Abstract: This article introduces the composition and principle of a thyristor temperature controller, elaborates on its implementation method, and focuses on the principle and implementation of PID control. Finally, it describes the application of the system. Keywords: Thyristor temperature controller; PID regulation; trigger circuit; PCI bus In laboratory analysis, the temperature of the sample must be controlled within an appropriate range, and sometimes it needs to be heated and cooled according to a specified temperature curve. If the traditional contactor on/off control method is used, not only is the temperature control accuracy low, but the energy consumption is also high, and many controlled temperatures cannot meet the specified requirements. With the further acceleration of new product development, the temperature requirements for sample analysis are becoming increasingly stringent. The search for energy-saving and environmentally friendly heating and temperature control equipment has led to the discovery of thyristor temperature controllers as an effective method. 1 Composition and Principle of Thyristor Temperature Controller Temperature measurement and control involves thermocouples collecting signals, which are then measured and output by a PID temperature regulator. The 0-10mA or 4-20mA control trigger board controls the conduction angle of the thyristor, thereby controlling the current of the heating element in the main circuit and maintaining the resistance furnace at the set operating temperature. The thyristor temperature controller consists of a main circuit and a control circuit. The main circuit consists of a thyristor, an overcurrent protection fast-acting fuse, an overvoltage protection RC circuit, and the heating element of the resistance furnace. The control circuit consists of a DC signal power supply, a DC working power supply, a current feedback loop, a synchronization signal loop, a trigger pulse generator, a temperature detector, and a PID temperature regulator. [align=left] 2 Implementation Method of Thyristor Temperature Controller 2.1 Temperature Detection and PID Regulator Composition Industrial resistance furnaces are a common type of industrial controlled object with nonlinearity, large hysteresis, and large inertia. Resistance furnaces are widely used in laboratory sample melting, segmented heating and cooling of workpieces in heat treatment, etc. Different types of PID regulators can be selected to control the temperature within an appropriate range according to the different temperature accuracy requirements of the process. For resistance furnaces that require constant temperature control without temperature recording, a digital temperature display regulator with PID regulation is used to display and regulate the temperature. The output of 0-10mA is used as a DC signal input to control the thyristor voltage regulator or trigger board to change the conduction angle of the thyristor to adjust the output power, which can fully meet the requirements, has low investment cost, is convenient and intuitive to operate, and is easy to maintain. For complex control systems requiring high temperature control accuracy and multi-point temperature control and recording, small computer control is ideal. A control system composed of a standard PC and PCI bus input/output modules can replace multiple digital temperature indicators and controllers, achieving not only equipment upgrades but also full compatibility with existing equipment. The system uses a standard PC and analog input/output boards from Kangtuo Industrial Control. The analog input board uses a PCI bus DC/DC optically isolated 32-channel 12-bit A/D board (PCI5413D), with a range of 0–312.5mV, to acquire thermocouple temperature signals. The analog output board uses a PCI bus DC/DC optically isolated 8-channel 12-bit D/A board (PCI5416D), with a range of 0–10mA. The system software completes the driver installation and initialization settings of the board software installation program; the thermocouple millivolt lookup table converts millivolt values ​​into temperature values ​​according to the thermocouple type, and the deviation between the temperature setpoint or the program-given curve value is used as the input for the digital PID controller. Due to the pure time delay characteristic of the electric resistance furnace, the digital PID design adopts the Dalin control algorithm, so that the closed-loop transfer function of the system has a first-order inertial element with pure time delay, so that the pure delay time is equal to the pure delay time of the controlled object. However, the tuning of PID parameters is relatively complicated. Based on the requirements of the process for furnace temperature stability and accuracy, the two-dimensional fuzzy controller is chosen, which is easier to implement in software design and debugging. Fuzzy control does not require the establishment of an accurate mathematical model of the controlled object. It only requires the summarization of the experience and data of manual operation into a more complete language control rule. The design of a typical two-dimensional fuzzy controller usually includes the following four components: (1) Fuzzification: The assignment table of fuzzy variables is determined by normal distribution, and the accurate quantities of temperature error and error change are converted into fuzzy quantities. (2) Fuzzy reasoning: Fuzzy reasoning is performed according to the language control rule to find the control rules corresponding to all fuzzy relations of the system and place them in the rule base. (3) Fuzzy decision: The fuzzy quantities of control parameters are obtained by methods such as "maximum membership method" and "weighted average decision method". (4) Defuzzification: The result after fuzzy decision is converted from fuzzy quantity into accurate quantity that can be used for actual control. [align=left]2.2 Trigger Circuit The trigger circuit of the thyristor should meet the following requirements: the width of the trigger pulse should ensure the reliable conduction of the thyristor; the trigger pulse should have sufficient amplitude; it should not exceed the gate voltage, current and power rating, and be within the reliable triggering area; it should have good anti-interference performance, temperature stability and electrical isolation from the main circuit. Using a single junction transistor or triode circuit is relatively simple, reliable and easy to adjust, and can also be implemented with integrated circuits produced by professional manufacturers. The system can use the ZK-1 thyristor voltage regulator as the trigger circuit, which can conveniently realize the manual and automatic adjustment of the equipment. 2.3 Selection of thyristor The main parameters of the thyristor are: (1) Rated voltage Off-state repetitive peak voltage u: the positive peak voltage that can be repeatedly applied to the device when the gate is open and the junction temperature is at the rated value. Reverse repetitive peak voltage: the reverse peak voltage that can be repeatedly applied to the device when the gate is open and the junction temperature is at the rated value. Usually, the smaller value of the thyristor and the reverse repetitive peak voltage is taken as the rated voltage of the device. When selecting, the rated voltage should have a certain margin. Generally, the rated voltage should be 2 to 3 times the peak voltage that the thyristor can withstand during normal operation. (2) Rated current: The average value of the maximum power frequency sinusoidal half-wave current allowed to flow when the stable junction temperature of the thyristor does not exceed the rated junction temperature under ambient temperature of 40°C and specified cooling conditions. When using, the thyristor should be selected according to the principle that the actual current is equal to the effective value of the average current in the on-state. A certain margin should not be left. Generally, it should be 1.5 to 2 times. 2.4 Installation and operation: Since the main circuit current of the thyristor temperature controller is relatively large, it is very important to select a suitable line cable diameter and ensure reliable connection of the line to prevent the load from short-circuiting and breaking down the thyristor. Considering that the thyristor is easily damaged when the current changes suddenly, the current should be manually adjusted to rise slowly when the furnace is turned on and the current should be reduced when the furnace is turned off. 3. Application of Silicon Controlled Temperature Controllers Selecting high-quality refractory materials such as advanced alumina, refractory fiber, and lightweight bricks for the furnace body is crucial. Temperature control equipment using silicon molybdenum rods, silicon carbide rods, and other electric heating elements provides the heat source. Employing silicon controlled temperature controllers ensures stable furnace operation and significantly improves real-time performance and control accuracy. Furthermore, with computer and PCI bus control, one computer can simultaneously control multiple resistance furnaces. This not only achieves automatic program control but also enables multi-point temperature display, recording, storage, and alarm functions. The system allows for the interchangeability of most components, such as trigger circuits, enabling upgrades to traditional equipment. This automates equipment management and simplifies equipment maintenance and repair. [ Click to download: Application of Silicon Controlled Temperature Controllers in Resistance Furnaces Editor: Chen Dong]