Introduction to the Component Functions of Thermostatic Electric Solder Irons
The circuit diagram is designed, and the next step is to arrange the components. The constant temperature adjustable electric soldering iron is mainly controlled by thermocouples and integrated circuits, with high temperature control accuracy and adjustable welding temperature. It is a high-strength engineering plastic handle, mainly composed of these components: two black and red diodes, a soldering iron core, a light-emitting diode, a thermocouple, an adjustable resistor, a sensor, HA17358, two electrolytic capacitors, a metal film resistor, and a voltage regulator.
Each component has its own purpose: adjustable resistors are used to adjust temperature, voltage regulators and metal film resistors are used to protect circuits, and electrolytic capacitors are used to filter and convert AC to DC. Thermocouple is used to detect the temperature of the soldering iron core, and it stops heating when the temperature of the soldering iron core reaches the temperature of the adjusting handle.
This is to emphasize the application principle of thermocouple temperature measurement:
The application principle of thermocouple temperature measurement:
Thermocouples are one of the most commonly used temperature detection components in industry. Its advantages are:
① High measurement accuracy. Due to the direct contact between the thermocouple and the measured object, it is not affected by the intermediate medium.
② Wide measurement range. Common thermocouples can measure continuously from -50 to+1600 ℃, while some special thermocouples can measure temperatures as low as -269 ℃ (such as gold iron nickel chromium) and up to+2800 ℃ (such as tungsten rhenium).
③ Simple construction and convenient use. Thermocouples are usually composed of two different types of metal wires, and are not limited by size or beginning. They have a protective sleeve on the outside, making them very convenient to use.
a. The basic principle of thermocouple temperature measurement
Solder two different materials of conductors or semiconductors A and B together to form a closed circuit. When there is a temperature difference between the two attachment points 1 and 2 of conductors A and B, an electromotive force is generated between the two, resulting in a current of varying magnitude in the circuit. This phenomenon is called the thermoelectric effect. Thermocouples work by utilizing this effect.
b. Types and Structure Formation of Thermocouples
(1) Types of thermocouples
Commonly used thermocouples can be divided into two categories: standard thermocouples and non-standard thermocouples. The standard thermocouple referred to is a thermocouple that has a national standard that specifies the relationship between its thermoelectric potential and temperature, allowable errors, and a unified standard graduation table. It has accompanying display instruments available for selection. Non standardized thermocouples are not as good as standardized thermocouples in terms of usage range or magnitude, and generally do not have a unified graduation table. They are mainly used for measurement in certain special occasions. Standardized thermocouple
(2) In order to ensure the reliable and stable operation of thermocouples, the structural requirements for thermocouples are as follows:
① The welding of the two thermoelectric electrodes that make up the thermocouple must be firm;
② The two thermoelectric electrodes should be well insulated from each other to prevent short circuits;
③ The connection between the compensating wire and the free end of the thermocouple should be convenient and reliable;
④ The protective sleeve should ensure sufficient isolation between the thermoelectric electrode and harmful media.
c. Temperature compensation of thermocouple cold end
Due to the fact that the materials of thermocouples are generally expensive (especially when precious metals are used), and the distance between the temperature measurement point and the instrument is very far, in order to save thermocouple materials and reduce costs, compensation wires are usually used to extend the cold end (free end) of thermocouples to the control room with relatively stable temperature and connect them to the instrument terminals. The function of the thermocouple compensation wire is only to extend the thermoelectric electrode, causing the cold end of the thermocouple to move to the instrument terminal in the control room. It itself cannot eliminate the impact of temperature changes at the cold end on temperature measurement and does not have a compensation effect. Therefore, other correction methods need to be used to compensate for the impact of the cold end temperature t0 ≠ 0 ℃ on temperature measurement.
