Automatic level control system and method

A system for continuously maintaining the level of dry, powdered cement between lower and upper limits, comprising:

• a surge tank wherein the level of dry, powdered cement is to be maintained between lower and upper limits, said surge tank having an inlet through which dry, powdered cement is input into said surge tank;
• a weight sensor responsive to weight of said surge tank and weight of the dry, powdered cement in said surge tank;
• a first valve, said first valve connected to said inlet of said surge tank, and said first valve having a fluid responsive valve member movable through a plurality of positions to adjust the flow of dry, powdered cement into said surge tank;
• a second valve, said second valve connected to said first valve to provide fluid control to said first valve member, and said second valve responsive to electrical control;
• a potentiometer responsive to positioning control of said first valve so that said potentiometer provides an electrical feedback signal in response to the position of said valve member of said first valve;
• a computer connected to said weight sensor;
• and
• a controller connected to said computer, said potentiometer and said second valve so that said controller operates said second valve in response to an electrical control signal from said computer dependent upon the level of dry, powdered cement in said surge tank as determined in response to the sensed weight of the dry, powdered cement in said surge tank and predetermined criteria in said computer and further in response to said electrical feedback signal from said potentiometer dependent upon the position of the valve member of said first valve, wherein said predetermined criteria in said computer include a selected density value and selected lower and upper level limits and further wherein said computer, said potentiometer and said controller provide continuous control of said first valve when the level of dry, powdered cement in said surge tank is between the predetermined lower and upper limits.

A method of continuously replenishing dry material in a surge tank, comprising:

• sensing weight of dry material in a surge tank;
• comparing the sensed weight to predetermined criteria and generating a control signal in response thereto;
• sensing the state of a valve through which dry material is input to the surge tank;
• controlling the state of the valve in response to the control signal and the sensed state of the valve;
• and
• wherein generating a control signal includes generating the control signal to fully open the valve when the sensed weight is less than a low limit criterion predetermined in response to a selected density value, and generating the control signal to fully close the valve when the sensed weight is greater than a high limit criterion predetermined in response to the selected density value, and generating the control signal to operate the valve to a proportionately open position between fully open and fully closed in response to the proportion the sensed weight is below the high limit criterion relative to the range between the low limit criterion and the high limit criterion.