PLC Control Program Design of Concrete Mixing Plant

1. Automatic feeding algorithm
The automatic feeding adopts the circular control algorithm. First, the total production task is divided into each large round of batching in the unit of mixing chamber volume, and then each large round of batching is divided into each small round of batching. Each small round of batching is batched according to the normal maximum range of the smallest metering bucket in each metering bucket, and the rest is batched synchronously with the smallest hopper according to the batching proportion. Each batch of large batch and small batch is counted separately to calculate the tasks that have been produced. The specific algorithm is as follows:
Initialization: total amount of each ingredient = total amount of required production × Percentage of each ingredient.
The large wheel count and small wheel count are cleared respectively.
As other batching weighing procedures are similar to aggregate, aggregate and powder are batched at the same time, which can reduce batching time and improve production efficiency. Because water and additives are directly added to the mixing host, and the amount is not particularly large and the batching is relatively fast, you can choose to open the pre mixing silo and carry out batching at the same time.
2. PLC control program design
The modular PLC system of Siemens s7200 is selected as the field control device, and the program is initialized in the first scanning cycle of PLC power on. In the initialization program, the total production, the capacity of the pre mixing bin, the percentage of each ingredient, the standard moisture content and each counter are initialized. At the same time, the total demand of each ingredient and the maximum feeding amount of each raw material in a large round of ingredient are calculated and saved to the corresponding storage area to prepare for automatic production. In the batching process, PLC collects the weighing sensor signals of aggregate metering bucket, cement metering bucket and fly ash metering bucket, stores them in the PLC data register, compares and calculates the set values given by PLC and host computer, and then PLC outputs the control signals of solenoid valves, motors and other actuators according to the obtained results and conditions, and sends out corresponding feeding Discharge control action. Taking aggregate batching as an example, when weighing each aggregate hopper, feed quickly before the weight reaches 85% of the set value, feed slowly after reaching 85%, and stop feeding when the set value is reached. In order to improve the measurement accuracy, the aggregate hopper is equipped with two feeding doors. At the beginning of measurement, open the two feeding doors at the same time. When the weight reaches 85% of the set value, close the large opening feeding door and feed only by the small door until the weight reaches the set value.

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