How to choose the right wind volume meter and anemometer?
The flow velocity measurement range from 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 of 0 to 5m/s; the rotary probe of the anemometer is ideal for measuring the flow velocity of 5 to 40m/s; result. An additional criterion for proper selection of an anemometer's velocity probe is temperature, and typically an anemometer's thermal sensor operates at a temperature of approximately +-7˚C. The rotor probe of the special anemometer can reach 35˚C. Pitot tubes are used above +35˚C.
The working principle of the thermal probe of the anemometer
It is based on the cold impact airflow taking away the heat on the heating element. With the help of a regulating switch to keep the temperature constant, the regulating 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, the indication value of the thermal anemometer flow sensor is often higher than that of the rotary probe. The above phenomenon can be observed in the pipeline measurement process. Depending on the design of the managed pipe turbulence, even at low speeds. Therefore, the anemometer measurement process should be carried out in the straight line part of the pipeline. The starting point of the straight line part should be at least 10×D (D=pipe diameter, unit is 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.
(edges, heavy suspension, objects, etc.) Rotary probe of anemometer
The working principle of the rotating wheel probe of the anemometer is based on converting the rotation into an electrical signal. First, it passes through a proximity sensor, stops the "counting" of the rotation of the rotating wheel and generates a series of pulses, and then converts and disposes it through the detector. Get the speed value. The large-diameter probe (60mm, 100mm) of the anemometer is suitable for measuring turbulent flow with medium and small flow rates. The small-caliber probe of the anemometer is more suitable for measuring the air flow where the cross-section of the pipe is more than 100 times larger than the cross-sectional area of the exploration head. the
Positioning of the anemometer in the air flow
The correct adjustment position of the rotor probe of the anemometer is that the airflow direction is parallel to the axis of the rotor. When the probe is turned slightly in the airflow, the indicated value will change accordingly. When the reading reaches a maximum value, it indicates that 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 is relatively small. the
Anemometer measures the air flow velocity in the pipeline
Theory proves that the 16mm probe of the anemometer is very useful. Its size not only ensures good permeability, but also can accept flow velocity up to 60m/s. As one of the feasible measurement methods, the air flow velocity measurement in the pipeline is applicable to the air measurement by the indirect measurement procedure (grid measurement method). the
VDI12080 provides the following procedures:
Square cross-section grid, measuring common specifications
Circular cross-section grid, measure centroid axis specification
Circular cross-section grid, measuring range linear specification
The measurement of the anemometer in the extraction and exhaust
The air vent will greatly change the relatively balanced distribution state of the airflow in the pipe: a high-speed area is formed on the surface of the free air vent, and a low-speed area is formed in other parts, and a vortex is generated on the grid. According to the different design methods of the grid, the airflow section is relatively stable at a certain interval (about 20cm) in front of the grid. In this case, the caliber runner of the large anemometer is usually used for measurement. Due to the larger caliber, the unbalanced flow rate can be uniformed, and its uniform value can be calculated in a larger range. the
The anemometer uses a volume flow funnel to measure at the suction hole:
Even if there is no grid interference at the suction point, the path of air flow has no direction, and its airflow section is extremely uneven. The reason is that the partial vacuum in the pipe draws the air into the air chamber in a funnel shape. Even in the area close to the pumping, there is no position that meets the measurement conditions for measurement operations. For example, the grid measurement method with the average value calculation function is used for measurement, and the volume flow method is used for measurement, and the volume flow is determined, etc. Only the pipe or funnel measurement method can provide repeatable measurement results. In this case, measuring funnels of different sizes can meet the application requirements. The application of the measuring funnel can generate a fixed cross-section that meets the flow velocity measurement conditions at a certain distance in front of the sheet valve, measure and locate the center of the cross-section and fix the cross-section, measure and locate the center of the cross-section and fix the cross-section, measure and locate the center of the cross-section and fix it here. The measured value obtained by the flow rate probe is multiplied by the funnel coefficient to calculate the extracted volume flow. (eg funnel factor 20)
Wind speed test method
The wind speed test includes the test of the uniform wind speed and the test of the turbulent flow component (wind turbulence 1 ~ 150KHz, which is different from the fluctuation). The methods for testing the uniform wind speed include thermal type, ultrasonic type, impeller type, and skin type.
Thermal wind speed test method
This method is to test the resistance change when the sensor is cooled by the wind when it is powered on, so as to test the wind speed. No information on wind direction can be derived. In addition to being easy and convenient to carry, the cost-performance ratio is high, and it is widely used as a standard product of anemometers. The elements of thermal anemometers use platinum wires, thermocouples, and semiconductors, but our company uses platinum coiled wires. The material of the platinum wire is materially stable. Thus, there are advantages in long-term stability and in temperature compensation.
