使用Allegro角传感器的指南
使用Allegro角传感器的指南
B.y Simon Tima, Stéphane Réant, Loïc Messier, and Andreas Friedrich,
一种llegro MicroSystems, LLC
Introduction
不同行业的亚博尊贵会员许多应用，例如在工业自动化和汽车传感器和致动器中，需要监测旋转轴的角度在轴上或轴外布置。此应用笔记专门用于审查轴上的磁性应用。亚博尊贵会员
磁传感器集成电路（ICS）通常用于执行此任务。本文档提供了基于圆形垂直大厅（CVH）技术的角度传感器的指导，这是每个核心一种llegro angular position sensor在本文中提到。
任何角度测量系统的设计基于特定应用的需要，例如气隙，精度和温度范围，以及传感器的性质。本文档提供了磁体选择的介绍以及对确定这些系统的准确性的影响。
一种magnetic angle measurement system has two main sources of error:
- sensor IC related errors
- magnetic input related errors
图1: Angle Measurement Errors and Their Origins
Each Allegro sensor is tested and calibrated during production using a homogenous magnetic field. Intrinsic IC nonlinearity and temperature drift are therefore reduced to a minimum before the sensor is shipped to customers. Refer to product data sheets for temperature drift information.
When using a magnet in a design, the magnetic input will most likely not be homogenous, and the intensity of the field may not be constant over the rotational range. These are errors related to the magnetic input that cause measurement error in the system.
Field nonlinearity and field strength can contribute to the overall error of the system. Both depend on the mechanical position of the magnet relative to the sensing elements. In later sections of this document, nonlinearity will be described as accuracy error (refer to Accuracy Error Definition below).
机械尺寸的定义，X / Y感测
In a Cartesian coordinate system, the sensor is considered a reference, with its package surface parallel to the X/Y plane. The center of the CVH transducer area is defined as the origin (0,0,0). The magnet will rotate around the Z-axis.
Ideally, the magnet rotation axis will be perpendicular to the X/Y plane, and there will be no offset from the origin (0,0). In the following section, offset from the origin will be referred to as “misalignment”, in other words, misalignment in Figure 2 is zero.
图2.: Application Placement
The distance between the magnet and the sensor along the Z-axis is commonly known as air gap. Refer to Figure 6: Air Gap Definition for details.
Sensing Element Location
The magnetic field is not uniform over the entire face of a typical magnet. The location of the magnetically sensitive CVH transducer needs to be considered in the mechanical design of the application. The sensitive area of the CVH transducer is defined in the datasheet for every Allegro angle sensor IC.
The dual die device shown in Figure 4 contains two identical chips in a side by side arrangement. This allows redundancy with very compact package outlines.
图3.: CVH Transducer Placement in the TSSOP-14 Package
图4.: CVH Transducer Placement i the TSSOP-24 Dual Die Package
磁性选择
The choice of magnets is not limited simply to type of material and size; there are also some basic shapes that serve as a good starting point for any system design. Three magnets have been chosen as examples for the measurements in later sections of this document.
图5.: Size Comparison of the Three Magnets Selected
These magnet examples were selected to give basic guidelines. Magnets1图5中的A和B专为角度传感器而设计，可从德国的公司MagnetFabrik Bonn GmbH获得。
Magnet C is a simple, diametrically magnetized disc with compact dimensions. Table 1 lists some of the characteristics of the magnets. For specific questions on magnet materials and shapes, please contact a preferred magnet material supplier.
| Magnet | 一种 | B. | C |
|---|---|---|---|
| 直径 | 18 mm | 9 mm | 6 mm |
| Height | 2.5毫米 | 2.5毫米 | 4.mm |
| Material | Sprox 13/21 p | Neofer 48/60 | Neofer 25/60 |
| Composition | 硬铁氧体+ PA6 | NdFeB + PA11 | NdFeB + PA11 |
| 最大连续工作温度2 | 160ºC. | 14.0ºC | 14.0ºC |
| 温度剩余系数 | -0.19％/ k | -0.12％/ k | -0.12％/ k |
| 制造过程 | Injection Molding | Injection Molding | Injection Molding |
参数定义
一种ir Gap
Two different air gap definitions can be used when talking about magnetic field sensors: package air gap and crystal air gap.
图6：气隙定义
包装气隙
封装气隙被定义为传感器壳体顶部与磁体的最近面之间的距离。
Crystal Air Gap
Crystal air gap is defined as distance between the sensing element in the sensor housing and the nearest face of the magnet.
In this document, air gap is defined as the crystal air gap. The sensing elements are 0.36 mm below the top surface of the package. Refer to Figure 6.
