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Sensors and Actuators are referred to as Transducters, that is a device that converts one physical quantity into another. Transducers that convert physical quantities into electrical signals will be used to produce inputs and will be referred to as Sensors.
Transducers that take electrical input signals and control or affect an external physical quantity will be referred to as Actuator. Almost any physical property of a material that varies in response to some excitation can be used to produce a Sensor. Commonly used devices include those whose operation is:. We will look the more important terms that describe Sensors and Instrumentation Systems to quantify their characteristics and Performance. The Range is the value between the Maximum and Minimum Values of the quantity that the Sensor can measure.
It is usually expressed as a percentage of the Range. The Accuracy describes the maximum expected error associated with a measurement or a Sensor and may be expressed as an absolute value or as a percentage of the Range of the System. Devices with high precision will produce repeated readings with very little spread.
Figure If the Output of a Sensor is linearly proportional to the quantity being measured, the Sensor will be a perfectly linear device. The Sensitivity measures the change produce at the output for a given change in the quantity being measure. Resistive Thermometers measure the temperature using the variation of the Resistance R of a piece of metal since this changes with the Temperature, such devices as Platinum Resistance Thermometers PRTs.
Thermistors measure the temperature as the Resistive Thermometers do giving much improved sensitivity. However, they are Non-Linear. The Diodes conduct electricity in one direction The Diode is Forward-Biased but opposes the flow of electricity in the other direction when the Device is Reverse-Biased.
For more information, see Chapter 16 Semiconductors and Diodes. Light falling on a PN Junction produces a voltage and can be used to generate power. Photodiodes can be used to measure light intensity, since the Output Voltage produced depends a not related linearly of light falling on them.
In absence of light it will behave like any other diode and conduct only a negligible leakage current. However, if light is allowed to fall on the device, charge carriers will be formed in the junction region and a current will flow. The Current I is proportional to the intensity of the incident light.
They respond to different wavelengths of light in a manner similar to the human eye. Strain Gauge use those two principles to measure the force applied to it since the shape of it will change with it.
Piezoelectric Sensors are built with Piezoelectric Materials which have can generate a non proportional Electrical Ouput Signal to the applied force. Displacement or Position may be sensed using various methods: resistive, inductive, mechanical and optical techniques. Tacho-generator can be used to measure rotational speed and Radars use the Doppler Effect to measure linear motion.
Sound represents variation in air pressure, the objective of the microphone is to measure these variations and to represent them by some form of electrical signal as the Figure Carbon Microphones are composed by a Diaphram that detects sound waves which form one side of an enclosure containing Carbon Particles. These carbon particles are striked by the sound waves, being compressed to a greater or lesser degree and thus affecting their resistance.
Capacitance Microphones operate the same way that Carbon Microphones using a variation in Capacitance rather than Resistance. Moving-Coil Microphones are the most common form of microphone. They consist of a permanent magnet and a coil connected to a diaphragm. Sound waves move the diaphragm which causes the coil to move with respect to the magnet generating an electrical signal.
The Piezoelectric Force Sensor can also be used as microphone. The diaphragm is made of a piezoelectric material which is distorted by sound waves producing electrical signal.
Sensor Interfacing are a relatively simple Circuitry required to generate the Output of one device compatible with the Input of another device. One way of converting a changing resistance into a changing voltage is to use the sensor in a Potential Divider Circuit, as illustrated in Figure To produce a Voltage Vo that is linearly related to the resistance of a sensor, a constant Current I can be passed through the device, as shown in Figure The Constant current I comes from some external Circuity.
This Circuits are called Constant Current Sources. Switches have two contacts, which are connected electrically when the switch is in one state the closed state and disconnected or open circuit when the switch is in the other state as Figure When the switch is closed, the Output Voltage Vo is connected to the 0 Volts.
When the switch is open, the Output Voltage is connected to the V Volts. Switch Bounce is a problem of Switches that it tends to bounce as Figure Other solution is to use Opto-Switch Sensor. They do not produce Bounce Switch. We will leave further consideration of such circuits until later. Learn more about Scribd Membership Home. Much more than documents. Discover everything Scribd has to offer, including books and audiobooks from major publishers.
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Jump to Page. Search inside document. For more information, see Chapter 16 Semiconductors and Diodes Sanjay Gomasta. Torstein Lillevik. Raman Buzaubak Tegi. Arbi Hamin Lakibul. Boniface Kariuki. Elpidio Storolli. Narendra Mali. Mon Jhio San Juan. Hi there. Erick Parra. Roger Backman. Moazam Ali. Malik Hamza.
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