Anemometer measurement technology and selection guide method!
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/anemometer is used for the best measurement of 0 to 5m/s; the rotary probe of the anemometer/anemometer is ideal for measuring the flow velocity of 5 to 40m/s; and the pitot tube can be used Best results are obtained in the high speed range. An additional criterion for the correct selection of the flow rate probe of the anemometer / anemometer is the temperature. Usually, the temperature of the thermal sensor of the anemometer / anemometer is about +-70C. The rotor probe of the special anemometer/anemometer can reach 350C. Pitot tubes are used above +350C.
Thermal probes for anemometers/anemometers
The working principle of the thermal probe of the anemometer/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, thermal anemometer/anemometer flow rate sensors tend to give higher readings than wheel probes. 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, anemometer/anemometer measurements should be made on straight sections 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 should be at least 4×D behind the measuring point. The flow section must not be obstructed in any way. (angles, resuspensions, objects, etc.)
Rotary Wheel Probe for Anemometers/Anemometers
The working principle of the rotary probe of the anemometer/anemometer is based on converting the rotation into an electrical signal, first passing through a proximity sensor, "counting" the rotation of the rotor and generating a pulse series, and then converted by the detector , to get the speed value. The large-diameter probe (60mm, 100mm) of the anemometer/anemometer is suitable for measuring turbulent flow with medium and small flow rates (such as at the outlet of the pipeline). The small-caliber probe of the anemometer/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 the anemometer/anemometer in the air flow
The correct adjustment position of the rotor probe of the anemometer/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 the maximum value, 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/anemometer is relatively small.
Anemometer/Anemometer Air velocity measurement in ducts
Practice has proved that the 16mm probe of the anemometer/anemometer is the most versatile. 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 air flow velocity measurement in the pipeline is suitable for air measurement by the indirect measurement procedure (grid measurement method).
VDI12080 provides the following procedures:
●Square cross-section grid, measuring common specifications
●Circular cross-section grid, measuring centroid axis specification
●Circular cross-section gate, measuring range linear specification
Anemometer/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, measurements are usually made with a large-bore anemometer/anemometer wheel. This is because the larger bore is able to average the unbalanced flow rate and calculate its average value over a larger range.
