Cup anemometer
It is the most common type of anemometer. The rotating cup anemometer was first invented by Robinson in the United Kingdom. It was four cups at that time, and then it was changed to three cups. The three parabolic or hemispherical empty cups fixed to each other on the shelf are all on one side, and the whole shelf together with the wind cup is mounted on a shaft that can rotate freely. Under the action of the wind, the wind cup rotates around the axis, and its rotational speed is proportional to the wind speed. The rotational speed can be recorded with electrical contacts, tachogenerators or photoelectric counters, etc.
propeller
It is an anemometer with a set of three- or four-bladed propellers rotating around a horizontal axis. The propeller is mounted on the front of a wind vane so that its plane of rotation is always facing the wind
Anemometer direction, its rotational speed is proportional to wind speed.
**Anemometer
A metal wire heated by current, the flowing air makes it dissipate heat, and the heat dissipation rate and the square root of the wind speed are linearly related, and then linearized by the electronic circuit (for easy scale and reading), the accurate anemometer can be made. **The anemometer is divided into two types: side heating and direct heating. The side heating type is generally manganese copper wire, and its resistance temperature coefficient is close to zero, and its surface is additionally equipped with a temperature measuring element. The direct heating type is mostly platinum wire, which can directly measure the temperature of the body itself while measuring the wind speed. **The anemometer has high sensitivity at low wind speed and is suitable for measuring small wind speed. With a time constant of only a few hundredths of a second, it is an important tool for atmospheric turbulence and agrometeorological measurements.
Digital Anemometer
The digital anemometer is a large-scale intelligent wind speed sensing and alarm device specially developed for various large-scale mechanical equipment.
The microprocessor is used as the control core, and the peripheral adopts advanced digital communication technology. The system has high stability, strong anti-interference ability, and high detection accuracy. The wind cup is made of special materials, with high mechanical strength and strong wind resistance. The design of the display case is novel and unique, sturdy and durable, and easy to install and use. All electrical interfaces are in line with international standards, no debugging is required during installation, and they are suitable for different working environments.
The digital anemometer is used to measure the instantaneous wind speed and average wind speed, and has functions such as automatic monitoring, real-time display, and over-limit alarm control.
Acoustic Anemometer
The wind speed component in the direction of sound wave propagation will increase (or decrease) the sound wave propagation speed. An acoustic anemometer made with this characteristic can be used to measure the wind speed component. Acoustic anemometers have at least two pairs of sensing elements, each pair including a sounder and a receiver. Make the sound waves of the two sounders travel in opposite directions. If one group of sound waves propagates along the wind speed component and the other group just travels against the wind, the time difference between the sound pulses received by the two receivers will be proportional to the wind speed component. If two pairs of elements are installed in the horizontal and vertical directions at the same time, the horizontal wind speed, wind direction and vertical wind speed can be calculated respectively. Due to the advantages of anti-interference and good directionality of ultrasonic waves, the frequency of the sound waves emitted by the acoustic anemometer is mostly in the ultrasonic section.
Anemometer Applications
Anemometers are widely used and can be used flexibly in all fields. They are widely used in electric power, steel, petrochemical, energy saving and other industries. There are other applications in the Beijing Olympics, such as sailing competitions, rowing competitions, field shooting competitions, etc. Need to use anemometer to measure. The anemometer has been relatively advanced, in addition to measuring the wind speed, it can also measure the wind temperature and air volume. There are many industries that need to use anemometers. The recommended industries are: sea fishing, various fan manufacturing industries, industries that require exhaust systems, and so on.
Different seasons and different geographical conditions of anemometers will cause the wind direction in the atmosphere to change continuously. If the wind direction is different day and night by the sea, there are also different monsoons in winter and summer. Studying wind direction can help us predict and study climate change. Studying wind direction requires the use of an anemometer. Most of the anemometers are designed in the shape of arrows, and some are also made into animal shapes, like roosters. The feather part of the anemometer will rotate with the wind direction. The anemometer should be installed in a place where there are no buildings or trees, etc., to block the movement of the wind. Uses and scope of application QDP series thermal bulb electric anemometers are used in heating, ventilation, air conditioning, meteorology, agriculture, refrigeration and drying, labor hygiene surveys, etc., and can be used when it is necessary to measure the air velocity of indoor and outdoor or models. It is a basic instrument for measuring low wind speed. In 1987, this product was rated as the best product in Beijing by the Beijing Economic Commission. Working principle This instrument is composed of two parts: hot ball sensor and measuring instrument. At the head of the sensor is a tiny glass ball that houses a nichrome wire coil that heats the glass and two thermocouples connected in series. The cold end of the thermocouple is connected to the phosphor bronze pillar and is directly exposed to the air flow. When a certain amount of current passes through the loop, the glass ball is heated to a certain temperature. This temperature is related to the speed of the air flow, and the flow rate is small. The higher the temperature, the lower the temperature.
