Monitoring and control systems
| English | Chinese | Pinyin |
|---|---|---|
| sensors | 传感器 | chuán gǎn qì |
| actuators | 执行器 | zhí xíng qì |
| monitoring | 监控 | jiān kòng |
| control system | 控制系统 | kòng zhì xì tǒng |
| feedback loop | 反馈回路 | fǎn kuì huí lù |
| ADC | 模数转换器 | mó shù zhuǎn huàn qì |
Computers that watch and act
- Many computers connect to the physical world through sensors 传感器 and actuators 执行器.
- Some only watch (monitoring 监控); others watch and act (control).
- The key idea that lets a system correct itself is feedback.
Monitoring vs control
- Both read sensors — the difference is what they do next.
- Monitoring collects and reports data but takes no action (a weather station logging readings).
- A control system 控制系统 uses the data to decide and act through actuators, usually in a feedback loop 反馈回路 (a thermostat turning a boiler on/off).
Monitoring reports data; a control system acts through a feedback loop
Inside a microphone: sound vibrates the diaphragm and coil to produce a current
The key difference between a monitoring system and a control system is that a control system:
Both read sensors, but a control system uses the data to act (via actuators), while monitoring only collects and reports.
A pure monitoring system takes action through actuators to change its environment.
Monitoring only collects and reports data — it does not act. Acting through actuators is what makes it a control system.
Sensors and actuators
- A sensor turns a physical quantity into a signal: temperature (thermistor), pressure (strain gauge), light, sound.
- An analogue sensor signal must pass through an ADC 模数转换器 before the processor can use it.
- An actuator does the reverse — turns a signal into an action: a motor, valve, heater or buzzer.
An FDM 3D printer builds an object layer by layer by melting plastic filament
Match each device to whether it is a sensor (input) or an actuator (output).
A sensor turns a physical quantity into a signal; an actuator turns a signal into a physical action.
A sensor:
A sensor measures the world and outputs a signal. An actuator does the reverse — it turns a signal into an action.
Which is an actuator?
An actuator carries out an action (motor, valve, heater, buzzer). The others are sensors/inputs.
Feedback
- In a control system the actuator changes the environment, which the sensors then re-measure — a feedback loop.
- Without feedback the system cannot correct itself or know when to stop.
- A thermostat with no temperature feedback would just heat forever.
A thermistor: a temperature sensor whose resistance changes with heat
The control feedback loop
Tap round the loop a thermostat or autopilot repeats. A control system doesn't just read the world — it acts, then re-measures, correcting itself again and again.
Why is feedback essential in a control system?
Feedback closes the loop: the actuator changes the environment, the sensors re-measure it, and the system adjusts — e.g. a thermostat stops heating once the target is reached.
You've got it
- monitoring = read sensors and report (no action); control = read sensors and act via actuators
- a sensor turns a physical quantity into a signal (analogue needs an ADC)
- an actuator turns a signal into an action
- a feedback loop lets a control system correct itself