(A) PCB thermal design of the test method: Thermocouple
Of course, the practical application of thermoelectric phenomena is the use of thermocouples to measure temperature. Electron energy and scattering the complex relationship between the making of different metal thermoelectric power are different. Since the thermocouple is such a device, and its thermoelectric power between the two electrodes is the difference between the hot end and cold end of thermocouple temperature difference between the instructions, if all the thermoelectric power of metals and alloys are different, not may be used to measure the temperature of the thermocouple. The potential difference is called sebe (Scebeek) effect. A pair of conductors of different materials A and B, one of its contacts to maintain the temperature T1, the two free end maintained at a lower temperature To. Contacts and the free end are located in the area of uniform temperature, while the two conductors have experienced the same temperature gradient. In order to measure the free end of A and B difference between the thermoelectric power, a conductor on the same material C, respectively, in the temperature to A and B connected with the conductor, received the detector temperature T1. Very clear that the Seebeck effect is the connection point never phenomenon, but with the temperature gradient of the situation. In order to correctly understand the performance of the thermocouple, regardless of how this can not be overstated.

The use of thermocouple very wide variety of problems are encountered. Therefore, this chapter can only be involved in a number of important aspects of thermocouple temperature measurement. Thermocouple temperature in many industries are still the main means of measurement, especially in the steel and petrochemical industry especially. However, with the progress of electronics, the resistance thermometer in the industry, more and more widespread application, and the thermocouple is no longer only the most important industrial thermometer.

Resistance thermometers and thermocouple compared (resistance measurements and thermoelectric power measurements in comparison), two components of its working principle advantage of the fundamental difference between. Resistance thermometer resistance components where direct temperature region, along with lead and lead independent of the temperature gradient. However, the thermocouple cold junction by measuring the potential difference between the two electrodes to measure the cold end and hot end temperature difference between. For an ideal thermocouple, potential difference only with the ends of the temperature difference. However, an actual thermocouple, temperature gradients in the wire of a galvanic heterogeneity will lead to changes in potential difference, which is still limit the accuracy of a thermocouple element.

Seven internationally adopted thermocouple, the so-called "standard thermocouple," listed in the table 5-3. Table 5-3 also lists the name of each electrode elements, each alloy of common trade names and thermocouple letter code. These letters originally code-named by the American Instrument Society (InstrumentSocietyofAmerican) are introduced, but is now widely used around the world. These letters can be used as various types of code.

(B) PCB thermal design of the test method: temperature rise test
For thermal design, we must work in the follow-up to the actual verification to determine chip temperature are within the normal limits. Are generally larger than the chip select and heating components to test its maximum load of the operating temperature, that is, long look at the operating temperature at full load conditions. Before the test designers to determine hot from the large chips and components, while the maximum temperature point for the chip as required (maximum temperature points can be compared with the infrared heat into the instrument to determine, as shown in Figure 5-4 for the infrared heat into the phase diagram).

Temperature measurement using thermocouple wire, 2m length is generally about the election, the thread of connection points to be placed in the measuring points, and fixed with adhesive tape (adhesive tape to a high temperature and high viscosity, to ensure a high temperature and the temperature is not out of measurement accuracy of the data). Also, be aware line can not break, otherwise it will affect test accuracy.