Transducer, Sensors and Actuators
Transducer
A transducer is any device which converts one form of energy into another.
Examples of common transducers include the following:
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A microphone converts sound into electrical impulses and a loudspeaker converts electrical impulses into sound (i.e., sound energy to electrical energy and vice versa).
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A solar cell converts light into electricity and a thermocouple converts thermal energy into electrical energy.
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An incandescent light bulb produces light by passing a current through a filament. Thus, a light bulb is a transducer for converting electrical energy into optical energy.
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An electric motor is a transducer for conversion of electricity into mechanical energy or motion.
Types of transducer
Electrochemical Transducers
Some common electrochemical transducers include the following:
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pH probe – Converts chemical energy into an electrical energy.
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Molecular electric transducer – Converts motion in an electrolytic solution into electrical energy.
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Battery – Converts chemical energy directly into electrical energy.
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Fuel cell – Converts the energy from a reaction within a fuel cell to electrical energy.
Electroacoustic Transducers
Common electroacoustic transducers:
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Loudspeaker – Converts an electrical signal into sound
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Microphone – Converts sound waves in air into an electrical signal
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Hydrophone - Converts sound waves in water into an electrical signal.
Electromagnetic Transducers
Common electromagnetic transducers:
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Magnetic cartridge – Converts motion in a magnetic field into an electrical energy.
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Generator – Converts motion in a magnetic field into electrical energy.
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Strain gauge – Converts the deformation (strain) of an object into electrical resistance.
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Galvanometer – Converts the electric current of a coil in a magnetic field into movement.
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Generators – Converts mechanical energy (motion) into electrical energy.
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Motor – Converts electrical energy into mechanical energy.
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Electric motor
Electrostatic Transducers
Common electrostatic transducers:
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Electrometer – Converts static or energy from a vibrating reed into electricity.
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Van de Graaf generator – Converts static into high voltage.
Photoelectric Transducers
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Cathode ray tube (CRT) – Converts electrical signals into light energy for a visual output.
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Light bulb – Converts electrical energy into visible light and heat.
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Laser diode – Converts electrical energy into light energy.
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Photodiode - Converts light energy into electrical energy.
Photodiode
Thermoelectric Transducers:
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Thermocouple – Converts heat energy into electrical energy.
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Temperature sensitive resistor (Thermister) – a variable resistor affected by temperature changes (heat energy to electrical energy).
Other types of Transducers:
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Geiger-Müller tube – Converts radioactive energy into electrical energy.
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Quartz Crystal – Converts mechanical stress into electricity (electrical energy).
Sensor
A sensor is a device that receives and responds to a signal. This signal must be produced by some type of energy, such as heat, light, motion, or chemical reaction. Once a sensor detects one or more of these signals (an input), it converts it into an analog or digital representation of the input signal.
Based on this explanation of a sensor, you should see that sensors are used in all aspects of life to detect and/or measure many different conditions.
Human beings are equipped with 5 different types of sensors:
Eyes detect light energy, ears detect acoustic energy, a tongue and a nose detect certain chemicals, and skin detects pressures and temperatures. The eyes, ears, tongue, nose, and skin receive these signals then send messages to the brain which outputs a response. For example, when you touch a hot plate, it is your brain that tells you it is hot, not your skin.
Basic Concepts of Sensors
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Sensors detect the presence of energy, changes in or the transfer of energy. Sensors detect by receiving a signal from a device such as a transducer, then responding to that signal by converting it into an output that can easily be read and understood. Typically, sensors convert a recognized signal into an electrical – analog or digital – output that is readable. In other words, a transducer converts one form of energy into another while the sensor converts the output of the transducer to a readable format.
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Transducers convert one form of energy to another, but they do not quantify the conversions. For example, a battery converts chemical energy into electrical energy but it does not quantify exactly how much electrical energy is being converted. If the purpose of a device is to quantify an energy level, it is a sensor.
Types of Sensors
Mechanical Sensors
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Pressure sensor – measures pressure.
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Barometer – measures atmospheric pressure.
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Altimeter – measures the altitude of an object above a fixed level.
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Liquid flow sensor – measures liquid flow rate.
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Gas flow sensor – measures velocity, direction, and/or flow rate of a gas.
