Dual liquid level monitor
 A liquid level monitoring system functions by applying an alternating voltage to a probe. When the liquid level in a reservoir touches the probe, a low impedance to ground is present, thereby permitting current to flow to ground. When the liquid level falls below the probe, a high impedance to ground is created and current flows to a detector. The detector switches on an alarm which flashes an appropriate warning. 
Eaton Corporation
G
G01F
inventional
Martin W. Donald J.
Hamilton Betts