Apparatus and method for verifying the volume of liquid dispensed by a liquid-dispensing mechanism

• US 20060272387A1
• Filed: 08/11/2006
• Published: 12/07/2006
• Est. Priority Date: 04/08/2003
• Status: Active Grant

• Current Assignee: Abbott Laboratories Incorporated
• Original Assignee: Abbott Laboratories Incorporated
• Inventors: Matuszewski, Paul A., Dempski, James L., Klosterman, Kurt M., Rajagopal, Ganesh, Abunimeh, Noman A., Tipotsch, David M., Jibson, Larry R., Stewart, Jeffrey W., Swanson, Jeffrey R., Youngs, Randall E.
• Granted Patent: US 8,434,345 B2
• Time in Patent Office: Days
• US Class Current: 73/1.740
• CPC Class Codes: B01L 2200/148 Specific details about calibrations
• CPC Class Codes: B01L 3/0293 for liquids
• CPC Class Codes: G01F 25/0092 for metering by volume
• CPC Class Codes: G01G 17/04 for weighing fluids, e.g. gases, pastes
• CPC Class Codes: G01N 2035/00217 involving measurement of weight
• CPC Class Codes: G01N 35/1016 Control of the volume dispensed or introduced

Abstract

An apparatus for improving the procedure for quantifying the volume of liquid dispensed by a liquid-dispensing mechanism of an analytical instrument. The apparatus of this invention comprises (a) at least one weigh cup; (b) at least one standard mass; (c) at least one transducer assembly to convert a value of weight to an electrical response; and (d) at least one electronic circuit for converting the electrical response to a measurement of volume. This invention provides a method for calibrating readings of the volume of liquid dispensed by a liquid-dispensing mechanism of an analytical instruments so that absolute measurements of the volume of liquid dispensed can be obtained.

Claims

1. An apparatus for determining the volume of liquid dispensed by a liquid-dispensing mechanism or the flow of gaseous fluid in the vicinity of a liquid-dispensing mechanism, said apparatus comprising:

(a) at least one weigh cup;

(b) at least one standard mass;

(c) at least one transducer assembly to convert a value of weight to a an electrical response; and

(d) at least one electronic circuit for converting said electrical response to a measurement of volume of liquid dispensed.

2. The apparatus of claim 1, further comprising an electrical connector for electrically connecting said apparatus to an analytical instrument that employs said liquid-dispensing mechanism.

3. The apparatus of claim 1, wherein said at least one standard mass comprises an object having a mass of up to 3.3 g.

4. The apparatus of claim 1, wherein said apparatus is of such a size that it is capable of being inserted into a channel of said analytical instrument having dimensions no greater than 1 inch×

4 inches×

8 inches.

5. The apparatus of claim 1, further including a housing.

6. The apparatus of claim 1, wherein said at least one circuit comprises an analog electronics section and a digital electronics section.

7. The apparatus of claim 6, wherein said analog electronics section comprises at least one instrumentation amplifier.

8. The apparatus of claim 1, wherein said apparatus comprises at least two transducer assemblies.

9. The apparatus of claim 1, wherein said at least one transducer assembly comprises at least one strain gauge.

10. The apparatus of claim 9, wherein said at least one transducer assembly comprises a plurality of strain gauges.

11. The apparatus of claim 10, wherein said at least one transducer assembly cell comprises four strain gauges.

12. A method for verifying the volume of a liquid dispensed by a liquid-dispensing mechanism, said method comprising the steps of:

(a) providing an apparatus comprising;

(1) at least one weigh cup;

(2) at least one standard mass;

(3) at least one transducer assembly to convert a value of weight to an electrical response; and

(4) at least one electronic circuit for converting said electrical response to a measurement of volume of liquid dispensed;

(b) recording the value of weight of said at least one standard mass;

(c) recording the value of weight of said at least one weigh cup when said at least one weigh cup is empty;

(d) computing the gain of said apparatus;

(e) measuring a plurality of volumes of liquid dispensed in sequence; and

(f) calculating the mean value of said volumes of liquid dispensed.

13. The method of claim 12, wherein said step (f) comprises the steps of:

(a) recording the reading of the voltage after a standard mass of known value has been inserted into a weigh cup;

(b) removing said standard mass from said weigh cup and recording the value of said empty weigh cup;

(c) computing the gain of said apparatus;

(d) dispensing a sequence of volumes of liquid into said weigh cup and measuring the voltage, while compensating for drift of the voltage measurement;

(e) converting the voltage readings to readings of volume by taking into account the density of said liquid dispensed;

(f) calculating the absolute volume for each volume of liquid dispensed by means of the gain of said apparatus and said measurement in step (d);

(g) repeating steps (d), (e), and (f) for a plurality of dispensations of said liquid; and

(h) calculating the mean value of volume for said plurality of dispensations of said liquid.

15. The method of claim 13, wherein step (f) comprises the steps of:

(a) continuously measuring the voltage of said weigh cup for a period of time prior to dispensing of said liquid;

(b) dispensing a volume of liquid into said weigh cup;

(c) detecting a monotonic increase in the value of the voltage of said weigh cup above a threshold voltage over a period of time;

(d) measuring a period of delay from the moment that said threshold voltage is detected to allow time for said liquid to settle after said liquid is dispensed into said weigh cup;

(e) repeatedly measuring the voltage of said weigh cup for a period of time subsequent to said period of delay;

(f) computing the mean value of the voltage of said weigh cup for said period of time prior to dispensing said liquid;

(g) re-computing the mean value of the voltage of said weigh cup for said period of time prior to dispensing said liquid upon discarding a certain number of individual readings deemed to constitute noise;

(h) computing the mean value of the voltage of said weigh cup for said period of time subsequent to dispensing said liquid;

(i) re-computing the mean value of the voltage of said weigh cup for said period of time subsequent to dispensing said liquid upon discarding a certain number of individual readings deemed to constitute noise; and

(j) computing the difference between said mean value of the voltage of said weigh cup prior to dispensing said liquid (step g) and said mean value of the voltage of said weigh cup subsequent to dispensing said liquid (step i).

14. The method of step 13, further comprising the step of calculating the standard deviation for said plurality of dispensations of liquid.

16. A method for verifying the volume of a gaseous fluid dispensed in the vicinity of a liquid-dispensing mechanism, said method comprising the steps of:

(a) providing an apparatus comprising;

(1) at least one weigh cup;

(2) at least one standard mass;

(3) at least one transducer assembly to convert a value of weight to an electrical response; and

(4) at least one electronic circuit for converting said electrical response to a measurement of volume of liquid dispensed;

(b) recording the value of weight of said at least one standard mass;

(c) recording the value of weight of said at least one weigh cup when said at least one weigh cup is empty;

(d) computing the gain of said apparatus;

(e) determining rate of flow of gaseous fluid that is applying a force to said at least one weigh cup; and

(f) calculating the mean value of said rate of flow of gaseous fluid.