IoT Sensors - Acceleration Sensors

summarize

accelerationstransducersThere are many uses in industry and consumption; high-sensitivity accelerometers are used in inertial navigation systems for aircraft and missiles; vibrations in rotating machines are monitored by accelerometers, and they are used in tablets and digital cameras so that the image on the screen is always displayed upright; in drones, accelerometers help to stabilize flight. When two or more accelerometers are coordinated with each other, they can measure differences in proper acceleration, especially gravity, because of their separation in space : the gradient of the gravitational field, uniaxial and multiaxial accelerometers can detect the magnitude and direction of proper acceleration as a vectorial quantity and can be used for detecting direction (because of changes in the direction of the weight), coordinated acceleration, vibrations, shocks, and in resistive media Decrease (increase from zero for changes in proper acceleration).

The principle is Newton's second law, the law of acceleration, which is the balance of forces, A (acceleration) = F (inertial force) / M (mass); some medium is deformed by acceleration and the deformation is measured and used, and the associated circuitry is converted to a voltage output.

Micromechanical microelectromechanical systems (MEMS) accelerometers are increasingly found in portable electronic devices and video game controllers to detect changes in the position of these devices, which are already integrated in most of the smartphones we use.

Sensor Classification

piezoelectricity (physics)

The principle of piezoelectric sensors utilizes the piezoelectric effect of piezoelectric ceramics or quartz crystals. When the accelerometer vibrates, the force applied by the mass to the piezoelectric element changes. When the measured vibration frequency is much lower than the intrinsic frequency of the accelerometer, the change in force is proportional to the measured acceleration.

(a) shows that in the absence of mechanical stress, the centers of the negative and positive charges of the molecule coincide, which means that the molecule is electrically neutral. (b) shows that the application of a mechanical force deforms the structure and separates the centers of the positive and negative charges of the molecule, thus creating many small dipoles in the material. Some fixed charges appear on the surface of the piezoelectric material. The amount of charge generated is proportional to the applied force

piezoresistive

MEMS silicon micromachining technology, piezoresistive accelerometer sensors with small size, low power consumption and other characteristics, easy to integrate with a variety of analog and digital circuits, widely used in automotive collision experiments, test instruments, equipment vibration monitoring and other fields

The piezoresistive effect is the change in semiconductor resistivity when mechanical strain is applied. In contrast to the piezoelectric effect, the piezoresistive effect causes only a change in resistance, not a change in potential

capacitors

Capacitive accelerometer sensors are capacitive sensors with variable pole pitch based on the capacitance principle. Capacitive accelerometer sensors/capacitive accelerometers are more generalized accelerometer sensors. They are irreplaceable in certain areas such as airbags, cell phones and mobile devices. Capacitive accelerometers/capacitive accelerometers utilize a microelectromechanical systems (MEMS) process that becomes economical in mass production, thus ensuring low cost .

In automotive applications, accelerometers are used to activate airbag systems. Cameras use accelerometers for active image stabilization, and computer hard drives rely on accelerometers to detect external shocks that can damage the device's read/write heads.

Hall's class (astronomy)

The vibration system of the sensor consists of the "mk" system, which is the same as a normal accelerometer, but with a solenoid coil attached to the mass m. This solenoid coil is used for the vibration of the sensor. When there is an acceleration input on the base, the mass deviates from its equilibrium position. It is detected by a displacement sensor, amplified by a servo amplifier and converted to a current output. The current flows through the electromagnetic coil and generates an electromagnetic restoring force in the magnetic field of the permanent magnet, which tries to keep the mass in its original equilibrium position in the instrument housing, so the servo sensor operates in a closed loop.

