Contactless Piston Position Transducer With Axial Excitation

Existing piston position transducers require either drilling precise hole into the piston bar, or mounting permanent magnets or measuring device inside the pressurized cylinder. We present a new solution for aluminum pneumatic cylinders, which uses the ferromagnetic bar inside the solenoid as a marker and linear array of fluxgate sensors as a scale. Instead of relying on dc remanence we use active ac excitation; the reading is resistant against external fields, both dc and ac. Using sensor array allows to compensate for temperature effects. The linear stroke of the individual sensor is 40 mm, so that array density should be about 30 mm. 1 mm position resolution is achievable. The weak point of the new transducer is the response time: for fast moving pistons the excitation frequency should be high, which leads to weaker signal and lower resolution.