Acceleration is the rate at which the velocity of an object changes relative to time (it is the derivative of the velocity vector in the form of a function of time a = dv / dt). It is the Net result of any and all forces acting on an object.
- Overall, we will have two basic measurement definitions for acceleration:
- Acceleration due to vibration of the tested object
- Acceleration is the result of a change in the velocity of an object, as a vehicle (car, airplane)
There is a big difference in the implementation of the two purposes of measurement
It is also very common when you also use accelerometer measurement to measure velocity and displacement.
The principles of integrals are different. When integrating the motion of a vehicle, static acceleration will lead to a change in velocity (and displacement). We need to know that when the acceleration measurement has an error, the speed and distance results will also be skewed. These deviations depend on the quality of the accelerometer sensor. For example, with high-quality sensors, submarines can run for weeks and still count
Acceleration measurements are divided into the following types:
Oscillation- an object is said to oscillate when it makes an oscillatory motion towards an equilibrium position. Vibrations are found in shipping and aerospace environments or simulated by a shaker system.
Shock- a sudden transient stimulus of a structure is generally a resonant stimulus of the structure.
Motion- movement is a slow-motion event such as the movement of a robotic arm or suspension measurement
WHAT IS AN ACCELEROMETER SENSOR?
Accelerometer sensor, also known as accelerometer, is a device that generates electrical signals (voltage, charge, ...) corresponding to the acceleration undergone. There are several techniques for converting acceleration into electrical signals. We'll give an overview of most of those cases and then briefly look at a few other sections.
BASIC PRINCIPLES OF ACCELEROMETER SENSORS:
Most sensors that measure acceleration are based on Hooke and Newton's first and second laws.
Hooke's law states that the force F required to stretch or compress a spring is proportional to the change of distance x by a factor k (a constant characteristic coefficient of the spring). The equation is F = k * x.
Newton's I law states that an object is stationary or constantly moving at a constant velocity unless acted upon by another force. His second law states that the force F produced by a moving body is equal to its mass m multiplied by the acceleration a, for the equation F = m * a.
The most general way, to take advantage of these laws, is to hang a mass onto a spring from a frame that surrounds the mass (as shown in the figure below). When the frame is shaken, it begins to move, dragging along the lunging mass
TYPES OF ACCELEROMETER SENSORS:
Accelerometers are designed using different sensing principles. Here's a quick overview and summary for you to better understand them:
- Piezoelectricity- Works based on the ability to change the potential of piezoelectric materials when under stress. They offer unique advantages, compared to other accelerometer sensors. They have a wide dynamic range, excellent linearity, wide frequency range (from a few Hz to 30 kHz), are the only type of accelerometer sensors capable of measuring alternating acceleration, but not capable of measuring DC response. Since they have no moving parts, durability is increased. And unlike other sensors, they do not require lateral power
- Potential – The wiper arm of the potentiometer is attached to the spring mass, resulting in a change or resistance as the spring moves. The natural frequencies of these devices are typically less than 30 Hz, limiting them to low-frequency vibration measurements. Application of frequency measurements from 0 Hz (DC feedback)
Hall effect- A magnet is attached to a spring, when a force is applied, it moves causing a change in the electric field of the Hall element.
Magneto resistive- Works similarly to the effect sensor
THE ACCELEROMETER SENSOR WORKS ON THE PRINCIPLE OF PIEZOELECTRICITY
Piezoelectricity is the ability of some materials (especially crystals and some pottery–known piezoelectric materials such as quartz, tourmaline, ceramic (PTZ), GAPO4,..) to generate an electric potential in response to mechanical stress. This may be in the form of the separation of charge through the crystal lattice. If the material is not short-circuited, the charge applied creates a voltage on the material. Materials that create an electric charge when a force is applied to them exhibit the so-called piezoelectric effect.
Required piezoelectric acceleration measurement sensor
IEPE accelerometer sensor:
All sensors that measure acceleration in this voltage mode are powered by a regulated DC voltage and a constant sensor excitation current of 2 to 20 mA on a simple two-wire diagram. The built-in electronics converts the high impedance charge signal generated by the piezoelectric material into a usable low impedance voltage signal right inside the probe. Since the output has low impedance, the signal can be transmitted over long cable distances and used in dirty environments or medium environments.
Charge accelerometer sensor:
In contrast to IEPE, charge-type sensors do not need external excitation voltage, the sensing elements will output 1 charge when affected by force, these charges have a high impedance so the charge signal is very sensitive to interference from the surrounding environment and some important precautions need to be taken to have the The measurement is suitable, especially the charge signal in the sensor can only be transmitted over short distances and requires the cable to have good resistance to interference. Outgoing pressure materials
IEPE vs Charge sensor comparison:
STATIC ACCELEROMETER SENSOR- MEMS SENSOR:
Both charge sensors and IEPE have a common limitation: they cannot measure static acceleration. They usually start measuring from 0.3 Hz to 10 Hz, depending on the sensor. For static or very low frequency measurements, the user needs to use a different type of sensor. A very popular type is the MEMS sensor. They have excellent sensitivity and the transmission mechanism is not sensitive to temperature.
A typical MEMS accelerometer consists of a movable proof mass of socks
