In the production process of fine chemical industry, automatic batching system is a very important process, which consists of two subsystems: pre and post batching. Before the dosage system under the control of the general control microcomputer system, solid raw materials such as sodium pentasodium, manganese nitrate, soda ash and liquid raw materials such as caustic soda, sulfonic acid, effervescent soda ash, water, etc. are stirred in the dosage pot to form a slurry. After aging and temporary storage, the slurry is pumped into the powder spraying tower by high pressure pump, and the base powder is formed after drying by hot air. The former batching mainly accomplishes the weighing and proportioning of the main material and various ingredients. After batching, the base powder formed by the former system is sent into the premixer through belt scale and conveyor belt, and mixed with the pumped raw materials such as flavor, non-ionic and so on, and then sent into the finished product warehouse by the conveyor belt. The post batching realizes the measurement of the flow of conveyed materials. The automatic batching system adopts DCS centralized control mode, and Siemens S7-300 PLC is used to form the data acquisition and control system, which is modularized design and economical and practical. The human-machine interface monitoring software adopts "Configuration King", which is the leading configuration software in the field of industrial control in China and has the advantages of good openness, easy maintenance and secondary development. All process control data and equipment operation status can be centrally managed, recorded in real time, and printed and consulted at any time.

Batching structure and function

Weighing and batching system consists of computer, cabinet and peripheral equipment (front batching scale, rear batching scale, material level machine).

1、Automatic batching system monitoring system consists of two computers as the human-machine interface of the whole system. One of them is the master station, which accomplishes all the system parameters setting, process monitoring and data recording; the other one is the slave station, which takes the master station as the support, and is in charge of the data setting and process monitoring of the back batching system. The master station communicates directly with Siemens S7-300 PLC system, automatic control instrument of front batching scale and rear batching scale.

The front dosage monitoring system adopts sealed junction box, which is dustproof and moisture-proof, and can ensure reliable signal transmission. The front batching scale instrument adopts special industrial process controller, which communicates with the central control room through RS-485 bus, and can be controlled independently or realized PLC on-line control. The signal detection of each valve position and unloader position adopts load cell, which has the characteristics of non-contact, anti-interference, anti-dust and humidity resistance. The bin level adopts heavy hammer type material level meter, which can realize continuous bin level detection. The main scale of the post-dosing monitoring system adopts high-precision dosing belt scale, the attached material adopts reduction scale (loss-in-weight scale), and the non-ionic pump, flavor pump, flow detection adopts the indirect method, that is, real-time detection of pipeline pressure through the pressure transmitter, and judging by the pressure change to see whether the discharge port and inlet are clogged or not.

2、The monitoring function of the feeding system has the functions of human-computer interaction, communication, display and storage, printing, etc. It also has the function screen of data and graphic display, status monitoring, data input, information storage and other kinds of related operations. The weighing and batching system can realize real-time process data monitoring, simulation display of process flow, real-time data record checking, system operator privilege setting, process parameter setting, setting alarm for running process events and switching between manual and automatic control. The on-site weighing instruments in the monitoring system display real-time flow, load, totalized value and temperature. Temperature indication is transmitted to centralized display in the control room through the on-site temperature display instrument, pressure indication through the on-site pressure display instrument and motor current through the on-site display instrument. Frequency converter regulation is equipped with automatic switching switch and communicates with the main control computer.

Batching system monitoring and control process

1、Automatic weighing control unit is mainly for Taiwan weighing instrument, PLC as auxiliary control system, computer human-machine interface display proportioning parameters (formula) and monitoring and recording of real-time data. In automatic control mode, click the automatic dosage "start" button in the front process screen or the front control cabinet "start" button, the weighing control instrument will open the weighing valve of 10 scales according to the set formula. If the system detects that the dosage valve of a scale is not closed, an alarm occurs and the system enters a pause state. Each scale has an advance quantity according to the weighing speed. When the control instrument detects that the weighing weight of the scale reaches the set value, the advance quantity will be subtracted and the control instrument will close the feeding valve. The advance amount can be corrected manually or automatically, so that the control instrument can control the dosage scale to reach the set target value every time the dosage accuracy.

2、Automatic batching is to put the weighed raw materials into the stirring pot in a certain order, and turn on the stirring and heating at the same time. This control process is accomplished by temperature control meter and PLC. The temperature control meter controls the upper limit of temperature, and the heating is controlled by PLC. There are two kinds of control methods for automatic batching: fixed order and programmable. In the fixed-order mode, the order of discharging all kinds of raw materials is fixed and cannot be changed. Under the programmable mode, the order of various raw materials can be set according to the formula on the human-machine interface.

