DIGITAL CAPACITANCE SYSTEM FOR MASS, VOLUME, AND LEVEL MEASUREMENTS OF LIQUID PROPELLANTS

Abstract

A method of using a digital capacitance to balance a bridge electronically has been applied to the measurement of quantities of propellants. Solid state switches connect into the bridge that combination of n capacitors which most nearly balances the bridge. The capacitors have values proportional to the binary scale. The measurement is directly in binary digital code that is easily converted to multiple scale analog output. The response of the systems to a step input is rapid (about one bit per millisecond), linear, and without overshoot. The system is conveniently adaptable to time sharing of the sensor; an important application of which occurs in propellant utilization control. The electronic circuits are adaptable to automatic checkout and are interchangeable with a minimum of adjustment. Applications of the method to propellant quantity measurements include the measurement of mass independent of temperature and temperature gradient and the measurement of level and volume independent of density. The mass measurement is particularly suited to pure dielectric fluids such as hydrogen and oxygen. The measurement of level and volume is suitable for fluids having a wide range of dielectric constants and has been generalized for application to conducting fluids. The system is flexible in application, accurate, free from moving parts, insensitive to acceleration, and suitable for use in rocket environments.