Sensing level of submerged solids. At least some of the example embodiments are methods including: inserting a level sensing apparatus through an aperture at a top of a reservoir such that a bottom end of an inner tube abuts an upper surface of the submerged solids in the reservoir; utilizing the submerged solids such that the upper surface of the submerged solids recedes and the level sensing apparatus moves downward with the receding upper surface of the submerged solids; constraining downward movement of an outer tube when the upper surface of the submerged solids reaches a predetermined low level; and as the upper surface of the submerged solids continues to recede, sensing relative movement of the outer tube and an inner tube as an indication that the upper surface of the submerged solids is below the predetermined low level.

Sensing level of submerged solids. At least some of the example embodiments are methods including: inserting a level sensing apparatus through an aperture at a top of a reservoir such that a bottom end of an inner tube abuts an upper surface of the submerged solids in the reservoir; utilizing the submerged solids such that the upper surface of the submerged solids recedes and the level sensing apparatus moves downward with the receding upper surface of the submerged solids; constraining downward movement of an outer tube when the upper surface of the submerged solids reaches a predetermined low level; and as the upper surface of the submerged solids continues to recede, sensing relative movement of the outer tube and an inner tube as an indication that the upper surface of the submerged solids is below the predetermined low level.

A sensing system for detecting degradation of a machine fluid is disclosed. The sensing system may comprise a tag having electrical contacts. The tag may be configured to transmit a wireless signal when the electrical contacts are in electrical communication. The sensing system may further comprise a dissolvable element separating the electrical contacts and obstructing electrical communication between the electrical contacts. The dissolvable element may be configured to dissolve and allow electrical communication between the electrical contacts when an acid content of the machine fluid reaches a level indicative of the degradation of the machine fluid.