System and method for sensing liquid levels

• US 8,180,582 B2
• Filed: 04/13/2009
• Issued: 05/15/2012
• Est. Priority Date: 06/12/2008
• Status: Active Grant

• Current Assignee: Illinois Tool Works Inc.
• Original Assignee: Illinois Tool Works Inc.
• Inventors: Knowles, Terence J.
• Primary Examiner(s): Teixeira Moffat, Jonathan C
• Assistant Examiner(s): Hwang, Timothy H
• Application Number:
  US12/422,379
• Publication Number:
  US 20090312965A1
• Time in Patent Office: 1,128 Days
• Field of Search: 702/55, 702/159
• US Class Current: 702/55
• CPC Class Codes: G01F 23/2962 Measuring transit time of reflected waves

Abstract

A system for detecting a presence of a liquid within a receptacle includes a sensor and a processor. The sensor includes a transmitting probe and a receiving probe positioned within the liquid receptacle. The transmitting probe includes a first transducer and the receiving probe includes a second transducer. The processor is in electrical communication with the first and second transducers and monitors the first and second transducers to determine the presence and level of the liquid within the liquid receptacle based on a time between generation of a first extensional wave by the first transducer and reception of a second extensional wave by the second transducer.

Claims

1. A system for detecting a presence of a liquid within a liquid receptacle, the system comprising:

a sensor comprising a transmitting probe and a receiving probe positioned within the liquid receptacle, said transmitting probe comprising a first transducer and said receiving probe comprising a second transducer, said first transducer generating a first extensional wave through said transmitting probe that produces a compressional wave in a liquid contained within the liquid receptacle when the first extensional wave contacts an interface between said transmitting probe and a surface of the liquid, the compressional wave contacting said receiving probe and generating a second extensional wave within said receiving probe that is received by said second transducer; and

a processor in electrical communication with said first and second transducers, said processor monitoring said first and second transducers to determine the presence and level of the liquid within the liquid receptacle based on a time between generation of the first extensional wave by said first transducer and reception of the second extensional wave by said second transducer, wherein said processor detects a transmit time for the first extensional wave to travel down a length of said transmitting probe, reflect, and return, wherein said processor detects an elapsed time from initiation of a transmit pulse in said first transducer to detection of a leading edge of the second extensional wave in said receiving probe, wherein said processor determines a difference between the elapsed time and the transmit time as time in the liquid, and wherein said processor determines the level of the liquid by multiplying a difference between the elapsed time and the time in the liquid plus a dry time in the dry portions of one or both of said transmitting and receiving probes by a length of one or both of said transmitting and receiving probes and dividing by the transmit time.

2. The system of claim 1, wherein one or both of said transmitting and/or receiving probes comprises a solid rod.

3. The system of claim 1, wherein one or both of said transmitting and/or receiving probes comprises a planar strip.

4. The system of claim 1, wherein one of said transmitting or receiving probes comprises a hollow open-ended cylinder within the liquid receptacle and the other of said transmitting or receiving probes comprises a solid rod within said hollow open-ended cylinder.

5. The system of claim 1, wherein each of said first and second transducers comprises a piezoelectric or electromagnetic acoustic transducer (EMAT) transducer.

6. The system of claim 1, wherein said transmitting and receiving probes are coupled together through a buoyant sliding carriage, wherein said buoyant sliding carriage includes passages through which said transmitting and receiving probes are slidably positioned, wherein a position of said buoyant sliding carriage with respect to said transmitting and receiving probes depends on the level of the liquid within said liquid receptacle, and wherein the level of the liquid determined by said processor depends on a position of said buoyant sliding carriage along said transmitting and receiving probes.

7. The system of claim 1, wherein said processor detects another time from initiating the transmit pulse by said first transducer to detecting a second leading edge of a third extensional wave in said receiving probe.

8. The system of claim 1, wherein said processor monitors said first and second transducers to determine one or both of conductivity and/or viscosity of the liquid within the liquid receptacle.

