Density and Temperature Gaging of Supercritical Hydrogen and Oxygen for the Apollo Fuel Cells

The densities of supercritical hydrogen and oxygen are gaged by capacitance sensors -- concentric aluminum tubes which are mounted across the diameter of the spherical tanks. The capacitance of the sensor is a function of fluid density as shown in the Clausius-Mossotti (C-M) relationship. An all-electronic signal conditioner converts the capacitance into a d-c signal output, linearly proportional to the fluid mass. Corrections for the nonlinearity of the C-M equation and for the effects of temperature on the sensors are made by means of diode networks. A platinum resistance temperature sensor is mounted on each sensor and is used with another signal conditioner to provide a d-c signal as a function of fluid temperature.