What is an Accelerometer Sensor?
An accelerometer sensor is a sensor that can measure acceleration. It is usually composed of masses, dampers, elastic components, sensitive components, and adaptive circuits. In the process of acceleration, the sensor obtains the acceleration value by using Newton's second law, measuring the inertial force on the mass block. According to the different sensitive components of the sensor, common accelerometer sensors include capacitive, inductive, strain gauge, piezoresistive, piezoelectric and so on.
I. Working Principle of Accelerometer Sensor
The principle of the accelerometer sensor is Newton's second law, the law of acceleration, which is the balance of force, A (acceleration) = F (inertial force) / M (mass). We only need to measure F. How? Just use electromagnetic force to balance this force. The relationship between F and current can be obtained. Only need to use experiments to calibrate this proportional coefficient. Of course, the signal transmission, amplification, and filtering in the middle are the matter of the circuit.
Most accelerometer sensors work according to the principle of the piezoelectric effect.
The so-called piezoelectric effect is "for a heteropolar crystal without a center of symmetry, the external force applied to the crystal will not only deform the crystal but also change the polarization state of the crystal and establish an electric field inside the crystal. This is due to mechanical force. The phenomenon of polarizing the medium is called the positive piezoelectric effect.
The general accelerometer sensor uses the characteristics of crystal deformation caused by acceleration. Since this deformation generates 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 methods to make accelerometer sensors, such as piezoresistive technology, capacitance effect, thermal bubble effect, light effect, but the most basic principle is that a certain medium is deformed due to acceleration, and the deformation is measured and used. The related circuit is converted into a voltage output. Each technology has its own opportunities and problems.
Piezoelectric technology is mainly used in industry to prevent machine failures. Using this sensor can detect potential machine failures to achieve self-protection and avoid accidental injury to workers. This sensor is sought after by users, especially users in the quality industry. The reproducibility, stability, and self-generating nature.
When using an accelerometer sensor, sometimes the output signal is distorted when measuring in low-frequency occasions, and the cause of the failure can not be found for a time using multiple measurement judgment methods. After analysis and summary, the main factor that causes the measurement result to be distorted is: poor low-frequency response of the system, The low-frequency signal-to-noise ratio of the system is poor, and the influence of the external environment on the measurement signal. Therefore, as long as there is the distortion of the low-frequency measurement signal of the accelerometer sensor, compare the above three points to see which factor is causing it, and solve it in a targeted manner.
II. Types of Accelerometer Sensor
1. Piezoelectric Accelerometer Sensor
A piezoelectric accelerometer sensor is also called a piezoelectric accelerometer. It is also an inertial sensor. The principle of the piezoelectric accelerometer sensor is to use the piezoelectric effect of piezoelectric ceramic or quartz crystal. When the accelerometer is vibrated, the force applied by the mass to the piezoelectric element also changes. When the measured vibration frequency is much lower than the natural frequency of the accelerometer, the force change is proportional to the measured acceleration.
2. Piezoresistive Accelerometer Sensor
Based on the world's leading MEMS silicon micromachining technology, the piezoresistive accelerometer sensor has the characteristics of small size, low power consumption, etc., easy to integrate with various analog and digital circuits, and is widely used in automobile crash experiments, test instruments, equipment vibration monitoring, etc. field.
3. Capacitive Accelerometer Sensor
The capacitive accelerometer sensor is a capacitive sensor with a variable pole pitch based on the principle of capacitance. A capacitive accelerometer sensor/capacitive accelerometer is a more general accelerometer sensor. There is no substitute in some areas, such as airbags, mobile phones, and mobile devices. The capacitive accelerometer/capacitive accelerometer adopts the micro-electromechanical system (MEMS) process, which becomes economical in mass production, thus ensuring a lower cost.
4. Servo Accelerometer Sensor
The servo accelerometer sensor is a closed-loop test system, which has the characteristics of good dynamic performance, large dynamic range, and good linearity. Its working principle, the vibration system of the sensor is composed of the "mk" system, which is the same as the general accelerometer, but an electromagnetic coil is connected to the mass m. When there is acceleration input on the base, the mass deviates from the equilibrium position. The displacement sensor detects it and is amplified by the servo amplifier and converted into a current output. The current flows through the electromagnetic coil and generates an electromagnetic restoring force in the magnetic field of the permanent magnet, trying to keep the mass in the original balance position in the instrument housing, so The servo accelerometer sensor works in a closed-loop state.
Due to the feedback function, the anti-interference ability is enhanced, the measurement accuracy is improved, and the measurement range is expanded. The servo acceleration measurement technology is widely used in inertial navigation and inertial guidance systems and is also used in high-precision vibration measurement and calibration.
