Component function introduction of constant temperature electric soldering iron
Function introduction of some components
After the circuit diagram is designed, the next step is to arrange the components. The thermostatically adjustable electric soldering iron is mainly controlled by thermocouples and integrated circuits. It has high constant temperature precision, adjustable welding temperature and high-strength engineering plastic handle. The device consists of two black and red diodes, a soldering iron core, a light-emitting diode, a thermocouple, an adjustable resistor, a sensor, one HA17358, two electrolytic capacitors, a metal film resistor and a voltage regulator tube and so on.
Each component has its own use: the adjustable resistor is used to adjust the temperature, the voltage regulator tube and the metal film resistor are used to protect the circuit, and the electrolytic capacitor is used to filter and convert AC to DC. The thermocouple is used to detect the temperature of the soldering iron core, and when the temperature of the soldering iron core reaches the temperature of the adjustment handle, the heating is stopped through it.
This is what needs to be emphasized is the application principle of thermocouple temperature measurement:
The application principle of thermocouple temperature measurement:
Thermocouples are one of the most commonly used temperature sensing elements in industry. Its advantages are:
① High measurement accuracy. Because the thermocouple is in direct contact with the measured object, it is not affected by the intermediate medium.
②Wide measurement range. Commonly used thermocouples can measure continuously from -50 to +1600°C, and some special thermocouples can measure as low as -269°C (such as gold-iron-nickel-chromium) and up to +2800°C (such as tungsten-rhenium).
③The structure is simple and easy to use. Thermocouples are usually composed of two different metal wires, and are not limited by size and opening. There is a protective sleeve outside, which is very convenient to use.
a. Basic principles of thermocouple temperature measurement
Weld two conductors or semiconductors A and B of different materials to form a closed loop. When there is a temperature difference between the two attachment points 1 and 2 of the conductors A and B, an electromotive force is generated between the two, thus forming a large and small current in the circuit. This phenomenon is called the thermoelectric effect. Thermocouples use this effect to work.
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 refers to the thermocouple that the national standard specifies the relationship between thermoelectric potential and temperature, allowable error, and has a unified standard graduation table. It has matching display instruments for selection. Non-standardized thermocouples are not as good as standardized thermocouples in terms of range or magnitude of use, and generally do not have a unified graduation table, and are mainly used for measurement in some special occasions. Standardized thermocouple
(2) The structural form of the thermocouple In order to ensure the reliable and stable operation of the thermocouple, its structural requirements are as follows:
① The welding of the two hot electrodes that make up the thermocouple must be firm;
②The two thermal electrodes should be well insulated from each other to prevent short circuit;
③The connection between the compensation wire and the free end of the thermocouple should be convenient and reliable;
④The protective sleeve should be able to ensure that the hot electrode is fully isolated from the harmful medium.
c. Temperature Compensation of Thermocouple Cold Junction
Since thermocouple materials are generally expensive (especially when precious metals are used), and the distance from the temperature measurement point to the instrument is very far, in order to save thermocouple materials and reduce costs, compensation wires are usually used to connect the cold end of the thermocouple (free Terminal) extends to the control room where the temperature is relatively stable, and connects to the instrument terminal. The role of the thermocouple compensation wire is only to extend the hot electrode, so that the cold end of the thermocouple moves to the instrument terminal in the control room. It cannot eliminate the influence of the temperature change of the cold end on the temperature measurement, and does not have a compensation effect. Therefore, other correction methods need to be used to compensate the influence on the temperature measurement when the cold junction temperature t0≠0℃.
When using thermocouple compensation wires, it is necessary to pay attention to the type matching, the polarity cannot be wrongly connected, and the temperature at the connection end of the compensation wire and the thermocouple should not exceed 100°C.
