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Practical Application of PLC in Cement Bulk Loading Machines 1 Composition of the Bulk Loading Machine The SZ series of fixed cement bulk loading machines consist of components such as a feed connection, a telescopic discharge sleeve with a bulk loading head, a discharge cone, a winch system (including a rope-release switch device and a full-load controller), a dust collection system, a dust removal system, a discharge valve, an air supply valve, and gates. The bulk loader can be installed either at the bottom of the warehouse or on the side of it, and is used in conjunction with the corresponding unloading device. The bulk loader on the warehouse side is equipped with an air-conveying chute (including a dedicated high-pressure centrifugal fan), while the bulk loader at the bottom of the warehouse is fitted with a short chute for transportation (including a dedicated high-pressure centrifugal fan), in order to meet the requirements of the process layout. 2 Principle and process of the bulk loader: After the cement tank truck arrives at the designated location, the \"lower\" button on the control device is pressed to lower the loading head to the tank truck’s feeding port, preparing it for loading. Press the “Load” button to load. At this time, the high-pressure centrifugal fan operates, allowing the material to pass smoothly through the conveying chute after the discharge solenoid valve is opened ； At the same time, the air supply solenoid valve opens to connect to the air supply ； The dust collection fan starts simultaneously; the dust collection solenoid valve opens, causing the cylinder to move and push the flap inside the housing into an open position. At this point, the dust removal solenoid valve is closed, the air storage tank holds gas, and the dust collection system enters operation mode ； At the same time, the level control fan and the activated ash fan are turned on. 0.5 seconds later, the unloading solenoid valve opens, driving the cylinder to open the unloading valve for loading. The dust-containing gas inside the loading container is drawn from the dust collection interface into the corresponding dust collector through the interlayer channel in the telescopic sleeve, thereby removing the dust-containing gas. It is adsorbed onto the cloth bag, enabling dust-free operations at the work site. When the material reaches the preset height or the container is full, the material inside the loading container will block the air duct connection below the bulk head, triggering a full-load alarm and automatically shutting off the discharge solenoid valve to stop loading. One minute after the discharge solenoid valve closes, the ash fan stops operating; 30 seconds later, the dust collection fan shuts down as well, and its solenoid valve closes. At this point, the flap inside the housing is in the closed position. The dust removal solenoid valve opens to clean the filter for about 2–3 minutes before stopping automatically. The material level fan and the high-pressure centrifugal fan also cease operating, and the air supply is stopped. Finally, press the “Raise” button to lift the bulk head to the predetermined position. Filling completed. 2. Advantages of PLC control: At present, the electrical control systems of cement bulk handling equipment in China mostly rely on sequential logic control circuits composed of a large number of time relays and intermediate relays to determine the timing and sequence of starting and stopping various valves and motors. Throughout the operation process, these components operate frequently; time relays, in particular, are prone to damage under harsh field conditions, resulting in a high failure rate. It often forces the loading process to be interrupted, reducing efficiency. The use of a PLC control system **avoids the aforementioned problems. Compared with relay control systems, PLC control systems have the following advantages: 2.1 Control method – Relay control is implemented through hardware wiring; control logic is created by combining the series or parallel connection of relay mechanical contacts as well as the delayed action of delay relays, and it can only carry out pre-defined logical controls. In contrast, PLCs use stored logic; their control logic is stored in memory in the form of programs. To change the control logic, it is sufficient to modify the programs, which makes it convenient and fast. 2.2 Control Speed: The relay control logic relies on the mechanical action of contacts to achieve control; it operates at a low frequency, in the millisecond range, and mechanical contacts exhibit jittering. A PLC uses programmed instructions to control semiconductor circuits, enabling fast operation at the microsecond level, with strict synchronization and no jitter. 2.3 Delay control: The relay control system relies on the delayed operation of time relays to achieve delay control; however, time relays have low timing accuracy and are highly affected by environmental factors. PLCs use semiconductor integrated circuits as timers; the clock pulses are generated by crystal oscillators, offering high precision, easy time adjustment, and immunity to environmental influences. 2.4 Data Upload: As cement plants become more automated, the requirements for DCS systems in these plants also increase. Therefore, in terms of electrical systems, we need to achieve the following functions: (1) To enable the automatic completion of the entire process, from starting up the dust collector equipment to filling the cement tankers. ⑵During operation, it can feedback the operating signals of various devices to the control room. ⑶Once the control room is ready, it is possible to remotely start and stop the equipment. ⑷In the parked state, it provides a signal indicating that the equipment is ready. ⑸In the event of a fault during operation, a fault signal can be sent to the control room. ⑹Monitor in real time the amount of cement in the cement tank truck. Specific implementation of control by three PLCs: Based on the above considerations, we selected the S7-200 programmable controller produced by German company Siemens as the control core, and programmed it to enable the operation of various devices. The system’s hardware components include the following: one Siemens S7-200 series CPU, one digital input/output expansion module EM223, and one analog input/output expansion module EM231. The status and control signals of various motors and valves are connected to the PLC, which is used to control these devices ； EM231 can receive the weight signal of tank trucks as a 4-20mA current signal. We can also use the EM277 module to connect the system to the plant’s PROFIBUS-DP bus via the PROFIBUS-DP protocol, upgrading the system to a PROFIBUS-DP slave station and thereby enabling control of the bulk handling area from the control room.