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Lesson 3 - Sensors

Flowcharts and sequencing

Software can be used to create sequences in a flowchart, to view onscreen simulations.

Examples include:
  • Flowol
  • Logicator
  • Crocodile Clips

Basic flowchart symbols

Name Symbol Usage
Terminator

Starts or stops a process.

Input or output

An input is data received by a computer. An output is a signal or data sent from a computer.

Process

An instruction or a command.

Decision

A decision, either yes or no. For example, a decision based on temperature that turns a central heating system on or off.

Line tool

Connects the symbols. The arrow indicates direction.



Flowcharts and sequencing

Software can be used to create sequences in a flowchart, to view onscreen simulations.

Examples include:
  • Flowol
  • Logicator
  • Crocodile Clips

Basic flowchart symbols

Name Symbol Usage
Terminator

Starts or stops a process.

Input or output

An input is data received by a computer. An output is a signal or data sent from a computer.

Process

An instruction or a command.

Decision

A decision, either yes or no. For example, a decision based on temperature that turns a central heating system on or off.

Line tool

Connects the symbols. The arrow indicates direction.



control

The role of sensors in control

Sensors are used to measure physical quantities such as temperature, light, pressure, sound, and humidity. They send signals to the processor, processor shorthand for central processing unit (CPU). For example:

  • A security alarm system may have an infrared in communications, an infrared beam modulates (switches on/off) to a receiver that interprets the modulations as data sensor which sends a signal when the beam is broken.
  • A heat sensitive sensor in the corner of a room may detect the presence of a person.
  • Temperature sensors could be used to control the heating in a large building.
  • Magnetic sensors are used to detect metal and can be placed in roads to monitor traffic flow.

Other physical quantities that can be transmitted directly to the computer's processor include:

  • rainfall/water levels
  • radiation level
  • pH level
  • oxygen level

A computer-controlled greenhouse

To get the best plant growing conditions, the temperature and humidity (moisture in the air) have to be controlled.

The greenhouse therefore has temperature and humidity sensors linked to a computer, and the computer has a control program storing details of the correct temperature and humidity settings. The greenhouse is fitted with a heater, sprinkler and window motor which are also linked to the computer.

If the humidity falls below the values stored in the program, the computer activates the sprinklers and closes the windows. If the temperature falls outside the values stored in the program, the heater is activated by the computer.

Greenhouser

The system monitors the conditions all day and night and responds immediately to any changes. To alter the growing conditions the values in the computer program can of course be changed.

Remember to consider the role of the sensors, interface box and control program when explaining the control process.

Making decisions

A diamond box is used when a decision needs to be made. This might include comparing the input states or comparing a count to a set limit. The outcome of the decision must be either yes or no. These can be in combination used to act as logic gates.

Decision box

Task 1 - Automatic Home

Decision box

Help with task 1

Decision box

Task 2 - Greenhouse


Update your objectives

control

You should now be able to assess yourself against your objectives:

  1. I can identify common types of sensors used in control systems
  2. I can break down complex problems into smaller parts to find a solution
  3. I can develop a control solution for a system that uses two flowcharts operating in sequence


  • Learning Objectives

  • I can identify common types of sensors used in control systems.
  • I can break down complex problems into smaller parts to find a solution.
  • I can develop a control solution for a system that uses two flowcharts operating in sequence.

Flowcharts and sequencing

Software can be used to create sequences in a flowchart, to view onscreen simulations.

Examples include:
  • Flowol
  • Logicator
  • Crocodile Clips

Basic flowchart symbols

Name Symbol Usage
Terminator

Starts or stops a process.

Input or output

An input is data received by a computer. An output is a signal or data sent from a computer.

Process

An instruction or a command.

Decision

A decision, either yes or no. For example, a decision based on temperature that turns a central heating system on or off.

Line tool

Connects the symbols. The arrow indicates direction.