Drop detection method and apparatus

• US 5,415,641 A
• Filed: 11/02/1992
• Issued: 05/16/1995
• Est. Priority Date: 04/01/1991
• Status: Expired due to Term

• Current Assignee: Covidien AG (Medtronic Plc)
• Original Assignee: Sherwood Medical Company (Medtronic Plc)
• Inventors: Yerlikaya, Denis Y., Krohn, Randall J.
• Primary Examiner(s): Yasko, John D.
• Assistant Examiner(s): Mendez, Manuel A.
• Application Number:
  US07/970,323
• Time in Patent Office: 925 Days
• Field of Search: 604/250, 604/253, 604/65-67, 604/246, 604/251, 604/255, 604/30-31, 128/DIG. 12-DIG. 13
• US Class Current: 604/251
• CPC Class Codes: A61M 5/1689 Drip counters
• CPC Class Codes: G01V 8/14 using reflectors
• CPC Class Codes: G02B 5/10 with curved faces

Abstract

A drop detector circuit and method are provided for a drop detector of the type including a drop chamber and a light emitter and corresponding detector located on opposite sides of the drop chamber. The detector is saturated by light emitted from the light emitter to produce a saturated detector output signal. The detector circuit senses variations in the detector output signal caused by drops passing through the drop chamber between the emitter and detector that block light emitted by the emitter from reaching the detector. The detector circuit senses the slope of the variations in the detector output signal and produces a control signal when the slope exceeds a threshold value.

Claims

1. A drop flow detector comprising:

a drop chamber;

a light source for passing light through said chamber;

a light detector responsive to said light after it has passed through said chamber for producing an electrical detector output signal related thereto; and

,

circuit means, responsive to said detector output signal, for determining the existence of drop flow, including;

means for detecting the slope of voltage changes in said detector output signal;

means for determining that the slope detected by said means for detecting exceeds a threshold value; and

,

means, responsive to a determination by said means for determining that the slope detected by said means for detecting exceeds said threshold value, for generating a control signal.

2. The drop detector of claim 1 wherein said light detector is saturated with light emitted from said light source, thereby producing said detector output signal at a saturation level;

and,

wherein said circuit means detects the variation in said detector output signal from the saturation level when a drop passes through said drop chamber.

3. The drop detector of claim 1 wherein said circuit means for determining the existence of drop flow further includes filtering means for removing frequency components of said detector output signal above the expected frequency of drop formation, said filtering means located between said light detector and said means for detecting.

4. The drop detector of claim 3 wherein said filtering means has a variable cut-off frequency.

5. The drop detector of claim 4 wherein said detector is part of a system, said system including a motorized pump and a microprocessor for controlling the speed of said pump, said microprocessor also deriving a second control signal related to said speed, said second control signal being applied to said filtering means to vary the cut-off frequency.

6. The drop detector of claim 1 wherein said control signal has a first value when the slope of the detector output signal exceeds the threshold value and has a second value when the slope of the detector output signal does not exceed the threshold value.

7. The drop detector of claim 1 wherein said means for detecting comprises a differentiator amplifier having two inputs and an output, one of said inputs receiving said detector output signal.

8. The drop detector of claim 7 wherein said means for determining comprises means for biasing, at a constant voltage, said input of said differentiator amplifier not receiving said detector output signal, said constant voltage chosen to set the threshold value of the slope of said detector output signal to be detected.

9. The drop detector of claim 8 wherein said means for generating a control signal is said output of said differentiator amplifier.

10. The drop detector of claim 1 further comprising means for preventing ambient light from impinging on said light detector.

11. The drop detector of claim 10 wherein said means for preventing comprises an ambient light shield surrounding said drop chamber except where said light source and said light detector are directed toward said drop chamber, said shield made of material opaque to the light detected by said light detector.

12. In a drop flow detector having a drop chamber, a light source for passing light through the chamber, a light detector responsive to the light after it has passed through the chamber for producing an electrical detector output signal related thereto, the detector output signal having varying voltage levels in response to drops passing through the drop chamber between the light source and the light detector whereby the drop blocks part of the light emitted from the light source and prevents the blocked light from impinging on the light detector, circuit means responsive to the detector output signal for determining the existence of drop flow comprising:

means for detecting the slope of voltage changes in the detector output signal;

means for determining that the slope detected by said means for detecting exceeds a threshold value; and

,

means, responsive to a determination by said means for determining that the slope detected by said means for detecting exceeds said threshold value, for generating a control signal.

13. The drop detector of claim 12 wherein said circuit means for determining the existence of drop flow further includes filtering means for removing frequency components of said detector output signal above the expected frequency of drop formation, said filtering means located between said light detector and said means for detecting.

14. The drop detector of claim 13 wherein said filtering means has a variable cut-off frequency.

15. The drop detector of claim 14 wherein said detector is part of a system, said system including a motorized pump and a microprocessor for controlling the speed of said pump, said microprocessor also deriving a second control signal related to said speed, said second control signal being applied to said filtering means to vary the cut-off frequency.

