Description
Measuring the tilt angle of an object is a common application of the acceleration sensor. Although the test principle is very simple, there are still many problems encountered in the implementation process, such as the accuracy of the tilt angle and the environmental interference problem. This article will discuss the accuracy problem and give a simplified calculation.
Fundamental
Since the acceleration sensor is subjected to gravity when it is placed at rest, there is a gravitational acceleration of 1 g . Using this property, the tilt angle in the vertical plane can be calculated by measuring the component of the gravitational acceleration on the X/Y axis.
As shown, there are Ax=gsinα and Ay=gcosα . Then Ax / Ay = tanα , that is, α = arctan ( Ax / Ay ).
According to the above principle , the tilt angle on the plane of XY can be measured according to the 2- axis acceleration sensor .
However, in practical applications, it is difficult to ensure that the tilt only occurs in the XY plane. Therefore, the formula for calculating the inclination of the three-axis sensor can be extended as follows:
The above formula basically solves the dip angle calculation in the static environment. We consider a more complicated scene. To calculate the dip angle under the motion condition, we need to add another qualification condition, namely:
Hardware implementation
At present, the acceleration used in consumer products is mainly digital output ( I2C/SPI ), which can communicate with the MCU very simply and realize the measurement function. ST offers products in accordance with precision into LIS2DH12TR (12bit), LIS2HH12TR (16bit ), car rules acceleration AIS328DQTR (12bit).
The relationship between the accuracy of the tilt angle and the resolution of the acceleration value:
The 8bit ADC can be 3.4. Above accuracy
The 10bit ADC can be 0.8. Above accuracy
The 12bit ADC can be 0.2. Above accuracy
The 14bit ADC can get 0.05. Above accuracy
The 16bit ADC can be 0.0124. Above accuracy
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