The working principle of various acceleration sensors

The working principle of various acceleration sensors An acceleration sensor is a test instrument used to convert the physical signal of acceleration into an electrical signal that is easy to measure. It is a common testing instrument for shock and vibration measurement in many fields such as industry and national defense.

So how does the acceleration sensor work?

The sensing element converts the acceleration signal of the measuring point into a corresponding electric signal and enters the preamplifier circuit. The electric signal passes the signal conditioning circuit to improve the signal to noise ratio of the signal, and then performs analogto-digital conversion to obtain a digital signal. Finally, the digital signal will enter the computer, and the computer will store and display the data.

When the sensing element moves with acceleration a, the mass is subjected to an inertial force opposite to the acceleration direction, and a deformation a proportional to the acceleration occurs, so that the cantilever beam also generates stress and strain. This deformation is felt by the diffusion resistance attached to the cantilever beam. According to the piezoresistive effect of silicon, the resistance of the diffusion resistance changes in proportion to what it should become.

Using this resistance as an arm of the bridge, the acceleration can be measured by the change in the output voltage of the bridge.

The principle of a linear accelerometer is the principle of inertia, which is the balance of forces. A (acceleration) = F (inertial force) / M (mass). We only need to measure F. How to measure F? Just use electromagnetic force to balance this force. Then we can get the relationship between F and current. It is only necessary to use experiments to calibrate this scale factor. Of course, the intermediate signal transmission, amplification, and filtering are the matter of the circuit.

Most acceleration sensors work on the principle of the piezoelectric effect. The so-called

piezoelectric effect is "For an external force applied to a crystal of a heteropolar crystal that does not have a symmetrical center, in addition to deforming the crystal, it will also change the crystal's polarization state, an electric field is established inside the crystal. This phenomenon of polarizing the medium due to mechanical force is called the positive piezoelectric effect. " An acceleration sensor uses the characteristic of crystal deformation caused by acceleration in its interior. Because this deformation generates a voltage, as long as the relationship between the generated voltage and the applied acceleration is calculated, the acceleration can be converted into a voltage output. Of course, there are many other ways to make acceleration sensors, such as piezoresistive technology, capacitive effect, thermal bubble effect, light effect. However, the most basic principle is that a certain medium is deformed due to acceleration, and the amount deformation will be measured and converted into a voltage output by using the relevant circuit.

Piezoresistive acceleration sensors have developed fastest due to their wide application in the automotive industry. As safety is increasingly becoming a selling point for automakers, such additional systems are also increasing.

Piezo technology is mainly used in industry to prevent machine failure. Using this sensor can detect potential failures of the machine to achieve self-protection and avoid accidental injury to workers. This sensor has the repeatability and stability sought by users. But in many new application fields, many users have no awareness of using such sensors. Vendors who venture into this undeveloped market will face a lot of trouble, because end users don't know much about the problems and solutions caused by using such sensors. If these problems can be solved, it will promote the rapid development of piezoelectric sensors.

When using an acceleration sensor, sometimes the output signal is distorted when measuring in low-frequency occasions. Multiple measurement judgment methods can not find the cause of the fault. After analysis and summary, the main factors that cause the distortion of the measurement result are: poor low-frequency response , the low-frequency signal-to-noise ratio of the system is poor, and the influence of the external environment on the measurement signal.

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