Monitoring and Controlling System Based on Configuration Software of Microwave Vacuum Drying Machine Qinghua Han, Shujun Li*, ifan Li, Jin Wang, Jiwei Ma, Donglin Zhao Chinese Academy of Agricultural Mechanization Sciences, Beijing 100083, China. ABSTRACT The design scheme, hardware and software of monitoring and controlling system for microwave vacuum drying machine developed based on configuration software, Integration industrial workstation (IIW) and programmable logic controller (PLC) were comprehensively analyzed. The customized PLC program and IIW software of monitoring and controlling system could monitor and control real-time temperature and vacuum level, starting and stopping of the pumps and values, material feeding and discharging process controlling through the communication between IIW and PLC. The whole drying process video in the airtight drying chamber was monitored through the CCD camera communicated with IIW. The software functions realized including safety mechanism, parameters set, data acquisition, main display of the process, real-time parameter display, real-time and historic data curve illustrating, database inquiry of parameters set and operational parameters. Keywords: Monitoring; Controlling; Configuration software; Programmable logic controller (PLC); Integration industrial workstation (IIW); Microwave vacuum drying machine ITRODUCTIO Microwave vacuum drying combines the advantages of both microwave heating and vacuum drying. The combination of the low temperature conferred by vacuum drying with the rapid energy transfer of microwave heating generates very rapid and low-temperature drying, and obtains dried products of high quality. The microwave vacuum drying technology can be widely applied in the field of agro-products processing, especially suitable for heat sensitive materials and high additional value products drying. [1,2] The aims of this study was to design monitoring and controlling system based on configuration software for microwave vacuum drying machine so as to improve the control performance and consequently reduce the operational cost. In this system, drying process in the microwave vacuum drying machine is controlled by PLC and managed by the IIW. A control program was developed based on configuration software, to provide a user-friendly interface allowing easy setting of the operating parameters, visual monitoring of process and drying status, direct access to the database, processing parameters real time control and centralized management. [3] COFIGURATIO OF THE MOITORIG AD COTROLLIG SSTEM In consideration of the drying technology requirement of dried materials in the microwave vacuum drying machine, the drying processing parameters could be set optionally such as drying temperature, microwave power, vacuum level, transferring speed and drying time. Drying temperature was controlled by microwave power to adjust the
magnetic field current of magnetron in accordance with the values of actual temperature taken by the Infrared thermal transducer. Vacuum level was monitored by the pressure transducer employed for the dying room and controlled by releasing valve to adjust the air flow rate of drying chamber. Transferring speed was controlled by hydraulic value to adjust the flow of hydraulic oil according to the required drying time of the dried materials. The material feeding and discharging process was automatically finished by cycle sequence control of feeding valves and discharging valves. The whole drying process video was monitored through the CCD camera employed in the airtight drying chamber. The pumps and values starting and stopping could be operated optionally such as vacuum pump, hydraulic pump, vacuum valve, and so on. IIW PLC CPU Output Terminal Analog Input Input Terminal Vacuum Pump Motor Temperature Transducer Pressure Transducer Vacuum Pump Button & Overload Protection Hydraulic Pump Motor Vacuum Value Temperature Vacuum Level Hydraulic Pump Button & Overload Protection Material Feeding Switch Hydraulic Value Microwave Power Air Flow Rate Material Discharging Switch 4 Feeding Values Magnetic Field Current Releasing Valve 4 Discharging Values Magnetron Figure 1. Block diagram of the monitoring and controlling system The block diagram of the monitoring and controlling system is illustrated in Figure 1. The control center of the system is composed of IIW, PLC and analog input modules. Input components include analog signals provided by temperature transducer and pressure transducer, switches and overload of protections vacuum pump and hydraulic pump, switches of material feeding and discharging [4,5]. PLC analog input is connected with temperature and pressure transducers to get the real-time measurements, and on-off signals are acquired from switch knobs and overload protections which are wired to the PLC input terminal. Output elements include several valves and motors, on-off commands are sent from the PLC output terminal to the motors of vacuum pump and hydraulic pump, the
