Temperature Measurement Quiz

Which of the following describes the principle of operation for a thermocouple?

• The change in resistance of a metal with temperature.

• The change in resistance of a semiconductor material with temperature.

• The Seebeck effect, where a voltage is generated at the junction of two dissimilar metals due to a temperature difference.

• The change in magnetic reluctance in response to displacement.

Answer explanation

The correct choice describes the Seebeck effect, which is the principle behind thermocouples. It states that a voltage is generated at the junction of two dissimilar metals when there is a temperature difference.

An RTD (Resistance Temperature Detector) measures temperature by relying on which of the following properties?

• The piezoelectric effect.

• The Hall effect.

• The thermionic emission from a heated wire.

• The change in electrical resistance of a conductive material with temperature.

Answer explanation

An RTD measures temperature based on the change in electrical resistance of a conductive material with temperature. This property allows for accurate temperature readings, making it the correct choice.

Thermistors are known for their high sensitivity. Which of the following is a key characteristic of a thermistor's construction?

• They use a primary winding and two secondary windings to measure displacement.

• They are composed of semiconductor materials whose resistance changes drastically with temperature.

• They are typically made from two dissimilar metals joined at a junction.

• They consist of a long, thin wire of a pure metal like platinum.

Answer explanation

The correct choice highlights that thermistors are made from semiconductor materials, which exhibit a significant change in resistance with temperature, making them highly sensitive to temperature variations.

The primary purpose of a Linear Variable Differential Transformer (LVDT) is to measure:

• Temperature

• Linear displacement

• Flow rate

• Pressure

Answer explanation

The primary purpose of a Linear Variable Differential Transformer (LVDT) is to measure linear displacement. It converts the position of a movable core into an electrical signal, making it ideal for precise displacement measurements.

In the construction of an LVDT, what role does the core play?

• It provides a constant reference voltage for the output.

• It is a movable ferromagnetic rod that links the primary and secondary coils.

• It serves as the sensor's temperature-sensitive element.

• It is a non-conductive bobbin on which the coils are wound.

Answer explanation

The core in an LVDT is a movable ferromagnetic rod that links the primary and secondary coils, allowing for the measurement of displacement by varying the magnetic coupling between the coils.

A key advantage of thermocouples over RTDs is their:

• Requirement for a constant current source.

• Wider temperature range and faster response time.

• Higher sensitivity to small temperature changes.

• Exceptional long-term stability and accuracy.

Answer explanation

Thermocouples have a wider temperature range and faster response time compared to RTDs, making them suitable for extreme conditions and quick measurements, which is a key advantage.

What is the primary difference in the working principle of an NTC (Negative Temperature Coefficient) thermistor compared to an RTD?

• An NTC thermistor's resistance decreases with an increase in temperature, while an RTD's resistance increases.

• An NTC thermistor is a voltage-generating device, while an RTD requires an external power source.

• An NTC thermistor uses the Seebeck effect, while an RTD uses a resistance change.

• An NTC thermistor is more linear than an RTD.

Answer explanation

The primary difference is that an NTC thermistor's resistance decreases with increasing temperature, while an RTD's resistance increases. This fundamental behavior distinguishes their working principles.

The construction of a standard LVDT includes a primary winding and two secondary windings. How are the two secondary windings typically arranged?

• They are wound with different numbers of turns to produce a larger output signal.

• They are wound in parallel and are in phase with the primary winding.

• They are wound on separate bobbins and are connected to provide a positive voltage.

• They are wound coaxially with the primary winding but are connected in series-opposing.

Answer explanation

The two secondary windings in an LVDT are wound coaxially with the primary winding and connected in series-opposing. This arrangement allows for differential output based on the position of the core, enhancing measurement accuracy.

Which of the following describes a key construction difference between a thermocouple and a thermistor?

• A thermocouple is a voltage-generating device, while a thermistor's operation is based on a change in resistance.

• A thermocouple uses a semiconductor material, while a thermistor uses a metal junction.

• A thermocouple has a much faster response time than a thermistor.

• A thermocouple is a passive device, while a thermistor is an active device.

Answer explanation

The correct choice highlights that a thermocouple generates voltage based on temperature differences, while a thermistor operates by changing its resistance with temperature, illustrating their fundamental construction differences.

A key advantage of an LVDT for displacement measurement is its:

• Low sensitivity to displacement.

• Infinite resolution and no friction.

• High friction and wear on its moving parts.

• Requirement for periodic recalibration.

Answer explanation

An LVDT (Linear Variable Differential Transformer) offers infinite resolution and operates without friction, making it highly accurate and reliable for displacement measurement, unlike the other options listed.