外文翻译----传感器和传感器激励和测量技术.docx

附录ATransducer and sensor excitation and measurement techniquesMany of todays industrial and instrumentation applications involving sensor. The function of the sensor system is to monitor changes, and then this data back to the main controller. For a simple voltage or current measurement sensors may be resistance in nature. However, some sensor system may be inductive or capacitive in nature, that is to say, the frequency range of the sensor resistance change is nonlinear. Impedance sensors such typical example is the proximity sensor - a campaign for the detection of the relative distance of objects; In addition, capacitive sensors or sensor sensibility - in the medical devices used to measure blood flow or blood pressure or blood qualitative analysis. In order to use these complex impedance sensors, the realization of measurement, to provide an exchange of (AC) excitation source frequency in the frequency range of the sensor for scanning. This article attempts to explain how the use of single-chip digital waveform generator to easily achieve this up to 10 MHz frequency scanning. Also introduced a kind of integrated incentive, response and digital signal processor (DSP) features a complete single-chip sensor solution that suited the requirements of up to nearly 50 kHz frequency applications. Sensors: working principle.Inspired by the frequency of sensor signals based on sensor values of L or C to show the corresponding instantaneous magnitude, frequency or phase changes. For example, the ultrasound will show a flow of phase offset, while the proximity sensor will cause the rate to change. Tracking changes in impedance that is the most commonly used to monitor the resonant frequency circuit. Capacitance value of the resonant frequency is equal to the frequency where the inductance value point. This is also the largest frequency curve frequency impedance value of the corresponding point. Under normal circumstances, for example, in static conditions, the sensor L, R and C has a unique value, in the resonant frequency impedance to Department with the greatest value. When a moving object near the sensor, then sensor L and C values will be changed and a new resonant frequency. By monitoring the changes in resonant frequency (and thus lead to changes in impedance), it is possible to speculate that the relative movement of objects moving away from the sensor.Calculated resonant frequency: calculation circuit measuring the resonant frequency of the need for the relationship between frequency and impedance, in particular, need a certain frequency range with the ability to scan the waveform generator. A simple, low-cost method is based on the AD5930 waveform generator. AD5930 with a group of pre-set in the frequency range of the ability to provide a linear scan. Once the conditions for setting, on the need for further control, in addition to a frequency scan for the start of the trigger. AD5930 has many advantages: the output frequency resolution of 28 bit, so you can be less than the control accuracy of 0.1 Hz output frequency. The output frequency range of 0 10 MHz, thus the selection of sensors with a lot of flexibility. For example, some sensors a very narrow frequency range, but the requirements in this frequency range with high resolution. Some sensors may require a wide frequency range, but lower resolution requirements. This approach is easy to calculate the resonant frequency of the sensor. System block diagram: typical block diagram of such a system as shown in Figure 3. Through the BF-535 DSP processor AD5930 digital waveform generator set. AD5930 needs arising from the sinusoidal output voltage waveform for low-pass filtering and amplification in order to eliminate the master clock (MCLK), mirroring the frequency and high frequency noise generated by feed through. After filtering the sensor signal can be used as a source of excitation frequency. According to the impedance of the sensor response signal amplification may be needed in order to enter the ADC (ADC) dynamic range. Sensor output and the frequency of the source of both incentives into the AD7266 12 bit, 2 MSPS dual simultaneous sampling ADC. ADC output data will be stored in memory in order to do further analysis to calculate the phase and amplitude of the sensor offset. Complete integrated sensor solutions: separation described above is a common solution for impedance measurement of the sensor solution. The program may require many discrete components, so the sensor is a cost-analysis solution. These separate components will increase their own sources of error. The design of active components will increase the number of phase error, which is the need for correction. In addition, the DSP also need to deal with some complex mathematical