The MLW Series of Long Stroke Linear Position Sensors from Macro Sensors can determine displacements up to 1.2m with accuracy.
Macro's Magnetostrictive Sensor
Their sizes vary from 300 to 1200mm. They can either be externally mounted on or integrated into hydraulic cylinders.
It relays current via a pipe attracted by a magnet. The sensor uses the flight time to identify the magnet located on the tube. The time-based position measurement is translated into an output signal. The devices are powered by 24VDC and have less than ±0.25% linearity and ±0.01% repeatability across the range with outputs of analog voltage, current and SSI. Even when there is no power supply, there is no loss of data.
The devices exhibit good stroke to length ratio (range/length of unit) in longer ranges. They have stainless steel probes that are dust proof and adhere to all industry standards. They can be used to determine the position of components on heavy machinery that is being deployed in harsh industrial environments such as the paper industry, turbine blades, construction, test equipment in the automotive industry and flight simulators. The optional float kit provided with the magnet helps use the device to identify the water level in a tank.