GB1086954A - Improvements in or relating to contents gauges - Google Patents

Abstract

1,086,954. Measuring liquid level. HUNTING ENGINEERING Ltd. Dec. 7, 1965 [Sept. 25, 1964], No.39158/64. Heading G1N. The level of fluent material in a container 1, Fig.1, is determined by means of two capacitive elements 3, 4 extending over different ranges of height in the container, the elements being connected between respective sources of alternating voltage and the input terminals of respective amplifiers, and the outputs from the amplifiers being compared to give an indication of the depth of material. In Fig.2, cross-coupling capacitors C1, C2, equal in capacitance to elements 4 and 3, respectively, when the container is empty, give rise to equal inputs to amplifiers G1, G2 when the level of material is below that at which element 3 is completely covered. Above this level, the difference between the output voltages from the amplifiers is a function of the level. Preferably the gain of G2 is adjusted until the outputs are equal, and the adjustment may be made automatically by a servomotor. The motor may drive a potentiometer slider connected to a meter. Alternatively R1 and R2 may be made variable and adjusted to give zero output voltage, <SP>v</SP>out. The range may be increased by adjusting the gain of both G1 and G2. In a modification Fig. 3 (not shown), the capacitive elements are energized in inverse proportion to their maximum capacitances and the cross-coupling capacitors are energized by corresponding voltages in phase opposition thereto. Resistors are provided in parallel with the capacitors to compensate for the leakage resistance of the probes. The amplifiers in this case have equal gain and the difference between their outputs is indicated directly by a meter. The probes may each consist of a strip of aluminium foil positioned on a wall of glass fibre container 1, each strip being cut in halt-longitudinally to form the two electrodes of a probe. The strips are insulated by a layer of epoxy resin. One probe may be ten times as long as the other, and may extend only to the top of the shorter probe. To obtain an average level of an uneven surface of a fluent solid material probes may be provided on two or more walls and connected in parallel. The shorter probe may extend horizontally instead of vertically, the longer probe then being L-shaped.