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Lecture 4

IAT267_Week 4.docx

3 Pages

Interactive Arts & Tech
Course Code
IAT 267
Helmine Serban

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Temperature Sensing Thermal resistors-electrically conductive elements that are designed to change electrical resistance in a predictable manner with changes in applied temperature Resistance temperature devices (RTDs)-based on the tendency of naturally occurring materials to change physical dimensions with changes in temperature Thermistors-semiconductors with a negative temperature coefficient (semiconductor’s resistance decreases with an increase in temperature Thermocouples -most popular temperature sensors as they are cheap, interchangeable, have standard connectors and can measure a wide range of temperatures -main limitation is accuracy, system errors of less than 1 degree Celsius which can be difficult to achieve -relies on the Seebeck Effect (junction between two metals generates a voltage which is a function of temperature) -although almost any two types of metals can be used to make a thermocouple, a number of standard types are used because they possess predictable output voltages and large temperature gradients Light sensing Light-a form of electromagnetic radiation Light detectors essentially can be broken into two categories Quantum detectors-convert incoming radiation directly into an electron in a semiconductor device, and processes the resulting current with electronic circuitry -offer the best performance for detection of optical radiation E.g. photodiode Thermal detectors-operate by absorbing infrared radiation and measuring the change in temperature with a thermometer -performance is limited by the availability of sensitive and small heat capacity thermometers If conditions allow the use of a quantum detector, such a detector will outperform a thermal detector by several orders of magnitude therefore; thermo detectors come into their own in situations which simply don’t allow quantum detectors Proximity and Presence Sensors-used for sensing the closeness of objects -their range varies with the type of sensor, sensitivity and the material being sensed Choosing the right sensor  Decide first what parameters of the external environment are important E.g. temperature, humidity, pressure, light  Determine what kind of sensor is optimal for measure that parameter on the basis of quality parameters Quality Parameters Transfer function-the functional relationship between physical input signal and electrical output signal -for expensive sensors which are individually calibrated; this might take the form of the certified calibration curve Sensitivity-the ratio between a small change in electrical signal to a small change in
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