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1、精选优质文档-倾情为你奉上压力传感器合理进行压力传感器的误差补偿是其应用的关键。压力传感器主要有偏移量误差、灵敏度误差、线性误差和滞后误差，本文将介绍这四种误差产生的机理和对测试结果的影响，同时将介绍为提高测量精度的压力标定方法以及应用实例。 目前市场上传感器种类丰富多样，这使得设计工程师可以选择系统所需的压力传感器。这些传感器既包括最基本的变换器，也包括更为复杂的带有片上电路的高集成度传感器。由于存在这些差异，设计工程师必须尽可能够补偿压力传感器的测量误差，这是保证传感器满足设计和应用要求的重要步骤。在某些情况下，补偿还能提高传感器在应用中的整体性能。 本文以摩托罗拉公司的压力传感器为例，所
2、涉及的概念适用于各种压力传感器的设计应用。 摩托罗拉公司生产的主流压力传感器是一种单片压阻器件，该器件具有3类： 1. 基本的或未加补偿标定； 2. 有标定并进行温度补偿； 3. 有标定、补偿和放大。 偏移量、范围标定以及温度补偿均可以通过薄膜电阻网络实现，这种薄膜电阻网络在封装过程中采用激光修正。 该传感器通常与微控制器结合使用，而微控制器的嵌入软件本身建立了传感器数学模型。微控制器读取了输出电压后，通过模数转换器的变换，该模型可以将电压量转换为压力测量值。 传感器最简单的数学模型即为传递函数。该模型可在整个标定过程中进行优化，并且模型的成熟度将随标定点的增加而增加。 从计量学的角度看，测量
3、误差具有相当严格的定义：它表征了测量压力与实际压力之间的差异。而通常无法直接得到实际压力，但可以通过采用适当的压力标准加以估计，计量人员通常采用那些精度比被测设备高出至少10倍的仪器作为测量标准。 由于未经标定的系统只能使用典型的灵敏度和偏移值将输出电压转换为压力，测得的压力将产生如图1所示的误差。 这种未经标定的初始误差由以下几个部分组成： a. 偏移量误差。由于在整个压力范围内垂直偏移保持恒定，因此变换器扩散和激光调节修正的变化将产生偏移量误差。 b. 灵敏度误差，产生误差大小与压力成正比。如果设备的灵敏度高于典型值，灵敏度误差将是压力的递增函数（见图1）。如果灵敏度低于典型值，那么灵敏度
4、误差将是压力的递减函数。该误差的产生原因在于扩散过程的变化。 c. 线性误差。这是一个对初始误差影响较小的因素，该误差的产生原因在于硅片的物理非线性，但对于带放大器的传感器，还应包括放大器的非线性。线性误差曲线可以是凹形曲线，也可以是凸形曲线。 d. 滞后误差：在大多数情形中，滞后误差完全可以忽略不计，因为硅片具有很高的机械刚度。一般只需在压力变化很大的情形中考虑滞后误差。 标定可消除或极大地减小这些误差，而补偿技术通常要求确定系统实际传递函数的参数，而不是简单的使用典型值。电位计、可调电阻以及其他硬件均可在补偿过程中采用，而软件则能更灵活地实现这种误差补偿工作。 一点标定法可通过消除传递函数
5、零点处的漂移来补偿偏移量误差，这类标定方法称为自动归零。 偏移量标定通常在零压力下进行，特别是在差动传感器中，因为在标称条件下差动压力通常为0。对于纯传感器，偏移量标定则要困难一些，因为它要么需要一个压力读取系统，用以测量其在环境大气压力条件下的标定压力值，要么需要获取期望压力的压力控制器。 差动传感器的零压力标定非常精确，因为标定压力严格为0。另一方面，压力不为0时的标定精确度取决于压力控制器或测量系统的性能。 选择标定压力 标定压力的选取非常重要，因其决定了获取最佳精度的压力范围。实际上，经过标定后实际的偏移量误差在标定点处最小并一直保持较小的值。因此，标定点必须根据目标压力范围加以选择，
6、而压力范围可以不与工作范围相一致。 为了将输出电压转换为压力值，由于实际的灵敏度往往是未知，因此在数学模型中通常采用典型灵敏度进行单点标定。 红色曲线表示进行偏移量标定（PCAL=0）后的误差曲线，可以发现误差曲线相对于表示标定前误差的黑色曲线产生了垂直偏移。 这种标定方法与一点标定法相比要求更为严格，实现成本也更高。然而与一点标定法相比，该方法可显著提高系统的精度，因为该方法不仅标定了偏移量，还标定了传感器的灵敏度。因此在误差计算中可以使用灵敏度实际值，而非典型值。 绿色曲线表示精度提高。在这里，标定是在0至500兆巴（满标度）条件下进行。由于在标定点上误差接近于0，因此为了在期望的压力范围
7、内得到最小的测量误差，正确地设定这些点就显得尤为重要。 某些应用中要求在整个压力范围内保持较高的精确度。在这些应用中，可以采用多点标定法来得到最理想的结果。在多点标定法中，不仅考虑了偏移量和灵敏度误差，还考虑了大部分的线性误差，紫红色曲线所示。这儿用的数学模型与每个标定间距（在两个标定点之间）的两级标定完全一样。 三点标定 如前所述，线性误差具有一致的形式，且误差曲线符合二次方程的曲线，具有可预测的大小和形状。对于未采用放大器的传感器更是如此，因为传感器的非线性从本质上是基于机械原因（这是由硅片的薄膜压力引起）。 线性误差特性的描述可以通过计算典型实例的平均线性误差，确定多项式函数（a2+bx
8、+c）的参数而得到。确定了a、b和c后得到的模型对于相同类型的传感器都是有效的。该方法能在无需第3个标定点的情况下有效地补偿线性误差。 摩托罗拉MPX2300的补偿实例，MPX2300是一种主要应用于血压测量的温度补偿传感器。多项式模型可由10个传感器的平均线性误差得到，补偿后的误差约为最大初始线性误差的十至二十分之一，如图3虚线所示。 该误差补偿方法只需两点标定即可将低成本传感器改进为高性能器件（误差小于满标度的0.05%）。 当然设计工程师要根据实际应用的精确度要求，选择最适合的标定方法，此外还需要考虑系统成本。由于有多种集成度和补偿技术可供选择，设计工程师可根据不同的设计要求选择适当的方
9、法。Pressure sensors Reasonable pressure sensor error compensation is the key to its application. Pressure sensors are mainly offset error, sensitivity error, linear error and lag errors, the paper will introduce the four errors on the mechanism and the effects of the test results, will be presented a
