This paper introduces the automatic control equipment in the control system of grain dryer by using the upper computer and programmable logic controller (PLC). The technological process of the dryer and the software and hardware of the control system are analyzed in detail.
Grain dryer is a kind of artificial grain drying equipment. It uses a certain way and medium to transfer heat energy to grain heap. Under the action of heat energy, the moisture in grain evaporates, and the medium takes it out of grain heap to achieve the purpose of grain precipitation. At present, the automation level of grain drying production in China is relatively backward. In the process of production, the failure rate of equipment is high, which affects the quality of grain after drying and increases the production cost. Therefore, the use of advanced, mature and stable PLC technology to achieve grain drying is the trend of the times.
The automatic control system of grain drying is controlled by programmable logic controller (PLC). The upper computer monitors the running state through the man-machine interface, and can watch the equipment failure alarm online. PLC control has the characteristics of high reliability, simple programming, convenient use, good versatility, on-line modification ability, shortening the design, construction, commissioning trial period, easy and reliable maintenance, small size and so on. The equipment adopts the control mode of combination of field induction switch, thermostatic element PLC and host computer, which makes the electronic control system of the equipment simple and compact, easy to modify and maintain software and hardware, and has high reliability. First, click the “Select button” with the mouse, and then select the “Warehouse 1 Select” or “Warehouse 2 Select” button. At this time, the conditions for driving have been met. After the mouse clicks the “Dry Start button”, the whole set of equipment is started according to the time set in the program, and the sequence of the process flow is from back to front.
When one of the equipments in the system fails, all the equipments in the front of the equipment stop immediately to prevent blocking and damage the equipment. At the same time, the fault signal is fed back to the screen of the host computer, so that the operator can quickly and accurately determine the location of the fault. The “high material level” of the dryer in the figure is used to control the action of “valve 1” or “valve 2”. When the “warehouse 1 selection” button is selected, the “valve 1” action, on the contrary, the “valve 2” action. When the grain of the dryer is full, there will be “high material level”, “valve 1” or “valve 2” closed. When the grain of the dryer is not full, there will be no “high material level”, “valve 1” or “valve 2” open. The process flow of the system is shown in Figure 1. The whole system is controlled by digital switches. The equipment can run automatically and continuously, or operate individual equipment manually.
Therefore, there are many input points and output points of action status information to be displayed. If these input/output signals are displayed by electric buttons and indicator lights, the hardware modules and electrical connections will be greatly increased, and the corresponding failure rate will also be increased. 。 A total of 32 digital switches are designed for the whole drying automatic control system. Among them, there are 4 stroke switches, 4 stall switches, 3 blocking switches, 4 deviation switches and 4 emergency stop switches.
The main control unit uses CPU315-2DP, a PLC product of S7-300 series of SIEMENS, plus two digital expansion modules (SM32 1 and SM322, one each). Figure 3 is a program block diagram. The control program is programmed in the form of menu. The automatic functions include the running, stopping and resetting of the equipment. Using the button function of Siemens Wincc configuration software, when clicking on the “System Start” button on the upper computer screen, each device can be started in sequence when it is free of malfunction. By clicking on the “Reset” button, the corresponding intermediate relay of the PLC can be reset to make it possible. PLC controls the equipment; condition monitoring: monitoring the operation of various equipment in the system, such as abnormal state of the equipment, PLC gives the parking order, and gives alarm prompts.
The STEP7 software of Siemens is used to program on the upper computer. After the program is compiled successfully, the program is downloaded to the PLC through the communication cable between the upper computer and the PLC. The electric control scheme combined with PLC and PC and the control system combined with mechanical equipment and sensor technology are simple to operate and reliable in performance. Maintainability and flexibility of the equipment have been significantly improved and can be widely used in grain drying and logistics industry. Author’s brief introduction: Shi Zhuangbo, bachelor’s degree, Siping National Grain Reserve, engineer, research direction: grain drying automation.