9. A method of detecting a presence of a liquid within a liquid receptacle, the method comprising:

positioning a sensor having a transmitting probe and a receiving probe within the liquid receptacle;

generating a first extensional wave through a first transducer mounted on the transmitting probe;

producing a compressional wave in a liquid contained within the liquid receptacle when the first extensional wave impinges upon a liquid surface;

receiving the compressional wave at the receiving probe;

producing a second extensional wave within the receiving probe when the compressional wave contacts the receiving probe; and

using a processor to monitor the first and second transducers to determine the presence and level of the liquid within the liquid receptacle based on a time between generation of the first extensional wave and reception of the second extensional wave at the transducer,

wherein said using comprises;

detecting a transmit time for the first extensional wave to travel down a length of the transmitting probe, reflect, and return;

detecting an elapsed time from initiation of a transmit pulse in the first transducer to detection of a leading edge of the second extensional wave in the receiving probe;

determining a difference between the elapsed time and the transmit time as time in the liquid; and

determining the level of the liquid by multiplying a difference between the elapsed time and the time in the liquid plus a dry time in the dry portions of one or both of the transmitting and receiving probes by a length of one or both of the transmitting and receiving probes and dividing by the transmit time.

10. The method of claim 9, comprising coupling the transmitting and receiving probes together with a buoyant sliding carriage, wherein the buoyant sliding carriage includes passages through which the transmitting and receiving probes are slidably positioned, wherein a position of the buoyant sliding carriage with respect to the transmitting and receiving probes depends on the level of the liquid within the liquid receptacle, and wherein the level of the liquid determined by the processor depends on a position of the buoyant sliding carriage along the transmitting and receiving probes.

11. The method of claim 9, comprising using the processor to monitor the first and second transducers to determine one or both of conductivity and/or viscosity of the liquid within the liquid receptacle.

12. A sensor for detecting a presence of a liquid within a liquid receptacle, the sensor comprising:

a transmitting probe comprising a first transducer, said transmitting probe configured to be positioned within the liquid receptacle;

a receiving probe comprising a second transducer, said receiving probe configured to be positioned within the liquid receptacle, said transmitting and receiving probes being spaced a known distance apart,

said first transducer operable to generate a first extensional wave through said transmitting probe, said first extensional wave contacting a surface of a liquid and producing a compressional wave in the liquid,

said receiving probe generating a second extensional wave within said receiving probe when the compressional wave contacts said receiving probe, the second extensional wave being received by said second transducer; and

a processor configured to detect a transmit time for the first extensional wave to travel down a length of said transmitting probe, reflect, and return, wherein said processor detects an elapsed time from initiation of a transmit pulse in said first transducer to detection of a leading edge of the second extensional wave in said receiving probe, wherein said processor determines a difference between the elapsed time and the transmit time as time in the liquid, and wherein said processor determines a level of the liquid within the liquid receptacle by multiplying a difference between the elapsed time and the time in the liquid plus a dry time in the dry portions of one or both of said transmitting and receiving probes by a length of one or both of said transmitting and receiving probes and dividing by the transmit time.

13. The sensor of claim 12, wherein one or both of said transmitting and/or receiving probes comprises a solid rod and/or a planar strip.

14. The sensor of claim 12, wherein one of said transmitting or receiving probes comprises a hollow open-ended cylinder within the liquid receptacle and the other of said transmitting or receiving probes comprises a solid rod within said hollow open-ended cylinder.

15. The sensor of claim 12, wherein each of said first and second transducers comprises a piezoelectric or electromagnetic acoustic transducer (EMAT) transducer.

16. The sensor of claim 12, wherein said transmitting and receiving probes are coupled together through a buoyant sliding carriage, wherein said buoyant sliding carriage includes passages through which said transmitting and receiving probes are slidably positioned, wherein a position of said buoyant sliding carriage with respect to said transmitting and receiving probes depends on the level of the liquid within said liquid receptacle, and wherein the level of the liquid determined by said processor depends on a position of said buoyant sliding carriage along said transmitting and receiving probes.