With the increasing demands for refined operation and management of blast furnaces, blast furnace smelting places higher requirements on the raw materials and fuels fed into the furnace. This applies not only to the type and quality of these materials but also to their quantity. As a crucial component of the charging system, the automatic weighing control system under the blast furnace trough is receiving increasing attention for its automatic control and weighing accuracy. Inaccurate weighing directly leads to errors in the furnace charge ratio and deviations in composition control. The accumulated errors from frequent weighings over time are substantial, directly impacting furnace condition control and smelting costs. Therefore, applying a closed-loop control system to the weighing process and using software to automatically correct weighing parameters and compensate for weighing errors is highly significant. The control algorithm introduced in this paper possesses this automatic compensation function and has been successfully applied in the blast furnace trough of Xuan Steel's No. 9 blast furnace. 1. Equipment and Process Flow under the Blast Furnace 9# The feeding system under the blast furnace 9# blast furnace mainly consists of 6 sinter ore bins, 2 pellet bins, 2 miscellaneous ore bins, 4 coke bins, and corresponding feeders, vibrating screens, weighing hoppers, feeding belts, sinter and pellet return bins, crushed coke, crushed ore classification, and coke recovery systems. Other auxiliary equipment includes ventilation and dust removal facilities, hydraulic stations, and lubrication systems. The blast furnace ore and coke bins are arranged in a single row. Ore and coke are dispersed, screened, and weighed under the bins without intermediate weighing hoppers. The ore falls onto the same feeding belt and is then transported to the top of the furnace via the main belt. The workflow of each piece of equipment is as follows: 1) Raw materials (coke or ore) in each bin are loaded into the bins by the raw material moving belt trolley above the bins. 2) Each bin is equipped with a feeder and vibrating screen below it. Raw materials in the bins are loaded into the corresponding weighing hoppers from below the bins via the feeder and vibrating screen as needed. 3) When the feeding equipment is working, the raw materials are continuously weighed into the corresponding weighing hoppers. When the weighing value reaches the stop screen value, the feeder stops working, the vibrating screen stops after a delay, and the remaining amount is equalized by the impulse on the vibrating screen. (The magnitude of the impulse can be set on the screen.) 4) After the weighing hoppers are filled with material, they are in a standby state. When the blast furnace is charged, a material request signal is sent from the top of the furnace, the gate of the corresponding weighing hopper is opened, and the raw materials are transported to the top of the furnace via the feeding belt and the main belt and loaded into the blast furnace for smelting. 5) When the weight of the weighing hopper is less than the empty material value (the empty material value can be set on the screen), an empty material signal is sent, the gate of the weighing hopper is closed after a delay, and then the vibrating screen and feeder are started to feed material into the weighing hopper. 6) The above equipment working process is repeated cyclically. 2. Automatic Weighing Compensation Control Algorithm 2.1 Design Concept of Weighing Compensation Algorithm Based on the aforementioned process flow of the under-tank feeding equipment, each weighing hopper will generate weighing errors during each weighing process due to differences in raw material particle size and viscosity, as well as the impact inertia of the feeding machinery. If these weighing errors are not compensated, they will accumulate and directly affect the operational accuracy of the blast furnace. Therefore, it is necessary to suppress these errors. The suppression methods are: firstly, adjusting the vibration screen impulse for the next weighing based on the error value generated by each weighing, so that the set impulse is as close as possible to the actual impulse, reducing the error generated by each weighing; secondly, correcting the screen stop value for the next weighing based on the error value of each weighing, thus compensating for the weighing error. 