In position measurement with ultrasound (US), a US signal is issued, which is reflected by the moving body. The duration of the system measured in this way is proportional to the distance travelled.
A distinction is made between direct US measurements, which are relatively inaccurate (±0.1 mm), but can measure lengths of up to 5 m, and US measurement with magnetostrictive wave guide (Figure U 13). Here current pulses flow to the wave guide, the magnetic field of which meets with a permanent solenoid on the moved part and sends out a US signal, the duration of which is read again. The process is significantly more accurate and suitable for lengths of up to around 2 m. It has a theoretically infinite resolution and is suitable for high traversing speeds. Both processes are among the digital measurement processes and are well suited to integration in cylinders.
Figure U 13: Ultrasound position measurement, magnetostriction (above), senders and receivers (below)