10、t the same time to improve the measurement accuracy of pressure calibration method and application examples . Currently on the market a variety of sensor types, which allows design engineers can choose the pressure sensor system. These sensors not only include the most basic converter, but also more
11、 complex circuits with on-chip, highly integrated sensor. Because of these differences, the design engineer must be enough as far as possible compensation of pressure sensor measurement error, which is to ensure that the design and application of sensors to meet the requirements of an important step
12、. In some cases, compensation can increase the sensor in the application of the overall performance. Based on Motorolas pressure sensor as an example, the application of the concept involved in the design of a variety of pressure sensor applications. Motorola mainstream production pressure piezoresi
13、stive sensor is a monolithic device, the device has 3 categories: 1. Basic calibration or without compensation; 2. There are calibration and temperature compensation; 3. There are calibration, compensation and amplification. Offset, the scope of calibration and temperature compensation can be throug
14、h the thin film resistor networks, the thin film resistor networks in the process of laser package amendments. The sensor is usually used in conjunction with the micro-controller, and microcontroller embedded software itself, established a mathematical model of the sensor. Microcontroller reads the
15、output voltage through the ADC conversion, the model can be converted to the pressure of the volume of voltage measurements. The simplest sensor is the transfer function of the mathematical model. The model calibration over the entire optimization process and maturity model will be marked with the f
16、ixed-point increase. From the point of view of metrology, measurement error has a very strict definition: it is characterized by measurement of pressure and the difference between the actual pressure. Usually can not directly be the actual pressure, but through the use of appropriate criteria to est
17、imate the pressure, the measurement accuracy are usually more than those measured using equipment at least 10 times higher than the instrument as a measurement standard. Without calibration of the system as a result can only use the typical value of sensitivity and offset the output voltage is conve
18、rted to pressure, the pressure measured will have a margin of error as shown in Figure 1. This initial error without calibration by the following components: a. offset error. As the pressure in the entire range of vertical shift to maintain a constant, so the proliferation and laser conditioning con
19、verter changes the amendment would have offset error. b. The sensitivity of error, resulting in errors in direct proportion to the size and pressure. If the device is higher than the typical value of the sensitivity, the sensitivity of the error will be incremental pressure function (see Figure 1).
