电子工程温度测量热电偶大学毕业论文外文文献翻译及原文Word格式文档下载.docx

1、温度测量 - 热电偶文献、资料英文题目：文献、资料来源：文献、资料发表（出版）日期：院 （部）： 专 业：班 级：姓 名：学 号：指导教师：翻译日期： 2017.02.14University of TasmaniaSchool of EngineeringKNE222 Electronic EngineeringTemperature Measurement ThermocouplesIntroduction.A thermocouple is formed when two dissimilar metals are joined. If a second joint is made fr

2、om the same materials, and one joint is heated with respect to the other, then a current will flow round the loop. Alternatively, if the circuit is opened, then a small voltage will appear at these terminals, proportional to the difference in temperature between the junctions. This voltage is known

3、as the Seebeck voltage, after Thomas Seebeck who discovered the phenomenon in 1821. Figure 1. Conceptual Application of a Thermocouple（Ref: ”Operational Amplifier Circuits Theory and Applications” E.J Kennedy. HRW Inc.） In order to use a thermocouple to measure temperature with one junction, a refer

4、ence temperature must be established for the other. This can be done as illustrated in Figure 1, where a 0 C ice bath is provided for the reference junction. However an ice bath is not really practical for everyday measurements. Fortunately it is possible to introduce a correction voltage into the c

5、ircuit so that the reference junction appears to be at zero degrees C. An example of this will be presented later.Thermocouple Characteristics.Table 1 provides a list of commonly used thermocouple materials, together with the useful range of temperatures for each. While the Seebeck voltage increases

6、 with the junction temperature difference, the relationship is unfortunately not entirely linear. The proportionality constant is known as the Seebeck coefficient, , and has the units V/C. Table 1 provides typical values at 25 C; it also gives some idea of how varies over the useable temperature ran

7、ge for each thermocouple. Table 1. Characteristics of common Thermocouples “Operational Amplifier Circuits Theory and Applications” E.J Kennedy. HRW Inc.）Figure 2 shows the variation of as a function of temperature for K and T Type thermocouples. The K type device offers almost constant values over

8、much of its useful range, and therefore is useable there without linearization. In contrast, the Seebeck coefficient of the T type thermocouple varies considerably with temperature and as a result these devices must be corrected using a linearization algorithm in order to obtain accurate temperature

9、 measurements. Figure 2. Variation of the Seebeck Coefficient with Temperature, T and K Type Thermocouples. ”Operational Amplifier Circuits Theory and Applications” E.J Kennedy. HRW Inc.）Finally, figure 3 shows the Seebeck Voltage as a function of temperature difference for the thermocouples listed

10、in Table 1. In each case the reference junction （sometimes called the cold junction）, is held at zero C, thus all these curves pass through the origin. Because they are slightly non-linear, it is common to apply a linearization algorithm to the Seebeck Voltage （E）, in order to obtain the correct tem

11、perature （T）. In its simplest form this algorithm assumes that the relationship between Seebeck Voltage and temperature is linear and an equation of the form is used. This assumption results in errors, particularly over a wide range of temperatures. For more accurate results, higher order polynomial

12、s are used.Figure 3. Seebeck Voltage as a function of Temperature Difference. （Note: The Reference Junction temperature is 0 C.） （Ref:A Practical Thermocouple Circuit.The schematic shown in Figure 5 is that of an electronically compensated thermocouple amplifier. In this case a J type thermocouple （

13、Iron-Constantan） has been used. The two metallic junctions that make up this thermocouple, J1 and J2, are shown on the diagram. J1 is the sense junction, while J2 is the reference junction. Ideally J2 should be held in an ice bath at 0C, as shown in Figure 1, however this is generally inconvenient.

14、Instead it is more usual to provide electronic reference junction compensation. This involves measuring the temperature of the reference junction and adding a compensating voltage to the thermocouple, so that the residual Seebeck voltage matches that of a similar thermocouple with its reference junc

15、tion held at 0C.Generation of a Compensation VoltageTable 2 shows the Seebeck voltage as function of temperature for J type thermocouples, （referenced to 0C）. From this we see that the thermocouple voltage will be 1.277mV when the sense junction is at room temperature, （25C or 298K）. Therefore this voltage must be subtracted from the thermocouple potential, when the reference junction is at 25C, in order to leave a potential proportional only to the sense junction temperature.If we can keep th