This chart illustrates basic concepts in error-proof system design. The illustration is of a hierarchical boiler control, in which the routine operation is automatic, and the operator is a supervisor, who needs to solve problems.
The routine control in this example is by automation, using a thermostat. The operator is not involved in the routine control, and is free to do other tasks.
The thermostat is used here for rebounding. Each time the temperature goes below the low threshold, the thermostat activates (connects) the boiler. Each time the temperature raises above the high threshold, the thermostat deactivates (disconnects) the boiler.
Because temperature control is automatic, the operator is free to do other tasks. The primary system-related task is supervision, namely, responding to unexpected hazards.
Updated on 08 Feb 2017.