Abstract: In recent years, with the rapid development of computer technology, DCS (Distributed Control System) has been widely used, especially in replacing relays, completing logic control, sequential control, and interlocking protection, showing unique advantages and thus achieving great success in the industrial field. Keywords: DCS; molecular sieve dryer; air compressor; timing control 1 Overview In recent years, with the rapid development of computer technology, DCS (Distributed Control System) has been widely used, especially in replacing relays, completing logic control, sequential control, and interlocking protection, showing unique advantages and thus achieving great success in the industrial field. With the advancement of distributed control system technology, especially with the decentralized system structure, enhanced computing power, and improved communication networks, distributed control systems have rapidly expanded from the original field mainly based on analog quantities to continuous control, and have begun to enter the industrial fields of batch control and process control, which were traditionally considered to be dominated by relay groups and instruments. For a real control process, whether it is the control of a production line or the equipment of an engineering project, it is often a mixture of intermittent and continuous control. At present, distributed control systems have made new breakthroughs in concept, design, performance-price ratio, and application fields. Its high reliability, flexible combination, simple programming, clear monitoring, and convenient maintenance are precisely the hopes for industrial automation. In particular, distributed control systems integrate computers, instruments, and electrical controls, making industrial production process control systems more practical, economical, and reliable, thus becoming an ideal tool for achieving industrial automation. 2. Process Requirements The molecular sieve system is a complete set of equipment配套 (matching) air separation equipment for purifying air. The air compressor is used to compress and transport air for the oxygen generator, serving as the raw material air for the air separation equipment. During production, the instrumentation and control system is a crucial component of the equipment, responsible for setting process parameters, monitoring detection points, and controlling loops. The molecular sieve unit's program switching system uses an electronic switcher for automatic control. Previously, the dryness-resistance reset button and time setting button on the programmable controller were mechanical. During the automatic regeneration control of the dryer, the timing of the four processes—pressure reduction, heating, cold blowing, and pressure increase—needed to be controlled. These mechanical buttons would malfunction over time, frequently crashing and becoming inoperable, significantly impacting the production process, causing various faults, severely affecting production, and making control feasibility difficult to guarantee. The original instrumentation and control system of the air compressor used an outdated DDZ-III type unit-combination instrument. After long-term use, its outdated control methods and logic operations could no longer meet the increasingly evolving process requirements. The control circuits primarily used mechanical relay groups; to achieve alarm interlocking functionality at a single measuring point, a large number of relays were often required, inevitably increasing mechanical failures such as relay coil burnout, excessive contact actuation leading to carbon buildup, and relay control malfunction. To ensure reliable operation of the process flow, the instrumentation and control systems of the molecular sieve dryer and air compressor underwent upgrades. After comparing the cost-effectiveness of various options, we ultimately selected the JX-300 DCS system developed by Zhejiang University to upgrade the aforementioned instrumentation and control systems. 3. Hardware Configuration The automatic control system for the molecular sieve system dryer and air compressor requires solenoid valves, contactors, etc., so the intermediate relays output by the DCS must have a certain contact capacity. Therefore, we selected the JX-300F programmable controller developed by Zhejiang University for the automatic control of the molecular sieve system dryer regeneration system and the air compressor automatic control system. The JX-300 controller has the advantages of complete functionality, reliable operation, and dual redundancy. Its system hardware configuration is compact, which greatly simplifies wiring, optimizes design, and improves equipment reliability. The basic components are shown in Figures 1 and 2. The DCS's switch output signals are used to trigger relays and alarms, while the input signals are used to receive detection signals and feedback signals during operation, providing a basis for the intelligent control of the molecular sieve instrumentation control system and the air compressor automatic control system. 4. System Software Design and Programming The DCS control program is written using the Zhejiang University JX-300 programmer. The program design for the molecular sieve dryer regeneration control system is based on process requirements. In the programming flow of the molecular sieve dryer regeneration control system, a step-by-step button program was added to facilitate process operation, such as when the equipment is first started up or in other situations. Regardless of the step in the control process, pressing the step-by-step button will automatically jump to the next step, greatly facilitating production. The DCS uses program control logic; when the control logic needs modification, only the program needs to be modified. Therefore, it is highly flexible and expandable, while also greatly facilitating system maintenance. 5. Implementation and Characteristics of Intelligent Control of the Unit DCS Since the DCS program is executed sequentially in a scanning manner, time pulse trigger programs are programmed using timers in the DCS to send a pulse signal at regular intervals to trigger a detection program, thereby achieving the function of timed detection. T0 is a time delay relay, and the data register D stores the time interval for sending pulses; M0 is the pulse signal, which can be used to trigger the execution of a DCS program (as shown in Figure 3). The molecular sieve instrument control system uses DCS control mainly to complete the four processes in the molecular sieve regeneration process. It can perform logical judgment, timing, counting, memory, and arithmetic operations. The air compressor automatic control system adopts DCS control, mainly used to complete the acquisition of process data during air compressor operation, and to control unit start-up, shutdown, and parameter over-limit alarm functions. The DCS control system, primarily based on loop regulation and supplemented by sequential control, conforms to the logic algorithm for unit start-up and shutdown. Furthermore, the DCS uses programmable control logic; when the control logic needs modification, only the program needs to be modified. Therefore, it is highly flexible and expandable, greatly facilitating system maintenance. 6. Conclusion In the molecular sieve dryer regeneration instrumentation and control system and the air compressor automatic control system, the adoption of the DCS automatic control system has ensured consistently good operating conditions since its commissioning. The DCS automatic control system is reliable, stable, has strong anti-interference capabilities, and is convenient to operate and maintain, creating significant economic benefits for us.