Measuring and testing – Particle size
Reexamination Certificate
1999-10-04
2002-08-27
Raevis, Robert (Department: 2856)
Measuring and testing
Particle size
Reexamination Certificate
active
06439068
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process and device, herein a method and apparatus with which to determine the volumes of liquid droplets, in particular to determine the quantities of precipitates.
BACKGROUND OF THE INVENTION
High requirements on measurement techniques are placed on reliable determination of volumes of minimal liquid quantities in droplet form. The measurement range is approximately 1 &mgr;ltr to the maximum drop size. It is known to determine volume by weighing, but this procedure requires scales for comparatively small forces which are susceptible to such interference as air flows, temperature changes, microphonics etc. Using weighing, it is practically impossible to measure the particular volume of each droplet when such droplets follow each other rapidly.
It is further known to ascertain the droplet volume optically by analyzing the image of the droplet shape by resort to their shadows or using similar procedures. In such tests, optical transparency (particle-induced changes in transmission) and reflectivity of the liquid droplet negatively affect measurement accuracy.
Apparatus to measure the boundary-layer tension between two liquids of different densities is known from U.S. Pat. Nos. 4,697,451 and 4,569,226. The two liquids are present inside a cylinder where they form a boundary layer. Using a pipette, one liquid is dripped into the other underneath latter's liquid level. The pipette is made of an electrically conducting material and is connected to a voltage source. The liquid in the lower part of the cylinder is connected to an electrometer time-integrating the charge of the transiting liquid droplets. Furthermore the drop frequency is transmitted through the electrometer. Using a variable voltage source, the boundary-layer capacitance of the droplets formed in the liquid is indirectly determined iteratively from the slope of a straight line.
The European patent document A 0,286,419 describes apparatus with which to measure the pH value of a solution. Droplets are formed at the end of fiber optics, the end of the fiber optics being located between the plates of a capacitor.
The German patent document A 26 53 166 discloses apparatus with which to measure the concentration of components in a flowing liquid. This apparatus makes use of the electrokinetic effect. The liquid is converted into a stream of droplets transporting the generated stream drained by a drain electrode of a collecting vessel. Volumetry of the droplets is not provided.
OBJECTS AND SUMMARY OF THE INVENTION
The objective of the present invention is to create such a method and apparatus that liquid-droplet volumes can be determined more accurately and more economically.
This problem is solved by the falowing and apparatus.
Inventive method for measuring the volumes of liquid droplets is characterized by the following method steps:
separating a liquid volume into individual droplets,
electrically charging the droplets relative to their ambience, such a charge being a function of the drop's potential difference and its capacitance relative to its ambience,
measuring the droplet's capacitance or a value dependent on the capacitance, and
determining the droplet volume from the measured potential jump or from a derivative value.
Inventive method for measuring liquid drops is characterized by the following method steps:
separating a liquid volume into individual droplets,
raising the droplets to a potential different from that of their ambience,
determining the droplet charges by converting the charges into voltage jumps or a test value dependent on the voltage jumps,
determining the droplet capacitances from the measured voltage jump or from the test value dependent on the voltage jump, and
computing droplet volumes from their capacitances.
Inventive apparatus with which to carry out the two (
2
) inventive methods set forth immediately above, and characterized by the following elements:
a liquid drop collecting vessel (
2
,
40
) comprising a drop dripper (
4
,
42
) to deliver individual drops,
a device to electrically charge the individual drops formed by the dripper (
4
,
42
),
a measurement device (
8
,
44
) mounted underneath the liquid-droplet collecting vessel (
2
,
42
) connected to a droplet collector electrode (
16
,
46
) to determine the capacitances of the droplets or derivative test values, and
an analyzer to determine the drop volume from the measured capacitance or a derivative test value.
An inventive apparatus as set forth above, further characterized in that the droplet charging device comprises a voltage source (
12
,
62
) connected to the liquid-drop collecting vessel (
2
) or to the dripper (
4
) or to the collector electrode (
46
) to charge them to an electric potential different from that of the ambience.
Inventive apparatus as set forth above further characterized in that the dripper (
4
) is fitted with a potential guide needle (
10
).
Inventive apparatus as set forth above further characterized in that the potential guide needle (
10
) is conductively connected to the liquid droplet trap (
2
), the drop being connected by this potential guide needle to the potential of the collecting vessel (
2
).
Inventive apparatus as set forth above further characterized in that the droplet collector electrode (
16
,
46
) is connected to a measurement amplifier of which the output is a peak voltage value which is a function of the voltage jump caused by the change in potential at the collector electrode (
16
) by the droplet charge, or is proportional to the voltage jump, or is a function of the voltage jump caused by the change in capacitance of the collector electrode (
46
) due to the droplet capacitance or is proportional to this voltage jump.
Inventive apparatus as set forth above further characterized in that the measurement amplifier is a charge/voltage converter (
20
,
48
).
Inventive apparatus as set forth above further characterized in that a peak voltage detector (
24
,
50
) is connected to the measurement amplifier or charge/voltage converter (
20
,
48
) for interim storage of the peak voltage value until ensuing analysis.
Inventive apparatus as set forth above further characterized in that it includes an exponentiator (
26
,
52
) to raise the peak voltage value to the third power in order to provide a measurement value which is linear with the droplet volume.
Inventive apparatus as set forth above further characterized in that the peak voltage value detector (
24
,
50
) is resettable following retrieval of the peak voltage value.
Inventive apparatus as set forth above further characterized in that the measurement device (
8
) includes a screening field electrode (
14
) enclosing the droplet's falling trajectory.
Inventive apparatus as claimed set forth above further characterized in that it comprises a compensation electrode (
22
) associated with the collector electrode (
16
) and together with the collector electrode (
16
) forming a capacitor of which the capacitance depends on the dielectric constants of the ambient medium and which thereby compensates capacitance changes in drops of equal sizes due to a changing dielectric constant.
Inventive apparatus as set forth above further characterized in that the voltage source (
12
,
62
) comprises a high voltage converter.
Inventive apparatus as set forth above further characterized in that the collector electrode (
46
) is connected to a constant current source or, through a high resistance, to a voltage source (
62
).
Inventive apparatus as set forth above further characterized in that a comparator (
30
,
56
) is connected to the output of the peak value detector (
24
,
50
) and will emit a transfer command signal in the presence of measurement values and in that the peak value detector is resettable by a one-shot multivibrator (
32
,
66
) driven by a transfer confirmation signal.
The method of the invention makes use of the feasibility to impart charges (relative to their environment) to masses suspended in an insulated manner or floating or falling, on a
Raevis Robert
Schlesinger Arkwright & Garvey LLP
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