Liquid level sensing is a requirement in many applications in which knowledge of the volume of a liquid is necessary, for example, in fuel storage systems and chemical processing.

A wide range of liquid level sensing techniques have been reported based around mechanical, electrical, and optical methods. Electrical liquid level sensors are widely employed, but their applicability is compromised if the liquid to be monitored is conductive or if the environment is potentially explosive.

Optical fibre sensors offer well-established advantages under these conditions. The optical fibre is a dielectric, and thus is non-conducting, and the sensor may be configured such the light is confined within the fibre, reducing the likelihood of ignition of a flammable environment.

In this paper a liquid level sensor is demonstrated by exploiting the refractive index sensitivity of long period gratings (LPGs) to measure the length of the fibre immersed in a liquid.