2Brief Overview Types of Sensors and how they work Sensor Applications Advantages and DisadvantagesSensors that will work with our project
3Types of Temperature Sensors ThermocouplesResistance Temperature Detectors (RTDs)ThermistorsInfrared SensorsSemiconductors
4Thermocouples Two wires of different metal alloys. Converts thermal energy into electrical energy.Requires a temperature difference between measuring junction and reference junction.Easy to use and obtain.
6Thermocouples Advantages Disadvantages Simple, Rugged High temperature operationLow costNo resistance lead wire problemsPoint temperature sensingFastest response to temperature changesLeast stable, least repeatableLow sensitivity to small temperature changesExtension wire must be of the same thermocouple typeWire may pick up radiated electrical noise if not shieldedLowest accuracy
7Resistance Temperature Detectors (RTDs) Wire wound and thin film devices.Nearly linear over a wide range of temperatures.Can be made small enough to have response times of a fraction of a second.Require an electrical current to produce a voltage drop across the sensor
8RTD Applications Air conditioning and refrigeration servicing Furnace servicingFoodservice processingMedical researchTextile production
9RTDs Advantages Disadvantages Most stable over time Most accurate Most repeatable temperature measurementVery resistant to contamination/corrosion of the RTD elementHigh costSlowest response timeLow sensitivity to small temperature changesSensitive to vibration (strains the platinum element wire)Decalibration if used beyond sensor’s temperature ratingsSomewhat fragile
10Thermistors A semiconductor used as a temperature sensor. Mixture of metal oxides pressed into a bead, wafer or other shape.Beads can be very small, less than 1 mm in some cases.The resistance decreases as temperature increases, negative temperature coefficient (NTC) thermistor.
11Thermistors Most are seen in medical equipment markets. Thermistors are also used are for engine coolant, oil, and air temperature measurement in the transportation industry.
12Thermistors High sensitivity to small temperature changes Advantages DisadvantagesHigh sensitivity to small temperature changesTemperature measurements become more stable with useCopper or nickel extension wires can be usedLimited temperature rangeFragileSome initial accuracy “drift”Decalibration if used beyond the sensor’s temperature ratingsLack of standards for replacement
13Infrared SensorsAn infrared sensor intercepts a portion of the infrared energy radiated by an object.Many types Optical Pyrometers, Radiation Pyrometers, Total Radiation Pyrometers, Automatic Infrared Thermometers, Ear Thermometers, Fiber optic Thermometers, Two-Color Pyrometers, Infra-Snakes, and many more.
14Infrared Applications Manufacturing process like metals, glass, cement, ceramics, semiconductors, plastics, paper, textiles, coatings.Automation and feedback controlImprove safety in fire-fighting, rescues and detection of criminal activities.Used to monitor and measure human body temperatures with one second time response.Reliability and maintenance needs from building heating to electrical power generation and distribution
15Infrared Sensors Advantages Disadvantages No contact with the product requiredResponse times as fast or faster than thermocouplesNo corrosion or oxidation to affect sensor accuracyGood stability over timeHigh repeatabilityHigh initial costMore complex - support electronics requiredEmissivity variations affect temperature measurement accuracyField of view and spot size may restrict sensor applicationMeasuring accuracy affected by dust, smoke, backgroundradiation, etc.
16SemiconductorsAre small and result from the fact that semiconductor diodes have voltage-current characteristics that are temperature sensitive.Temperature measurement ranges that are small compared to thermocouples and RTDs, but can be quite accurate and inexpensive.
17Semiconductor Applications Hard Disk DrivesPersonal ComputersElectronic Test EquipmentOffice EquipmentDomestic AppliancesProcess ControlCellular Phones