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Accelerometer – measures acceleration.
Electrical Sensors
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Ohmmeter – measures resistance.
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Voltmeter – measures voltage.
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Galvanometer – measures current.
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Watt-hour meter – measures the amount of electrical energy supplied to and used by a residence or business.
Digital multi-meter for measuring
voltage, current and resistance
Thermal Sensors
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Thermometer – measures absolute temperature.
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Thermocouple gauge– measures temperature by its affect on two dissimilar metals.
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Calorimeter – measures the heat of chemical reactions or physical changes and heat capacity.
A thermocouple is a device that directly converts thermal energy into electrical energy. When two dissimilar metal wires are connected at one end forming a junction, and that junction is heated, a voltage is generated across the junction. If the opposite ends of the wires are connected to a meter, the amount of generated voltage can be measured. This effect is known as the Seebeck Effect or Seebeck coefficient. The voltage created in this situation is proportional to the temperature of the junction.
Chemical Sensors
Chemical sensors detect the presence of certain chemicals or classes of chemicals and quantify the amount and/or type of chemical detected.
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Oxygen sensor – measures the percentage of oxygen in a gas or liquid being analyzed
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Carbon dioxide detector – detects the presence of CO2 (see diagram below)
Optical
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Light sensors (photodetectors) – detects light and electromagnetic energy.
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Photocells (photoresistor) – a variable resistor affected by intensity changes in ambient light.
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Infra-red sensor – detects infra-red radiation.
Infra-red sensor
Acoustic
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Seismometers – measures seismic waves.
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Acoustic wave sensors – measures the wave velocity in the air or an environment to detect the chemical species present.
Others types of sensor include:
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Motion – detects motion
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Speedometer – measures speed
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Geiger counter – detects atomic radiation (see graphic)Biological – monitors human cells
Motion sensor
Actuator
An actuator is a device that actuates or moves something. An actuator uses energy to provide motion. Therefore, an actuator is a specific type of a transducer.
Basic Concepts of Actuators
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An actuator is something that actuates or moves something. More specifically, an actuator is a device that coverts energy into motion or mechanical energy. Therefore, an actuator is a specific type of a transducer.
Types of actuators
Thermal Actuators
One type of thermal actuator is a bimetallic strip. This device directly converts thermal energy into motion. This is accomplished by utilizing an effect called thermal expansion.
When a material is heated, the average distance between atoms (or molecules) increases. The amount of distance differs for different types of material. This microscopic increase in distance is unperceivable to the human eye. However, because of the huge numbers of atoms (or molecules) in a piece of material, the material expands considerably and, at times, is noticeable to the human eye.
Thermal thermometer that uses a bi-metal strip
Electric Actuators
An electric motor is a type of an electric actuator. Most direct current (DC) motors operate by current flowing through a coil of wire and creating a magnetic field around the coil. The coil is wrapped around the motor's shaft and is positioned between the poles of a large permanent magnet or electromagnet. The interaction of the two magnetic fields causes the coil to rotate on its axis, rotating the motor's shaft. Thus, an electric motor is a transducer and an actuator because it converts electrical energy to magnetic energy to mechanical energy or motion.
Mechanical Actuators
Mechanical actuators convert a mechanical input (usually rotary) into linear motion. A common example of a mechanical actuator is a screw jack. The figure below shows a screw jack in operation.
Rotation of the screw causes the legs of the jack to move apart or move together. Inspecting the motion of the top point of the jack, this mechanical rotational input is clearly converted into linear mechanical motion. Mechanical actuators can produce a rotational output with the proper gearing mechanism.
Screw jack
Summary
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A transducer is a device which converts one form of energy into another. Transducers are used in all aspects of life to measure changes in the environment, to enhance everyday applications, and to learn more about the world around us.
An actuator is a device that converts energy into motion. Therefore, it is a specific type of a transducer. When the output of the transducer is converted to a readable format, the transducer is called a sensor.
A sensor is a device that receives and responds to a signal. This signal must be produced by some type of energy, such as heat, light, motion, or chemical. Once a sensor detects one or more of these signals, it converts it into an analog or digital representation of the input signal.
Transducers, sensors and actuators can be found in the macroscale (those visible to the naked eye) and the microscale (microscopic).