1717.温度测量技术英文翻译

温度测量技术在现实世界中，传感器能够通过软件检测到将要发生的事情。本文研究的是各种温度传感器，并说明其怎么样连接处理器。温度是现实世界中一个重要的特征，并且是系统所需要的措施。许多工业生产过程，从干结制造到半导体执照，都依赖对温度的控制。一些电子产品的需要来测量自己的温度，如电脑显示器，其CPU或马达控制器必须知道电源驱动IC的温度。热敏电阻有各种不同类型的传感器来测量温度。其中之一是用热敏电阻器，或温度敏感的电阻器。热敏电阻有负温度系数（NTC） ，意思是随着温度的下降，电阻上升。所有被动的温度测量传感器，热敏电阻具有最高的灵敏度（电阻随温度变化而变化）。热敏电阻没有一个线性温度/阻力曲线。表1: 典型的NTC热敏电阻器的数据温度 CR/R25温度 CR/R25-5039。03300。8276-4021。47400。6406-3012。28500。5758-207。28600。4086-104。46700。295402。81800。2172101。82900。1622201。211000。12992511100。09446一个典型的NTC热敏电阻器的数据如表1所示。这一数据是为Vishay-Dale热敏电阻器，但它是典型的NTC热敏电阻器的一般问题。电阻作为一个比率（ r/r25 ） 。很多时候，许多热敏电阻在一个系统中，将有类似的特点和相同的温度/电阻曲线。1个热敏电阻从这个系统与电阻位在25 C 10K的将有电阻28。1k在0 C和电阻4。086k在60 同样，热敏电阻与R25的5 K将有电阻14。050k在0 。图1 ：热敏电阻/温度曲线图1显示了这热敏电阻曲线图形。可以看到，电阻/温度曲线不是直线，而热敏电阻器的数据，这是由于在10度的递增，一些热敏电阻表有5度或什至1度递增。在某些情况下，需要知道的温度之间的两点，放在桌上。您可以通过曲线估算，或者您也可以计算直接电阻。阻抗计算公式如下：其中T是开尔文温度，A，B， C和D是依赖热敏电阻的常数。这些参数必须提供由热敏电阻的制造商提供。热敏电阻从一个宽松样本限制了它们的重复性。通常容忍范围从1 至10 ，这取决于具体的使用部分。一些热敏电阻均设计为可以互换，在申请的地方，是不切实际的，需要有一个调整。这种应用可能包括文书当用户或现场工程师已取代热敏电阻，并没有独立的手段来校正。这些热敏电阻比普通零件更准确，但相当多的昂贵。图2 ：热敏电阻电路图2显示一个典型的电路，可以用来允许一个微处理器来测量温度使用热敏电阻。一电阻（ R1的）拉动热敏电阻到一个参考电压。这通常是一样的ADC参考，所以vref将5V的如果ADC参考人5V的。热敏电阻/电阻组合作出了分压器，以及不同的热敏电阻的结果在不同电压的交界处。路径的准确性，取决于热敏电阻宽容、电阻、宽容和参考的准确性。自热由于热敏电阻是一个电阻，通过电流通过它会产生一些热量。电路设计师必须确保该上拉电阻是够大，以防止过多的自加热，或该系统将最终测量热敏电阻耗散而不是环境温度。 数额的权力，热敏电阻已消退影响温度是所谓的耗散常数，和是多少毫瓦需要，以提高热敏电阻温度1 上文C环境。耗散常数随包在其中热敏电阻提供，带头衡量（如铅装置） ，类型的封装材料（如热敏电阻封装） ，以及其他因素。 金额自加热允许，因此，大小的限流电阻，取决于对测量精度的需要。制度要求的精度 5 C可以容忍更多的热敏电阻自加热超过系统必须精确到 0。1 长请注意，该上拉电阻必须计算，以限制自热耗散在整个测量温度范围。对于给定电阻，热敏电阻将改变在不同温度下，因为热敏电阻变化。图3 热敏电阻器结构有时你需要规模热敏电阻的投入得到妥善解决。图3显示一个典型的电路，扩大了10-40 c范围横跨0-5 V输入的ADC。公式的输出运算放大器是如下：一旦你有一个热敏电阻规模（如果需要） ，您可以有一张图表，显示实际的阻力随温度的价值观。你需要的图表，因为热敏电阻不是直线，所以该软件需要知道什么ADC值期望为每个在某一温度。精确的表程度递增或五度的递增-取决于对精度您的应用需要。宽stackup 在任何热敏电阻器的应用，你必须选择传感器和任何其他元件，在输入电路，以符合您需要的精度。一些应用可能只需要1 ，电阻器，但其他人可能需要0.1 电阻。在任何情况下，应该有一个试算表显示的效果在所有元件，包括电阻和参考，以及热敏电阻本身。 如果您需要更多的准确性，比你能负担得起的组件，您可能必须校准系统后，它是建立在。在某些应用中，这是不是一种选择，由于电路板和/或热敏电阻必须实地更换。不过，在情况下，设备不领域的更换，或在该领域的技术人员有一个独立的手段来监测温度，是有可能让软件建立一个表温度与艺发局的价值观。必须有一些手段来投入的实际温度（测量与独立的工具） ，使该软件可以构建表。在一些系统，如热敏电阻，必须实地更换，您可以校准更换组件（传感器或整个模拟前端）在工厂，并提供标定数据在磁盘或其他存储媒介。当然，软件必须提供一种手段，适用于标定数据时，这些组件改变。在一般，热敏电阻提供一个符合成本效益的方式来衡量温度，而仍然易于使用。明年我们将看看的RTD与热电偶温度传感器。电阻温度探测器电阻温度检测器（热电阻）是一个线的变化随温度的阻力。典型的RTD材料包括铜，铂，镍，镍/铁合金。一的RTD元素可以是一线或电影，镀金或喷上基质，如陶瓷。图4 ：温度/电阻曲线：与热敏电阻的RTD的RTD阻力是指定在0 长一个典型的铂的RTD与一零零瓦特阻力位在0 丙有阻力百点三九瓦特在1 C和电阻的119.4瓦特，在50 长图4显示的比较典型的RTD温度/阻力曲线来表示，一个热敏电阻。耐受性rtds优于热敏电阻，通常不等，从0.01 ，铂，以0.5 的镍。除了更好的宽容和整体较低的阻力，界面的RTD是一个类似为一热敏电阻。热电偶1热电偶是一个交界处的两个异种金属，产生一个微小的电压时，激烈的。金额电压取决于哪两个金属加入。三种常见的热电偶组合铁康铜（ J型） ，铜-康铜（ T型） ，以及chromel - alumel （ K型） 。电压所产生的一热电偶交界处很小，通常只有几个毫伏计。一K型热电偶的变化，只有约40 V的每1 c温度的变化;测量温度与0.1 C精度，测量系统必须能够衡量一个4V合金的变化。图5 ：热电偶因为任何两个异种金属将产生热电偶交界处时加入，连接点的热电偶，以测量系统也将作为热电偶。这一效应通常是最小化，把连接在一个等温块，所以这两个连接点是在相同温度下，尽量减少错误。在某些情况下，温度块测量，使补偿温度的影响。图5显示等温座与一补充说：二极管用于温度测量。 增益要求来衡量一热电偶通常是在范围100到300 ，和任何噪音回升，由热电偶将扩增同样数额。 1仪表放大器是常用的，因为它拒绝普通模式噪音在热电偶布线。小康-现成的热电偶信号的条件，例如模拟装置a d594/595，简化硬件接口。固态最简单的半导体温度传感器是一个PN结，如一个信号，二极管或基地发射交界处的晶体管。如果目前的通过前瞻性的偏见，硅PN结是举行常数，远期下降降低了约1.8mv 长一些集成电路利用这个半导体特性测量温度。这些部分包括格言max1617 ，美国国家半导体lm335 ，和lm74 。半导体传感器有不同的接口，包括以串行SPI的电压输出。微线界面 范围内现有的温度传感器是广泛。与权利相结合的软件和硬件，你应该能够找到一个适合您的应用程序。