Fluid level maintenance sensor for use in a tank test system

Claim 1

A level sensor for maintaining the level of fluid in a vertical level sensing tube comprising: (a) a dual coil bobbin mounted on the level sensing tube having an upper portion and a lower portion; (b) an upper sensor coil winding having a pair of leads mounted on the upper portion of said dual coil bobbin; (c) a lower sensor coil winding having a pair of leads mounted on the lower portion of said dual coil bobbin; (d) a shield mounted around said dual coil bobbin; (e) a non-magnetic bracket mounted in the level sensing tube; (f) said non-magnetic bracket having an upper end disposed above the fluid level in the level sensing tube, and a lower end disposed below the fluid level in the level sensing tube; (g) a monofilament line mounted in tension between said non-magnetic bracket upper and lower ends; (h) a float, made from a non-absorbent material, having an axial opening therethrough for the slidable reception and mounting of the float on the monofilament line; (i) a ferromagnetic ring mounted about the circumference of the float; (j) an insulator block mounted on said shield; (k) an electrical connector member mounted on the insulator block and having an upper contact connected to one lead from the upper sensor coil winding, a lower contact connected to one lead from the lower sensor coil winding, and a center contact connected to the other lead of each of the sensor coil windings; (l) the upper, lower and center contacts are adapted to be connected to a source of electrical energy during use to energize the coil windings; (m) the ferromagnetic ring is disposed about the circumference of the float at an exact center set point position between the upper and lower sensor coil windings when the fluid in the level sensing tube is at an exact selected level, whereby if the fluid level in the level sensing tube rises above said set point position of the ferromagnetic ring, the float and the ferromagnetic ring will move upwardly above the set point position into the upper sensor coil winding and a signal will be induced in the upper sensor coil winding and sent to a fluid level transfer means to transfer fluid out of the level sensing tube to cause the float and ferromagnetic ring to move down and return to the set point position, and if the fluid level in the level sensing tube falls below said set point position of the ferromagnetic ring, the float and the ferromagnetic ring will move below the set point position into the lower sensor coil winding and a signal will be induced in the lower sensor coil winding and sent to the fluid transfer means to transfer fluid into the level sensing tube to cause the float and the ferromagnetic ring to move up and return to the set point position.