角度错误定义
角度误差是由传感器装置测量的磁体的实际位置与磁体的位置之间的差异。通过读取传感器输出并将其与高分辨率编码器进行比较来完成此测量（参见图7）。
E = α传感器- α.Real
图7：角度误差和精度错误定义
准确性错误定义
在本文档中进一步下降，将角度误差显示为未对准的函数。为此目的，有必要引入全旋转的单个角度误差定义（参见图7）。一个完全旋转的“总结”角度误差定义为角度精度误差，并且根据以下公式计算：
一种ngular Accuracy Error = (Emax– E闵）/ 2
换句话说，它是从0到360度之间的完美直线的偏差的幅度。
一种verage Magnetic Field and Air Gap Dependency
系统设计的第一步是为应用气隙选择合适的磁铁。通常，气隙的范围为2至4mm。图8示出了作为图5所示磁体的气隙的函数的磁场。
B.y default, many Allegro angle sensors are trimmed to provide optimum performance at 300 Gauss (30 mT). However, unlike other angle sensors, Allegro sensors can be specifically trimmed for field strengths beyond 700 Gauss (70 mT). Please contact anAllegro代表for additional information regarding specific field strength trimming.
图8：关于三个磁体的气隙的磁体场
Figures 9 through 11 show the angular accuracy error of Allegro’sA1334IC when tested with the reference magnets. At each air gap, the magnet was rotated one full turn, and the angular accuracy error was calculated.
图9.: Magnet A, Angular Accuracy Error vs. Air Gap
图10：磁体B，角度精度误差与气隙
图11.: Magnet C, Angular Accuracy Error vs. Air Gap
表2总结了最佳空气隙。
| Magnet A | Magnet B | Magnet C | |
|---|---|---|---|
| 一种ir Gap | 4.mm | 3..5 mm | 2毫米 |
In all three cases (magnet A, B, C), the angular accuracy error is influenced by the air gap. The best results are achieved at calibration air gap, that is, the distance where the magnet field strength equals the calibration field strength (300 G). Note that scales in Figures 9 to 11 differ.
Tolerance to Misalignment
由于机械放置公差，CVH换能器不会总是在磁体的中心处完美地放置。要了解这种未对准如何影响测量角度的准确性，每个磁体都经过不同的未对准，相对于其直径。
The plots show the results of a multitude of measurements. The air gap was set to the calibration air gap (refer to Figures 9 through 11). Depending on its size, the magnet was misaligned by up to ±1.5 mm from the X/Y origin. At every point in the X/Y plane, the angular accuracy error was calculated for a full turn and displayed in colors. When comparing the plots, Figures 12 through 14, note that the scale differs.
图12.: Angular Accuracy Error of Magnet A at 4 mm Air Gap
图13：磁体B的角度精度误差为3.5 mm气隙
图14.: Angular Accuracy Error of Magnet C at 2 mm Air Gap
Summary of Measured Error
The plots provide answers to the following questions:
- What accuracy can be expected with a certain magnet and given mechanical placement tolerance?
- 什么磁铁应该用于给定准确性和机械耐受性？
- 机械公差是允许对于一个给定的magnet and accuracy?
| 一种ngle Accuracy | Magnet A | Magnet B | Magnet C |
|---|---|---|---|
| 0.5º | ±0.5 mm | ±0.25毫米 | ±0.1 mm |
| 1º | ±0.75毫米 | ±0.65 mm | ±0.5 mm |
To demonstrate the tolerance to misalignment at different air gaps, magnet B was mapped with a misalignment of ±1 mm on X and Y axis at 2 different air gaps. Figures 15 and 16 demonstrate that tolerance to misalignment changes only slightly with air gap.
图15：磁体B的角度精度误差为3.5 mm气隙
图16：磁体B的角度精度误差为4.5 mm气隙
Repeatability
The repeatability of the angle reading depends on the intensity of the magnetic field input. A high input field improves signal to noise ratio. Applying this to magnetic sensors means that the repeatability is best at close air gaps. Figure 17 shows the standard deviation of 100 angle readings for different magnets. Depending on the possibilities of averaging in the application, this error may be negligible.
图17：磁铁A，B和C与气隙的角度读数的标准偏差4.
Conclusion
特别是在苛刻的汽车或工业环境中，磁角传感器已被证明是传感器和执行器应用的有价值的解决方案。亚博尊贵会员其他功能，如线性化，诊断功能和冗余，也支持高安全性关键应用，例如汽车转向系统。亚博尊贵会员
The design of a magnetic circuit for angle sensors is a complex task, where many influencing parameters need to be considered. This document shows some of the interdependencies that exist between magnet selection, mechanical tolerances, and accuracy requirements for on-axis applications.
请联系ANAllegro代表for any remaining questions or support.
1Magnetfabrik Bonn product reference numbers: 67.043-2 and 67.043-1.
2Maximum operating temperature is determined by magnet material and shape. Exceeding these ratings can be tolerated for limited duration. Contact the supplier to select appropriate magnets for the application temperature profile.
3.Please contact Allegro for available options for specific input field range other than 300 Gauss.
4.Measurement done 100 time for each Air Gap (device in default mode 1 sample per reading).
Originally published inDesign News，2015年1月。