2.2 Algorithm Design in Weighing Compensation Process 2.2.1 Automatic Calculation of the Set Weight O_SP and Screening Stop Value SP_H_SJ of the Weighing Hopper Before Each Loading Before each loading, the planned loading weight is calculated based on the set weight O_SP of the weighing hopper and the weight PCZ required to compensate for the previous weighing error (the algorithm is automatically calculated by the program): O_SP1 = O_SP - PCZ In order to reduce the loading deviation caused by mechanical inertia and residual vibration of the feeding equipment, the controller must issue a full material signal in advance to stop the feeding equipment. The full material signal is issued when the weight of the weighing hopper reaches the screening stop value SP_H_SJ. Only in this way can the weighing error be minimized. The stopping value SP_H_SJ is calculated using the following formula: SP_H_SJ = O_SP - SP_H - PCZ O_SP: Weighing hopper setpoint; SP_H: Set impulse; PCZ: Deviation between the previous actual and set values. After each emptying of the weighing hopper, the actual net loaded weight SG_SJ and loading deviation PCZ are automatically calculated, ending the loading process. When material needs to be discharged from the furnace top, the weighing hopper gate is opened, and the weight on the electronic scale is automatically tracked. When the weight in the weighing hopper is less than the empty weight, an empty weight signal is issued, and the weighing hopper gate is closed after a delay. After the discharge process, the weight of the remaining material in the electronic scale is measured, denoted as LL_W. When the weighing hopper is full, the full weight HH_W can be measured. As shown above, the actual blast furnace charge is: SG_SJ = HH_W - LL_W. 2.2.2 Automatic calculation of the next compensation amount PCZ: After each weighing hopper is emptied and charging is completed, the accumulated error is automatically calculated, and the next compensation amount is calculated based on the accumulated error. Our principle is that the accumulated error of this weighing should be compensated from the next weighing. PCZ = HH_W - LL_W – O_SP. Where PCZ is "+" indicating overloading and "-" indicating underloading. We can use the current charging deviation to correct the next screen stop value, thus making the actual charging amount closer to the planned charging amount. The program also sets an option not to perform compensation, LL_LIMIT (which can be set at the operator station), i.e., when O_SP is set... 3. Software Implementation of Weighing Compensation Algorithm The weighing system and the actions of each device under the tank are automatically controlled by the Siemens PCS7 control system. The electronic scale signals of each weighing hopper are measured and converted through analog input templates. The weighing process can be divided into a material preparation process and a material discharging process according to the process sequence. The program design of these two processes is introduced here. 3.1 Material Discharging Process The conditions for starting the material discharging process are: the weighing hopper has been emptied and the gate has been closed. The planned material preparation weight O_SP and the material full stop screening value SP_H_SJ are calculated according to the algorithm. Then, a command to start the feeding equipment is issued. The feeding equipment works, and the raw material in the silo is continuously loaded into the weighing hopper. When the weight of the weighing hopper reaches or exceeds the material full stop screening value SP_H_SJ, the program issues a "material full" signal, stops the feeding equipment, delays for several seconds, and waits for the feeding equipment to stop and the residual vibration to finish discharging, thus ending the material preparation process. The flowchart is shown in Figure 1: Figure 1, Loading Process 3.2 Discharging Process The loading process is complete, the weighing hopper is full, and the feeding equipment has stopped working. According to the loading procedure, when it is the turn of the weighing hopper to discharge, the furnace top sends a material request signal, the gate of the selected weighing hopper opens, and the material in the weighing hopper is transported into the furnace top via the feeding belt and the main belt. The weight of the weighing hopper continuously decreases. When the weight of the weighing hopper reaches or falls below the empty weight value, the program sends a "empty" signal, delays for several seconds, and closes the weighing hopper gate. At this time, the weighing hopper is empty, and the weight of the weighing hopper is the empty weight. Then, the next screening stop value and deviation value are calculated according to the aforementioned algorithm. The discharging process ends here, waiting for the next material preparation process to begin. The discharging process and the material preparation process always alternate and repeat in a cycle. The flowchart is shown in Figure 2: Figure 2, Charging Process 4, Conclusion Applying the PCS7 system to automatically control the weighing process under the blast furnace trough, it is crucial to study its control algorithm. A good algorithm can simplify the control process and improve control accuracy. The algorithm introduced in this paper features automatic parameter optimization and error correction. It has been practically applied in Xuan Steel's No. 9 blast furnace. Practice has proven that this algorithm optimizes parameters quickly, prevents oscillations, and achieves high compensation accuracy. This algorithm also has significant application value in other situations requiring continuous weighing control.