Measurement technology and selection guide of the

2022-09-23
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Measurement technology and selection guide of anemometer

probe selection of anemometer

the 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 anemometer is used for accurate measurement from 0 to 5m/s; The runner probe of anemometer has the best effect on measuring the flow rate of 5 to 40m/s; The best results can be obtained in the high-speed range by using the pitot tube. An additional standard for the correct selection of the velocity probe of the anemometer is temperature. Generally, the temperature of the thermal sensor of the anemometer is about +-70c. The runner probe of the special anemometer can reach 350C. Pitot tube is used above +350c

thermal probe of anemometer

the working principle of thermal probe of anemometer is based on the cold impact air flow to take away the heat on the thermal element. With the help of an adjusting switch, the temperature is kept constant, and then the qualified environment can be adjusted to ensure the accuracy of the detection results of concrete pressure testing machine. The current is in direct proportion to the flow rate. When the thermal probe is used in turbulence, the airflow from all directions impacts the thermal element at the same time, which will affect the accuracy of the measurement results. When measuring in turbulence, the indication value of the thermal anemometer flow sensor is often higher than that of the runner probe. The above phenomena can be observed during pipeline measurement. According to the different design of managing pipe turbulence, it will appear even at low speed. Therefore, the anemometer measurement process should be carried out in the straight part of the pipeline. The starting point of the straight part shall be at least 10 in front of the measuring point × D (d= pipe diameter, in cm); The end point is at least 4 after the measuring point × Place D. The fluid section shall not be blocked. (edges and corners, heavy suspension, objects, etc.)

the runner probe of anemometer

the rotation Application Manual of anemometer should be provided with two copies. The working principle of the wheel probe is based on converting the rotation into an electrical signal. First, after an adjacent induction start, the rotation of the runner is "counted" and a pulse series is generated, and then the speed value can be obtained after the conversion and processing of the detector. The large diameter probe (60mm, 100mm) of the anemometer is suitable for measuring the turbulence of medium and small flow velocity (such as at the outlet of the pipe). The small diameter probe of the anemometer is more suitable for measuring the airflow with the cross-section of the pipe more than 100 times that of the exploration head

positioning of anemometer in the air flow

the correct adjustment position of the runner probe of anemometer is that the air flow direction is parallel to the runner axis. When the probe is gently rotated in the air flow, the indicated value will change as the equipment cannot move up and down. When the reading reaches the 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 turbulence has relatively little impact on the thermal probe and pitot tube of the anemometer

anemometer in the measurement of air flow velocity in the pipeline

practice has proved that the 16mm probe of anemometer is the most widely used. Its size not only ensures good permeability, but also can withstand a higher flow rate of 60m/s. As one of the feasible measurement methods, the measurement of airflow velocity in the pipeline, and the indirect measurement procedure (grid measurement method) is applicable to air measurement

vdi12080 provides the following procedures:

● square section grid, measurement of general specification

● circular section grid, measurement of centroid axis specification

● circular section grid, measurement of range linear specification

anemometer measurement in exhaust gas extraction

vent will greatly change the relatively balanced distribution of air flow in the pipe: high speed area is generated on the surface of free vent, and the rest is low speed area, And create vortices on the grid. According to the different design methods of the grid, the air flow section is relatively stable at a certain distance (about 20cm) in front of the grid. In this case, the diameter runner of the gale velocimeter is usually used for measurement

because a larger diameter can average the uneven flow velocity and calculate its average value in a larger range

the anemometer uses a volume flow funnel to measure at the air extraction hole:

even if there is no grid interference at the air extraction point, the air flow path has no direction, and its air flow section is extremely uneven. The reason is that the local vacuum in the pipe extracts the air in the air chamber in a funnel shape. Even in the area close to the extraction, there is no position that meets the measurement conditions for measurement operation. For example, if the grid measurement method with the function of average value calculation is used to measure, and the volumetric flow method is used to determine the volumetric flow, only the pipe or funnel measurement method can provide repeatable measurement results. In this case, measuring funnels of different sizes can meet the use requirements. Using the measuring funnel, a fixed section meeting the flow rate measurement conditions can be generated at a certain distance in front of the flaky valve, the section center can be measured and positioned, the section center can be measured and positioned, the section center can be measured and positioned, and the section center must be kept clean and fixed here. The measured value obtained by the flow rate probe is multiplied by the funnel coefficient to calculate the pumped volume flow. (end)

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