Three chang instrument analytical basic knowledge of the thermocouple with the story

Whether you are to build the temperature sensing device still need to add to the larger system, you should be familiar with thermocouples and understand how to design the thermocouple interface. Bob Perrin in 1999 Circuit Cellar online articles & other; The basic knowledge of thermocouple & throughout; Described in the theme, and more.

a mathematician, a physicist and an engineer at lunch. The barman three Sir, & other; I heard so many what?

mathematician replied, & other; The ratio of PI is the perimeter of a circle to its diameter.

physicist answered and said to them, & other PI is 3. 14159265359.

engineer looked up and said gently, & other; Oh, about three PI, & throughout; And then quickly back to his napkin back graffiti.

the problem is not the engineer is careless, careless or social incompetence. The key is we are very practical. We are in an ideal world not part of the solution. This means that we must be able to apply the concept to the actual problem, and know that some effects can be neglected in our application.

for example, when a first or second order filter is designed, considering the tolerance and temperature dependence of the element is affordable 3 is often close enough to the approximation of PI.

but, before we can run and make a rough estimate, we must know that we are involved in the design of the system of physics. Seems to be a rough estimate of the theme, there is no strong understanding of issues involved with thermocouple temperature measurement.

thermocouple temperature sensor is simple, consisting of two different metal wire. The device has the advantages of simple structure, easy to use. But, like any electronic components, they need a certain amount of interpretation. The purpose of this article is to introduce and explain how to use the thermocouple and how to design the thermocouple interface. Two metal tail

figure 1 a shows the thermocouple. A knot is specified as the hot junction. Another node is designated as cold junction or reference. In the loop of electric current and thermal contact and is proportional to the temperature difference between the cold junction. Thermocouple measuring temperature differences, rather than the absolute temperature.

understand why current form, we must return to the physical. Unfortunately, I'm not a physicist, so this explanation could bend a concept or two, but I still continue.

consider a uniform wire. If applying heat in the end, the end electronics become more energy. They absorb energy and removed from its normal state and enter a higher energy state. Some will be fully released from their atoms. The new release of high-energy electrons to move to the cold end of the wire. As these electrons along the wire to slow down, they will transfer their energy to other atoms. This is the energy ( Hot) From the hot end of the line to the cold.

when the electrons are accumulated in the cold end of the wire, they experience the electrostatic repulsion. On the cold end less high-energy electrons to move to the hot end of the wire, this is how to remain neutral charge in the conductor.

from the hot end of the cold end to the mobile electronic colder than from the hot end to move to the high-energy electrons move more slowly. But, at the macro level, keep the balance of charge.

when using two different metal thermocouple loop, as shown in figure 1 a, the differences of two metal to electron affinity of makes when the two junction temperature difference between can produce electric current.

with electrons from the cold and moved to the hot junction, the less high-energy electrons can be in a kind of metal is easier to move than another. Move from the hot end to the cold end electronic has absorbed a great deal of energy, almost the same and free to move in two lines. This is why the reasons of the current in the circuit.

I may miss some of the more sophisticated physical points, but I think I played. If anyone can provide a more in-depth or detailed explanation, please email me. Write one of the best things for technical audience to learn from my readers.