The principle of linear accelerometer is the principle of inertia, that is, the balance of force, A (acceleration) =F (inertial force) /M (mass) we only need to measure F on it. How to measure F? Using electromagnetic force to balance the force can be. We can get the relationship between F and current. Just use the experiment to calibrate the scale factor. Of course, the middle of the signal transmission, amplification, filtering is the circuit.
Modern science and technology require acceleration sensor cheap, superior performance, easy to mass production. In the fields of military industry, space system and scientific measurement, it is necessary to use the acceleration sensor with small volume, light weight and stable performance. It is difficult to fully meet the requirements of the acceleration sensor manufactured by traditional machining methods. So the application of the new micro machining technology to produce micro acceleration sensor came into being. The sensor has the advantages of small size, light weight, low power consumption, quick start, low cost, high reliability and easy realization of digitization and intelligence. Moreover, due to the micro mechanical structure is accurate, reproducible, easy to integrate, suitable for mass production, its performance to price ratio is very high. It can be predicted that in the near future, it will be dominant in the accelerometer market.
The micro acceleration sensor has piezoresistive, piezoelectric, capacitive and other forms.
Piezoelectric sensor is based on the principle of spring mass system. Sensitive core quality by generating a vibration acceleration effect is proportional to the acceleration force of piezoelectric materials by the stress along the surface of the formation of the charge signal is proportional to the force. The piezoelectric acceleration sensor with large dynamic range, wide frequency range, durable, small interference and piezoelectric material stress generated from the charge signal does not need any external power supply etc, is one of the most widely used vibration measurement sensor. Although the structure of the piezoelectric acceleration sensor is simple, the commercial use of history is very long, but because of the performance index and the properties of the material, design and processing technology is closely related to the actual performance parameters of similar sensors so in the market as well as its stability and consistency of the difference is very big. Compared with the resistance and capacitance, the biggest disadvantage is that the piezoelectric acceleration sensor can not measure the signal of zero frequency.
The structure of the piezoelectric acceleration sensor is shown in fig.. 1 pieces of metal sheets are sandwiched between a piezoelectric wafer (a quartz crystal or a piezoelectric ceramic) on the surface of the two pieces of silver, and a lead wire is led out of the output signal. 1 mass blocks are placed on the piezoelectric wafer, and a pre compression load is applied to the piezoelectric element with a hard spring. The magnitude of static preload should be much larger than the maximum dynamic stress of the sensor in the vibration and impact tests. So, when the sensor moves upward, the inertial force mass produced by the piezoelectric element on the compressive stress increased; on the other hand, when the sensor moves downward, the piezoelectric element stress decrease, and thus output acceleration into electric signal in direct proportion.
The whole component of the sensor is arranged on a base seat and is sealed by a metal shell. In order to isolate any strain of the specimen to be transferred to the piezoelectric element, the size of the base is larger. The base of the sensor is rigidly connected with the test piece. When the vibration frequency of the test piece is far lower than the resonant frequency of the sensor, the output charge (or voltage) of the sensor is directly proportional to the acceleration of the test piece.
The sensitive core of the piezoresistive accelerometer is a resistance measuring bridge made of semiconductor material. With the development of modern micro machining technology, the design of piezoresistive sensitive core has great flexibility to suit different requirements. In the sensitivity and range, from the low sensitivity to the impact of a wide range of measurement, to the high sensitivity of the low frequency measurement of the piezoresistive accelerometer. At the same time pressure frequency range of piezoresistive accelerometer measurements are also available from the DC signal to have high stiffness, high frequency measurement frequency range to tens of khz. Miniaturization design is also a highlight of piezoresistive sensor. It is necessary to point out that despite the great flexibility of design and application of pressure sensitive core, but for a specific design of the piezoresistive core the use range is generally less than the piezoelectric sensor. Another disadvantage of piezoresistive accelerometer is that it is affected by temperature, so the practical sensor needs to compensate the temperature. In terms of price, the cost price of piezoresistive sensor used in large quantities has great market competitiveness, but the manufacturing cost of the sensitive core for special use is much higher than that of piezoelectric accelerometer.
The structural form of the capacitive accelerometer is generally based on the spring mass system. When the mass is affected by the acceleration motion, the gap between the mass block and the fixed electrode is changed so as to change the capacitance value. Capacitive accelerometer compared with other types of acceleration sensor has the characteristics of high sensitivity, zero frequency response and good environmental adaptability, especially under the influence of temperature is relatively small; but the shortcomings in the input and output signals are nonlinear, the range is limited, by the influence of capacitance of the cable, and the capacitance of the sensor itself is a high impedance signal the source, so the output signal of capacitance sensor circuit for subsequent through often need to improve. In practical applications, capacitive acceleration sensor is widely used in low frequency measurement, and its universality is not as good as the piezoelectric accelerometer, and the cost is much higher than the piezoelectric accelerometer.
Acceleration transfer
