AIR BUBBLE DETECTOR

• US 20100212407A1
• Filed: 02/05/2010
• Published: 08/26/2010
• Est. Priority Date: 02/06/2009
• Status: Active Grant

• Current Assignee: Zevex (Moog Incorporated)
• Original Assignee: Zevex (Moog Incorporated)
• Inventors: MILLIS, ROGER, BLAINE, DAVID, STRINGHAM, MARK, FOLEY, JOHN
• Granted Patent: US 8,539,812 B2
• Time in Patent Office: Days
• US Class Current: 73/61.750
• CPC Class Codes: G01N 2291/02433 Gases in liquids, e.g. bubbles, foams
• CPC Class Codes: G01N 2291/048 Transmission, i.e. analysed material between transmitter and receiver
• CPC Class Codes: G01N 2291/102 one emitter, one receiver
• CPC Class Codes: G01N 29/032 by measuring attenuation of acoustic waves
• CPC Class Codes: G01N 29/036 by measuring frequency or resonance of acoustic waves
• CPC Class Codes: G01N 29/348 with frequency characteristics, e.g. single frequency signals, chirp signals measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00

Abstract

Air bubbles may be characterized by an air bubble detector by choosing an optimum set of frequencies and then comparing a return signal from a sensor receiving those frequencies against an internal reference. The number of pulses that exceed the internal reference represents a width and may be counted. The width, as counted, may be correlated to bubble characteristics including volume.

Claims

1. A bubble detection system comprising:

a fluid path;

a piezoelectric transmitter and a piezoelectric receiver disposed adjacent the fluid path for detecting bubbles therein;

control circuitry for operating the transmitter and receiver comprising;

a circuit for generating a wide range frequency sweep in the transmitter;

a circuit for analyzing the receiver output and determining a resonant frequency for the piezoelectric transmitter and receiver and fluid path;

memory for storing the resonant frequency; and

a circuit for operating the transmitter at a reduced frequency range at the resonant frequency in order to thereby detect bubbles in the fluid path.

2. The system of claim 1, further comprising:

a comparator circuit for comparing the receiver signal while detecting bubbles to a signal threshold to determine if bubbles are present.

3. The system of claim 2, wherein the comparator circuit determines the time period for which a signal exceeds the signal threshold and determines bubble size based on the time period.

4. The system of claim 1, wherein the circuit for generating a wide range frequency sweep in the transmitter comprises a voltage ramp generating circuit and a voltage driven frequency generation circuit.

5. The system of claim 1, wherein the fluid path comprises a tube for delivering a liquid.

6. The system of claim 1, wherein the circuit for analyzing the receiver out and determining a resonant frequency for the piezoelectric transmitter and receiver and fluid path comprises a comparator circuit.

7. A bubble detection system comprising:

a fluid path;

a piezoelectric sensor coupled with the fluid path and configured for detection of bubbles in the fluid path;

an internal receiver signal reference; and

a comparator circuit configured to detect bubbles and determine bubble size within the fluid path by determining the length of time an output signal of the sensor exceeds the internal reference.

8. The system of claim 7, further comprising:

an input signal source configured for sweeping a broad range ultrasonic signal through the sensor;

a circuit for analyzing the received signal from the broad range ultrasonic signal to thereby determine a sympathetic frequency for operation of the sensor;

a circuit for storing the sympathetic frequency;

a circuit for operating the sensor at a narrow range ultrasonic frequency surrounding the sympathetic frequency;

9. The system of claim 7 wherein the output signal is comprised of pulses and the comparator circuit is configured to determine bubble size by counting the number of pulses of the output signal of the sensor that exceed the internal reference.

10. A method of detecting bubbles comprising:

sending an ultrasonic signal through a fluid path by an ultrasonic transmitter;

reporting a detected signal by an ultrasonic receiver;

selecting an internal receiver signal reference;

determining the amount of time the detected signal exceeds the internal reference; and

calculating bubble size based on the amount of time the detected signal exceeds the internal reference.

11. A method of detecting bubbles in a fluid path comprising:

transmitting a broad frequency range of ultrasonic signals through a fluid path;

receiving the broad range ultrasonic signals after transmission through the fluid path;

determining a sympathetic frequency for the fluid path based on the strength of the received broad range signals;

storing the sympathetic frequency;

transmitting a narrow frequency range of ultrasonic signals surrounding the sympathetic frequency through the fluid path to detect bubbles; and

receiving the narrow range ultrasonic signals to detect bubbles.

12. The method of claim 11, further comprising:

for a period of time, repeatedly transmitting the narrow range ultrasonic signals through the fluid path to detect bubbles; and

transmitting a broad frequency range of ultrasonic signals through a fluid path;

receiving the broad range ultrasonic signals after transmission through the fluid path;

determining a new sympathetic frequency for the fluid path based on the strength of the received broad range signals;

storing the new sympathetic frequency.

13. The method of claim 11, wherein the method comprises;

storing an internal threshold received signal level;

comparing the received narrow range ultrasonic signals to the threshold to determine when the received signals exceed the threshold to thereby determine the presence of a bubble.

14. The method of claim 13, wherein the method comprises:

determining the time duration when the received signals exceed the threshold and calculating the bubble size based on the time duration.

15. The method of claim 14, wherein the received signals are separate signal pulses, and wherein the method comprises counting the number of times the signal pulses exceed the threshold to thereby determine the bubble size.

16. The method of claim 11, wherein the method comprises:

for a period of time, repeatedly transmitting the narrow frequency range of ultrasonic signals surrounding the sympathetic frequency through the fluid path;

receiving the narrow range ultrasonic signals to detect bubbles;

after a predetermined event, transmitting a broad frequency range of ultrasonic signals through a fluid path;

receiving the broad range ultrasonic signals after transmission through the fluid path;

determining a new sympathetic frequency for the fluid path based on the strength of the received broad range signals; and

storing the new sympathetic frequency.

17. The method of claim 16, wherein the predetermined event is a change in physical conditions in the fluid path.

18. The method of claim 16, wherein the predetermined event is the passage of a set time period.