Introduction to Anemometers
An anemometer is an anemometer.
An anemometer is an instrument that measures the speed of air. There are many kinds of it. The most commonly used in meteorological stations is the wind cup anemometer. It consists of three parabolic cone empty cups fixed on the bracket at 120° to each other. The concave surface of the empty cups are all in one direction. The entire induction part is installed on a vertical rotating shaft. Under the action of the wind, the wind cup rotates around the shaft at a speed proportional to the wind speed. Another type of rotary anemometer is the propeller anemometer, which consists of a three-blade or four-blade propeller to form a sensing part, which is installed at the front end of a wind vane so that it can be aligned with the direction of the wind at any time. The blades rotate about the horizontal axis at a speed proportional to the wind speed.
Anemometer Principle
The basic principle of the anemometer is to put a thin wire in the fluid, and the wire is heated by current to make the temperature higher than the temperature of the fluid, so the wire anemometer is called "**". When the fluid flows through the wire in the vertical direction, it will take away part of the heat of the wire, causing the temperature of the wire to drop. According to the theory of forced convection heat exchange, it can be deduced that there is a relationship between the maximum dissipated heat Q and the velocity v of the fluid. The standard anti-probe consists of two brackets tensioned with a short, thin wire, as shown in Figure 2.1. Metal wires are usually made of metals with high melting points and good ductility such as platinum, rhodium, and tungsten. The commonly used wire has a diameter of 5 μm and a length of 2 mm; the smallest probe is only 1 μm in diameter and 0.2 mm in length. According to different uses, the probe is also made into double wire, three wire, oblique wire, V-shaped, X-shaped and so on. In order to increase the strength, sometimes a metal film is used to replace the metal wire, and a thin metal film is usually sprayed on a thermally insulating substrate, which is called a thermal film probe, as shown in Figure 2.2. **Probes must be calibrated before use. Static calibration is carried out in a special standard wind tunnel, measuring the relationship between flow rate and output voltage and drawing a standard curve; dynamic calibration is carried out in a known pulsating flow field, or adding in the heating circuit of the anemometer. The last pulsating electrical signal is used to verify the frequency response of the anemometer. If the frequency response is not good, the corresponding compensation circuit can be used to improve it.
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 measurements from 0 to 5m/s; the rotor probe of the anemometer is ideal for measuring flow velocity from 5 to 40m/s; and the use of a pitot tube can be obtained in the high speed range* best results. An additional criterion for the correct selection of an anemometer's flow probe is temperature, usually the temperature of the thermal sensor of an anemometer is about +-70C. The rotor probe of the special anemometer can reach 350C. Pitot tubes are used above +350C.
Anemometer Calibration Maintenance
The anemometer is a kind of measuring instrument for safety protection and environmental monitoring. In addition to the corresponding calibration report required for factory sales, it is also required to go to the National Air-Conditioning Equipment Quality Supervision and Inspection Center or China Academy of Building Research Building Energy and Energy and Energy and Environmental Engineering every year in accordance with the requirements of JJG (Construction) 0001-1992 "Thermal Ball Anemometer Verification Regulations". The environmental testing center performs regular calibration and adjusts all aspects of the instrument to obtain the best working condition according to the legal calibration certificate issued by it.
In addition to maintaining the accuracy of daily data, pay attention to the following points in daily maintenance and use:
1. It is forbidden to use the anemometer in a flammable gas environment.
2. It is forbidden to put the anemometer probe in flammable gas. Otherwise, fire or explosion may result.
3. Please use the anemometer correctly according to the requirements of the instruction manual. Improper use may result in electric shock, fire and sensor damage.
