Displacement Sensing: Selecting the Correct Sensor (Thermistor, LVDT, Photodiode, Bimetallic Strip)
Displacement means a change in position. In instrumentation, displacement is commonly measured using sensors that convert linear or angular position changes into an electrical signal. Among the options given, the sensor specifically designed for measuring displacement is the LVDT because it converts the relative movement of a movable core into a measurable differential voltage.
By contrast, a Thermistor is for temperature measurement, a Bimetallic strip is also for temperature/thermal detection, and a Photodiode is primarily for light intensity/optical position sensing rather than direct displacement measurement (unless used as part of a dedicated optical position system).
The correct choice for “Which sensor is used for measuring displacement?” is: (ii) LVDT.
LVDT (Linear Variable Differential Transformer) Working Principle
Key idea: “Built for displacement” vs “can be used indirectly”
- LVDT is engineered to measure linear displacement via transformer action and core movement.
- Thermistor measures temperature because resistance changes with temperature.
- Bimetallic strip measures temperature-related deflection, not position/linear displacement directly.
- Photodiode measures light, and displacement would require an optical arrangement (e.g., beam interruption or coded targets).
How to identify the correct displacement sensor from a list
- 1Step 1
If the sensor is fundamentally a temperature sensor, it won’t directly measure displacement.
- 2Step 2
Displacement sensors provide an electrical output proportional to movement (linear or angular).
- 3Step 3
Thermistor and bimetallic strip outputs correspond to temperature changes/thermal bending, not positional displacement.
- 4Step 4
LVDT output changes when the core position changes relative to coils, enabling displacement measurement.
Mapping the Options to Their Primary Measurands
Higher means the sensor is directly intended for that measurand.
Common confusion points
Pro Tip
In multiple-choice questions, the “correct” displacement sensor is the one whose name/working principle explicitly involves position or a movable core—not a temperature or light-only sensor.
Knowledge Check
Which sensor is used for measuring displacement in the given options?