Abstract: A liquid level sensor for detecting when an upper level of a liquid in a reservoir has reached a predetermined or critical point in the reservoir. The sensor includes a first input plate and a second input plate disposed concentrically relative to the first input plate. Each of the input plates are further of a shape such that an imaginary line extending through the centroid of the first input plate divides each of the first and second input plates approximately in half. An output or receiver plate is positioned closely adjacent the two input plates. The input plates are further disposed in the reservoir such that the centroid is at the predetermined or critical level in the reservoir. The two input plates are alternately electrically excited and the signals coupled to the output plate are detected and repeatedly compared against one another. The output signals will differ in magnitude because of the difference in the dielectric constant of air and the liquid in the reservoir.

Abstract: A method of calibrating a gamma counter that makes two separate measurements over the peak of the standard source of I.sup.129 and a computational technique to obtain the center of that peak. A microcomputer controlling the instrument's operation changes the high voltage on the instrument's photomultiplier (PM) tube to find the setting which generally brings the I.sup.129 peak into the range of the preset pulse height analyzer (PHA) window. Each measurement in the first pass takes a relatively short period of time and looks for the arbitrarily defined end points of the peak. The microcomputer temporarily defines the midpoint of this range as the location of the I.sup.129 peak. In the second pass, the instrument takes longer measurements, for greater accuracy, at six points on either side of the temporary peak.