An Interpretive Approach for Interactive Real-Time Control Through a Network

Abstract

The CERN Super Proton Synchrotron (SPS) accelerator represents a large industrial control problem, with the additional complication that the control strategies are not fixed. Right from the beginning, it was decided to use an interpretive language for the control process. The main goal of this approach was to reduce the amount of programming effort needed for a proper control of the accelerator, by allowing the actual users — physicists, engineers and technicians — to write the control programs they needed. It very quickly appeared that this method was ideal for providing interactive tools for a control system based on a network.The requirement for interactive network control has been implemented by leaving to the user the choice of those parts of the network best suited for the execution of sections of his program. For that reason interpreter instructions have been defined, allowing the user to define where in the network a logical unit of his algorithm should be executed, and where individual items of the data should be stored.This strategy allows easy access to all the hardware through a distributed data-base. The interpreter being basically a string handler, equipment control can be packed into a module which is called from the program through a name with a standard input-output scheme. All this allows algorithm exportation, while network transfers are minimized.Such a system has been in operation since 1976. Many non-professional programmers are regularly writing or modifying ‘network procedures’ for ever-changing control purposes. The simplicity and flexibility of the interpretive method has enabled many technical innovations to be installed over the years, and some of these are described.