vacuum value, the hydraulic value, 4 feeding Values and 4 discharging Values to control the starting and stopping of the motors and valves. HARDWARE DESIG Hardware consists of PLC, analog input module EM231, temperature transducer WR, pressure transducer ZR, vacuum pump button 1SS,1SF, and its overload protection 1FR, hydraulic pump button 2SS,2SF, and its overload protection 2FR, material feeding switch 1SA, material discharging switch 2SA, vacuum pump relay 1KA, hydraulic pump contactor KM and its signal lamp HL, hydraulic value relay 2KA, vacuum value relay 4KA, 4 feeding values relay 5~8KA controlling 2 knife-edge gate valves, vacuum retaining value and vacuum venting value, 4 discharging values relay 9~12KA controlling 2 knife-edge gate valves, vacuum retaining value and vacuum venting value, connection cables PPI, IIW and camera CCD. The principle of the hardware system is shown in Figure 2. Figure 2. Principle diagram of the hardware system The IIW as the upper computer employed in the system is RPC-515L to monitor and control the drying process. The developed configuration software can be run on the IIW which is communicated with PLC through PPI cable connecting between the COM on IIW and the RS485 port on PLC, converting data between RS232 and RS485, to send commands to or receive from PLC. [6] Camera CCD is communicated with IIW through digital video acquisition card DVR0204LB to monitor the whole drying process video in the airtight drying chamber. PLC used in the system is a Siemens S7-200 that is the PLC of integrated and compacted type with good costperformance ratio. The modules can be easily combined to form various controllers. [7] The model of PLC is CPU226, having 24 digit inputs and 16 digit outputs, to receive digit signals of the buttons, switches and overload protections, and send digit signals to control the relays, contactor and signal light. There is also an extension
module EM231 being adapted to the system, with 4 analog inputs, to convert the analog temperature and pressure signals into digital. Temperature measurements are taken by CI3A Infrared thermal transducer. The sensor is suitable for on-line measure with non-contact method. The temperature measurement capacity is 0 115 C with an accuracy of ±2%, and an analog voltage output of 0~10V with the temperature measurement range of 0~500 C. Pressure transducer is CPCA-140Z with the pressure measurement range of 100Pa~100kPa, an accuracy of 0.5% and an analog current output of 4~20mA. SOFTWARE DESIG AD PROGRAMMIG PLC Programming The Monitoring and controlling program was designed as a composition of modules, consisted of a main program and several subroutines. The block flow diagram of the program is shown in Figure 3. The main program invokes subroutines, initializes the process,controls the PLC running and the starting and stopping of the vacuum pump, vacuum value, hydraulic pump and hydraulic value. Three subroutines perform individually as analog input for drying temperature and vacuum level, drying processing parameters setting, and material feeding and discharging process controlling. [5] 0~10V output signals of the temperature sensor are corresponding to the PLC s values of input as 0~32000, and 4~20 ma output signals of the pressure sensor are corresponding to the PLC s values of input as 6400~32000.Therefore, the real time temperature and vacuum level values can be determined as, y y t i v i xi 64 xi 6400 99.9 0.1 25600 (1) where y ti is the real time temperature, C; y vi is the real time vacuum level, kpa. The subroutine of material feeding and discharging process controlling automatically finished the cycle sequence of material feeding and discharging process. The vacuum environment and atmospheric environment of material feeding and discharging alternately changed through controlling the starting and stopping of 4 feeding values and 4 discharging values. The material discharging process was similar to the material feeding process. Figure 4 shows the block flow diagram of the material feeding process controlling.