16. The drop detector of claim 12 wherein said means for detecting comprises a differentiator amplifier having two inputs and an output, one of said inputs receiving said detector output signal.

17. The drop detector of claim 16 wherein said means for determining comprises means for biasing, at a constant voltage, said input of said differentiator amplifier not receiving said detector output signal, said constant voltage chosen to set the threshold value of the slope of said detector output signal to be detected.

18. The drop detector of claim 17 wherein said means for generating a control signal is said output of said differentiator amplifier.

19. A drop flow detector comprising:

a drop chamber for passing a drop therethrough;

a light source for passing light through said chamber;

a light detector producing an electrical detector output signal responsive to said light after said light has passed through said chamber, wherein, when no drop is passing through said drop chamber between said emitter and said detector, said light emitted from said emitter saturates said detector and said resulting detector output signal is at a constant first level and, wherein, when a drop passes through said drop chamber between said emitter and said detector, a portion of the light emitted from said emitter is blocked by the drop and is prevented from impinging on said detector thereby causing said light detector to produce an electrical detector output signal at a second level which second level differs from said first level; and

,

circuit means, responsive to said detector output signal, for determining the existence of drop flow, said circuit means including means for detecting the variation in said detector output signal from said first level to said second level.

20. The drop detector of claim 19 wherein said circuit means includes:

means for detecting the slope of voltage changes in said detector output signal;

means for determining that the slope detected by said means for detecting exceeds a threshold value; and

,

means, responsive to a determination by said means for determining that the slope detected by said means for detecting exceeds said threshold value, for generating a control signal.

21. A drop flow detector comprising:

a drop chamber;

a light source for passing light through said chamber;

a light detector responsive to said light after it has passed through said chamber for producing an electrical detector output signal related thereto, wherein said light detector is saturated with light emitted from said light source, thereby producing said detector output signal at a saturation level;

circuit means, responsive to said detector output signal, for determining the existence of drop flow, including;

means for detecting the slope of voltage changes in said detector output signal;

means for determining that the slope detected by said means for detecting exceeds a threshold value; and

,

means, responsive to a determination by said means for determining that the slope detected by said means for detecting exceeds said threshold value, for generating a control signal,

wherein said circuit means detects the variation in said detector output signal from the saturation level when a drop passes through said drop chamber.

22. A drop flow detector comprising:

a drop chamber;

a light source for passing light through said chamber;

a light detector responsive to said light after it has passed through said chamber for producing an electrical detector output signal related thereto, wherein said light detector is saturated with light emitted from said light source thereby producing said detector output signal at a saturation level;

circuit means, responsive to said detector output signal, for determining the existence of drop flow, including;

means for detecting the slope of voltage changes in said detector output signal, said means for detecting comprising a differentiator amplifier having two inputs and an output, one of said inputs receiving said detector output signal;

means for determining that the slope detected by said means for detecting exceeds a threshold value, said means for determining comprising means for biasing, at a constant voltage, said input of said differentiator amplifier not receiving said detector output signal, said constant voltage chosen to set said threshold value of the slope of said detector output signal to be detected;

means, responsive to a determination by said means for determining that the slope detected by said means for detecting exceeds said threshold value, for generating a control signal, said means for generating a control signal being said output of said differentiator amplifier, said control signal having a first value when the slope of the detector output signal exceeds said threshold value and having a second value when the slope of the detector output signal does not exceed said threshold value;

wherein said circuit means detects the variation in said detector output signal from the saturation level when a drop passes through said drop chamber; and

,

filtering means for removing frequency components of said detector output signal above the expected frequency of drop formation, said filtering means located between said light detector and said means for detecting, said filtering means having a variable cut-off frequency;

wherein said detector is part of a system, said system including a motorized pump and a microprocessor for controlling the speed of said pump, said microprocessor also deriving a second control signal related to said speed, said second control signal being applied to said filtering means to vary the cut-off frequency.

23. A method for detecting drops passing through a drop chamber having a light source passing light through the chamber and a light detector responsive to the light after it has passed through the chamber, the light detector producing an electrical detector output signal related to the amount of light impinging on the light detector, the method comprising the steps of:

illuminating the light detector with light emitted from the light source with a sufficient intensity to saturate the light detector, thereby producing a detector output signal at a saturation level;

detecting the variation in the detector output signal from the saturation level when a drop passes through the drop chamber.

24. The method of claim 23 further comprising the step of shielding the drop chamber with a shield made of material opaque to the light detected by the light detector, said shield surrounding the drop chamber except where the light source and the light detector are directed toward the drop chamber.

25. A method for detecting drops passing through a drop chamber having a light source passing light through the chamber and a light detector responsive to the light after it has passed through the chamber, the light detector producing an electrical detector output signal related thereto, the method comprising the steps of:

detecting the slope of voltage changes in the detector output signal;

determining that the slope detected exceeds a threshold value; and

,

generating, is response to a determination that the slope detected exceeds said threshold value, a control signal.