A novel transformer-based sensor for a pneumatic cylinder enables measurements of the piston position to be made through a thick conductive cylinder. Unlike existing industrial solutions, which are mainly based on a moving magnet, our se nsors do not require modifications to the parts inside the cylinder. Finite element analysis results are compared with me asurements at various piston positions and excitation fre quencies. Using a suitable model for the magnetic properties of the iron piston bar, we achieved good agreement between the model and reality. When the sensor is operated at 100 Hz, the sensitivity is 200 mV/FS and the raw linearity error is 1.6% of the full 400 mm stroke.