PE2-4.5 Applications: Sound, Temperature & Humidity Measurement
You can compare microphone types, select among thermistors, resistance wire and semiconductor thermometers and thermocouples for a temperature measurement, and describe proximity sensing and hygrometry.
Temperature is the most measured physical quantity in industry, and the four devices here trade range against linearity and cost: thermocouples span enormous ranges with a small nonlinear voltage, RTDs are linear and expensive, thermistors are sensitive and very nonlinear. Choosing correctly means starting from the required range and accuracy, not from familiarity. Microphones are worth a careful look as the acoustic case of the transducer principles from Unit 3.
Work through these
Microphones and their types
Turning sound into a signal, by several principles with different characteristics. Choosing one is a matter of what the recording is for.
Thermistors
Temperature from a resistance that changes steeply and non-linearly. The steepness is the sensitivity and the non-linearity is the work.
Resistance wire thermometers
The alternative, which is far more linear and far less sensitive. The comparison with the item above is the content.
Semiconductor thermometers
The semiconductor version, which is cheap, linear over a modest range and often already inside your microcontroller.
Thermocouples and cold junction compensation
Temperature from two dissimilar metals, and the reference junction problem that always comes with it. The compensation is the detail that catches everyone building their first one.
Choosing a temperature sensor by range, linearity and cost
The item that makes the four above worth having read: choosing between them against range, linearity and cost. That is the actual engineering decision.
Proximity sensing in application
The proximity devices from the earlier topic, seen in a working application. It grounds the classification in something that ships.
The hygrometer
Measuring humidity, which closes the subject. It is harder than temperature and the calibration drifts, which is worth knowing before trusting one.
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