Temperature Measurement TechniqueSensors enable software to detect what is happening in the real world. This article surveys various temperature sensors and describes how they interface to a processor. Temperature is one of the most common real-world characteristics that systems need to measure. Many industrial processes, from steel manufacturing to semiconductor fabrication, depend on temperature. Some electronics products need to measure their own temperature, such as a computer that monitors its CPU or a motor controller that must know the temperature of the power driver IC. Thermistors Various types of sensors are used to measure temperature. One of these is the thermistor, or temperature-sensitive resistor. Most thermistors have a negative temperature coefficient (NTC), meaning the resistance goes up as temperature goes down. Of all passive temperature measurement sensors, thermistors have the highest sensitivity (resistance change per degree of temperature change). Thermistors do not have a linear temperature/resistance curve. Table 1: Typical NTC thermistor dataTemp CR/R25Temp CR/R25-5039.03300.8276-4021.47400.6406-3012.28500.5758-207.28600.4086-104.46700.295402.81800.2172101.82900.1622201.211000.12992511100.09446Data for a typical NTC thermistor family is shown in Table 1. This data is for a Vishay-Dale thermistor, but it is typical of NTC thermistors in general. The resistance is given as a ratio (R/R25). Often, many thermistors in a family will have similar characteristics and identical temperature/resistance curves. A thermistor from this family with a resistance at 25C (R25) of 10K would have a resistance of 28.1K at 0C and a resistance of 4.086K at 60C. Similarly, a thermistor with R25 of 5K would have a resistance of 14.050K at 0C. Figure 1: Thermistor resistance/temperature curveFigure 1 shows this thermistor curve graphically. You can see that the resistance/temperature curve is not linear. While the data for this thermistor is given in 10-degree increments, some thermistor tables have five-degree or even one-degree increments. In some cases, you need to know the temperature between two points on the table. You can estimate this by using the curve, or you can calculate the resistance directly. The formula for resistance looks like this: where T is the temperature in degrees Kelvin and A, B, C, and D are constants that depend on the characteristics of the thermistor. These parameters must be supplied by the thermistor manufacturer. Thermistors have a tolerance that limits their repeatability from one sample to the next. This tolerance typically ranges from 1% to 10%, depending on the specific part used. Some thermistors are designed to be interchangeable in applications where it is impractical to have an adjustment. Such an application might include an instrument where the user or a field engineer has to replace the thermistor and has no independent means to calibrate it. These thermistors are much more accurate than ordinary parts, but considerably more expensive. Figure 2: Thermistor circuitFigure 2 shows a typical circuit that could be used to allow a microprocessor to measure temperature using a thermistor. A resistor (R1) pulls the thermistor up to a reference voltage. This is typically the same as the ADC reference, so Vref would be 5V if the ADC reference were 5V. The thermistor/resistor combination makes a voltage divider, and the varying thermistor resistance results in a varying voltage at the junction. The accuracy of this circuit