Measuring and testing – With fluid pressure – Porosity or permeability
Reexamination Certificate
1999-01-22
2001-04-10
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Porosity or permeability
C073S037000
Reexamination Certificate
active
06212941
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a permeameter, i.e. a device for the purpose of measuring the air permeability or fluid permeabilty of porous materials which can notably be in sheet form.
It applies particularly though not exclusively, to the measurement of the air permeability of cigarette papers, wrappers and/or oversleeves.
2. Description of the Prior Art
Generally, it is known that, in order to measure the permeability of a test piece which can consist of an object of any shape whatsoever, two opposite sides of this test piece are subjected to a difference in pressure so as to bring about, within the material included between these two sides, an air stream of which the flow rate is measured.
This difference in pressure is obtained either by generating a partial vacuum at one of the sides while bringing the other side to atmospheric pressure, or conversely, by subjecting one of the sides to air pressure while the other side is brought to atmospheric pressure.
The measurement of the flow of air passing through the test piece is then obtained by maintaining the partial vacuum or pressure applied to the test piece at a constant level, and by measuring by means of a flow meter, the flow of air circulating in the circuit and generating the partial vacuum or pressure as the case may be.
In compliance with ISO 2695 and CORESTA recommendation No. 40, the value VUC in CORESTA unit, (UC being equal to the flow of air (cm
3
.min−1) passing through a 1 cm
2
surface of the test piece at a measuring pressure of 1 kPa), of the permeability at a given pressure can then be obtained from the following formula:
VUC
=
“
Q
(
cm
3
/
mn
)
A
(
cm
2
)
·
d
(
kPa
)
”
in which:
d is the variance in pressure between the two sides of the test piece (usually 1 kPa)
Q is the flow of air passing through a cross-section A of the test piece (usually 2 cm2) defined by the measuring head.
It so happens that the permeability of objects is very variable, as are therefore the air flows to be measured as a function of the test space area, the ambient test conditions and the applied pressure variance.
Moreover, it is frequently useful to measure, for the same test piece, the flow rate at two different pressures (or partial vacuums), usually 0.25 kPa and 1 kPa, with a view to determining a coefficient (called coefficient of &Rectversolid;persillage&Rectversolid;) expressing the linearity of the flow/pressure characteristic.
Finally, it may be desirable to plot a graph of the flow/pressure characteristics of the air flow passing through the test piece, especially with a view to determining the exact equation thereof.
Taking into account the fact that, in order to plot such a graph, the pressure (or partial vacuum) must necessarily be varied within a very wide range, the problem stemming from the narrowness of the measurement range of the flow meter is particularly acute. Hitherto, this problem made it necessary for the operator to step in to make scale changes. Total automation of this type of measurement was therefore not conceivable.
OBJECT OF THE INVENTION
The main object of this invention is to remedy the preceding disadvantages, particularly to provide a permeameter enabling such automation without any ensuing alteration of the measurement results.
SUMMARY OF THE INVENTION
Accordingly, there is provided a permeameter using a measuring head enabling the test piece to be at least partially imprisoned in an airtight manner, and comprising two chambers opening respectively onto two separate sides of the test piece, one of these chambers, known as the measurement chamber, being connected to a measuring circuit successively comprising at least one flow meter and a pumping means capable of generating pressure or a partial vacuum in the measuring circuit, an adjusting means being provided to maintain the circuit at a given pressure.
According to the invention, this permeameter is characterized in that it comprises an electronic circuit comprising a plurality of calibrated amplifiers of which the inputs are connected to the analog output of the flow meter and of which the outputs are connected to the respective inputs of a multiplexer driven by a processor. The output of this multiplexer is connected to an analog-to-digital converter of which the output is connected to the processor.
This processor is programmed so as to control both the multiplexer and a generator of set pressure values on the aforesaid adjusting means, and to compute the permeability of the object as a function of the pressure value and flow value it receives in digital form from the analog-to-digital converter.
According to one feature of the invention, the output voltage of the flow meter is applied to the input of a plurality of amplifiers.
By way of this arrangement, it becomes possible to measure, with an excellent degree of resolution, the flow detected in the measuring circuit for a very wide range of flow rates.
REFERENCES:
patent: 3577767 (1971-05-01), Stedile
patent: 3590634 (1971-07-01), Pasternak et al.
patent: 3839899 (1974-10-01), McMillen
patent: 4401147 (1983-08-01), Beck et al.
patent: 4480463 (1984-11-01), Schumacher et al.
patent: 4495795 (1985-01-01), Gupta
patent: 4513603 (1985-04-01), Baillie
patent: 4531404 (1985-07-01), Phelps et al.
patent: 4543821 (1985-10-01), Davis, Jr. et al.
patent: 4555934 (1985-12-01), Freeman et al.
patent: 4599891 (1986-07-01), Brauer et al.
patent: 4638447 (1987-01-01), Odeh
patent: 4718270 (1988-01-01), Storr
Drucker William A.
Societe Nationale d'Exploitation Industrielle des Tabacs et
Wiggins David J.
Williams Hezron
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