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ResistanceTemperatureDetectorRTD'sJosiah Rom and Lestter Diaz

Overview• A materials electrical resistance

changes with temperature� Resistance of the metal increases as

temperature increases

• Predictable relationship between resistance and surrounding temperature� Allows for consistently accurate

measurements� Accurate to within .1 to .2 C

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Creation• Invented by C.W. Siemens

• First model consisted of� Copper wire� A battery� A galvanometer

• Later discovered platinum was more accurate

• To this day platinum is the most commonly used material

How It Works• Resistance in metal is consistent with temperature

� As temperature increases, resistance increases

• Sensor identifies the change in resistance with a change in temperature

• Sensor will give a reading according to the resistance

• More wires gives more accuracy� Most common is 3 wire

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Types of RTD's• Thin Film

� Reliable� Low cost� Resists shock� Functional

• Wire-wound� Most accurate� Glass core

� Can be immersed in many liquids

� Ceramic core� Accurately measures high temperature

RTD versus Thermocouple• Advantages

� RTD provides greater accuracy� Repeatable Measurements for years� Contamination Resistant� Better Sensitivity� Generally Immune to electrical noise

• Disadvantages� Higher Cost� Current Source required� Self-Heating� Slower Response Time� Lower Temperature Range� Less Durable

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RTD versus Thermistor• Advantages

� Larger Temperature Range� More Stable over time

• Disadvantages� Slower Response Time� High Cost� Less Accurate

Applications• Measuring Air Temperature

� Air Ducts� Labs, Clean Rooms� Highly Pressurized Environments� Inside Ovens

• Surface Temperature� Heat Sinks� Industrial Manufacturing Facilities

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Questions?