Ch 4: Temperature Sensors Flashcards
Q: What is a thermocouple?
A: A sensor that measures temperature using the voltage generated by two dissimilar metals.
Q: Define a thermistor.
A: A temperature-sensitive resistor whose resistance changes with temperature.
Q: What is a diode temperature sensor?
A: A sensor that measures temperature based on the voltage across a forward-biased diode.
Q: What is a transistor temperature sensor?
A: A sensor using a transistor’s temperature-dependent voltage drop to measure temperature.
Q: What is the advantage of using a thermistor?
A: High sensitivity to temperature changes./thermistors are essentially a single-piece resistor
Q: What is the disadvantage of thermocouples?
A: Nonlinear output requiring compensation.
Q: What is a platinum resistance thermometer (PRT)?
A: A sensor using platinum to measure temperature due to its stable resistance-temperature relationship.
Q: How does ambient temperature affect sensors?
A: It can alter sensor accuracy and response time.
Q: What is a temperature coefficient?
A: The rate of change of resistance with temperature.
Q: What is a bimetallic strip?
A: A mechanical sensor that bends with temperature changes due to different expansion rates of metals.
Q: How is temperature measured with infrared sensors?
A: By detecting emitted infrared radiation from an object.
Q: What is self-heating in thermistors?
A: Heat generated by current passing through the thermistor, affecting its reading.
Q: What is the Seebeck effect?
A: The generation of voltage due to temperature differences across a conductor.
Q: What is a resistance temperature detector (RTD)?
An RTD (Resistance Temperature Detector
A: A sensor that measures temperature based on the resistance change in a metal.
Q: What is the purpose of a temperature sensor in HVAC systems?
A: To regulate and maintain desired temperature levels.
Q: Why are thermistors nonlinear?
A: Because their resistance-temperature relationship is exponential.
Q: How is a thermocouple calibrated?
A: By comparing its readings against a known temperature standard.
Q: What is the main advantage of RTDs?
RTD (Resistance Temperature Detector)
A: High accuracy and stability over a wide temperature range.
Q: What is the temperature range of PRTs?
A: Typically -200°C to 850°C.
Q: What is the response time of a temperature sensor?
A: The time it takes to reach a stable output when temperature changes.
Q: How does an analog temperature sensor work?
A: It converts temperature into an analog voltage signal.
Q: What are NTC thermistors?
(NTC Thermistors )
A: Negative Temperature Coefficient thermistors, where resistance decreases with temperature increase.
Q: What are PTC thermistors?
A: Positive Temperature Coefficient thermistors, where resistance increases with temperature increase.
Q: What is a thermal couple junction?
A: The point where two metals in a thermocouple are joined.
Q: What is the advantage of digital temperature sensors?
A: They provide direct digital output without additional circuitry.
Q: How does a Zener diode temperature sensor behave when held with human fingers?
A: the voltage reach an stability at finger tem.
Q: What is the expected voltage of an LM335 Zener diode at 298 K?
A: +2.98 V.
Q: What is the main advantage of Zener diodes over thermistors?
A: Stability and linearity in voltage output.
Q: What happens to a Zener diode sensor’s output when improperly cooled?
A: It provides inaccurate readings due to uncontrolled self-heating or heat dissipation.
