Abstract : This paper introduces the application of a programmable logic controller (PC) on a 250t hydraulic baler, and discusses the problems encountered in practical application and corresponding solutions. Keywords : Programmable logic controller; Baler; Solenoid valve; Relay Introduction With the determination of Taiyuan Iron & Steel Group's (TISCO) 500,000-ton stainless steel production target, the difficulties faced by processing plants in ensuring scrap steel supply will increase. How to utilize existing sites, equipment, and limited funds to serve steelmaking units is a challenge we face. It is well known that after sorting, large quantities of light, fragmented, and thin stainless steel scrap will occupy a large area if directly piled up, while direct feeding into the furnace will increase charging time and furnace consumption, seriously affecting steel output and quality. Currently, baling and pressing are widely used to solve this problem, which can reduce the floor space, reduce charging time, increase the heavy material ratio, improve smelting efficiency, and reduce furnace consumption. The baler is the main equipment for realizing this processing method. With the continuous progress and improvement of science and technology, PC technology is widely used in balers. [b]1 Composition and Working Principle of the PC Control System for the 250t Baler 1.1 PC Control System[/b] The 250t hydraulic baler uses the F-series PC from Mitsubishi Corporation of Japan, which boasts high anti-interference capabilities and high reliability, for electrical automatic control. This series of PCs is an ideal control tool for small industrial processes and equipment, highlighting its ease of operation and convenient application. Based on equipment requirements, a control system composed of the basic unit F1-60MR-UL and the expansion unit F1-40ER-UL is used. This system uses a single-chip microprocessor as its core, primarily employing switch control. With the support of a monitoring program, it performs logical operations and control on 60 input points (36 points for the main unit and 24 points for the expansion unit) and 40 output points (24 points for the main unit and 16 points for the expansion unit). In terms of hardware, it mainly consists of a power supply module, opto-isolated DC input interface circuit, micro relay contact output interface circuit, keyboard display interface circuit, microprocessor, monitoring program memory, user program memory, backup battery power supply, and expansion modules. Its operating voltage is available in two types: AC110V～120V+10% (50/60Hz) and AC220V～240V+10% (50/60Hz). Here, AC220V (50Hz) power is used. [b][align=center]For details, please click: Application and Modification of PC in a 250t Packing Machine[/align][/b]