Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Surface tension
Reexamination Certificate
1999-02-11
2001-02-13
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Surface tension
C073S064480
Reexamination Certificate
active
06185989
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for dynamic measurement of the surface tension at boundary surfaces between liquids and gasses according to the method of evaluation of the maximum bubble pressure.
2. Description of the Related Art
A device of this type and a measurement process for this is described in greater detail in, for example, EP 0 149 500 A2.
For the theory and for further understanding of the measurement method, reference is made to the company publication: Blasendrucktensiometer BP2, Benutzerhandbuch, Krüss GmbH, Hamburg 1995.
The mentioned devices are suitable for stationary laboratory testing of liquids. Very high demands are made on the measurement conditions. Thus, for example, the state of fullness or, rather, the immersion depth of the capillary in the measurement liquid must be adjusted with millimeter precision with the aid of a sinking device, in which process a height adjustment up to the “jumping” of the liquid onto the capillary must first be undertaken manually and with very great care. The installation location is to be chosen with great care, since, for example, vibrations due to personnel walking by or drafts ensure a serious adulteration of the measurement results. Also, the measurement apparatus is to be carefully aligned. By reason of the demanding design of the measurement place and the high weight of about 20 kg, mobile application is prohibited. A further reason for the fixed design of the measurement place is that for the generation of bubbles relatively high pressures are required, for which, in turn, large external pressure-gas producers must be available and, obviously, an electrical connection must be present. The regulation of the bubble formation and/or bubble frequency takes place in a demanding manner by means of analog valves. The evaluation can take place only on a personal computer.
Furthermore, devices are known that for the purpose of continuous measurements are in constant contact with a particular liquid to be tested (DE 41 12 417 A1, DE 43 03 133 A1), and which are very expensive. An external air compressor, two compressed-air hoses, two valves, and two different precision capillaries, immersed to exactly the same depth, are necessary for the generation of the gas bubbles, as well as a pressure-difference gauge at the capillary feeds. The evaluation takes place on a personal computer. Disturbances, caused by a bubble break-off at one of the capillaries, makes an evaluation difficult.
In all known devices the pressure or rather the pressure difference between two capillaries is measured as an absolute value, for which purpose relatively cost-intensive pressure sensors with a very precise calibration are required.
Finally, from DE 44 23 720 C1 is known a generically different device for measuring the surface tension of preferably molten metals, with one capillary for the gas supply, which capillary is conducted for example vertically through the bottom of a crucible receiving the molten metal and terminates at a nozzle for the formation of the gas bubbles. With knowledge of the surface tension of cast iron, by means of this device conclusions can be made regarding the graphite morphology of the carbon contained in the cast iron, and the sulfur content of the pig iron or even the refinement processing of aluminum-silicon alloys can be judged.
It is a matter here of an elaborate apparatus to be operated in a stationary manner, with which apparatus the frequency of the gas bubbles emerging from the nozzle into the molten cast iron is determined. The relatively long capillary with an inner diameter of only 0.7 to 1.5 mm causes a considerable flow resistance for the gas the thus necessitates a high expenditure of energy during the measuring process. Beyond that, during the operation the moistening characteristics and the inner diameter of the capillary are altered by the measurement melt penetrating more or less into the capillary, and thus the measurement parameters are also altered uncontrollably, which leads, finally, to uncertain measurement results. Moreover, after every measurement a careful purging of the capillary or, better, its replacement is necessary. Both of these are time-consuming and expensive.
SUMMARY OF THE INVENTION
The task of the invention is to create a compact device for a nearly universal, simple, reliable and low-maintenance use. The device should make possible good measurement precision even with relatively large fill-state tolerance of the liquid in the container, and have a low power usage, a low weight, and greatly reduced production costs. In particular, the carrying out of its application should be possible in a mobile manner, whereby the constant sending in of test samples to a laboratory is just as dispensable as with an apparatus that is bound to one installation. Further, it should be possible to measure even the smallest amounts of liquid.
The task is accomplished through the characterizing features of the first claim. Advantageous further developments are specified in the dependent claims.
With the apparatus according to the invention, industry is given a small, light measurement device that is not dependent on an electrical means or air pressure, in short is mobile, that is relatively robust and simple to operate, and nevertheless is capable of delivering good measurement results with low acquisition cost and universal application. The measurement apparatus is operated via an input keypad and has different operating modes. The selected operating mode and the measurement results and/or error messages can be read off from a display. An internal volumetric-flow source generates the necessary gas pressure, the quality of the gas bubbles is measured by an internal pressure sensor, and the evaluation takes place by means of a microprocessor. An internal power supply supplies all power consumers independently of an electrical means as desired. It consists of a 110/220-volt power unit and/or a rechargeable or expendable battery.
Used advantageously as a volumetric-flow source is a controllable low-voltage membrane pump that is capable of building up a sufficiently constant gas pressure. When the nozzle according to the invention is used, the necessary gas pressure amounts to only about {fraction (1/10)} of the pressure in the standard devices.
For the pressure sensor is used, according to an especially preferred implementation, a sound-pressure transducer, namely a mini-microphone. This is cost-effective and delivers at its output the first derivative of the measured bubble pressure, thus a measurement signal that is independent of the immersion depth of the nozzle.
The measurement apparatus has four selectable operating modes, namely a calibration mode, a first measurement mode for surface-tension measurement with a constant, selected bubble frequency, a second measurement mode for surface-tension measurement with automatic bubble-frequency through-flow, and a purging mode, as well as an additional error mode.
According to an advantageous implementation, a nozzle directed toward the surface of the liquid is installed in the sensor head, the length of which nozzle is very short in relation to the nozzle opening. By this means an undisturbed bubble break-off is produced in the direction of the lifting force of the bubbles, which contributes to the precision of measurement. Moreover, the nozzle shape makes a purging considerably easier, and the required gas pressure for the production of gas bubbles in the measurement liquid sinks by an order of magnitude, which is of particular significance for a battery-operated, handheld measurement apparatus.
Obviously, instead of the measurement nozzle a capillary can be arranged in the sensor head (
1
) for generating the gas bubbles.
Since the surface tension becomes lower with a rising temperature, in a further configuration of the invention provision is additionally made in the sensor head for a temperature sensor for the evaluation of the measurement results.
In addition, in the region of the measurem
Collard & Roe P.C.
Garber Charles
Sita Messtechnik GmbH
Williams Hezron
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