Application of Yudian Intelligent Instrument AI-808 in Constant Temperature Control System

1. Overview

With the increasing use of electric heating equipment in industrial applications, various control methods have been implemented in different automatic heating systems. Traditionally, contactors were used to switch the main circuit on and off, aiming to regulate temperature. However, this method has several drawbacks. It lacks precision in temperature control, and the frequent switching of AC contactors when the set temperature is reached can lead to contact wear, welding, or even failure, resulting in loss of control over the temperature. Additionally, the repeated operation of contactors causes voltage fluctuations in the power grid and may damage the heating elements, negatively impacting the economic performance of enterprises.

To address these issues, our company has adopted advanced technology, including the AI series intelligent instruments and thyristor-based control systems from Yudian Automatic Technology Co., Ltd., to achieve more accurate and stable temperature regulation.

Intelligent power regulators are widely used in a variety of electric heating equipment such as hot rolling mills, electric ovens, drying chambers, and lighting systems. These devices offer flexible control modes, easy manual-to-automatic switching, and high-precision temperature control. The system typically includes an AI-808 intelligent controller, a thyristor module, a trigger, and a fast-acting fuse. By using non-contact control, the system enhances resistance to vibrations, corrosion, and interference, ensuring high stability and reliability. Its compact design makes installation and maintenance convenient, making it ideal for industries such as heat treatment, chemicals, textiles, food processing, automotive, and electronics.

2. System Structure and Working Principle

The temperature control system consists of an air switch, thyristor, trigger, and smart meter (as shown in Figure 1). The thyristor is mounted on a heat sink, with an exhaust fan and temperature switch also installed to ensure proper cooling and prevent overheating. This setup helps maintain optimal working conditions for the thyristor.

The thyristor is a bidirectional device that includes varistor or RC absorption protection and a fast fuse for safety. Specific selection should be based on the relevant technical manual.

The intelligent power regulator functions as a “zero-voltage switch” using thyristors. When the AC voltage crosses zero, the thyristor turns on for a certain number of cycles and then turns off for others, adjusting the duty cycle to control the load power. This zero-crossing triggering ensures a complete sine wave output, avoiding the generation of higher harmonics and reducing interference with the power grid and other equipment. It also improves the power factor and efficiency compared to phase-shifting regulators.

The AI-808 temperature controller integrates an embedded system with PID self-tuning capabilities. It allows users to set temperature rise or fall control based on specific needs. It supports various sensor types, such as thermocouples, thermistors, and linear voltage/current signals, and offers standard output signals like 0-10V, 1-10mA, and 4-20mA. Its output power is proportional to the control signal. The system supports both position adjustment and AI-based fuzzy logic PID control, along with parameter self-tuning for closed-loop or open-loop operations. Manual adjustments can also be made via a potentiometer for precise temperature control.

The AI-808 instrument also features segmented power limiting and multi-curve programming. It can communicate with a host computer to form a network for data acquisition and control of multiple temperature cabinets.

3. Application Conditions

- Load type: Capacitive or inductive - Power supply: Three-phase four-wire 380V ±10% 50Hz or single-phase 220V - Ambient temperature: -10°C to +45°C - Environment: No conductive dust, no corrosive gases, no severe vibration - Ventilation: The electrical cabinet must have good ventilation to ensure proper heat dissipation for the thyristor

4. System Debugging and Precautions

4.1 Input and Output Circuit Check

Ensure all wiring follows the system schematic diagram, especially the trigger circuit connections. Before use, the meter should be correctly configured. Set the input specifications according to the on-site temperature sensor type, and configure the output type based on the control signal received by the trigger.

4.2 Dummy Load Test

During testing without an actual load, connect a light bulb to the main circuit output. Set the meter to manual mode and press the > or < key to adjust the bulb's brightness. Observe if the brightness changes accordingly, which confirms that the trigger circuit and overall wiring are correct.

4.3 Manual Adjustment and Self-Tuning of Smart Meters

In real-world applications, users often adjust temperature within a specific range based on process requirements. The AI-808 instrument uses fuzzy logic PID control for precise regulation. With its self-tuning function, one or two auto-tuning cycles can be performed to achieve optimal control. Different time periods can be programmed to meet varying temperature control needs.

5. Conclusion

Since its commissioning, the temperature control cabinet produced by our company has operated smoothly with self-tuning based on on-site temperature readings. It fully meets user requirements and has been functioning properly for years without requiring any maintenance. This solution proves to be reliable, efficient, and suitable for long-term industrial use.

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