Servo-based accelerometers are closed-loop devices that are referenced to gravity, ensuring excellent accuracy, long-term stability and zero drift over time. They can be used in a variety of industrial and military applications that require high accuracy for ruggedized installations. The displacement detector senses motion and a current is fed to the coil to return the pendulum mass to its original position. This current will be proportional to the acceleration, which is converted to an output voltage.

thermal conduction

Heat transfer accelerometers consist of a single heat source centered on a substrate and suspended from a cavity. They include equally spaced temperature resistors on all four sides of the heat source. They measure the internal change in heat due to acceleration. When the acceleration is zero, the thermal gradient will be symmetric. Otherwise, under acceleration, the thermal gradient becomes asymmetric due to convective heat transfer

Applications for accelerometer sensors

Used to compensate for GPS navigation systems

Although inertial navigation systems do not directly measure velocity, by keeping track of what the acceleration is and how long it lasts, the INS can easily calculate what the velocity is by multiplying the acceleration by the time. For example, if it sees an acceleration of 2.5 m/s² for 5 seconds and assumes an initial velocity of 0 m/s, the INS must now have a velocity of 12.5 m/s (2.5 m/s² × 5 s = 12.5 m/s). Distance can also be calculated. Finding using s = 0.5 × at², and assuming that the inertial navigation system sees acceleration on the x-axis, it can calculate that it has moved 31.25 meters forward (0.5 × 2.5 m/s² × 5 s² = 31.25 meters).

GPSThe system ultimately determines the location of an object by receiving signals from three satellites distributed at 120 degrees. In some special occasions and terrains, such as tunnels, tall buildings, and jungle areas, GPS signals can become weak or even completely lost. By installing an accelerometer sensor and inertial navigation, the dead zone of the system can be measured. Once the accelerometer sensor is integrated, it becomes the amount of velocity change per unit time, thus measuring the movement of the object in the blind zone.

For automotive safety

Accelerometer sensors allow for quick determination of when an airbag has popped, so the accelerometer must respond immediately. By using a sensor design that can quickly reach a steady state rather than vibrate, the response time of the device can be shortened, and piezoresistive accelerometer sensors are the fastest growing due to their widespread use in the automotive industry.

Accelerometers have been widely used in the field of automotive electronics, mainly used in body control, safety systems and navigation, typical applications such as automotive airbags (Airbag), ABS anti-lock braking system, electronic stability program (ESP), electronically controlled suspension systems.

The entire airbag control system consists of a vibration sensor (Satellite Sensor) on the outside of the vehicle, accelerometer sensors (G-Sensor) placed in the doors, roof, front and rear seats, an electronic controller, and the airbag. The electronic controller is usually a 16-bit or 32-bit MCU to which the Satellite Sensor sends a signal within a few microseconds when the body is hit, and the invention of airbags has saved millions of lives over the years.

Application in Car Accident Alarm

In the modern era of rapid development of automobile industry, automobile has become one of the main means of transportation for people to travel, but the number of casualties caused by traffic accidents is also very large. In modern information technology, using high technology to save human lives will be one of the main research themes, and the acceleration-based car accident alarm system is based on this design concept.

Seismograph Design

A geophone is a special sensor used for geological exploration and engineering measurements. It is a sensor that converts ground vibrations into electrical signals. It can convert ground vibration caused by seismic waves into electrical signals, which are converted into binary data by analog/digital converter. Data organization, storage and calculation processing are performed. An accelerometer sensor is an electronic device that measures acceleration and is commonly used in cell phones, laptops, pedometers and motion detection.

Other Applications

• For inertial navigation systems, highly sensitive accelerometers are used.
• Detection and monitoring of vibrations in rotating machinery.
• Displays the image in an upright position on the digital camera screen.
• For flight stabilization of drones.
• Accelerometers are used to sense direction, coordinate acceleration, vibration, and shock.
• Used to detect the location of devices in laptops and cell phones.
• High-frequency recordings of biaxial and triaxial acceleration in biological applications for distinguishing behavioral patterns in animals.
• Machinery health monitoring.
• Detection of faults in rotating machines.
• These are also used in building and structural monitoring to measure the motion and vibration of structures when subjected to dynamic loads.
• Measure the depth of CPR chest compressions.
• The navigation system utilizes accelerometer sensors to know the direction.
• Remote sensing equipment also uses accelerometers to monitor active volcanoes.

Sensor Manufacturers

• TE
• omniinstruments
• StrainSense Limited
• Colibrys
• Oxtx
• HBK Corporation
• Bently Nevada
• Endevco
• Meggitt PLC
• Vishay Micro-Measurements
• Vibro-meter
• DTS
• Sensorex
• Wilcoxon
• Benstone

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