This figure illustrates the risks involved in automatic control, and the operator's role and risks as a supervisor.

In automatic control, the operator is part of the supervision loop, outside the control loop. The risks are as follows:

Control risks

• Boiler failure
• Thermostat failure

Supervision risks

• Operator's mistake
• Alarm malfunction

Common risks

• On-Off switch stuck open
• Thermometer malfunction

Secondary risks

In this example, the unit control is automated, and the unit supervision is manual. The operator's tasks include identifying and resolving risky conditions, including malfunction of the boiler, On-Off switch and thermostat and alarm.

The designer's task is make sure that:

• The operators will notice the risky situations even when they are busy doing something else, or tired.
• The operators will know what they should do to solve the problem
• The system will not crash even if the operators are absent, do not understand the operational instructions, or behave unexpectedly otherwise.

Updated on 23 Jan 2017.