4. During use, if the anemometer emits abnormal odor, sound or smoke, or liquid flows into the anemometer, please shut down immediately and remove the battery. Otherwise, there is a risk of electric shock, fire, and damage to the anemometer.
5. Do not expose the probe and the anemometer [2] body to rain. Otherwise, there may be a risk of electric shock, fire, and personal injury.
6. Do not touch the sensor part inside the probe.
7. When the anemometer is not used for a long time, please remove the internal battery. Otherwise, the battery may leak, resulting in damage to the anemometer.
8. Do not place the anemometer in a place with high temperature, high humidity, dust and direct sunlight. Otherwise, damage to the internal components or deterioration of the anemometer performance will result.
9. Do not wipe the anemometer with volatile liquid. Otherwise, the anemometer housing may be deformed and discolored. When there are stains on the surface of the anemometer, it can be wiped with a soft fabric and neutral detergent.
10. Do not drop or stress the anemometer. Otherwise, malfunction or damage of the anemometer will result.
11. Do not touch the sensor part of the probe when the anemometer is charged. Otherwise, the measurement result will be affected or the internal circuit of the anemometer will be damaged.
Anemometer use
1. Measure the speed and direction of the average flow.
2. Measure the pulsating speed of the incoming flow and its frequency spectrum.
3. Measure the Reynolds stress in turbulent flow and the velocity dependence and time dependence of two points.
4. Measure the wall shear stress (usually with a hot film probe placed flush with the wall, the principle is similar to that of precision speed measurement).
5. Measure the fluid temperature (pre-measure the change curve of the probe resistance with the fluid temperature, and then determine the temperature according to the measured probe resistance.
In addition to this, many professional uses have been developed.
How to use the anemometer
1. Before use, observe whether the pointer of the meter points to the zero point. If there is any deviation, adjust the mechanical adjustment screw of the meter lightly to make the pointer return to the zero point; 2. Put the calibration switch in the OFF position
3. Insert the plug of the measuring rod into the socket, place the measuring rod vertically upward, press the screw plug to seal the probe, set the "calibration switch" to the full scale position, and slowly adjust the "full scale adjustment" knob, so that the pointer of the meter points at full scale. degree position;
4. Set the "calibration switch" to "zero position", and slowly adjust the two knobs of "coarse adjustment" and "fine adjustment", so that the pointer of the meter points to the zero position
5. After the above steps, gently pull the screw plug to expose the measuring rod probe (the length can be selected as needed), and make the red dot on the probe face the wind direction. measured wind speed;
6. After measuring for a few minutes (about 10 minutes), the above steps 3 and 4 must be repeated once to standardize the current in the meter
7. After the test, the "calibration switch" should be placed in the off position.
An anemometer is a speed measuring instrument that converts the flow velocity signal into an electrical signal, and can also measure the temperature or density of the fluid. The principle is that a thin metal wire (called a ball) that is heated by electricity is placed in the air flow, and the heat dissipation in the air flow is related to the flow rate, and the heat dissipation causes the temperature change to cause the resistance change, and the flow rate signal is converted into an electrical signal.
It has two working modes: ①Constant flow. The current passing through the tube remains unchanged, and when the temperature changes, the resistance of the tube changes, so the voltage at both ends changes, so the flow rate is measured;
② Constant temperature type. The maximum temperature remains unchanged, such as 150 °C, and the flow rate can be measured according to the required applied current. The constant temperature type is more widely used than the constant flow type. The maximum length is generally in the range of 0.5 to 2 mm, the diameter is in the range of 1 to 10 microns, and the material is platinum, tungsten or platinum-rhodium alloy.
If a very thin (thickness less than 0.1 micron) metal film is used to replace the metal wire, it is a hot film anemometer.
**In addition to the ordinary single-wire type, it can also be a combined two-wire type or three-wire type to measure the velocity components in all directions. The electrical signal output from the sensor is amplified, compensated and digitized and then input to the computer, which can improve the measurement accuracy, automatically complete the data post-processing process, and expand the speed measurement functions, such as simultaneous completion of instantaneous value and time average value, combined speed and sub-speed, turbulent flow Measurement of degrees and other turbulence parameters.
**Compared with the pitot tube, the anemometer has the advantages of small probe volume and little interference to the flow field; fast response, can measure unsteady flow velocity; can measure very low speed (such as as low as 0.3 m/s).
