label: PCB thermal design,Printed-circuit board
First, the test methods PCB thermal design: Thermocouple
Of course, the practical application of thermoelectric phenomena is the use of a thermocouple to measure the temperature. The complex relationship between the electron energy and scattering, so that the thermoelectric potential of different metals from each other. Since the thermocouple is such a device, the thermoelectric potential difference between two electrodes which are indicative between thermocouple temperature difference between hot and cold end, if all metals and alloys thermoelectric power is not the same, it is impossible to use a thermocouple to measure the temperature. This potential difference is called Seebeck effects. One pair of conductors of different materials A and B, one contact is maintained at the temperature T1, the two free ends is maintained at a lower temperature To. The free end of the contact and are located in the region of uniform temperature, and the two conductors are subjected to the same temperature gradient. In order to measure the free end of the thermoelectric power between the difference A and B, a pair of conductor C of the same material, connected to point B, respectively, at a temperature of the conductor A, a temperature T1 to the detector. Very obvious, the Seebeck effect is by no means a connection point on the phenomenon, but with the temperature gradient related phenomena. In order to properly understand the thermocouple performance, regardless of how this can not be overstated.
Thermocouple using a very wide range of problems encountered are varied. Therefore, this chapter only involve certain important aspects of thermocouple. Means of thermocouples is still one of the main temperature measurement in many industries, particularly in the steel and especially in the petrochemical industry. However, with the progress of electronics, resistance thermometers used in industry are increasingly being used, the thermocouple is no longer only the most important industrial thermometer.
Resistance thermometers and thermocouples compared (resistance measurement and thermoelectric power measurements compared), the advantage lies in the fundamental difference between the two components works on. Resistance thermometer indicates the temperature of the resistance element in your area, it has nothing to do with the leads and leads along the temperature gradient. However, the cold end of the thermocouple is measured by the potential difference between the electrodes to measure the temperature of the cold end and the difference between the hot end. Ideal for a thermocouple, the temperature difference between the potential difference across the only relevant. However, for an actual thermocouple, temperature gradient of the thermocouple wire can cause some unevenness of the potential difference change, this is still a factor limiting the accuracy of the thermocouple.
Seven kinds of international adoption thermocouple, the so-called "standard thermocouple " , are listed in Table 5-3. Table 5-3 also lists the name of each electrode composition, common trade names for each alloy and the letter of the thermocouple. These letters originally introduced by the Code Instrument Society of America, but has now been widely adopted around the world. These letters can be used as various types of code.
Second, the test methods PCB thermal design: the temperature test
For thermal design must be verified in the subsequent actual work to determine the chip operating temperatures are within the normal range.
Select fever are generally larger than the chips and components to test its maximum load operating temperature, it is to see the situation for a long time working temperature at full load. Before the test is determined by the heat capacity of the chip designers and components, in addition to the highest point of the chip temperature also requested ( maximum temperature points can be used to phase infrared instrument to determine, as shown in Figure 5-4 is an infrared heat a phase diagram).
Temperature measurement using thermocouple wire, cable length is usually selected around 2m, the thread of connection points to be placed in the position of the measuring point and fixed with tape (tape must be a high-temperature and high viscosity to ensure that the high-temperature and temperature without departing measurement accuracy of the data). Also, pay attention to the line can not fold, otherwise it will affect test accuracy.
Source://www.seekic.com