depends on the thermistor tolerance, resistor tolerance, and reference accuracy. Self-heatingSince a thermistor is a resistor, passing current through it will generate some heat. The circuit designer must ensure that the pullup resistor is large enough to prevent excessive self-heating, or the system will end up measuring the thermistor dissipation instead of the ambient temperature. The amount of power that the thermistor has to dissipate to affect the temperature is called the dissipation constant, and is the number of milliwatts needed to raise the thermistor temperature 1C above ambient. The dissipation constant varies with the package in which the thermistor is provided, the lead gauge (if a leaded device), type of encapsulating material (if the thermistor is encapsulated), and other factors. The amount of self-heating allowed, and, therefore, the size of the limiting resistor, depends on the measurement accuracy needed. A system that require an accuracy of 5C can tolerate more thermistor self-heating than a system that must be accurate to 0.1C. Note that the pullup resistor must be calculated to limit self-heating dissipation over the entire measurement temperature range. For a given resistor, the thermistor dissipation will change at different temperatures because the thermistor resistance changes. Figure 3: Thermistor scalingSometimes you need to scale a thermistor input to get the proper resolution. Figure 3 shows a typical circuit that expands the 10-40C range to span the 0-5V input of the ADC. The formula for the output of the op amp is as follows: Once you have a thermistor scaled (if needed), you can make a chart showing the actual resistance vs. temperature values. You need the chart because the thermistor isnt linear, so the software needs to know what ADC value to expect for each given temperature. The accuracy of the table-one-degree increments or five-degree increments-depends on the accuracy your application requires. Tolerance stackup In any thermistor application, you have to select the sensor and any other components in the input circuit to match your required accuracy. Some applications may only need 1% resistors, but others may require .1% resistors. In any event, you should make a spreadsheet showing the effects of tolerance stackup in all the components, including the resistors and references, and the thermistor itself. If you need more accuracy than you can get with affordable components, you may have to calibrate the system after it is built. In some applications, this is not an option since the circuit boards and/or thermistor must be field-replaceable. However, in cases where the equipment is not field-replaceable, or where the field technicians have an independent means to monitor the temperature, it is possible to let the software build a table of temperature vs. ADC values. There must be some means to input the actual temperature (measured with the independent tool) so the software can construct the table. In some systems, where the thermistor must be field-replaceable, you may be able to calibrate the replaceable component (sensor or entire analog front end) at the factory and provide the calibration data on disk or other storage media. Of course, the software must provide a means to apply the calibration data when the