The ordinary electric valve is the implementation of a common unit, as an important execution device widely used in the field of industrial process control, and has an irreplaceable role. Valve electric device is a motor-powered, driven mechanical reduction device power to the valve, the final part of the valve open and closed, it is the core part of the electric valve. In recent years, the domestic production of electric valve manufacturers through the introduction of international advanced technology and absorption, as well as cooperation with international famous enterprises such as Limitorque, Rotork has gradually mastered the core technology of the mechanical transmission, manufacturing, combined with price advantage achieved a dominant position in the domestic market. With the improvement of the level of industrial automation, especially the emergence of fieldbus technology, the only on-site operation and a simple point-to-point control function of the electric control valve increasingly difficult to meet the needs of the market, major foreign companies have been offering fieldbus electric valve products, but expensive. Therefore, to improve the level of automation of our electric valve, domestic electric valve products to transform, to launch its own fieldbus products, improve the competitiveness of their products, the consolidation of the domestic market and gradually participate in international competition has important significance for the accession to the WTO today .
The field bus is used in the manufacturing or process regional field means and the control room automatic control device between the digital and serial data bus of the multi-point communications. It is also known as an open, digital, multi-point communication underlying control network. The emergence of the fieldbus for industrial automation solutions of the full distribution of smart field devices and the level of autonomy, ease of installation and maintenance of the system. Many different types of fieldbus, international fieldbus standard there are 13 kinds, CAN bus with its multi-master support, excellent short frame transmission performance, high reliability, non-destructive bus first grade through arbitration many semiconductor chip manufacturers Intel, Philips, Motorola and other support, as well as a relatively simple development tools and low development costs, making it a hot domestic fieldbus developed. This study valve control system based on CAN bus is applied to the micro-controller technology, CAN domestic universal electric valve, a valve with the same industrial control computer remote control system.
The overall design of the valve remote control systems
Universal valve control accuracy is not required, the operation is relatively simple, and only on, off, stopping three states. Under normal circumstances, the operating personnel at the scene through the operation of the valve controller to control the opening and closing of valves, the pointer instrument on the valve indicates valve opening. The need for protection, the controller in the electrical control valve failure state shutdown function, fault diagnosis can only rely on the experience of the operator, even opening the lid check to the maintenance inconvenience.
In this paper, the remote valve control system, including the upper and lower two control In addition to keeping the existing site operation function, operation of the valve through the host computer for remote operation. Host computer to provide easy to operate interactive interface, support for simple configuration of the system in different valves and valve database technology to achieve system running status and fault information management, and easy maintenance of the system, the host computer in addition to with lower machine communication fieldbus interfaces should also have the Ethernet interface to systems with external information exchange. The lower machine try to retain the electric device electrical structure of the premise, the introduction of the micro-controller technology, an embedded control system supports both the operation of the site, and also supports remote control of the host computer, the two can switch through the scene switch. Lower machine control system to increase the detection circuit and fieldbus interface, to achieve the acquisition of the valve run a large number of fault information.
Microcontroller on the one hand the site or host computer to set value of the valve opening control valves open and close in response to the host computer's data request, on the other hand can be uploaded to the host computer, valve operation. The fieldbus connection between the host computer, the next bit machine, both a clear division of labor, constitute the real distribution of fieldbus control system (FCS).
Based on the above analysis, this paper uses a centralized management and decentralized control of the upper and lower bit machine two control systems architecture, as shown in Figure 1.
Host computer using industrial control computer, in addition to the features mentioned above, but also designed to run statistical Print system alarm functions; lower machine based microcontroller as the core of the control unit, and embedded into the valve, and the valve electrical control part with control functions. The system communications choice is simple CAN bus, CAN bus protocol, include only the physical layer and the data link layer, users can define their own application layer, the transmission medium using shielded twisted pair signal transmission using short frame structure, each frame The number of valid bytes is eight, and the transmission time is short, the probability of interference is low. The bus communication rate up 1Mbps/40m, the direct transmission distances of up to 10km/5Kbps, the number of attached devices on the bus up to 110. When a node is a serious error, can be automatically removed from the bus, more literature on CAN bus technology, in this detail. Mentioned herein remote valve control system using CAN bus valve control logic functions, a small amount of information, combined with CAN bus data transfer speed, ease of development, technical support and cost of a wide range of considerations.
Host computer design
System host computer hardware selection the Advantech IPC IPC-6718V, together with Advantech dual-port CAN interface card PCL-841, stable performance, greatly shorten the development cycle of the system. The host computer software used the VB610 to design, facilitate the achievement of the various monitoring functions required by the user.
PC software, including several parts of the system security module, system communication parameter setting module, database module and valve control module. Figure 2 shows the relationship between the various software modules of the host computer, the PC software is not only to achieve a valve control functions, and fully taken into account as a control software system security, and database operations can be seen from Fig. Among them, the valve control module is the core of the PC software.
PC software's main function is to achieve the monitoring of the entire system within the valve status, and provide on-site valve remote control operation. After the start of the PC software, system initialization, after entering the system monitor running mode after the initial application initialization, but also according to the specific circumstances of the system configuration. In run mode, the host computer and the lower valve control unit corresponding data in the database using a question and answer exchange information, the host computer to analyze a variety of status and fault information of each valve returned refreshed and refresh the main Monitor the corresponding part of the interface. More valves on the main monitor interface only shows the basic operation of each valve status (start, stop, fault) and the degree of opening, if you want to view a detailed operating information of the valve, you can click interface single monitoring interface valves icon to switch to the valve, then in addition to the valve opening degree of the current, switch stop state can be given basic information can also be shown in the motor phase switch to the more limited motor overheating, such as alarm fault information. Figure 3 shows a software flow chart of this process.
