Sensors, Microprocessors & Actuators in Industry

🎯 Syllabus & Goals 3 min

Cambridge 6.1 · Automated systems Paper 1 · Computer Systems

By the end of this lesson you can:

1. Define an automated system and name its three hardware parts.
2. Describe how sensors, a microprocessor and actuators work together in a control loop.
3. Give the advantages and disadvantages of automating an industrial process.

Textbook: Chapter 6, §6.1.1–6.1.2 (pp. 217–221) — industrial applications.

Recap / Warm-Up 5 min

In Unit 3 you met sensors as input devices and actuators as output devices. Unit 6 puts them to work. Every system in this unit is the same three parts, arranged around a different real job.

Quick starter

A sensor in a freezer reads −12 °C. The target is −18 °C. Which part decides to switch the compressor on — the sensor, the microprocessor or the actuator?

🧠 Key Concept 14 min

1 · What is an automated system?

An automated system does a job by itself. It uses hardware and software together. No person needs to press a button each time. People usually still watch it, from a control room.

2 · The three parts and the control loop

• Sensor — an input device. It takes readings of a physical quantity (temperature, pressure, light…) and sends the data on.
• ADC — most sensors give an analogue signal. An analogue-to-digital converter turns it into digital data the processor can use.
• Microprocessor (or computer) — compares each reading with stored / pre-set values and decides what to do.
• Actuator — an output device. It turns an electrical signal into movement: motors, pumps, valves, pistons, solenoids.

3 · Industrial example A — a nuclear power station

4 · Industrial example B — making a medicine (paracetamol)

Two linked processes run here. Process 1 makes the medicine. Process 2 presses it into tablets. Sensors on both send data to a central computer. The computer checks its database and drives actuators: pumps, valves, heaters, stirrers and pistons.

It shares the nuclear plant's advantages. It adds three more: more efficient use of materials, higher productivity and more consistent results (every tablet the same).

Worked Example 12 min

(a) Keeping a reaction vessel at 80 °C — the loop, step by step

1. A temperature sensor in the vessel takes a reading continuously.you must name the sensor — "a sensor" alone rarely scores.
2. The analogue reading passes through an ADC, becoming digital data for the microprocessor.processors only handle digital data.
3. The microprocessor compares the reading with the stored value 80."compares with a stored/pre-set value" is the single most-awarded phrase.
4. If the reading is < 80, it sends a signal to an actuator to switch the heater on.state the condition AND the action.
5. If the reading is > 80, it signals the actuator to switch the heater off (or open a cooling valve).the examiner wants both directions.
6. The process repeats continuously — the sensor keeps sending new readings.the loop / feedback mark: never forget it.

The same logic in Cambridge pseudocode (one statement per line):

Pseudocode · temperature control loop

// Hold the vessel at the stored target temperature
CONSTANT Target ← 80
DECLARE Temperature : REAL
DECLARE Shutdown : BOOLEAN
Shutdown ← FALSE
REPEAT
  // read the sensor (value already converted by the ADC)
  INPUT Temperature
  IF Temperature < Target
    THEN
      OUTPUT "Heater ON"
    ELSE
      OUTPUT "Heater OFF"
  ENDIF
  INPUT Shutdown
UNTIL Shutdown = TRUE

How the marks are earned: one mark per step 1–6 above. An answer that says only "the sensor tells the computer to turn on the heater" scores 0 — sensors never decide.

(b) Filling in the textbook's analysis table — the paracetamol plant

The textbook advises summarising every scenario in one table. Here it is, worked for Example B.

1. Which sensors? Temperature, pressure, level/flow (and weight for tablets).pick sensors that match a quantity the process must control.
2. Function of the actuators? Run pumps and stirrers, open/close valves, switch heaters, drive the tablet pistons.actuators always cause physical movement or change.
3. Function of the computer? Compare readings with database values; decide; send signals to actuators; repeat.the decision is the computer's job, never the sensor's.
4. Additional notes? Remote operator can override; system runs 24/7; more consistent tablets.this row is where the advantages marks come from.

Try It Yourself 12 min

📝 Exam Practice 10 min

🗝️ Recap & Key Terms 3 min

Every automated system is a loop. Sensors measure, the microprocessor compares with stored values and decides, and actuators act. Industry automates for speed, safety and consistency. It pays in set-up cost, maintenance and cyber risk.

Automated system

Hardware and software designed and programmed to work automatically without human intervention.

Sensor

An input device that takes readings of a physical quantity and sends the data to a microprocessor.

Actuator

An output device that converts a signal from the microprocessor into physical movement (motor, pump, valve).

Microprocessor / controller

The processor that compares readings with stored values and decides which signals to send.

ADC

Analogue-to-digital converter: turns a sensor's analogue signal into digital data.

Distributed control system (DCS)

A powerful computer programmed to monitor and control a complex process without human interaction.

Homework 1 min

Task (≤ 15 min): A public swimming pool keeps its water at 28 °C and at the correct acidity (pH). Describe how sensors, a microprocessor and actuators maintain both conditions automatically. [6]