calculations, this may require external memory to store the original data of the ADC, which would further increase costs. Address the above-mentioned analysis of the issue of low-frequency sensor solutions AD5933 / 4 device, it will by the main processing module are integrated into one chip. The core of the chip, including three main modules: the frequency of scanning for the direct digital synthesizer (DDS) waveform generator; used to measure the sensors response to the 12 bit, 1 MSPS ADC; and, finally, to the ADC data for 1024 point Discrete Fourier Transform (DFT) calculations of the DSP engine. The results of DFT calculations to provide a real part (R) and an imaginary part (I) data, which can easily calculate the impedance. Using the following formula is easy to calculate the impedance amplitude and phase: In order to determine the actual value of the real impedance Z (), is typically required to perform frequency scanning. Can calculate the impedance of each frequency point, which can draw a relationship between frequency and amplitude curves. So it is easy to measure 100 20 M resistance within the scope. The system allows users to set up a 2 V peak-to-peak (PK-PK) of the sinusoidal signal as an external frequency source excitation load. Output range can be set to 1V, 500 mV and 200 mV. Frequency resolution can be 27 bit (0.1 Hz). The realization of the frequency of scanning: In order to achieve the frequency of scanning, the user must first set up the required frequency of scanning conditions: the need for a start frequency, frequency interval and sweep points. Then the need for a start command to start scanning. Frequency points in each scan, ADC completed the first 1024 samples, and then calculating the DFT in order to provide the waveform of the real and imaginary parts of the data. The real and imaginary parts of the data through the I2C interface in the form of two 16 bit words available to the user. DSP-chip processing unit user does not have the advantage of complex mathematical calculations, and need not store ADC raw data, only two 16 bit data. Therefore, it allows the DSP to choose cheaper solutions, as greatly reduce the processing power of the final requirements.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 . This initial error without calibration by the following components:1.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.2.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.3.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. 4.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 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. 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. 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 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.附录B传感器和传感器激励和测量技术当今的许多工业和仪器仪表应用都涉及传感器测量。传感器的功能就是监视系统中的变化，然后将此数据反馈给主控制器。用于简单的电压或电流测量的传感器可能是电阻性的。但是，有些传感器系统可能是电感性或电容性的，就是说在传感器频率范围内阻抗变化是非线性的。 这类复阻抗传感器的典型例子就是接近传感器用于检测一个运动物体的相对距离；另外，容性传感器或感性传感器在医用设备中用于测量血流或者分析血压或血质。 为了用这些“复阻抗传感器”实现测量，必须提供一种交流（AC）激励频率源在传感器的频率范围内进行扫描。本文试图说明如何采用单芯片数字波形发生器轻松实现这种高达10 MHz的频率扫描。还介绍了一种带集成激励、响应和数字信号处理器（DSP）功能完整的单芯片传感器解决方案，它适合要求高达近50 kHz激励频率的应用。 传感器工作原理：通过传感器的激励频率信号会根据传感器的L或C瞬时值表现出相应的幅度、频率或者相位的改变。例如，超声波液流计会表现出相位偏移，而接近传感器会引起幅度改变。 跟踪这种变化阻抗的最常用方法就是监视电路的谐振频率。谐振频率就是电容值等于电感值所在的频率点。这也是频率曲线上最大阻抗值对应的频率点。在正常情况下，例如在静态条件下，传感器的L，R和C都具有一个唯一值，在谐振频率Fo处具有最大阻抗值。当一个运动物体接近传感器时，那么传感器的L和C值就会改变，并且产生一个新的谐振频率。通过监测谐振频率的变化（从而导致阻抗的变化），就有可能推测出运动物体相对传感器的移动距离。 计算谐振频率：计算电路的谐振频率需要测量频率和阻抗的关系，尤其是需要一个能够在一定频率范围内具有扫描能力的波形发生器。一种简单、低成本的实现方法就是采用AD5930波形发生器。AD5930具有在一组预设置的频率范围内提供线性扫描的能力。一旦条件设定，就无需进一步的控制，除了一个用于启动频率扫描的触发器。 AD5930具有许多优点：输出频率的分辨率为28 bit，所以用户能以小于0.1 Hz的控制精度输出频率。其输出频率范围为010 MHz，从而对选择传感器具有很大的灵活性。例如，有些传感器的频率范围很窄，但是要求在此频率范围内具有很高的分辨率。还有些传感器可能需要很宽的调频范围，但是分辨率要求较低。采用这种方法很容易计算出传感器的谐振频率。 系统框图：通过BF-535 DSP处理器设置AD5930数字波形发生器。需要对从AD5930产生的正弦波输出电压波形进行低通滤波和放大以便消除主时钟（MCLK）、镜像频率和高频噪声产生的馈通。经过滤波的信号可用作传感器的激励频率源。根据传感器的阻抗响应信号可能需要进行放大以便使其进入模数转换器（ADC）的动态范围内。传感器的输出和激励频率源都输入到AD7266一种12 bit、2 MSPS的同步采样双ADC。将ADC输出的数据保存在存储器中以便做进一步的分析以计算出传感器的相位和幅度偏移。完整的集成传感器解决方案。 上面介绍的分立解决方案是一种常用的传感器阻抗测量解决方案。该方案可能需要许多分立元件，所以是一种高成本的传感器分析解决方案。这些单独的元件还会增加自身的误差源。设计中的有源元件还会增加相位误差，这也是需要校正。另外，还需要DSP处理一些复杂的数学计算，这样可能需要外部存储器来存储原始的ADC数据，从而会进一步增加成本。 解决上述低频率传感器分析问题的解决方案是AD5933/4器件，它将上述主要处理模块都集成到一颗芯片中。该芯片的内核包括3个主要单元：用于提供频率扫描的直接数字频率合成器（DDS）波形发生器； 用于测量传感器的响应的12 bit、1 MSPS ADC；以及最后能够对ADC测量数据进行1024点离散傅立叶变换（DFT）运算的DSP引擎。 DFT运算结果提供一个实部（R）和一个虚部（I）数据，从而可以方便地计算出阻抗。采用下面的公式很容易计算出阻抗的幅度和相位：为了确定实际的实数阻抗值Z()，通常需要进行频率扫描。可以计算出每个频率点的阻抗，从而可以得出一条频率与幅度的关系曲线。这样就很容易测量出100 20 M范围内的阻抗。该系统允许用户设置一个2 V峰峰值（PK-PK）的正弦信号作为外部负载的激励频率源。输出范围还可以设置为1V，500 mV和200 mV。频率分辨率可以达到27 bit（ 0.1 Hz）。 实现频率扫描：为了实现频率扫描，用户必须首先设置频率扫描所需要的条件：需要一个起始频率、频率间隔和扫频点数。然后需要一个启动命令开始扫描。在每个扫描频点，ADC先完成1024个采样，然后进行DFT计算以便提供该波形的实部和虚部数据。此实部和虚部数据通过I2C接口以两个16 bit字形式提供给用户。片内DSP处理单元的优点是用户不必进行复杂的数学计算，也无需存储ADC原始数据，只需提供两个16 bit的数据。因此，它还允许选择更便宜