IEEE Instrumentation and Measurement Technology Conference Ottawa, Canada, May 19-21, 1997
A Remote Controlled Automated Measurement System Francisco Alegria and Helena Geirinhas Ramos Centro de Electrotecnia Teórica e Medidas Eléctricas DEEC-I.S.T., Technical University of Lisbon 1096 Lisboa Codex PORTUGAL
Phone: 351-1-8417975, Fax: 351-1-8417672, email:
[email protected] Abstract - Control of instrumentation systems through network PC's is increasingly important nowadays, both in the industry and in the R&D centers. This paper will present an automated measurement system used to characterise a semiconductor device. The system can be controlled by any of the PC's integrated in a LAN network using a client/server technology. The server controls the instrumentation through an IEEE-488 interface bus. Keywords - networking, automatic measurement system, distributed instrumentation.
I. INTRODUCTION A major trend over the last few years has been the widespread adoption of local area networks (LAN) to replace the old model of a single computer serving all of the organisation's computational needs. Existing autonomous computers are connected together to constitute a computer network. One of the goals of interconnecting stands on the resource sharing possibility: data, programs and equipment are available to anyone on the network without regard to the physical location of the resource and the user. Measuring system have developed along the years. The introduction of mainframe computers, and later of personal computers, in the measuring system brought many benefits. Those benefits are today extended with the use of computer networks in measuring systems. This paper present an application illustrating the control of IEEE-488 instrumentation, located remotely, by any of the computers integrated on a LAN. The example chosen, more for pedagogical purposes than a serious
proposal, is a simple automated measurement system used to characterise a semiconductor device. The system can be easily adapted to a more sophisticated purpose. For example, results of tests on the printed circuit boards delivered by the production line can provide information to the network of the factory in order to exert some influence or control over the assembly line. Another field of application is in radio astronomy where big antennas are used to scan the universe for radio waves and need to be located in geographically remote regions (high altitude, away from light sources) for better performance. The people that operate those antennas can benefit from a system like this to control the antenna orientation and to retrieve the signals captured without needing to travel to the antenna’s location. II. SYSTEM ARCHITECTURE It represents a client/server environment based on a computer network with several computers. Each computer can act as a server or as a client. The server contains the resources that are made available to the client machines. It controls the instrumentation and acquires the data but it is mainly dedicated to serving the clients as it provides the access and control of the test instrumentation. Any of the clients is able to fully control the instrumentation by sending the required parameters to the measuring system and also the commands to initialise the process. The client side of the system also performs the user interface, graphics, report generation and data analysis. The communication between the client and the server is based on a messaging philosophy. Client processes send request messages to server processes and then
wait for a reply. Server processes accept request messages and send back reply messages. Each communication takes the form of a single message transmitted between two processes. The inter-process communication is based on socket pairs. Sockets are destination points to which messages may be sent and from which messages may be received. They are identified by an Internet address and a port number. For communication to take place between a pair of processes each must create its own socket and the two sockets are used as a pair. The protocol used is can be either connection oriented (TCP) or connectionless (UDT). With the TCP protocol the two processes must first establish a connection between the socket pair. The server creates a socket and binds an identifier to it; potential clients may then request connections to the server's socket. For communication between clients and servers, clients request connections and the server accepts them. When a connection is accepted, a new socket is created and pairs it with the client's socket. A connected pair of sockets can be used in subsequent communications until the connection is closed. In the UDT protocol for each message send a temporary connection is automatically established and broken after a particular message is sent.
