Electronic System. Operation

Programmable signal processing with the electronic system means that the executive functions of a process control system, e. g., is initiated and controlled by a program stored in a memory. On the basis of measured data collected from the process, the system performs the action laid down in the program.

The function is therefore not tied to the electrical wiring of the system; it can be adapted to changed operating conditions simply by changing the program.

All function units are connected to the bus and operate jointly with the controlling unit. The control unit may contain a microprocessor and may be mounted on a circuit board of the same type as the other units in the system. It can also consist of a mini-computer, in which case the system acts as an interface with the process.

The objects in the process determine the nature and number of input and output functions, regardless of the operation of the system.

The Fig. 2 shows schematically a system in which four of the function units (circuit boards) are used for connection to the process. They include analog and digital input units for transducers and position contacts, and analog and digital output units for control signals to regulators, relays and indicating devices.

The flow chart for the process shows how the executive components are to operate and perform the process. It serves as a basis for a program list, from which the program is transferred via a magnetic tape to programmable read-only memories.

The memory circuit board and a microprocessor circuit board together constitute the controlling unit, which controls the operation of the system. The control unit reads the input signals and supplies control signals for the executive components in the process on the basis of this.

The program sequence, the supply voltage and certain sections of the bus are checked in a supervising unit which operates an alarm if an error is detected, and makes the output functions safe in order to prevent the process assuming a dangerous state.