Measuring and testing – Sampler – sample handling – etc. – Analyzer supplier
Patent
1998-08-04
2000-06-06
Raevis, Robert
Measuring and testing
Sampler, sample handling, etc.
Analyzer supplier
G01N 100
Patent
active
060704764
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus which is capable of providing any desired ratio of two or more fluids or suspensions and whose relative concentrations may be varied accurately.
BACKGROUND ART
GB-B-2,068,544, discloses a method and apparatus in which the properties of a dilute sample of red blood cells are changed by osmosis to generate a set of related data which is characteristic of the health or physiological condition of the human or animal source of the blood cell sample. By subjecting cells to a number of solutions having different concentrations, the size and shape of the blood cells changes. When these changes are measured electronically, a detected electrical resistance increases to a peak and then falls as the critical concentration passes.
In particular, in GB-B-2,068,544 it is known to be desirable to obtain a series of hypotonic concentrations and thereby measure the characterisetics of blood cells at a series of different osmalolities. In the past, a conventional stepper motor has been used in combination with a lead-screw apparatus to drive a plunger of a first syringe containing a dilutent which is subsequently mixed with a different dilutent contained in a second syringe, the plunger of which is driven by a second stepper motor. A third syringe containing a prepared blood cell sample is discharged at a constant rate into a mixing chamber into which the first and second syringes simultaneously discharge their contents. During the test, the flow rate of fluid from the first syringe is typically decreased over a period of time whilst the flow rate of fluid from the second syringe is correspondingly increased over the same period to change the relative concentrations of the two dilutents whilst size, shape and count measurements are made of the blood cells in the resulting mixture. However, conventional stepper motors can only be driven at a limited number of predetermined stepping rates so that the velocity of fluid discharged from each syringe can only be changed in a stepwise manner, which therefore only very roughly approximates to a desired velocity profile. Each stepwise change in velocity of the conventional stepper motor leads to disturbances in the flow of fluid which affects the accuracy of the size, shape and count measurements made downstream. Accordingly, the accuracy of this conventional arrangement for determining cell osmalolity is only to within 2-3 mosm Kg.sup.-1, which is not sufficiently sensitive to detect certain health or physiological conditions.
DISCLOSURE OF INVENTION
According to a first aspect of the present invention, a fluid delivery method and apparatus comprises first and second delivery syringes, each delivery syringe comprising a syringe housing defining a tubular passage having a fluid outlet, and a syringe plunger arranged to slide axially within the tubular passage and seal one end of the tubular passage, the fluid delivery apparatus further comprising syringe plunger drive means for driving the syringe plunger of the first and second syringe along at least part of the length of the tubular passage according to a predetermined velocity profile for the delivery syringe and discharge fluid through the fluid outlet, wherein the predetermined velocity profile of each delivery syringe is such that, in use, a combined flow rate of fluid discharged simultaneously from the outlets of the plurality of delivery syringes is maintained substantially constant over at least a portion of the range of movement of the plurality of plungers.
In the present invention, means are provided to drive the plunger of each delivery syringe in a substantially continuous manner according to a desired velocity profile, a portion of which profile results in an acceleration in the rate of discharge of fluid. This profile may be any continuous function, whether linear or otherwise. The predetermined velocity profile for each syringe determines the rate at which fluid is discharged from the syringe over a range of movement of the syringe plunger. In an ap
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patent: 3726144 (1973-04-01), Klein
patent: 3902852 (1975-09-01), Lemieux et al.
patent: 5540498 (1996-07-01), Chu
Shine Ian Basil
Shine Thomas Adam
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