Fluid level monitoring through fluid cell protrusion

Apparatus for monitoring the level of a liquid in a reservoir, comprising:

• an integrally-formed transparent monitoring portion of said reservoir, said monitoring portion including
• a first transparent wall portion and
• a second transparent wall portion,
• a light source positioned outside of said reservoir for directing a beam of light toward said first wall portion along a first linear path,
• said first linear path passing through said wall portions and defining a monitoring line segment as that portion of said first linear path inside said wall portions,
• said monitoring line segment being a small fraction of the largest interior dimension of a monitoring cross section taken through said reservoir along a plane defined by said first linear path and an intersecting line normal to said first transparent wall portion, and
• a light sensor positioned outside said reservoir and directed at said second transparent wall portion along a second linear path,
• said second linear path being the path said beam of light takes upon exiting from said second wall portion when said monitoring portion is not occupied by liquid,
• said first and second wall portions being adapted when said monitoring portion is occupied by liquid to cause said beam of light transmitted by said source to be refracted within said monitoring portion and to emerge from said second wall portion along a third linear path not striking said sensor.