The automatic control system of the negative pressure hopper scale consists of a negative pressure conveyor, a filter, a storage bin, a bin door, and an Electronic scale. When the start button is turned to the "start" position, compressed air is supplied to the negative pressure conveyor. The negative pressure conveyor generates negative pressure to create a vacuum at the hopper, and the granular materials are transported through the pipeline into the hopper of the scale. The filter separates the materials from the negative pressure conveyor completely, preventing tiny particles in the materials from entering the negative pressure conveyor and polluting the atmosphere. When the suction time is over or the level sensor operates, the control system cuts off the air supply, and the negative pressure conveyor stops working. The bin door opens (the delay relay starts timing), and the materials fall into the hopper of the scale. At the same time, the reverse blowing circuit is activated to clean the filter, and it stops after 2 to 3 seconds. After the delay time is over, the bin door closes, and the negative pressure conveyor is re-supplied with air. This cycle repeats until the start button is turned to the "stop" position. 

The weighing hopper system automatically adds two or more materials to the hopper scale in a certain weight ratio, and then discharges the materials automatically after reaching the predetermined requirements through weighing. It adopts automatic control to achieve automatic control and supervision of processes such as raw material loading, weighing measurement, vacuum feeding, dispersion, and transportation. The dispersion time and cylinder number can be selected and adjusted on the computer according to production requirements. The opening and closing of the motor equipment and the opening and closing of the feeding valves are all controlled by the computer during the process. The weighing hopper machine is a common weighing equipment in industrial production, used to extract raw materials from storage containers or warehouses, and through automated equipment for measurement, weighing, etc., they are transported to the downstream production line for processing or assembly. The hopper scale is mainly used to extract raw materials from storage containers or warehouses and transport them to the Weighing system. Through precise weighing devices, the raw materials are weighed, and the measured raw materials are weighed in a certain proportion and then transported to the downstream production line. 

The photoelectric frequency conversion hopper scale mainly consists of two parts. One part is four storage bins and corresponding hoppers for four types of raw materials, a negative pressure Roto-blower and hopper machine forming the mechanical part, and the other part is the PLC control system, four sets of hopper electronic scales and frequency converters and other equipment forming the control part. When controlling the frequency conversion hopper scale using PLC, first, the content of the raw materials is input into the weighing control system, and the corresponding hopper ratio is calculated by the weighing control system. The hopper ratio provided by the weighing control system is then input into the PLC system. Next, the PLC controls the related equipment to proportionally obtain the material from the hoppers. During the material in the hoppers process, the hopper electronic scale monitors the hopper ratio of the raw materials. If the rated error value is within the allowable range, the PLC processor will simultaneously call relevant subroutines to correct the error based on the cumulative weight of the hoppers, so that the raw material hopper ratio is as close as possible to the target control quantity. 

After the automatic hopper scale calculates the required weight for each material based on the ratio, the negative pressure conveyor transports the materials from the vacuum to the storage bin. The electronic scale beneath the bin wall transmits the pressure change to the weighing instrument, converting it into a 0-24VDC standard electrical signal that enters the PLC control system. A weighing signal is sent into the frequency converter inside the rotor fan motor at the lower end of the bin, and the PID unit module inside it performs calculations based on the deviation between the actual value and the set value according to a predetermined algorithm. It outputs control signals (frequencies) to change the rotor fan motor speed, keeping the rotor fan output at a value close to the set value. The motors controlled by the PLC system respectively transport the materials in the negative pressure conveyor to the hopper, and the finished products after the hopper are transported to the outlet end. The hopper scale uses the PLC control system to perform two-speed speed control of the negative pressure rotor fan, achieving the functions of rapid and slow hopper and point-driven feeding control for the materials, thereby ensuring the accuracy and speed of the negative pressure rotor fan.