The principle of temperature measurement of T12 soldering iron tip

Thermocouple is a temperature sensing element. It measures the temperature directly and converts the temperature signal into a thermoelectric potential signal, which is converted into the temperature of the medium being measured by an electrical instrument. The basic principle of thermocouple temperature measurement is two different components of the material conductors form a closed loop, when the two ends of the temperature gradient exists, there will be a current through the loop, at this time there is an electric potential between the two ends of the electric potential - thermal electromotive force, which is known as the Seebeck effect (Seebeck effect). Two different components of the homogeneous conductor for the heat electrode, the higher temperature end for the working end, the lower temperature end for the free end.

By analysing it, we can know that the heating wire itself is the heat generator and the working end of the thermocouple. So and the positive pole of the soldering iron connected to the T12-OUTPUT end at the same time is also a thermocouple end, the collection of T12-OUTPUT end of the voltage can be calculated on the soldering iron head temperature. This may be asked, T12-OUTPUT voltage is not (5-20v)? How can it be thermoelectric potential, indeed, but do not forget that the T12-OUTPUT voltage is PWM wave, the theory is that there is a microcontroller PWM voltage of 0 v, and the T12-OUTPUT voltage at this time should be 0. But because of the thermoelectric potential it will have a weak voltage, which is what we need to measure the temperature voltage. This voltage is too small, the ADC function of the microcontroller can not test, need operational amplifiers for amplification.