Abstract: A system to determine fluid level in a tank using several tubes extending to different levels in the tank. Gas pressure in the tubes needed to release bubbles from the exit ends of the tubes indicates the hydrostatic head at the exit ends. A control unit compares the pressures in the tubes to find the highest fluid immersed bubbler tube. The proportion of fluid above the immersed tube is calculated from the pressure and added to the height of the immersed tube to get the total fluid depth. A spring loaded fixed length member, magnetically attached to the bottom of the tank, reliably secures the exit ends of the tubes at known fixed vertical locations.

Abstract: A potentiometer position switch circuit which includes a meter mechanism having a low friction potentiometer coupled to move therewith. The output of the low friction potentiometer is coupled together with the output of a set point potentiometer across the input terminals of a comparator. A magnetic latching double pole, double throw relay having set and reset relay coils is connected to the output of the comparator through the gate of a first voltage operated transistor and through sufficient resistance to minimize current drain and also through an invertor to the gate of a second voltage operated transistor and through a second resistor of sufficient resistance to minimize current drain. The output of the first voltage operated transistor is connected from a second voltage source through the set relay coil to ground and the output of the second voltage operated transistor is connected from a voltage source through said reset relay coil to ground.

Abstract: A leak detection system for detecting the leakage of fluids from storage tanks uses a reference container, such as a standpipe, having its bottom adjacent the level of the bottom of the tank, which is initialized to the same hydrostatic head pressure as the tank, and then closed off. The differential pressure between the hydrostatic head pressures of the standpipe and the tank is monitored over time in an externally mounted differential pressure gauge in order to detect the leakage of fluid from the storage tank. Shut off of valves are provided in a tank pressure pipe and a reference pressure pipe to isolate both sides of the differential pressure gauge. The very high sensitivity of available differential pressure gauges allows the detection of very small leaks and very low leakage rates. A leak detection system of unitary construction may be provided in which the standpipe is provided with an equalizing valve so that the system may be installed through a single hole in the top of a liquid storage tank.

Abstract: A densitometer for use by itself or in a net oil computer. The densitometer includes two differential pressure units to detect the difference in pressure between two corresponding pairs of points and the differences substracted to provide a corrected density output signal. This output signal is then essentially independent of viscosity and/or other variables.

Abstract: A net oil computer including a differential pressure unit and a turbine or positive displacement flowmeter. The flowmeter produces output pulses at a frequency directly proportional to the rate of volume flow through a pipeline. The output of the flowmeter is impressed upon the pole of a single-pole, double-throw electronic switch. One switch contact is connected to an indicator through a divider, a driver amplifier and a counter. The other contact is also connected to an indicator through a divider, a driver amplifier and a counter. The switch is operated by a gate generator connected from the differential pressure unit.