Research On The Calibration System Of The Batch Asphalt Mixing Plant Based On PLC

In the current, 90 percent of surface course material in domestic highway pavement is based on asphalt mixture, its mixing quality have a directly effects on the pavement performance and service life of asphalt pavement from the source. As the raw material of the asphalt mixture is unstable, so mostly the Batch Asphalt Mixing Plant is used to stirring the asphalt mixture, however the dynamic calibration is used for determining the primary grading of various specifications cold aggregate in the asphalt mixture. Up to now, it has been done manually, this method is Labor intensity and difficult to guarantee the precision of calibration curve. This article take the dynamic calibration of batch asphalt mixing plant as the study subject and mainly study the following contents:(1)In view of most mixing stations, the opening of the hopper covers in cold silo is adjusted by manual, leading to low accuracy and can’t control the output of asphalt mixture that matching the target proportioning. Based on these, automatic Regulating Strategy of the opening of the hopper covers in cold silo is confirmed, at the same time, designing a kind of automatic regulating mechanism that can adjust the height of the hopper covers in cold silo by Step Actuator. Analyze the relationship among feed flow of cold aggregate, height of the hopper covers, speed of aggregate motor and confirm the calibration value height of the hopper covers and speed of aggregate motor. According to the requirements of the dynamic calibration process of discharging weighing, Electronic belt scale weighing scheme is proposed, selecting the corresponding rational electronic belt and it has been improved in the structure. Installing the electronic belt scale in aggregate conveying inclined belt area, the automatic measurement of cold aggregate quality is realized.(2) According to the control requirements of the dynamic calibration process, the different control schemes are compared and analyzed to determine the whole control scheme of calibration system with PLC as the core. According to the control object, calibration system can be divided into three sub control system which including height setting of hopper cover, motor speed control system, belt scale measurement, at the same time, study the control scheme of three sub control system respectively.(3) Based on Siemens series S7-200 PLC, select the appropriate models for CPU and HMI and design the hardware circuit and the way of communication of Calibration system. Analysis and set the control parameters of the control objects in the process of calibration.(4)Flow charts of master control program and sub control system in automatic Calibration system were designed, at the same time, human-machine interface also was designed. By analyzing the characteristics of flow curve which get from the automatic Calibration system, the matching relationship between motor speed and quantity of flow is confirmed.