What is a piezoelectric sensor? What is a wind cup wind speed sensor?
1. Introduction to sensors
A sensor (English name: transducer/sensor) is a detection device that can sense the measured information and convert the sensed information into electrical signals or other required forms of information output according to certain rules to meet the requirements of information transmission, processing, storage, display, recording and control. Due to the many types of sensors, in this article, the editor only introduces the piezoelectric sensor and the wind cup wind speed sensor.
2. Piezoelectric sensor
First of all, let's take a look at some relevant knowledge of piezoelectric sensors. Pressure sensors are the most commonly used sensors in industrial practice, and the pressure sensors we usually use are mainly manufactured using the piezoelectric effect. Such sensors are also called piezoelectric sensors.
The piezoelectric materials mainly used in piezoelectric sensors include quartz, potassium sodium tartrate, and ammonium dihydrogen phosphate. Among them, quartz (silicon dioxide) is a natural crystal, and the piezoelectric effect is found in this crystal. Within a certain temperature range, the piezoelectric property always exists, but when the temperature exceeds this range, the piezoelectric property disappears completely (this high temperature is the so-called "Curie point"). Since the electric field changes slightly with the change of stress (that is, the piezoelectric coefficient is relatively low), quartz is gradually replaced by other piezoelectric crystals. Potassium sodium tartrate has great piezoelectric sensitivity and piezoelectric coefficient, but it can only be applied in an environment with relatively low room temperature and humidity. Ammonium dihydrogen phosphate is an artificial crystal, which can withstand high temperature and relatively high humidity, so it has been widely used.
3. Wind cup wind speed sensor
After understanding the relevant knowledge of the piezoelectric sensor, let's take a look at some content of the wind cup custom sensor.
The wind cup wind speed sensor is a very common wind speed sensor, which was first invented by Robinson in England. In China, the wind cup wind speed sensor has been widely used. The sensing part of the wind cup wind speed sensor is composed of three or four conical or hemispherical empty cups. The hollow cup shell is fixed on the three-pointed star-shaped brackets at 120° or on the cross-shaped brackets at 90° with each other. The concave surfaces of the cups are arranged in one direction, and the entire cross-arm frame is fixed on a vertical rotation axis.
When the wind blows from the left, the wind cup 1 is parallel to the wind direction, and the component force of the pressure of the wind on the wind cup 1 in the direction most perpendicular to the wind cup axis is approximately zero. Wind cups 2 and 3 intersect with the wind direction at an angle of 60 degrees. For wind cup 2, its concave surface faces the wind and bears the largest wind pressure; wind cup 3 has a convex surface facing the wind, and the wind around it makes the wind pressure smaller than that of wind cup 2. Due to the pressure difference between wind cup 2 and wind cup 3 in the direction perpendicular to the axis of the wind cup, the wind cup begins to rotate clockwise.
After the wind cup starts to rotate, because the cup 2 rotates along the wind direction, the pressure of the wind decreases relatively, while the cup 3 rotates against the wind at the same speed, the wind pressure increases relatively, and the wind pressure difference keeps decreasing. After a period of time (constant wind speed), when the partial pressure difference acting on the three wind cups is zero, the wind cups will rotate at a uniform speed. In this way, the wind speed can be determined according to the speed of the wind cup (revolutions per second).
When the wind cup rotates, it drives the coaxial multi-tooth cutting disc or magnetic rod to rotate, and obtains a pulse signal proportional to the speed of the wind cup through the circuit. The pulse signal is counted by the counter, and the actual wind speed value can be obtained after conversion. At present, the new rotor anemometer uses three cups, and the performance of the conical cup is better than that of the hemispherical one. When the wind speed increases, the rotor can quickly increase the speed to match the airflow speed. When the wind speed decreases, due to the influence of inertia, the wind speed will not drop immediately. Rotary anemometers usually indicate too high wind speed in gusts and have an outsized effect (produces an average error of about 10%).
