Patent ID: 7270141

Claim:
A control system for controlling a viscosity of a fluid in real time, comprising: a controller for controlling an actuator, the actuator being capable of controlling the viscosity of the fluid by delivering a gelling agent to the fluid; an observer for estimating the viscosity of the fluid at current time, the observer and the controller are being coupled together; a first control element having an input which represents an error measured between a desired viscosity and the viscosity estimated by the observer; an adaptive controller modifying an output of the first control element and generating a signal controlling an input of the actuator; a second control element having an input and an output; a system model having an input and an output, the input to the system model being a combination of the output of the first control element and the output from the second control element, the output from the system model being an estimation of the viscosity of the fluid; and a sensor model having an input and an output, the input to the sensor model being the output from the system model, the output from the sensor model being combined with a measured viscosity to form a viscosity error, the viscosity error being an input to the second control element.