In order to improve the response speed of the remote control, the host computer design system in a single valve remote control functionality, this mode of operation, the user will be asked to valve opening lower machine corresponding valve through a CAN bus pass by place under the control of the start and stop of the valve, and the operational status of the entire process to the host computer in real time. In practical applications, if the system valve linkage requirements, can also be achieved through the host computer programming.
Lower machine design
Action of the valve is to specify the degree of opening of the command will be received by embedding into place under the control valve, the next crew to analyze the operation of the valve, and a variety of state, if the valve is to allow the actions of the state, the next bit machine instruction is issued after the analysis (on or off), arrived at the designated opening to be the valve opening, perform the shutdown operation. Below from two aspects of hardware, software slave in a more detailed explanation.
Lower machine hardware design
The lower machine microcontroller control system has the function of "autonomy", on the basis of the original electrical control circuit fault signal acquisition and external communication CAN bus interface. Lower electromechanical road from the structure and function can be divided into the main control unit module, power supply monitoring module, data acquisition and control interface module, the man-machine interface module bus communication module. The relationship between them is shown in Figure 4.
(1) the main control unit module
The main control module is the core of the entire lower machine, constituted by the smallest single-chip system, coordinating other four modules work completed under machine control functions. The valve operation taking into account the number of points and fault information collection point of information collection and ease of system development, the system selected PHILIP company MCS51 series microcontroller 80C552 with 256 bytes of RAM read and write data memory, five 8 bit I / O port, an 8-bit input port, two 16-bit timer / counter, a configuration capture / compare module 16-bit timer, 15 interrupt sources, two interrupt priority, 8-channel 10-bit the A / D converter, 2-channel pulse width modulation output, two serial ports (asynchronous serial port and I2C bus port), integrated watchdog timer.
② power monitoring module
Valve in the course of their work, for some reason the main power circuit is powered down, the user requirements in this case, the the lower machine system monitoring part still short-term work, and this failure to timely upload to PC monitoring system , early detection, so that the operator immediately removed. For this reason, in this article the next bit machine control machine designed power monitoring module monitoring of valve power supply situation, and can switch between the main power and standby power circuit structure shown in Figure 5. Only SCM system power supply due to the main power circuit power-down, the standby power saving operation mode, in addition to the SCM system, lower power consumption and standby power using ordinary dry cells or rechargeable batteries. Experiments show that, in the case of main power circuit is powered down, the standby power can work more than 12h, fully meet the need for maintenance.
③ data acquisition and control interface modules
This part of the lower machine control system input, output section complete valve various alarm signal, the degree of opening of the acquisition, the valve opening and closing, stop control, and its structure is shown in Figure 6 below. Data acquisition circuit, in addition to the acquisition of basic running state, an increase of motor phase-limit torque, motor overheating, fuse damage, limit switch in place, such as an emergency brake status signal acquisition points to improve the monitoring capabilities of the next-bit machine. The majority of the valve in the acquisition and control signals for a strong signal, used in the circuit to the SCM system from being affected by the isolation, and increase the reliability of the system.
④ Human Interface Module
Valve operation in addition to remote control by the host computer, but also retain site control, mainly through the completion of the Field Communicator, it is lower in human-computer interface module. Communicator keyboard and digital tube display circuit. HART design extension of the input and output I2C interface chip the PCF8574 I2C bus technology, keyboard circuit, display circuit with a digital display with I2C interface driver chip SAA1064, microcontroller 80C552 itself is integrated I2C bus interface for the system's hardware and software design provides convenience. Handheld hardware structure shown in Figure 7. In addition, I2C bus supports hot plug, has brought great convenience to the use of the manual operator, users can be without prejudice to the case of the valve is working properly, disassembly Communicator.
⑤ The communication function module
Communication circuit is lower in CAN bus interface part, is a core part of the valve remote control. It is constituted by the CAN controller SJA1000 CAN drive 82C250 and optical isolation circuit, the circuit structure is shown in Figure 8. Due to the needs of the optical isolation module uses a DC-DC power supply module. Also designed in order to improve the versatility of the communication module, to meet the needs of different uses, the next bit machine micro switches, for setting different communication baud rates and the address selection of the different valves.
The lower machine software design
Lower computer software C51 language greatly improve the readability, portability. Lower computer software to complete the collection of the state and the failure of the valve, the valve opening collection, perform switching the stop valve action and communication functions. Because of limited space, only the following describes the main control program and CAN bus communication interrupt service routine.
① main program design
The lower machine software signal acquisition valve control valve movement, as well as respond to the request or command of the host computer. Enter the main program loop lower machine system initialization, in order to accurately captured the valve opening and avoid false alarms, simple digital filtering the input signal, the next bit machine to control the valve opening degree requirements after a comprehensive analysis of these signals on, off, to stop the action. The lower machine has site control, remote control two control modes, can be the scene switches to distinguish between these two control modes, the next crew can be in accordance with the requirements of the host computer running the data upload. Different site control, the operator in the field hand exercise control when the host computer can monitor only the next-bit machine, can not control; remote control, the next crew of the valve through the analysis of the host computer command Control. Lower machine main program software process is shown in Figure 9.
② CAN interrupt service routine design
When the host computer requests the data the downward-bit machine or command, the next crew will enter the CAN interrupt service routine. Into the CAN interrupt service routine, the first on-site protection, then read SJA1000 interrupt register analysis which interrupt and set the appropriate flag, the receive interrupt is set to receive data flag and read the data, and then release cache, final site restoration, and return from the interrupt. CAN interrupt service routine shown in Figure 10.
Lower confidential embedded into the cavity in the valve Denso serious electromagnetic interference in the design using a variety of soft and hardware anti-jamming design, because of space reasons, not going to elaborate.
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