3、After batching control is based on the flow detection of base powder scale. The control host detects the flow of base powder scale through RS-485 communication, and gives the control current of flavor pump and non-ion pump according to the ratio value.PLC outputs 4-20mA to control the inverter of flavor pump and non-ion pump, so that the discharging seedling of flavor and non-ion will be changed according to the flow of base powder scale, and the ratio control of flavor pump and non-ion pump will be PID regulation control. The flow of loss-in-weight scale and auxiliary material scale is collected to the control host through RS-485 communication. The host computer calculates the corresponding tracking flow rate according to the process requirements and transmits it to PLC, which gives 4-20mA control current to control the frequency converter of the loss-in-weight scale and auxiliary material scale, so that the corresponding dosage flow rate can be controlled in the range of tracking flow rate. Pre-mixer, conveyor belt conveyor, distribution belt conveyor and umbrella blower are equipped with on-site start/stop buttons, which are converted by remote control and connected to the central control room, so that the start/stop control of the equipment can be realized through the start/stop buttons, or the start/stop buttons on the man-machine interface can be manipulated and the start/stop buttons on the matching process after the man-machine interface can be realized through controlling the PLC.

Alarm event: when automatic weighing starts, if a discharge valve is not closed, or the system does not detect a signal to close the discharge valve, the system will sound an alarm, suspend the weighing process of the weighing instrument, and make the operation indicator light flash. If an alarm occurs, the automatic discharging will not be carried out, until the fault is eliminated or the cause of the alarm does not affect the discharging, press the reset button and then press the "Discharge" button, then the discharging will be resumed.

Switching alarm: When automatic discharging starts, the system first checks whether each kind of raw material is switched in place, if the switching is not in place or the switching is not consistent, the alarm system will start to alarm and the automatic discharging will not be carried out. Through checking, we think we can put the material, press the reset button, then press the "put the material" button, then start to put the material.

Dosing pot full alarm: If the dosing pot has been dosed with raw material pulp is not discharged, but still put the material into the pot, resulting in an alarm signal, automatic discharging can not be started. After checking and confirming that the material can be discharged, press the reset button, and then press the "Discharge" button, the automatic discharging will start.

Emergency stop: In the process of weighing, due to the emergency need to stop weighing, press the self-locking "weighing emergency stop" button, the feed valve of each scale will be closed, stop weighing. When you need to restart weighing, turn up the "Emergency Stop" button and press the "Start" button to restart weighing. When discharging automatically, press the "Discharge Emergency Stop" button, the system will close all discharge valves and stop discharging, mixing and conveying.

The human-machine interface of the master station and the slave station adopts the configuration software of Configuration King and the communication program developed by VB, which consists of pre-mixing process, post-mixing process, pre-mixing formula, parameter setting, historical curve and alarm information, etc. The main menu of the system consists of a series of buttons. The main menu of the system consists of a series of buttons. When the mouse rests on the menu buttons, the buttons are raised, and different buttons can be clicked to enter different screens. There are two main types of function screens for operation, one is the display operation screen, i.e. display data (display mode is digital, curve, historical trend, etc.), function soft switches and soft buttons for operators to operate, etc.; the other is the process screen, which displays the process arrangement of the equipment, the process flow and the corresponding test data.

Pre-dispensing process pre-dispensing process flow interface can be displayed in real time before the instantaneous flow of the dosage scale, the proportion of the formula, weighing and dosage status, material level and valve closure signals, the temperature of the pot, the motor current and so on. In the interface there are other operations, such as automatic / manual control buttons, automatic weighing of single and continuous switching buttons, material buttons and reset buttons.

Post-dispensing process: The interface of post-dispensing process can display the flow rate, cumulative value and weight of base powder scale, auxiliary material scale and loss-in-weight scale in real time, and display the load of base powder scale, current of pre-mixer, status of unloader, instantaneous flow rate of non-ion, instantaneous flow rate of flavor, and so on. The interface can also carry out some button control operations, such as the run and stop of the loss-in-weight scale, frequency adjustment, manual and automatic conversion, as well as the ratio setting of several materials.

Other human-machine interface: the parameter setting interface displays the instantaneous weight of the former dosage scale, the material level, the use status of the former dosage scale and the dosage sequence of various materials. The former dosage formula interface is some management of the former dosage formula, which can choose any kind of formula that has been set up, and also can modify the formula that has been proposed, or newly propose the formula. The report interface can complete the production records of the batching process in the molding workshop, including the pre-batching report and post-batching report of each shift. Pre-matching report records the weight, time and pot number of each material, while post-matching report records the amount of positive and negative products produced in each shift, the total amount of positive and negative products produced every day, and you can view the situation of the 3 shifts every day at any time through the time box. The instantaneous weight of the former dosage scale can be viewed from the history curve interface. The alarm interface can display the valve closing and alarm signals such as discharging timeout and feeding timeout.

The automatic feeding system is characterized by reliable operation, complete functions, low investment and easy upgrading, etc. It adopts full Chinese operation interface, online configuration, intuitive image and easy to operate. The monitoring system provides perfect system operation information and product information, creates a high-efficiency working environment for the field operators, realizes the more advanced process control and management technology level, and reduces the workload of system maintenance. Since the system has been put into operation, all the indexes meet the technical requirements, and greatly improve the operator's labor intensity, and obviously improve the production efficiency.