Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2002-09-11
2003-11-04
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S683000, C324S467000
Reexamination Certificate
active
06642723
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to apparatus monitoring the deposition of a liquid-to-pasty medium on a substrate.
BACKGROUND OF THE INVENTION
Such apparatus is described in the German patent document 4 217 736 C2. Therein each electrode is a sensor which is a component of a high-frequency oscillation circuit and as such detects a change in frequency when there is a change in the relative electric permittivity of the medium between the electrodes.
In this design the sensor is capacitive, that is it is inserted as a capacitor in the high-frequency oscillation circuit. Depending on the kind of medium between the two probes, that is, depending whether air is involved, or a substrate without a strip of glue or a substrate with a strip of glue of various thickness, the capacitance of such configuration will change. However the system capacitance strongly depends on the relative dielectric constant of the materials assuming much different values for air, glue and paper.
A typical change in system capacitance however also changes the frequency, allowing determining for instance whether the substrate comprises or not a strip of glue.
The known apparatus monitoring the deposition of a liquid-to-pasty medium on a substrate does its job well. However there may be malfunctions in some cases.
SUMMARY OF THE INVENTION
Based on the known apparatus of the German patent document 4 217 736 C2, it is the objective of the invention to create an apparatus that offers improved reliability and higher accuracy of measurement.
This problem is solved by the invention in accordance with which the apparatus measures the imaginary component of the permittivity of the substrate together with the medium between the two electrodes, the test electronics thereupon using this test value to determine the characteristic signal.
It is the insight of the invention that the permittivity, ie the dielectric constant, is a complex value, that is it comprises a real component and an imaginary component. Furthermore experiment has shown, with respect to the materials of significance herein, especially liquid-to-pasty glue such as is used in glue strips on cardboard, on paper mats or the like, that the imaginary components of the permittivity are larger, sometimes even by an order of magnitude, than the real components.
Based on such empirical findings, the invention concludes that, considering the numerically larger value of the imaginary component of the permittivity, measuring this imaginary component shall be simpler and more reliable when determining the nature of the tested material.
Derivation of the pertinent formulas is briefly discussed below. Further details can be found in the article “Frequenz-Zugang der komplexen Permittivität”, F H Duesseldorf [Germany] Labor Werkstoffkunde, Sep. 4, 1998, pp 1-14.
The individual microscopic effects noted when a dielectric material is situated in an alternating electric field are best stated by a complex permittivity
&egr;
r
=&egr;
r
′−j&egr;
r
″.
where &egr;
r
′ is the real component and &egr;
r
″ is the imaginary component of the permittivity
&egr;
r
.
The particular microscopic phenomena affecting this value will be not be elucidated herein. Basically, they involve effects of alignment, ionic and electronic polarizations. The permittivity, and both its components, are strongly frequency-dependent.
The term &egr;
r
″ describes the dielectric losses and accordingly it is a measure of the energy absorbed by the glue.
These dielectric losses behave like ohmic heat losses. This fact can be expressed also by the so-called loss tangent
tan &dgr;=&egr;
r
″/&egr;
r
′.
FIGS. 1 and 2
illustrate this matter.
FIG. 1
schematically shows the equivalent circuit of an actual lossy capacitor. When applying an AC voltage
U
, a current
I
is set up in the capacitor. This current comprises two parts, namely the current
I
c
which would be set up in ideal capacitor, and parallel thereto the loss current
I
v through a resistor, representing the dielectric losses as heat in the capacitor.
FIG. 2
is a diagram of the two components, namely lossy current and current through the idealized capacitor, which when added represent the total current I through the actual capacitor.
It follows from the equivalent circuit,
Y=G+j&ohgr;C,
where Y is the admittance, G the dissipative conductance and j&ohgr;C the reactive admittance in the loss-free capacitor.
In the event that a test object be present in the capacitor,
Y=j&ohgr;*C
material
.
The capacitance of a parallel plate capacitor is given by the formula
C=&egr;
o
&egr;
r
A/d
where A is the surface of each plate of a parallel plate capacitor and d is the distance between these plates, &egr;
r
being the relative dielectric constant of the material.
