Open loop and closed loop

Explain what an automatic system is and name its four basic elements (input or reference, controller, actuator and output or process), stating what each one does in a specific example.

Explain what the setpoint or reference value of a control system is and give two examples: one for a home thermostat and another for a car's cruise control.

State which sensor you would use to measure each quantity in an automatic system and what signal it sends to the controller: the temperature of a room, the ambient light of a street, and the open or closed position of a door.

Explain what an open-loop control system is and give two examples of everyday devices that operate this way (a toaster, a fan without a thermostat, timed irrigation...), justifying why they are considered open loop.

Classify these systems as open loop or closed loop, justifying your decision: (a) a dishwasher that executes its program by timer, and (b) an air conditioner that maintains the room temperature.

A ceiling fan is switched on and its speed is adjusted using a manual control. Describe its block diagram, reason whether it is open loop or closed loop, and explain what elements would need to be added to convert it into a closed loop that maintains the room temperature.

Explain what a closed-loop control system is and what it means to have "feedback". Give an everyday example (for instance, heating with a thermostat) and identify the sensor and the variable that is fed back.

In a closed loop, the "error" is the difference between the reference and the sensor measurement. Explain what the controller tries to do with this error and what happens when the error reaches zero.

In control systems, feedback is negative: the measurement is subtracted from the reference. Explain what would happen if it were added instead of subtracted (positive feedback), reasoning how the output would grow uncontrollably, and give an everyday example of positive feedback (acoustic feedback between a microphone and a loudspeaker).

A refrigerator regulates using bang-bang (on-off) control: the compressor turns on or off, with no intermediate power levels. Explain why the internal temperature oscillates slightly around the setpoint and what hysteresis or deadband is (the margin between the turn-on and turn-off temperatures), indicating its purpose (to prevent continuous starting and stopping of the compressor).

An underfloor heating system exhibits noticeable transport delay and thermal inertia: heat takes about $45$ minutes to diffuse through the slab into the room. In a home regulated by a conventional on/off thermostat set at $20{,}0\ ^\circ\text{C}$, it is observed that when the temperature drops to $19{,}5\ ^\circ\text{C}$ the boiler turns on, but the room continues cooling down to $18{,}0\ ^\circ\text{C}$; then, after reaching $20{,}0\ ^\circ\text{C}$ again and the boiler turning off, the room continues heating up due to inertia until reaching $23{,}5\ ^\circ\text{C}$.

1. a) Draw a qualitative temperature-time graph showing this behavior, identifying the setpoint, overshoot, and delay. Explain physically why high inertia causes these continuous oscillations in on/off control.
2. b) Justify and describe two technical control solutions (such as modulating control with weather compensation via an outdoor sensor or algorithms with inertia calculation) that stabilize the temperature without causing excessive oscillations.

The analog signal sent by a PT100 RTD installed next to a variable-frequency drive suffers from high-frequency electromagnetic interference. The system controller, configured with a setpoint of $60{,}0\ ^\circ\text{C}$, receives a sequence of consecutive readings taken every second: $59{,}2\ ^\circ\text{C}$, $60{,}5\ ^\circ\text{C}$, $58{,}7\ ^\circ\text{C}$, $61{,}1\ ^\circ\text{C}$, $59{,}4\ ^\circ\text{C}$, $60{,}8\ ^\circ\text{C}$, even though the actual fluid temperature remains stable at $59{,}9\ ^\circ\text{C}$.

1. a) Deduce the behavior that an on/off actuator (a relay controlling a cooling solenoid valve) connected to a direct comparator without signal conditioning will experience. Justify the electromechanical effects and the impact on component service life.
2. b) Design and justify two complementary technical modifications to solve the problem: one at the software/signal conditioning level for the sensor signal, and another at the comparator logic level (implementation of hysteresis or deadband), determining the width you would give to that band.