Flow measurement and control with bubble detection

Abstract

Systems and methods for liquid flow sensing and control for use with a variety of different types of liquid flow measurement and control systems. The liquid flow sensor system senses a flow signal indicative of the flow rate of the liquid flowing in a sensor conduit and analyzes the flow signal to determine, by detecting characteristic changes in the signal, whether a bubble is present in the sensor conduit. Where the system determines that a bubble is present, it may generate an alarm signal indicative of the presence of the bubble. A flow control system incorporating the flow sensor as a feedback source may respond to the detection of a bubble by temporarily freezing the flow control parameters until the bubble has exited the sensor conduit. The flow control system can implement procedures for clearing a bubble from the sensor conduit where the system detects that the bubble has become stuck.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 60 / 707,628, filed Aug. 12, 2005, entitled “Bubble Algorithm Design,” which is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION [0002] 1. Field of Invention [0003] The present invention relates to systems and methods for measuring and controlling liquid flow, and more specifically to systems and methods for measuring and controlling liquid flow in environments where bubbles may be present in the liquid flow. [0004] 2. Discussion of Related Art [0005] Several techniques exist for measuring a flow rate of a liquid flowing in a conduit, pipe, or tube. These include thermal flow meters, coriolis force flow meters, differential pressure flow meters, and ultrasonic flow meters. Generally, liquid flow meters sense one or more parameters of the flow that can be calibrated to correspond to the rate (e.g., volumetric or ...

AI Technical Summary

Benefits of technology

[0008] Applicants have developed systems and methods for achieving stable operation of liquid flow controls even when a bubble passes through the sensor system. The systems and methods developed by applicants can minimize the effect of the bubble on liquid flow measurements or on controlled liquid flow rates.

[0012] In accordance with another embodiment wherein the liquid flow sensor comprises an ultrasonic liquid flow sensor, and wherein the flow signal comprises an ultrasonic time-of-flight difference flow signal, the at least one parameter of the flow signal includes a magnitude of the ultrasonic time-of-flight difference flow signal. In accordance with a further embodiment, the act of determining includes an act of determining whether the magnitude of the ultrasonic time-of-flight difference flow signal deviates from the magnitude of a prior ultrasonic time-of-flight difference flow signal by more than a threshold value. In accordance with a still further embodiment of the present invention, the magnitude of the ultrasonic time-of-flight difference flow signal may be used in combination with detection of a bubble based upon the ultrasonic flow signal amplitude to provide early detection of the presence of a bubble in the sensor conduit.

Problems solved by technology

When a bubble enters a sensor conduit of any type of flow meter, the signal upon which the flow meter bases its flow measurement may be disturbed.

This can result in spurious measurements.

This can lead to instability in the controlled flow, which interferes with the purpose of the controller to provide a stable flow at a rate corresponding to a (typically user-set) setpoint.

Although the presence of bubbles can affect any type of flow meter or controller (and to varying degrees), it is especially problematic for ultrasonic-type flow meters, particularly where such ultrasonic flow meters are used to measure or control relatively low flow rates (e.g., between 5 to 50 ml / min, or less).

Applicants have recognized that conventional ultrasonic flow meters and flow controllers lack the ability to detect and respond to the presence of a bubble in a sensor conduit and to remain in a stable state despite the presence of the bubble in the sensor conduit, especially where they are used to measure and / or control such relatively low flow rates.

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