Initialization Increasing the releasing air flow rate Start the machine Set initial parameters Decreasing the magnetic field current Vacuum level preset lower limit? Starting and stopping of the vacuum pump & vacuum value Temperature preset upper limit? Starting and stopping of hydraulic pump & hydraulic value Compared vacuum level with preset value Material feeding process controlling Compared temperature with preset value Vacuum level preset lower limit? Temperature preset lower limit? Material discharging process controlling Decreasing the releasing air flow rate Increasing the magnetic field current Figure 3. Flow chart of the monitoring & controlling system program Upper knife-edge gate valve connecting 13 seconds Upper knife-edge gate valve disconnecting 6 seconds Vacuum retaining value connecting 20 seconds Vacuum retaining value disconnecting Under knife-edge gate valve disconnecting 13 seconds Under knife-edge gate valve disconnecting 6 seconds Vacuum venting value connecting 2 seconds Vacuum venting value disconnecting Figure 4. Flow chart of the material feeding process controlling
Configuration Software for the IIW The software was developed based on the configuration software MCGS (monitor and control generated system). MCGS is based on Windows, for quick composition and generation of monitoring and controlling software systems for the upper computer. The MCGS is consisted of configuration environment and operation environment. With configuration environment users can work out all the configuration of a monitoring and controlling system for their application. Operational environment is an independently running component, performing user designed objectives and functions with user defined handlings in the configuration database. The functions include safety managing, online data acquiring, real-time and historic data processing, process controlling, animated drawing displaying, curve illustrating, report printing, and so on. [8, 9] The function chart of the system is shown in Figure 5. Monitoring and controlling system MCGS configuration software Safety Setting DAQ & display Drying curves Database Inquiry Operational data inquiry Setting value inquiry Historic curves Real time curves Data display Main display Data acquisition Drying temperature Vacuum level Operator Authorization System Authorization Figure 5. Function diagram of monitoring and controlling system Figure 6. Frame of monitoring and controlling system interface
Safety mechanism built in the software requires the authorization of the system manager and the operator. System manager can log in with a password to play the system operation, parameter setting, and log out. The operator, after log in, can only run the software. The upper and lower limits of drying temperature and vacuum level can be set separately. DAQ function includes main display of the process, real-time parameter display, as well as data acquisition. As MCGS supports Siemens PPI communication protocol, it can be communicated with S7-200 PLC, obtain data from PLC and real-time database, and visualize the data and process. Drying curves show the changing of the drying parameters including real-time and historic data of drying temperature and vacuum level. Database inquiry can be made for parameters set and operational parameters, and also can be printed. Figure 6 shows one frame of the interface of the monitoring and controlling software system in operation. COCLUSIO The system has been verified through the test operation for apple slices drying in Beijing USHIUA Food CO., LTD. The system proved feasible for the real-time drying monitoring and controlling and centralized management for microwave vacuum drying machine. Safety mechanism, parameters set, data acquisition, main display of the process, real-time parameter display, real-time and historic data curve illustrating, database inquiry of parameters set and operational parameters were all performed satisfactory and reliable. The system needs only a limited number of components and has realized multiple control tactics, hence achieved a reasonable cost-performance ratio. It is also easy to be modified and extended so as to facilitate the system upgrading. ACKOWLEDGEMETS This work was supported by the High-Tech Research and Development Program of China (2007AA100406). REFERECES [1] Markowski M., Bondaruk J., Błaszczak W. 2009. Rehydration behavior of vacuum-microwave-dried potato cubes. Drying Technology, 27(2), 296 305. [2] Chauhan A.K.S.; Srivastava A.K. 2009. Optimizing drying conditions for vacuum-assisted microwave drying of green peas (Pisum sativum L.). Drying Technology, 27(6), 761-769. [3] Han Qinghua, Li Shujun, Zhang unchuan, et al. 2008. Remote monitoring system of edible fungus industrial cultivation environment. Transactions of the Chinese Society for Agricultural Machinery, 39 (8), 123~127. [4] Lu Jian, Chen Lixin. 2006. Measurement & control of liquid level basing on PLC and PC s monitor and control management software. Control & Autonation, 22(31), 121~123. [5] Han Qinghua, Mao Zhihuai, kang Ze. 2009. Configuration software based temperature and humidity monitoring and controlling system in tunnel-type dryer. American Society of Agricultural and Biological Engineers(ASABE), Mich., USA, 21-24 June, 2009. ASABE Paper o. 097315. [6] Zhu idan, Wu kaibo. 2006. S7-200 PPI Host-Slave Communication. Techniques of automation & applications, 5(25): 21~23. [7] an ingfu. 2006. Research of wrap-covering system based on PLC and configuration software. Control & Autonation, 22(31), 67~69. [8] He Qiang, Li Zhenxiao, Chen Baojun. 2006. Digital Detection System'S Performance Test. Cereals and Oils Processing, 9, 69~71. [9] Hu Guoliang, Gong Guofang, ang Huayong. 2007. Condition monitoring system of simulator test rig for shield tunnelling machine. Transactions of the Chinese Society for Agricultural Machinery, 38 (1), 164~167.