components are changed. In general, thermistors provide a cost-effective means to measure temperature, while still remaining easy to use. Next we will look at RTD and thermocouple temperature sensors. Resistance temperature detector A resistance temperature detector (RTD) is a wire that changes resistance with temperature. Typical RTD materials include copper, platinum, nickel, and nickel/iron alloy. An RTD element can be a wire or a film, plated or sprayed onto a substrate such as ceramic. Figure 4: Temperature/resistance curve: RTD vs. thermistorRTD resistance is specified at 0C. A typical platinum RTD with 100W resistance at 0C would have a resistance of 100.39W at 1C and a resistance of 119.4W at 50C. Figure 4 shows a comparison of a typical RTD temperature/resistance curve to that of a thermistor. The tolerance of RTDs is better than thermistors, typically ranging from .01% for platinum to .5% for nickel. Aside from better tolerance and overall lower resistance, the interface to an RTD is similar to that for a thermistor. Thermocouples A thermocouple is a junction of two dissimilar metals, which produces a tiny voltage when heated. The amount of voltage is dependent on which two metals are joined. Three common thermocouple combinations are Iron-Constantan (type J), Copper-Constantan (type T), and Chromel-Alumel (type K). The voltage produced by a thermocouple junction is very small, typically only a few millivolts. A type K thermocouple changes only about 40V per 1C change in temperature; to measure temperature with .1C accuracy, the measurement system must be able to measure a 4V change. Figure 5: ThermocoupleSince any two dissimilar metals will produce a thermocouple junction when joined, the connection point of the thermocouple to the measurement system will also act as a thermocouple. This effect is usually minimized by placing the connections on a isothermal block, so that the two connection points are at the same temperature, minimizing the error. In some cases, the temperature of the block is measured, allowing compensation for the temperature effects. Figure 5 shows an isothermal block with an added diode used for temperature measurement. The gain required to measure a thermocouple is typically in the range of 100 to 300, and any noise picked up by the thermocouple will be amplified by the same amount. An instrumentation amplifier is often used because it rejects the common mode noise in the thermocouple wiring. Off-the-shelf thermocouple signal conditions, such as the Analog Devices AD594/595, simplify the hardware interface. Solid state The simplest semiconductor temperature sensor is a PN junction, such as a signal diode or the base-emitter junction of a transistor. If the current through the forward-biased silicon PN junction is held constant, the forward drop decreases about 1.8mV per C. A number of ICs take advantage of this semiconductor characteristic to measure temperature. These parts include the Maxim MAX1617, the National Semiconductor LM335, and the LM74. Semiconductor sensors have different interfaces, ranging from a voltage output to a serial SPI/ Microwire interface. The range of available temperature sensors is wide. With the right combination of software and hardware, you should be able to find one that suits your application.