Contact displacement sensors measure displacement by directly contacting the measured object and detecting its physical changes. Among them, LVDT (Linear Variable Differential Transformer) and potentiometer are two typical representatives, and their working principles are as follows:

LVDT displacement sensor: Based on the principle of electromagnetic induction, it consists of a primary coil, two secondary coils connected in reverse series, a movable iron core, and a coil skeleton. After the primary coil is subjected to an AC excitation voltage, an alternating magnetic field is generated. When the iron core is at the center of the coil, the voltage induced by the two secondary coils is equal in magnitude and opposite in phase, and the output voltage is zero; When the iron core deviates from the center, the coupling with one secondary coil increases and the coupling with another decreases, resulting in an output voltage difference whose amplitude is proportional to the displacement of the iron core, and whose phase indicates the direction of displacement. This design improves sensitivity and linearity through differential output, and there is no direct contact between the iron core and the coil. It has the characteristics of no friction, long service life, and high resolution, and is suitable for high-precision and long-life industrial scenarios, such as monitoring the throttle position of aircraft engines.

Potentiometer type displacement sensor: composed of a resistance track and a movable electric brush, utilizing the characteristic that the resistance value changes with the position of the sliding contact. When the measured object is displaced, the electric brush slides on the resistance track, changing the length of the resistance connected to the circuit, thereby outputting a voltage signal proportional to the displacement. Its structure is simple and cost-effective, but due to friction and wear in contact measurement, its lifespan and accuracy are relatively limited. It is often used in cost sensitive and low precision scenarios, such as simple mechanical displacement monitoring.

LVDT achieves high-precision measurement through non-contact electromagnetic induction, while potentiometer relies on contact resistance changes to complete displacement detection. Both represent high-precision and low-cost technical routes in contact displacement sensors.