Abstract: Precise micro-displacement measurement is a foundational technology in advanced manufacturing
and scientific research.This paper presents a high-precision measurement system driven by gas expansion and
detected via the Hall effect.The system generates displacement by heating a sealed gas chamber to trigger
quasi-isobaric expansion,which moves a syringe piston. A Hall element is positioned within a non-uniform
magnetic field produced by a current-carrying circular coil;its output voltage varies with the position,enabling
indirect displacement measurement. The data,processed by an AD7606 ADC module and an STM32
microcontroller,is transmitted to a host computer via an HC-05 Bluetooth module.To account for deviations
between real and ideal gases,the van der Waals equation is introduced to refine the theoretical model.The
experimental results indicate that the system can stably measure millimeter-scale small displacements. The
minimum output readout interval is 0.2 mm,and the measured displacement range is 0 ~ 4.7 mm under the
experimental conditions,with a relative uncertainty of 5.8%.