Method for Operating a Segment of Cycle-Oriented Control Software

A method for operating a segment of cycle-oriented control software for controlling a process, the control software executing on a computer system within a runtime environment, in order to secure a system time of the computer system, a further safety time independent of the system time being requested in each cycle, a first time difference being formed from the system time of a current cycle and the system time of a previous cycle and a second time difference being formed from the safety time of the current cycle and the safety time of the previous cycle and a comparison of the first and second time differences with a pre-determined tolerance being performed and, in an event the deviation of the time differences exceeds the tolerance, an error signal being generated, the method comprising:

• generating a random number upon a start-up of the runtime environment, the generated random number being stored in a storage region and added to the storage region upon every further request for the safety time;
• calculating, in a control component, a deviation between the time differences at a start of a new cycle in the control software;
• and
• accessing, during each new cycle, the storage region by the control component, the random number being subtracted out of the safety time in the control component again before the calculation of the time differences, for an eventuality that a new start-up of the runtime environment has occurred, the new start-up of the runtime environment being diagnoseable based on the tolerance being exceeded, and the second time difference having an offset which is given by the safety time with a new random number of the current cycle and the safety time with the old random number of the previous cycle.