04-05-2012, 12:54 PM
Sensors and Transducers
[attachment=21256]
Simple stand alone electronic circuits can be made to repeatedly flash a light or play a musical note, but in order for an electronic circuit or system to perform any useful task or function it needs to be able to communicate with the "real world" whether this is by reading an input signal from an "ON/OFF" switch or by activating some form of output device to illuminate a single light and to do this we use Transducers.
Transducers can be used to sense a wide range of different energy forms such as movement, electrical signals, radiant energy, thermal or magnetic energy etc, and there are many different types of both analogue and digital input and output devices available to choose from. The type of input or output transducer being used, really depends upon the type of signal or process being "Sensed" or "Controlled" but we can define a transducer as a device that converts one physical quantity into another.
Devices which perform an input function are commonly called Sensors because they "sense" a physical change in some characteristic that changes in response to some excitation, for example heat or force and covert that into an electrical signal. Devices which perform an output function are generally called Actuators and are used to control some external device, for example movement. Both sensors and actuators are collectively known as Transducers because they are used to convert energy of one kind into energy of another kind, for example, a microphone (input device) converts sound waves into electrical signals for the amplifier to amplify, and a loudspeaker (output device) converts the electrical signals back into sound waves and an example of this is given below.
Simple Input/Output System using Sound Transducers
There are many different types of transducers available in the marketplace, and the choice of which one to use really depends upon the quantity being measured or controlled, with the more common types given in the table below.
Input type transducers or sensors, produce a proportional output voltage or signal in response to changes in the quantity that they are measuring (the stimulus) and the type or amount of the output signal depends upon the type of sensor being used. Generally, all types of sensors can be classed as two kinds, passive and active.
Active sensors require some form of external power to operate, called an excitation signal which is used by the sensor to produce the output signal. Active sensors are self-generating devices because their own properties change in response to an external effect and produce an output voltage, for example, 1 to 10v DC or an output current such as 4 to 20mA DC. For example, a strain gauge is a pressure-sensitive resistor. It does not generate any electrical signal, but by passing a current through it (excitation signal), its resistance can be measured by detecting variations in the current and/or voltage across it relating these changes to the amount of strain or force.
Unlike the active sensor, a passive sensor does not need any additional energy source and directly generates an electric signal in response to an external stimulus. For example, a thermocouple or photodiode. Passive sensors are direct sensors which change their physical properties, such as resistance, capacitance or inductance etc. As well as analogue sensors, Digital Sensors produce a discrete output representing a binary number or digit such as a logic level "0" or a logic level "1".
Analogue and Digital Sensors
Analogue Sensors
Analogue Sensors produce a continuous output signal or voltage which is generally proportional to the quantity being measured. Physical quantities such as Temperature, Speed, Pressure, Displacement, Strain etc are all analogue quantities as they tend to be continuous in nature. For example, the temperature of a liquid can be measured using a thermometer or thermocouple which continuously responds to temperature changes as the liquid is heated up or cooled down.
Thermocouple used to produce an Analogue Signal
Analogue sensors tend to produce output signals that are changing smoothly and continuously which are very small in value so some form of amplification is required. Then circuits which measure analogue signals usually have a slow response and/or low accuracy. Also analogue signals can be easily converted into digital type signals for use in microcontroller systems by the use of analogue-to-digital converters, or ADC's.
Digital Sensors
As its name implies, Digital Sensors produce a discrete output signal or voltage that is a digital representation of the quantity being measured. Digital sensors produce a Binary output signal in the form of a logic "1" or a logic "0", ("ON" or "OFF"). This means then that a digital signal only produces discrete (non-continuous) values which may be outputted as a single "bit", (serial transmission) or by combining the bits to produce a single "byte" output (parallel transmission).
[attachment=21256]
Simple stand alone electronic circuits can be made to repeatedly flash a light or play a musical note, but in order for an electronic circuit or system to perform any useful task or function it needs to be able to communicate with the "real world" whether this is by reading an input signal from an "ON/OFF" switch or by activating some form of output device to illuminate a single light and to do this we use Transducers.
Transducers can be used to sense a wide range of different energy forms such as movement, electrical signals, radiant energy, thermal or magnetic energy etc, and there are many different types of both analogue and digital input and output devices available to choose from. The type of input or output transducer being used, really depends upon the type of signal or process being "Sensed" or "Controlled" but we can define a transducer as a device that converts one physical quantity into another.
Devices which perform an input function are commonly called Sensors because they "sense" a physical change in some characteristic that changes in response to some excitation, for example heat or force and covert that into an electrical signal. Devices which perform an output function are generally called Actuators and are used to control some external device, for example movement. Both sensors and actuators are collectively known as Transducers because they are used to convert energy of one kind into energy of another kind, for example, a microphone (input device) converts sound waves into electrical signals for the amplifier to amplify, and a loudspeaker (output device) converts the electrical signals back into sound waves and an example of this is given below.
Simple Input/Output System using Sound Transducers
There are many different types of transducers available in the marketplace, and the choice of which one to use really depends upon the quantity being measured or controlled, with the more common types given in the table below.
Input type transducers or sensors, produce a proportional output voltage or signal in response to changes in the quantity that they are measuring (the stimulus) and the type or amount of the output signal depends upon the type of sensor being used. Generally, all types of sensors can be classed as two kinds, passive and active.
Active sensors require some form of external power to operate, called an excitation signal which is used by the sensor to produce the output signal. Active sensors are self-generating devices because their own properties change in response to an external effect and produce an output voltage, for example, 1 to 10v DC or an output current such as 4 to 20mA DC. For example, a strain gauge is a pressure-sensitive resistor. It does not generate any electrical signal, but by passing a current through it (excitation signal), its resistance can be measured by detecting variations in the current and/or voltage across it relating these changes to the amount of strain or force.
Unlike the active sensor, a passive sensor does not need any additional energy source and directly generates an electric signal in response to an external stimulus. For example, a thermocouple or photodiode. Passive sensors are direct sensors which change their physical properties, such as resistance, capacitance or inductance etc. As well as analogue sensors, Digital Sensors produce a discrete output representing a binary number or digit such as a logic level "0" or a logic level "1".
Analogue and Digital Sensors
Analogue Sensors
Analogue Sensors produce a continuous output signal or voltage which is generally proportional to the quantity being measured. Physical quantities such as Temperature, Speed, Pressure, Displacement, Strain etc are all analogue quantities as they tend to be continuous in nature. For example, the temperature of a liquid can be measured using a thermometer or thermocouple which continuously responds to temperature changes as the liquid is heated up or cooled down.
Thermocouple used to produce an Analogue Signal
Analogue sensors tend to produce output signals that are changing smoothly and continuously which are very small in value so some form of amplification is required. Then circuits which measure analogue signals usually have a slow response and/or low accuracy. Also analogue signals can be easily converted into digital type signals for use in microcontroller systems by the use of analogue-to-digital converters, or ADC's.
Digital Sensors
As its name implies, Digital Sensors produce a discrete output signal or voltage that is a digital representation of the quantity being measured. Digital sensors produce a Binary output signal in the form of a logic "1" or a logic "0", ("ON" or "OFF"). This means then that a digital signal only produces discrete (non-continuous) values which may be outputted as a single "bit", (serial transmission) or by combining the bits to produce a single "byte" output (parallel transmission).