The latter two formulas directly lead to
Y=j
&ohgr;*(&egr;
r
′−j&egr;
r
″)*&egr;
o
A/d.
Using herebelow
C
o
=&egr;
o
A/d
then
G+j&ohgr;*C=j
&ohgr;*(&egr;
r
′−j&egr;
r
″)+
C
o
G+j&ohgr;*C=&ohgr;*&egr;
r
″*C
o
+j&ohgr;*&egr;
r
′*C
o
whence
C=&egr;
r
′*C
o
.
However this indicates that only the real component of the permittivity accounts for the capacitance. Accordingly the heretofore conventional capacitance measurements will not detect the permittivity's complex component.
Attention is now drawn to Tables 1 and 2 below.
TABLE 1
C
r
/pF
1.4
C
s
/pF
0.2
f/MHZ
0.075
0.1
0.15
0.2
0.3
0.5
1
C/pF
100.28
99.80
99.17
98.74
98.16
96.44
96.41
C
k
/pF
99.48
98.0
97.37
96.94
96.94
95.64
94.61
G/&mgr;s
1.38
1.74
2.43
3.10
4.42
7.03
13.18
C
L
/pF
18.93
18.93
18.93
18.92
18.82
18.92
18.92
C
LN
/pF
17.13
17.13
17.13
17.12
17.12
17.12
17.12
&egr;
r
′
5.68
5.72
5.68
5.66
5.63
5.58
5.52
&egr;
r
″
0.17
0.16
0.15
0.14
0.14
0.13
0.12
tan &dgr;
0.03
0.028
0.026
0.025
0.025
0.023
0.022
TABLE 2
C
r
/pF
1.4
C
s
/pF
0.2
f/MHZ
0.075
0.1
0.15
0.2
0.3
0.5
1
C/pF
1187
965
879
653
548
459
381
C
k
/pF
1185.4
963.4
877.4
651.4
546.4
457.4
379.4
G/&mgr;s
4,074
4,163
4,293
4,374
4,447
4,620
4,935
C
L
/pF
16.55
16.55
16.55
16.54
16.54
16.54
16.54
C
LN
/pF
14.95
1495
14.95
14.94
14.94
14.94
14.94
&egr;
r
′
79.3
64.44
58.7
43.6
36.6
30.6
25.4
&egr;
r
″
578.3
443.2
304.7
233.0
157.9
98.4
52.6
tan &dgr;
7.29
6.88
5.19
5.34
4.31
3.22
2.07
Table 1 shows a number of test values for paper inserted between the plates of a parallel plate capacitor. Table 2 shows the corresponding test values for the dielectric between the capacitor's plates consisting of two paper layers sandwiching glue layers.
The notation used in these Tables is as follows: C
r
is the capacitance portion of the tested sample's capacitance taking into account the edge field of the parallel plate capacitor; C
s
is the capacitance portion taking into account the stray field to ground; f is the applied frequency, C is the measured capacitance, C
k
is the corrected measured capacitance, C
LK
is the corrected capacitance of the test system without a test sample, G is the admittance of the dielectric, C
L
is the capacitance of the test system without a test sample, &egr;
r
′ is the real component of the permittivity, &egr;
r
″ is the imaginary component of the permittivity, and tan &dgr; is the loss factor.
Further information also can be found in the aforementioned article by J Prochetta PhD.
It is immediately clear from the Tables that when the dielectric is glue, the absolute values of the imaginary component &egr;
r
″ of the permittivity are order(s) of magnitude larger than the real component &egr;
r
′. Consequently measuring this imaginary component of the permittivity will be far more revelatory about the dielectric situated between the two electrodes. This is the heart of the invention.
It is furthermore clear from the above that the ratio of glue &egr;
r
″ to paper &egr;
r
″ is more than two orders of magnitude larger than the ratio of glue &egr;
r
′ to paper &egr;
r
ITW Industrie GmbH
Le N.
Lowe Hauptman & Gilman & Berner LLP
Nguyen Vincent Q.
LandOfFree
Apparatus monitoring the deposition of a liquid-to-pasty... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus monitoring the deposition of a liquid-to-pasty..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus monitoring the deposition of a liquid-to-pasty... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3181830