Monitoring or control: watching versus doing

By the end of this lesson

By the end you can explain the difference between a monitoring system and a control system, and sort a real system into the right one.

Watching versus doing

Your smartwatch measures your heart rate all day. It shows it, logs it, maybe buzzes if it's odd, but it never changes it.

That's monitoring.

Your central heating measures the room temperature, then switches the boiler on or off to change it. That's control.

Definition

Monitoring system

A system that uses sensors to measure physical quantities; the computer records, displays or analyses the readings and may give a warning if they go outside set limits. It does not change the conditions it is measuring.

Definition

Control system

A system that uses sensors to measure physical quantities; the processor compares the readings with stored values and sends signals to actuators that change the conditions. The output affects the next input (feedback).

The parts

Sensor: measures a physical quantity (temperature, pressure…) and sends a signal, usually analogue.
ADC (analogue-to-digital converter): turns that signal into digital data the processor can use.
Processor: reads the sensors at regular intervals, compares each reading with stored values and decides what to do.
Actuator (control only): turns a signal from the processor into physical action, such as a motor turning or a valve opening.

Sensors never decide anything. They only measure; the processor makes every decision.

Worked example: Easy first: watch or act?

Sort each system into monitoring or control.

A A weather station logs wind speed and rainfall.
B A greenhouse opens its windows when it gets too hot.
C A burglar alarm sounds a siren when its sensor detects movement.
D A fridge switches its cooling on when the inside warms above 5 °C.

Have a go first?

Quick check

Multiple choiceQuestion 1 · Recall

Multiple choiceQuestion 2 · Apply

CalculateQuestion 3 · Recall

Answer the 3 questions above to continue.