Stroke measurement and proper positioning of hydraulic cylinders on off-highway equipment can be critical in preventing damage to nearby equipment and property. One method of measuring piston position is by using Temposonics-MH analog position sensors from MTS System Corp., Sensor Div., Cary, N.C. (www.temposonics.com), which are installed right in the hydraulic cylinder. The sensors use magnetostrictive technology in which the interaction between two magnetic fields creates a sonic pulse. A permanent magnet which moves along the waveguide in the tubular sensor provides one magnetic field. The other field comes from a current pulse or interrogation signal sent down the magnetostrictive waveguide. The resulting sonic pulse travels along the waveguide until it is detected at the end. The sensors then use elapsed time between interrogation and return signals to determine magnet position. This method generates no wear on the sensing components, so the sensors maintain accuracy and consistency over time.

The sensors are relatively small and can be built into hydraulic cylinders. They work regardless of hydraulic fluid used, measure displacements between 50 and 1,000 mm, and output dc signals between 0 and 5 V that are proportional to linear displacement. With direct outputs, no signal-conditioning electronics are needed when interfacing with controllers or meters. Operating temperatures range from -40 to 85°C, and sensors are pressure rated to 300 bar, shock rated to 50 g, and CE certified.