Liquid level sensor utilizing AC and resistance

Abstract

A liquid level detecting system for detecting a conducting liquid level in a non conductive container which utilizes a grounding rod mounted in a lower portion of the container and a conductive sensing rod mounted at a position above the grounding rod. An oscillator is provided having a frequency in the range of about 600 hertz to about 100 kilohertz. The output of the oscillator is applied to the sensing rod through a high impedance circuit and a high pass filter. In another embodiment, the high pass filter may have the higher end frequencies attenuated to produce a band pass filter which selectively passes the frequency of the oscillator. The voltage drop across the circuit which includes the conductive sensing rod to ground is detected by a voltage peak detector and a threshold detector to produce an output which detects the drops in voltage when the conductive fluid level in the tank rises so that both the sensing rod and the grounding rod are covered, completing the circuit. In another embodiment, multiple sensing rods may be positioned at various heights in the tank to detect various fluid levels. The use of the high pass or band pass filters in series with the sensing rod and ground will eliminate any DC current in the rods thereby reducing electrolysis. The filters also eliminate or significantly reduce interference or artifacts due to DC and 60 hertz.

Dependencies are inferred from the claim text.