square cross-section grid, measuring common specifications
●Circular cross-section grid, measuring centroid axis specifications
●Circular cross-section grid, measuring range linear specifications
