Anemometer probe selection NINGBO BLUEOCEAN AUTO PARTS CO.,LTD , https://www.blueoceancarparts.com
The flow rate measurement range of 0 to 100 m/s can be divided into three sections: low speed: 0 to 5 m/s; medium speed: 5 to 40 m/s; high speed: 40 to 100 m/s. Anemometer thermal probes are used for accurate measurements from 0 to 5 m/s; anemometer rotary probes are ideal for measuring flow rates from 5 to 40 m/s; pitot tubes are available at high speeds. An additional criterion for correctly selecting the anemometer's flow probe is the temperature. Usually the anemometer's thermal sensor is used at about +-70C. Special anemometer wheel probe up to 350C. Pitot tube for +350C or more.
Anemometer thermal probe
The principle of the anemometer's thermal probe is based on the cold-impact air flow to take away the heat from the thermal element. With a regulating switch, keeping the temperature constant, the current and the flow rate are regulated in direct proportion to each Other. When thermal probes are used in turbulent flow, airflow from all directions simultaneously impacts the thermal elements, which affects the accuracy of the measurement results. When measuring in turbulent flow, thermal anemometer flow sensor values ​​are often higher than those of rotary probes. The above phenomena can be observed during the pipeline measurement. Depending on the design of the turbulence in the management pipeline, it can even occur at low speeds. Therefore, the anemometer measurement process should be performed on the straight part of the pipeline. The starting point of the straight part should be at least 10 × D before the measuring point (D = pipe diameter in CM); the ending point is at least 4 × D after the measuring point. There must be no obstruction to the fluid section. (Angle, rehangs, objects, etc.)
Anemometer Rotary Probe
The working principle of the anemoscope's rotary probe is based on converting the rotation into electrical signals, first passing through a proximity sensor to start the “counting†of the rotation of the runner and generating a series of pulses, which can then be processed by the detector. Get the speed value. The anemometer's large-diameter probe (60mm, 100mm) is suitable for measuring turbulence in medium and small flow rates (eg at the outlet of pipes). The anemometer's small-caliber probe is more suitable for measuring air flow with a cross-section greater than 100 times more than the cross-section of the explorer.
Anemometer positioning in the air stream
The correct adjustment position of the anemometer's rotary probe is that the air flow is parallel to the axis of the runner. When the probe is gently turned in the airflow, the indication changes. When the reading reaches its 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 portion of the pipeline to the measuring point should be greater than 0XD, and the turbulence has relatively small influence on the anemometer thermal probe and pitot tube.
Anemometer measurement of airflow velocity inside a pipe
It has been proved that the 16mm probe of the anemometer is the most versatile. Its size guarantees both good permeability and high flow rates up to 60m/s. Measurement of airflow velocity in a pipe is one of the possible measurement methods. The indirect measurement procedure (gate measurement method) is applicable to air measurement.
VDI12080 provides the following procedures:
â— Square section gate, measuring common specifications
â—Circular section gate, measuring centroid axis specification
â—Circular section gate, measuring range linear specification
Measurement of anemometer in exhaust gas
The vent will greatly change the distribution of the air flow within the pipe to a relatively uniform state: a high-speed zone is created on the surface of the free air vent, and the rest is a low-speed zone, and a vortex is generated on the grid. According to the different design of the grid, the airflow cross section is relatively stable at a certain distance (about 20cm) in front of the grid. In this case, a large anemometer caliper wheel is usually used for measurement. Because larger calibers can average uneven flow rates and calculate their averages over a wide range.
The anemometer is measured with a volumetric flow funnel at the suction hole:
Even if there is no grid interference at the suction, there is no direction of the air flow path, and its airflow cross section is extremely uneven. The reason for this is the partial vacuum inside the pipe. The air is drawn out of the funnel in the air chamber, even in the area that is very close to the pumping air, and there is not a place that satisfies the measurement conditions and can be used for measurement operations. If measurements are made using a grid measurement method with an average calculation function, and by determining the volumetric flow method for measurement, and by determining the volume flow, etc., only the pipe or funnel measurement can provide repeatable measurement results. In this case, different size measuring funnels can meet the requirements for use. Using a measuring funnel, a fixed section can be generated at a certain distance in front of the sheet valve to meet the flow measurement conditions. The center of the section is located and the section is fixed. The center of the section is located and the section is fixed. The center of the section is located and fixed. Here. The measured value obtained by the flow velocity probe is multiplied by the funnel coefficient to calculate the volumetric flow volume. (eg funnel factor 20)