Feeding system work process is: dosage began to work, the plunger pump for reciprocating motion, the material pressure into the pipeline, the check valve opens, the material flows from the measurement reaction tank to the dosage system, differential pressure transmitter measured unit time measurement reaction tank bottom pressure changes, sent to the controller DR24, the actual flavoring dosage flow rate; will be measured in the tobacco flow rate signal into the DR24, the DR24 according to the proportion of the dosage and the DR24 controller according to the theory and the actual flow deviation e PID operation, and the digital valve position generated by the operation to analog current signal output, converted by the electrical converter, the current signal into a pneumatic signal to control the opening of the pneumatic thin-film valve, so that the amount of material sprayed with the changes in the flow of tobacco and changes in the actual flow rate as much as possible with the theoretical The actual flow rate matches the theoretical flow rate as much as possible to meet the technological requirements of the process.

In the feeding system, the quality of dosing depends on the accuracy of the differential pressure transmitter and the electronic belt scale. Differential pressure transmitter calculates the instantaneous flow rate according to the flow rate change in a period of time. This flow rate measurement method has a certain lag, which makes the dosage control accuracy worse and causes inaccurate dosage quantity. On the other hand, due to the large concentration of the material liquid, after a long time, the accuracy will be reduced due to scaling. When the material liquid flows through the differential pressure transmitter, the granular material in it will make the diaphragm of the transmitter squeeze and affect the accuracy, and the pipeline installation requirements are harsh, if the residual liquid or sediment in the process pipeline flows into the pressure guide tube, the pressure measurement will produce errors. In addition, the human-machine interface of DR24 controller is simple and rough, which can't intuitively display various working conditions in the production process, and also can't display various parameters, alarms and other information. For network communication requires specialized hardware and software, more complicated, difficult to maintain, and not suitable for large amounts of data transmission requirements, can not adapt to the more advanced field bus technology.

The feeding system needs to control more than twenty switches, four analog, need to complete a variety of arithmetic operations, logical operations and control operations, and need strong communication capabilities in order to exchange a large amount of data through the fieldbus, in addition to the industrial site taking into account the higher temperature, humidity, and dust, it is the choice of PLC as a controller, plus a touch-screen for the human-machine interface. Maintainability is better, and the programming language is more in line with the working habits of electrical maintenance personnel, PLC selection of products in line with IEC standards.

The weighing and feeding system uses a piston pump as the driving force of liquid flow, and there is a certain pulsation phenomenon in the liquid flow. This phenomenon will interfere with the measurement and control calculation of the dosage. So the improved dosage system uses compressed air as the power, this power is easy to get in the workshop, and relative to the dosage system requirements are very smooth, easy to realize the dosage control objectives, the actual dosage of a closed metering reaction tank (under the matching differential pressure transmitter), an open mouth storage reaction tank. Before starting the machine, the material should be pumped into the storage reaction tank. There is a magnetic float level gauge next to the tank, which indicates the level of the liquid in the tank, and the tank can be filled up to 80% of the full scale. When the temperature of the material is lower than the set temperature, the controller automatically opens the pneumatic valve and passes steam into the interlayer of the storage reaction tank to heat the material, and then turns off the pneumatic valve after reaching the set temperature. When the material liquid in the metering reaction tank reaches the set lower limit, the process controller automatically starts the feeding pump motor, so that the material liquid in the storage reaction tank is replenished to the metering reaction tank until the material liquid in the metering reaction tank reaches the set upper limit, or there is no material in the storage reaction tank. The check valve makes the material liquid flow in one direction, but the pressure of the metering reaction tank can not be returned. Constant air pressure is required in the metering reaction tank, generally set at 0.5MPa. The actuator for direct control of liquid flow uses a linear pneumatic control valve with a parabolic spool. The controller will valve opening degree to 4-20mADC electrical signal output to the electrical converter, the electrical converter will electrical signals corresponding to the conversion into 0.02-0.1MPa pneumatic signal, drive the pneumatic control valve action.

When the work starts, the electronic scale sends the tobacco instantaneous flow rate to the controller, after a delay, and then multiplies it with the pre-set proportioning coefficient to get the theoretical instantaneous flow rate value. It is worth mentioning that the electronic scale delay is necessary, because there is a time difference between the electronic scale and the nozzle, and only the delay is accurate, in order to better complete the control of the dynamic correspondence. The mass flow meter sends the feedback signal to the controller, which represents the actual instantaneous flow rate of the material. The instantaneous value is compared with the set amount, and the difference between them is used as the deviation amount for PID adjustment. Output 4-20mA current signal to the electrical converter, the electrical converter will be converted to this current signal 0.02-0.1MPa air pressure signal, with this air pressure to start the pneumatic control valve, so that it corresponds to the linear 0-100% control valve opening. The outflowing material enters the nozzle through the float flowmeter, and is sprayed onto the blade through the air pressure gas atomization. In this dosage system, the differential pressure transmitter is only used to measure the weight of the material in the metering reaction tank.

In order to improve the real-time response of the dosage, this dosage is based on the traditional PID regulation, according to the flow rate of the blade (leaf filament), the gas pressure in the metering reactor tank, the liquid level in the metering reactor tank, and so on, plus a level of feed-forward. Firstly, according to the feed-forward value, the valve opening is quickly and coarsely adjusted to the vicinity of the correct position, and then the equilibrium position is reached by PID regulation. The calculation of the feedforward value imitates the self-learning dosage, and the controller memorizes 100 discrete state points, and partially corrects the memorized value each time the control equilibrium is reached. This method is a better solution to an important problem that affects the accuracy of the dosage system, i.e., the fluctuation of incoming material from the belt scale.

In order to have self-checking capability, a differential pressure transmitter installed under the metering reaction tank is utilized to detect the failure of the mass flow meter at regular intervals. This avoids accidents caused by the failure of the measuring device. In addition, relying on the relatively strong programming ability of PLC, this system not only completes the main control work, but also relies on a number of photoelectric sensors as well as logic judgment within the program to monitor possible failures and drifts, greatly improving the reliability of the dosage system and dosage accuracy.

Temperature control belongs to the big hysteresis regulation, the dosage system adopts the control method to utilize the rate of temperature change to carry on the prediction control. That is, according to the rate of temperature rise or fall to judge the value of the liquid temperature in the reaction tank after a period of time, so as to control the opening of the valve in advance, avoiding the problem of temperature over-adjustment in the traditional method.

The delay of the instantaneous flow of the electronic scale is a necessary step. Here the stack method is used, the instantaneous flow signal of the electronic scale is sent to the PLC of the dosage system, and then processed by the stack (using first-in-first-out) for the delay. The principle is as follows: a stack of up to 100 variables, according to the signal of the clock pulse, these 100 variables are deposited into the stack in the order of priority, and when full, according to the principle of first-in-first-out, the first deposited variables are output first. The length of the clock pulse can be adjusted according to the need, here the second pulse is used, the longest delay can be 100 seconds, which is enough for this dosage system. After stack processing into a delayed electronic scale instantaneous flow signal.