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Lesson

Sensing, switching and regulating

Control is sensing, switching and regulating of events and processes

Sensing

Humans perceive the world through the five senses of sight, hearing, taste, touch and smell. Sensing in technological terms is quite similar. It refers to observing or perceiving events or objects and recording the observations. For technological systems to perform sensing they require sensors. Sensors are devices that respond to external physical stimuli in the form of energy. Examples of stimuli that sensors can detect include

  • thermal energy, (heat)
  • mechanical energy, (pressure, motion)
  • acoustic energy, (sound)
  • electromagnetic radiation (radio waves, light waves, magnetic fields)

Sensors are transducers. A transducer converts energy from one form to another. All sensors convert the energy from what they sense into electrical energy. Some sensors are designed to measure analog processes. Analog processes are those in which the energy being measured is constantly changing. Air pressure and temperature, voice and music are al forms of energy that are analog in nature. Other sensors are designed to measure digital events. Digital events are on/off events.

Sensors

  • convert the energy that has been measured into electrical energy
  • sent that electrical energy in the form of a signal to the application or system that will use the information

Switching

Switching is the process of turning something on or off. It is essentially a digital event. Switching is an external stimuli applied to a system. It can be a one time event, or it can happen over and over. It can be used to stop or start a process (example, turn a light on or off), or to send a signal (example, Morse code).

Regulating

Regulating is the process of continuously modifying the behavior of a system over time, for example, speeding up or slowing down a jogging machine (treadmill) by setting the speed control.

Control systems

Control systems employ sensing, switching and regulating simultaneously to ensure that a system operates within set parameters.

A thermostat, for example, regulates room temperature. It is a complete control system. It has a temperature sensor. As the sensor reads changes in temperature, and compares it to the temperature that you set, it turns the heating on and off to regulate the room temperature within a few degrees of the set temperature.

A control system uses the data collected by sensors to manage the operation of a system. The, thermostat described above, is a simple control system. More complex systems use a variety of sensors to regulate a number of processes.

Automobiles have sophisticated control systems, for example

  • Sensors collect data about exhaust gasses such as CO2, exhaust temperature, air temperature and pressure
  • The control system analyses the data and regulates
    • the amount of fuel, the air-fuel mixture, when the mixture is delivered to the engine,
    • the time, voltage and duration of the electrical spark used to ignite the gases

The sensing and control processes operate continuously. The system contributes significantly to the higher engine efficiency and lower maintenance costs of recent vehicles.

Airplanes use sensors to detect things ranging from airspeed to to pressures on various parts of the aircraft, from ice formation on the wings to the current position of, and forces acting on, flight control surfaces such as flaps, ailerons and the rudder. Control systems are used to automatically regulate many elements of the flight when the plane is on autopilot.

Ships use control systems to operate steering and propulsion as well as course heading. Semi-submersible drilling rigs employ sophisticated control systems to ensure that the rig maintains an exact height above the ocean floor and an exact position above the well opening on the ocean floor.

Remote sensing

Remote sensing is sensing from a distance such as from an airplane of from a satellite. Since the sensor is never in contact with what is being observed, remote sensing involves observing some form of electromagnetic radiation such as visible light, infrared and ultraviolet light, or radio waves.

Remote sensing systems usually produce some sort of ../images, which need to be manipulated and analyzed to provide useful information.

Remote sensing can be passive or active

  • Passive sensing relies mainly on the sun's energy to illuminate the target, and for most of the electromagnetic frequencies used, works only in the daytime. The sensor detects energy reflected from the earth's surface for example. Infrared radiation is an exception and can be detected day or night.
  • Active sensing relies on the sensor system to produce the energy that is used to 'illuminate' the target. Sonar and radar are active sensing systems. They have transducers that are energy sources and detect the return of that energy in the form of reflections or 'echoes'.

Remote sensing has a wide variety of applications, including

  • Identifying the structure and nature of the earth's crust as an aid to predicting earthquakes, finding minerals and hydrocarbon deposits
  • Tracking man-made artifacts and structures as an aid to identifying pollution and long term environmental effects, for planning and making war
  • Tracking temperatures, ocean currents, and oxygen levels over large ocean areas, and at various depths in the water column, as a means of identifying and predicting population trends in ocean plants, fish and animals, and for predicting large climate effects such as El Nina and El Nino.
  • Measuring CO2 and ozone in the earth's atmosphere as a means of calculating and predicting the effects of such things as green house gasses
  • Measuring and monitoring a variety of manufacturing by-products and effluent from specific locations.
  • Measuring and monitoring ice berg formation and ice floes in places like the Artic and North Atlantic

If you are interested in more information about remote sensing and its applications, please look at this detailed tutorial at the Canada Centre for Remote Sensing (CCRS). The CCRS has a listing of satellites used for remote sensing, including details about what their sensors measure. The CCRS also has sample images collected by remote sensing from various regions of Canada.

Activity

Assigned activities

Research and build a presentation on an application for

  • control systems

or

  • remote sensing

Include information of the type of sensors, what they measure and how the data is used. In the case of control systems indicate how the control systems regulates the system it is embedded in. For example, how does an autopilot keep a ship on its proper course?, or how is the action of a joystick in the pilots hand translated into changes in the planes direction?

Starting points for research include

Test Yourself

There is no self test for this lesson.