III. SYSTEM The experimental system was build using two PC’s connected through a LAN.
Helena
Fig. 1 System
Both PC’s were running Microsoft Windows 95 and communicated, through the LAN, using the TCP/IP protocol (connection oriented). The server PC was fitted with an IEEE-488 interface board. It was developed in Visual Basic 4.0 two applications, one for the server and another for the client. Both applications use a thirdparty custom control to manage the network communication (MYNET.VBX). The server application accesses the IEEE-488 interface board through a function library (IEEE488.DLL) supplied by the manufacturer. A. Automated measuring system The circuit assembled is used to establish the voltampere characteristic of a junction diode IN4153. It is just a resistance (R) in series with a diode. A voltage (VG) is applied to the circuit by a DC power supply having dual polarity and remotely programmed through a digital-to-analogue converter controlled through an IEEE-488 bus. The magnitude of the current that flows through the diode (ID) is calculated from the voltage across the resistance (VR): ID=VR/R. That voltage is measured by a digital multmeter having also IEEE-488 capabilities. The value of the resistance is chosen according to the characteristics of the diode. The voltage (VD) applied to the junction is determined by VD=VG-VR. B. Server The server application controls the instrumentation. The user first connects the DC power supply and the multmeter to the electrical circuit and to the IEEE-488 interface board in the PC. Then he runs the server application, supplying both instruments IEEE-488 address, the value of the resistance in the electrical circuit and the time interval between each point to be measured. The fields “Local name” and “Local address” allow the user to know the computer’s network address that he must later supply to the client application. The fields “Command send” and “Command received” are used to monitor the messages exchanged with the client. The caption of the window automatically changes from “Server” to “Serverconnected” when a connection is established. When the application loads the MYNET control is set up: Load Port number = 1101 Listen port number = 1100 End of message character = 10 Listen
The control automatically determines the name and address of the computer. The application then waits for the client to request a connection. When a connection between the client and the server MYNET control is established an event is generated in the application: Connected Initialize IEEE-488 boar7d The application now waits for a message from the client to start the measuring procedure. When a message arrive an event is generated: Data Received If the message is all received then Extract minimum voltage Extract maximum voltage Extract number of points If the parameters are correct Send START message Characterize diode Send results Else Send error message The characterization of the diode consists in sending IEEE-488 commands to the instrumentation through the IEEE-488 interface board. Characterize diode For each point Send generate voltage command Send measure voltage command Send receive measurement command Wait time interval Finally the results are send to the client: Send results Build message Send message
Fig. 2 Server application
C. Client The client application allows the user to input the parameters for the diode’s characterization and to view the results. The user must say which computer in the network is the server by supplying server’s name or address that can be obtained from the server’s application interface window. The fields “Command send” and “Command received” are used to monitor the messages exchanged with the client. The caption of the window automatically changes from “Client” to “Clientconnected” when a connection is established. When the application loads the MYNET control is set up: Load Port number = 1100 End of message character = 10 After saying which computer is the server the user can establish a connection by pressing the “Connect” button. Connect Get server address from window field Instructs the MYNET control to connect
After the parameters are input to the appropriate fields the user can click in the “Execute” button to send them to the server. Execute If the connection is established then Construct message with parameters Send message to server When the server finishes characterizing the diode it sends a message to the client with the results. Messages are also received from the server when the characterization starts and when there are errors with the parameters or the instrumentation. Data Received If the message is all received then If the message contains results then Extract results Draw graphic Else Open message box
IV. CONCLUSION In traditional automated measuring systems controlled by a PC the user interfaces with the same computer that is directly connected to the measurement system. Those systems are easily converted into remote controlled systems using the architecture presented in this paper. The software to control any system can be developed with little effort using common development tools that exist today like Visual Basic. The networking capabilities necessary are nowadays integrated in the PC operating system like Windows 95. The use of a remote controlled system gives the opportunity to put as controller any computer belonging to the local area network, probably at a more convenient or safer location. It allows a more easy and flexible use of an automated measuring system leading in some cases to reduction in operating costs.
The user can disconnect from the server by clicking in the “Disconnect” button.
REFERENCES [1] William Stallings, "Data and Computer Communications", Macmillan Publishing Company. [2] Michael Purser, "Data Communications for Programmers", Addison-Wesley Publishing Company.
Fig. 3 Client application
