Acting on the physical world.
WHAT ACTUATORS DO
Convert a signal into physical action: switching, moving, opening, heating.
WHAT COMMON TYPES ARE
Relays, switching higher-power circuits Motors and servos Valves Indicators and displays Locks
WHY CONTROL IS RISKIER THAN SENSING
A wrong reading is misleading; a wrong action causes physical consequence.
WHAT THAT DEMANDS
Confirmation before consequential actions Validation that the command is plausible Limits enforced on the device itself
WHY LIMITS ON THE DEVICE
The connection may be compromised, and the device must refuse impossible instructions regardless.
WHAT A SAFE STATE IS
The condition a device adopts on failure, loss of connection, or power loss.
WHAT TO DEFINE FOR EVERY ACTUATOR
What that state is.
WHY
Failure is certain, and undefined behaviour during it is dangerous.
WHAT TO NEVER DO
Depend on a network connection for a safety function.
WHAT TO IMPLEMENT
Local control that works without connectivity Manual override, physically accessible
WHAT TO CONFIRM
That an action actually occurred, by sensing the result.
WHY
Commanding is not the same as achieving.
