How to choose the appropriate air flow meter and anemometer?
The measurement range of flow velocity 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 sensitive probe of the anemometer is used for accurate measurement from 0 to 5m/s; The rotary probe of the anemometer has an ideal effect in measuring flow velocities ranging from 5 to 40m/s; The application of pitot tubes can achieve excellent results in the high-speed range. An additional specification for selecting the flow rate probe of an anemometer correctly is temperature, which is typically used with a thermal sensor of up to+-7 degrees Celsius ˚ C. The rotor probe of a specially designed anemometer can reach up to 35 ˚ C. Pitot tube for+35 ˚ Above C.
The working principle of the thermal sensitive probe of the anemometer
It is based on the fact that the cold impact airflow carries away the heat on the thermal element, and with the help of a conditioning switch, the temperature remains constant, and the conditioning current is proportional to the flow rate. When using a thermosensitive probe in turbulence, airflow from all directions simultaneously impacts the thermal element, which can affect the accuracy of the measurement results. When measuring in turbulence, the reading of the flow velocity sensor of the thermal anemometer is often higher than that of the rotary probe. The above phenomena can be observed during the pipeline measurement process. According to different designs for managing pipeline turbulence, it can even be present at low speeds. Therefore, the anemometer measurement process should stop locally on the straight line of the pipeline. The starting point of the partial straight line should be at least 10 times before the measurement point × D (D=pipeline diameter, in CM); The endpoint should be at least 4 after the measurement point × Location D. The fluid cross-section must not have any obstruction.
Wheel type probe for anemometers (edges, overhangs, objects, etc.)
The working principle of the rotary probe of the anemometer is based on converting the rotation into an electrical signal. First, it passes through a proximity sensing start, stops counting the rotation of the rotary wheel, and generates a pulse series. Then, it is converted and processed by the detector to obtain the speed value. The large-diameter probe of the anemometer (60mm, 100mm) is suitable for measuring turbulence at medium and small flow rates. The small caliber probe of the anemometer is more suitable for measuring airflow with a cross-sectional area greater than 100 times that of the exploration head.
Positioning of Anemometers in Air Flow
The correct adjustment position of the rotary probe of the anemometer is that the airflow direction is parallel to the rotary axis. When the probe is quietly rotated in the airflow, the reading will change accordingly. When the reading reaches a high value, it indicates that the probe is in the correct measurement position. When measuring in a pipeline, the distance between the starting point of the straight part of the pipeline and the measurement point should be greater than 0XD, and the influence of turbulence on the thermal sensitive probe and pitot tube of the anemometer is relatively small.
Measurement of airflow velocity in pipelines using an anemometer
Theoretical proof shows that the 16mm probe of the anemometer is very useful. Its size not only ensures good permeability, but also can accept flow rates up to 60m/s. The measurement of airflow velocity in pipelines is one of the feasible measurement methods, and the indirect measurement regulation (grid measurement method) is applicable to air measurement.
