Liquid level gauging apparatus

Abstract

A liquid level gauge for monitoring the height of liquid in a storage tank or the like. The gauge comprises an upright conducting probe adapted to be immersed in the liquid in the tank, and an upright series of electrodes closely adjacent the probe. The latter is adapted to be excited from a source of a.c. voltage generated by an astable multivibrator. Each of the electrodes is connected to the input of an amplifier through a rectifier circuit. The amplifiers are of the digital comparator type and have output terminals respectively connected by means of summing resistors to an electrical indicator such as a milliammeter, which provides an indication of the number of amplifiers being driven to full output at any particular time. The arrangement is such that each of the electrodes constitutes one plate of a capacitor, the other plate being formed by the single upright conducting probe. When a particular electrode is above the level of fluid in the tank, the magnitude of the a.c. signal received at the electrode is of a sufficiently small magnitude to provide only a low level drive voltage to its respective comparator amplifier, the latter thus assuming a low output signal level. Once a particular plate becomes submerged, the increased dielectric constant (fluid) effects an increase in the value of the capacitor, and a correspondingly larger drive signal to the amplifier results, causing the output thereof to assume a high level and yielding a contribution to the meter reading through the respective summing resistor. The meter reading thus responds to the number of electrodes submerged at any particular time, and provides an indication of the liquid level in the tank.

Dependencies are inferred from the claim text.