Appropriate selection of a control system for a complex industrial process is very difficult. The main part of control is often retained by men and, then, the computer function is limited to adequate determination and provision of comprehensive information concerning the plant operation status in a readable form to enable making optimal decision by a dispatcher. This kind of computer system has been applied to the open pit in Bełchatów Poland. It is one of the largest brown coal mines all over the world, with coal output of 38500000 Mg and overlay output of 125 Mm3 per annum. Coal is conveyed to a 4320MW power plant. The exploitation process employs the following machines:
Each machine has, among others, a measurement device providing an instantaneous output value and a current machine state (work/standstill) signal. For excavators there are available signals indicative of coal or overlay digging and for loader-dumpers - signals of conveying direction. Directly accessible signals have been insufficient for efficient manual control. Available information should take the following form, for convenience of the dispatcher:
The part of this information is important as it is used in economic accounts. Current information has to be provided continuously using a radio link. A dedicated real time computer system has been designed for this critical task. It measures signals and processes them to display required information in a readable form on a CRT display and it prints out reports. A report is printed out at request and automatically after the end of each shift. Considering the place where the computer system takes over the control hierarchy, its reliability is of decisive importance. Therefore, there were designed two identical computers working simultaneously but independently of each other. This ensures an increased hardware reliability. The next step towards the reliability improvement is a special algorithm construction. The computer system is designed to acquire and process data, and finally to display and print appropriate information describing the process state independently of the technologic and energy consumption points of view. Output data enable the dispatcher to control the work of all mining devices and guarantee:
The computer system consists of the following (fig):
The mentioned computers exchange data using the local network. The data acquisition and processing computer (APD) reads data from sensors at discrete intervals, processes them and saves the description of the mining process current state results. A system printer can be connected optionally to APD or MS. The result data from APD are provided to both computers by the local network. The monitoring station (MS) is responsible for displaying vital information about the current mining state on the 6 following CRT's designed for:
To increase reliability, monitoring stations equipped with additional CRT's can work as dispatcher workstations. In that case the possibility of standstill description in not available. The dispatcher workstation makes system configuration possible and enables the input of process parameters and data not available from sensors, e.g. substitution values for selected signals, standstill reasons, mining device names, power limits, current time and date, etc. Monitoring of the power supply system is divided into:
If ordered power is exceeded the system warns and aids reduction of current power.
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