III. Applications of Accelerometer Sensor
1. Accelerometer Sensor used in geophone design
The geophone is a special sensor used for geological prospecting and engineering measurement. It is a sensor that converts ground vibration into electrical signals. It can convert ground vibrations caused by seismic waves into electrical signals, which are converted into binary data through analog/digital converters. Carry out data organization, storage, and calculation processing. An accelerometer sensor is an electronic device that can measure acceleration and is typically used in mobile phones, notebook computers, pedometers, and motion detection.
2. Accelerometer Sensor used in car accident alarm
In the modern era of the rapid development of the automobile industry, automobiles have become one of the main means of transportation for people to travel, but the number of casualties due to traffic accidents is also very large. In modern informatization, using high technology to save human lives will be one of the themes of major research. Acceleration-based car accident alarm systems are based on this design concept. I believe that the promotion of this system will give the automobile industry a boost. Come for more security.
3. Accelerometer Sensor used to monitor galloping of high-voltage wires
Two main technical solutions, video image acquisition, and motion acceleration measurement are mostly used for wire galloping monitoring. The former not only has high requirements on the reliability and stability of video equipment under the conditions of high temperature, high humidity, severe cold, dense fog, sand, and dust in the field but also the effect of the captured video images will be affected. In actual use, It can only be used as an auxiliary monitoring method and cannot quantitatively analyze the wire movement parameters; while the accelerometer sensor is used to monitor the wire galloping, although it can quantitatively analyze the up and down vibration and left and right swings of a certain point of the transmission wire, but it can only measure the amplitude and the linear movement of the wire. Frequency, and for complex circular motion, it cannot be accurately measured. Therefore, we must accelerate the development of accelerometer sensors to adapt to applications in such environments.
4. Accelerometer Sensor used in car safety
accelerometer sensors are mainly used in safety performance aspects such as automobile airbags, anti-lock braking systems, and traction control systems.
In safety applications, the fast response of the accelerometer is very important. It is determined quickly when the airbag should pop out, so the accelerometer must react instantly. The response time of the device can be shortened by adopting a sensor design that can quickly reach a steady state instead of vibrating. Among them, piezoresistive accelerometer sensors are developing fastest due to their wide application in the automotive industry.
5. Accelerometer Sensor used to compensate the dead angles in GPS Navigation System
GPS system finally determines the position of an object by receiving signals from three satellites distributed at 120 degrees. On some special occasions and landforms, such as tunnels, tall buildings, and jungle areas, the GPS signal will become weak or even completely lost. This is the so-called blind spot. And by installing the accelerometer sensor and the inertial navigation that we have used before, the dead zone of the system can be measured. Once the accelerometer sensor is integrated, it becomes the amount of speed change per unit time, so as to measure the movement of the object in the dead zone.
IV. Installation of Accelerometer Sensor
The natural frequency of the accelerometer sensor is determined by the degree of coupling of the adhesive. Choosing the correct adhesive will be a very important step. Some important issues that must be considered are the weight of the accelerometer, the frequency, and bandwidth of the test, the amplitude, and the temperature of the test. Also consider some problems that may arise during the test: the limitation of the sine curve and the random vibration that appears during the test. Usually, engineers and technicians will choose the appropriate adhesive to bond the accelerometer sensor according to the different needs of the test.
Adhesives used in the adhesion and installation of accelerometer sensors generally include cyanoacrylate, magnets, double-sided tape, paraffin wax, thermal adhesives, etc. The key to the problem lies in how to effectively use these adhesives. In the bonding process of the accelerometer sensor, the amount of adhesive used plays a key role in whether the accelerometer sensor can achieve a good frequency response. Bonding the accelerometer sensor with the least amount of adhesive possible on a small film will make the accelerometer sensor's frequency response and transmission the best.
Before installing the sensor, use a hydrocarbon solution to clean the surface to be installed. When installing the sensor, usually use cyanoacrylate, magnet, double-sided tape, and paraffin, and apply it evenly to the adhesive accelerometer. The surface to be adhered should not be too thick or too thin. A proper thickness will have a good bonding effect. There are many precautions for the use of thermal adhesives. The most important thing is to pay attention to the setting time of thermal adhesives during installation.
Of course, when we use adhesive installation, we need to pay attention to that it is best not to use adhesive when it is close to the maximum temperature limit. It should be used after a period of time, otherwise, the adhesive itself will be damaged and the tensile strength of the adhesive will decrease. In any case, when we want to install the accelerometer sensor by bonding, all the limiting factors must be taken into consideration. Similarly, the installation of the above accelerometer sensor is only for most cases, and the most suitable sensor installation method is needed to measure acceleration on some special equipment.
