Remote, pneumatic, continuous sensor of the liquid level in a vacuum tank

Claim 1

A liquid sewage level measuring apparatus for measuring the level of liquid sewage inside a vacuum tank comprising gas filter means for drawing a flow of measurement gas, gas jet means coupled to said gas filter means for drawing a reduced flow of said measurement gas; gas reservoir means for receiving said reduced flow of measurement gas, said gas reservoir means being coupled on one end to said gas jet means; gas bubbler tube means for passing said reduced flow of measurement gas to the liquid sewage inside said vacuum tank, said gas bubbler tube means being coupled to the other end of said gas reservoir means and to a drain line means of said vacuum tank containing the liquid sewage; upper vent line means connected to said vacuum tank for venting the region above the liquid sewage inside said vacuum tank to a partial vacuum pressure which is less than the pressure of said reduced flow of measurement gas inside said gas reservoir means, wherein the pressure in said upper vent line means is the same as the partial vacuum pressure of the region above the liquid sewage inside said vacuum tank; and differential pressure transducer means coupled on one side by first hose means to said upper vent line means and coupled on the other side by second hose means to said gas reservoir means, wherein said differential pressure transducer means continuously senses and outputs signals corresponding to the level of liquid sewage inside the vacuum tank.

Claim 3

A method for continuously determining the level of liquid sewage inside a vacuum tank, said method comprising drawing a flow of measurement gas; reducing the flow of measurement gas using gas jet means; receiving said reduced flow of measurement gas in a gas reservoir means; passing said reduced flow of measurement gas from said gas reservoir means through bubbler tube means connected to lower drain line means of said vacuum tank into the liquid sewage in the form of gas bubbles which rise to the surface of said liquid sewage and pass off into the region above the liquid sewage inside said vacuum tank; venting the region above the liquid sewage inside said vacuum tank to a partial vacuum pressure using upper vent line means connected to said vacuum tank, wherein the pressure of the gas in said upper vent line means is the same as the partial vacuum pressure of the region above the liquid sewage inside said vacuum tank, and the pressure of said reduced flow of measurement gas inside said gas reservoir means is greater than the partial vacuum pressure of the region above the liquid sewage inside the tank; and measuring the difference in gas pressures using differential pressure transducer means between a) the partial vacuum pressure existing in said upper vent line means, and b) the pressure inside said gas reservoir means when bubbles of said measurement gas are passed to the liquid sewage in said vacuum tank, wherein said differential pressure transducer means provides a continuous electronic output signal which is proportional to the level of liquid sewage inside said vacuum tank.

Claim 4

A method for continuously determining the level of liquid sewage inside a vacuum tank, said method comprising drawing a flow of measurement gas; reducing the flow of measurement gas using gas jet means; receiving said reduced flow of measurement gas in a gas reservoir means; passing said reduced flow of measurement gas from said gas reservoir means through bubbler tube means connected to lower drain line means of said vacuum tank into the liquid sewage in the form of gas bubbles which rise to the surface of said liquid sewage and pass off into the region above the liquid sewage inside said vacuum tank; venting the region above the liquid sewage inside said vacuum tank to a partial vacuum pressure using upper vent line means connected to said vacuum tank, wherein the pressure of the gas in said upper vent line means is the same as the partial vacuum pressure of the region above the liquid sewage inside said vacuum tank, and the pressure of said reduced flow of measurement gas inside said gas reservoir means is greater than the partial vacuum pressure of the region above the liquid sewage inside the tank; and measuring the difference in gas pressures using differential pressure transducer means between a) the partial vacuum pressure existing in said upper vent line means, and b) the pressure inside said gas reservoir means when bubbles of said measurement gas are passed to the liquid sewage in said vacuum tank, wherein said differential pressure transducer means provides a continuous electronic output signal which is proportional to the level of liquid sewage inside said vacuum tank.