发布时间 : 星期五 文章电子元件目检设备设计更新完毕开始阅读9106b6120975f46526d3e197
??本科毕业设计说明书（论文）
Usually can not directly be the actual pressure, but through the use of appropriate criteria to estimate 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 converted 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 converter 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). 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 silicon, 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 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, adjustable 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 auto-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 pressure 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
30
??本科毕业设计说明书（论文）
strict demarcation 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 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 scope 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 curve, 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 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, calibration 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 high 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 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 shape. 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
31
??本科毕业设计说明书（论文）
average linear error 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, 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.
The 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. 、
32
??本科毕业设计说明书（论文）
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
33