静态和动态MEMS倾向仪的简介|电子设计

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What you’ll learn:

What are static and dynamic inclinometers?
Which one should you choose for your project?
Not sure you need one? We’ve included a range of applications where an inclinometer adds value.

在选择一个用于真实价值测量值时，倾斜计的精度和准确性是必不可少的标准。微电机电系统（MEMS）设备中的增益，偏移，噪声和横轴灵敏度是关键决定因素。

For many applications, the cost of a sensor often goes hand in hand with these key parameters. Because comprehensive calibration and trimming require additional time and equipment during manufacturing, higher-performance devices generally cost more.

Often used interchangeably, precision and accuracy are different(Fig. 1). Accuracy is the closeness of the device output to the true value. The closer the output is to the true value, the higher the accuracy.

Precision, on the other hand, is the closeness or grouping of the measurement points to each other. A wide spread of measurement data indicates low precision; a tight spread of measured points or grouping indicates a high precision. High-performance devices must provide both high accuracy and high precision data（图1C）.

Static Inclination Measurement

Static inclination is the effect of earth’s gravity (g = 9.81 m/sec² or 32.2 feet/sec²) on the sensor’s axes of interest. An accelerometer measures the projection of the acceleration due to gravity on the axes of the sensor. However, in a real-world scenario, an inclinometer also may measure external acceleration, noise, and offset of the device. The impact of these components on the measurement of gravity effects must be negligible to achieve an accurate tilt calculation. If these external events are significant, the measured data must be compensated accordingly.

基于MEMS的加速度计或倾斜计可用于测量相对于水平平面的物体的倾斜度。在所有三个轴上测量的力之和等于重力（1G）。一旦获得这些投影，就可以使用基本的三角方程来计算每个轴相对于每个轴的倾斜角度。旋转物体根据感应轴和水平面之间的倾斜角（α）的正弦会改变感应加速度的振幅。

The simplest tilt calculation is to use a single-axis inclinometer to measure the Earth’s gravity projected on the axis of interest.Figure 2使用单轴倾斜计显示倾斜度测量。

Figure 3说明了地球的引力,当一个组件two-axis inclinometer measures the tilt. A two-axis accelerometer eliminates the drawbacks of a single-axis device for tilt measurement by enabling almost linear sensitivity and high resolution not limited to small angles (around 0°). It also offers the possibility to measure over the full 360° range. However, two different scenarios must be considered.

A three-axis device offers all of the benefits. These include nearly constant tilt sensitivity, the possibility to measure over 360°, and the flexibility to mount the device on the PCB in any orientation that meets system-architecture requirements.

Dynamic Inclination Measurement

Dynamic inclination is the tilt and slope of an objects position when it experiences rotation, vibration, motion, and shock, in addition to earth’s gravity.

动态倾斜度的测量比静态倾斜度测量更为复杂。该解决方案必须包括一个加速度计以确定重力矢量和陀螺仪，以同时测量对象的旋转。

A MEMS-based dynamic inclinometer integrates both a three-axis gyroscope and a three-axis accelerometer for a real-time tilt measurement. In scenarios where accelerometer data is impacted by external acceleration interference, a three-axis gyroscope offers angular velocities around the three axes x, y, and z. This compensates for the interference. However, gyroscopes intrinsically suffer slight output data drift over time.

陀螺仪和加速度计的组合可确保可靠，准确的动态倾斜测量。通常，加速度计和陀螺仪的数据融合在一起，并通过基于扩展的卡尔曼过滤器的一组算法进行处理。这是传感器融合。⁶

Inclinometer Performance Requirements

Several key performance requirements are relevant when selecting an inclinometer. The device’s number of axes is the first important indicator to consider. Depending on the application and system requirements, a single-axis, two-axis or a three-axis device can be selected. The offset/bias and gain of the sensor and their drift over time and temperature are of great importance.

这些指标的值决定了需要校准传感器的频率。传感器的测量范围用于测量地球的重力和旋转是另一个重要规范。对于静态倾斜计，通常需要±1 g的全尺度，因为它需要地球的重力成分。

传感器的分辨率是另一个重要性能rmance metric. It depends on the noise, bandwidth, filtering, and ADC (analog-to-digital conversion) resolution of the device. Higher-noise sensors can require further calibration, depending on the accuracy requirement of the application.

The stability of the offset and sensitivity over temperature determine the sensor’s accuracy. Accuracy also depends on vibration rectification error (VRE). The rectification to dc of broadband ac vibrations can shift the offset of the inclinometer, leading to significant errors.

Operating temperature range and whether the interface is analog or digital also can be important in some applications. Other performance specs include offset/sensitivity calibration error, post solder drift, cross-axis sensitivity, and nonlinearity. These may be less relevant because they can be measured and addressed with post-assembly calibration at ambient temperature. This calibration is often required for a high-accuracy inclinometer.

倾斜计应用程序

MEMS inclinometers are used in many applications because of their high stability over time and temperature, cost-effectiveness, low power consumption, and small size. MEMS static inclinometers also are easy to integrate, and they deliver long-term reliability in addition to their technical and cost advantages.

倾斜仪用于监测结构健康，防止车辆滚动以及机器人技术和准确的天线和平台定位。

One application emerging in the last few years is structural health monitoring (SHM). Here, the goal is to identify potential problems before structure fail. This application is part of predictive monitoring for safety and cost benefits. Sensors in SHM collect data over long periods of time to provide information on the overall condition of the structure.

Vibration, inclination, temperature, pressure, strain, and force data are the major components of structural monitoring systems. Collected regularly at appropriate time intervals, the sensor data can indicate the state of system health.

动态斜率²are useful in applications that require time-dependent information on the slope position and tilt of an object by offering a six-degree-of-freedom solution. Dynamic inclinometers implement sensor data fusion from an accelerometer and a gyroscope. This helps them reliably measure the angle of an object in motion when subjected to spurious accelerations.

Another common use of dynamic inclinometers is to monitor multiple simultaneous movements in robotics. Self-driving cars are among the latest emerging applications. These require hundreds of sensors to reliably collect large amounts of data at very high rates to accurately determine the vehicle’s position in real-time.

Conclusion

The latest MEMS inclinometers offer high performance and accuracy, high stability over time and temperature, and low power consumption—while being very cost-competitive. They’re very small and power-efficient, which makes them an ideal choice for many applications.

A static inclinometer outputs the Earth’s gravity components to calculate static tilt angle and slope position. Thus, any external motion and acceleration impacts the static inclinometer’s accuracy. In contrast, dynamic inclinometers are suited to applications where there’s motion, rotation, vibration, and acceleration. With these capabilities, both types of inclinometers will find their way into a wide range of applications.