20、If the sensitivity is lower than the typical value, then the sensitivity of the error will be decreasing function of pressure. The cause of the error diffusion process is to change. c. Linearity Error. This is an initial error factor less affected, the error is the cause of the physical non-linear s
21、ilicon, but with the sensor amplifier, should also include non-linear amplifier. Linear error curve can be concave curve, it could be a convex curve. d. Lag Error: In most cases, the lag error can be ignored completely, because silicon has a higher degree of mechanical stiffness. Changes in general
22、just a lot of pressure to consider the case of hysteresis error. Calibration can eliminate or greatly reduce these errors, and compensation technique is usually required to identify the parameters of the actual transfer function, rather than simply the use of typical values. Potentiometer, adjustabl
23、e resistance, and other hardware can be used in the compensation process, while the software is able to achieve more flexibility in the work of this error compensation. Calibration method that can eliminate the transfer function against the Agency to compensate the offset drift error, such as the au
24、to-zero calibration method. Offset zero calibration is usually carried out under pressure, especially in the differential sensor, because under the conditions of the nominal differential pressure is usually 0. For pure sensor offset calibration will be difficult, because it either needs to read a pr
25、essure system to measure the atmospheric pressure in the environment under the conditions of the calibration of pressure or need to obtain the pressure of expectations of the pressure controller. Zero differential pressure sensor is very accurate calibration, because the pressure of strict demarcati
26、on is 0. On the other hand, the pressure of 0:00 is not the accuracy of the calibration depends on the pressure controller or the performance measurement system. Choice of calibration pressure Calibration is very important selection pressure, which determines the accuracy to obtain the best pressure
27、 range. In fact, after calibration offset actual standard fixed-point error in the Department and has been to maintain a smaller minimum value. Therefore, the reference points must be in accordance with the scope of the target selection pressure, and pressure range can not be consistent with the sco
28、pe of work. In order to convert the pressure of the output voltage value, usually as a result of the actual sensitivity is unknown, and therefore the mathematical model used for a typical single-point calibration sensitivity. Said that the red curve calibration offset (PCAL = 0) after the error curv
29、e, the error can be found that calibration curve relative to the black before the error had a vertical offset curve. This calibration method and calibration method that is more stringent requirements to achieve a higher cost. However, compared with the calibration point, the method can significantly
30、 improve the accuracy of the system, because the method is not only an offset calibration, the calibration of the sensor sensitivity. Therefore, the calculation error can be used in the actual value of sensitivity, and the atypical values. That improve the accuracy of the green curve. Here, calibrat
31、ion is trillion 0-500 bar (full scale) conditions. As the marked point on the error close to 0, so the pressure of expectations to be the smallest range of measurement error, the correct set of these points, it is particularly important. Some applications require the pressure in the whole range of h
32、igh accuracy. In these applications, can be used multi-point calibration method to get the best results. In multi-point calibration method, not only considered the error of offset and sensitivity, but also takes into account most of the linear error curve shown in purple. The mathematical model used
33、 here, with each calibration interval (between the two reference points) exactly the same as a two-tier calibration. Three-point calibration As mentioned earlier, the linear form of a consistent error and the error curve in line with the quadratic equation of the curve, with a predictable size and s
34、hape. Did not use the amplifier for the sensor, especially because of the nonlinear sensor is based on the nature of mechanical reasons (this is caused by the pressure of silicon thin-film). Linear description of the error characteristics of a typical example can be calculated the average linear err
35、or to determine the polynomial function (a 2 + bx + c) be the parameter. Determine the a, b and c of the model after the same type of sensor is valid. This method can be no fixed points marked the first three cases of linear error compensation effectively. Examples of compensation MPX2300 Motorola,
36、MPX2300 is a blood pressure measurement is mainly used in the temperature compensation sensor. Polynomial model can be an average of 10 sensors to be linear error compensation of the error after the initial maximum linearity error of about ten to one-twentieth, as shown in dotted line in Figure 3. T
37、he error compensation method can be only two points calibration for high-performance low-cost sensors to improve the device (full scale error of less than 0.05%). Of course, design engineers practical application in accordance with the accuracy requirements, choosing the most appropriate calibration method, in addition to the need to consider system cost. As a result of a variety of integration options and compensation technology, design engineers can design requirements according to different methods of selecting appropriate.专心-专注-专业