Method of measuring insulation resistance of capacitors

Details Method of measuring insulation resistance of capacitors Method of measuring insulation resistance of capacitors

1999-06-22

2002-05-07

Metjahic, Safet (Department: 2858)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

Reexamination Certificate

active

06384609

ABSTRACT:

Priority is claimed to Japanese Patent Application Nos. 10-174183, filed on Jun. 22, 1998, and 11-151198, filed on May 31, 1999, herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of measuring insulation resistance of capacitors to be used in judgment of conformance and nonconformance of capacitors, etc.
2. Description of the Related Art
In order to judge conformance and nonconformance of capacitors to a standard, a method of measuring insulation resistance of capacitors is known. This known method measures current (charging current) flowing through a capacitor after a direct-current voltage for measurement is applied to the capacitor and the capacitor has been fully charged. As a matter of course, conforming capacitors have less charging current.
Up to now, among such methods of measuring insulation resistance, a measurement method defined in JIS-C 5102 is known. Because this method requires measurement of the current in the state that the capacitor has been fully charged, a measuring time of, e.g., about 60 seconds was required. However, an improvement of productive capacity and quality of electronic parts such as capacitors, etc. is required in accordance with the needs of cost reduction and reliability improvement of electronic equipment. As such, the conventional measurement method, in taking such a long measuring time per capacitor, is not able to fulfill such requirements.
In order to measure insulation resistance of chip capacitors efficiently, a turntable is used. In measurement methods of insulation resistance using a turntable, there is a continuous production that, after capacitors have been advanced past a plurality of preliminary charging stations, the insulation resistance of the charged capacitors is measured one at a time. There is also a batch production that, after a fixed number of capacitors have been fed on a turntable, the turntable is stopped and at the same time preliminary electrical charge is given to a plurality of capacitors, and their insulation resistance is measured thereafter.
FIGS. 1 and 2
are the drawings showing the fundamentals of the above-mentioned two measurement methods. Capacitors
1
are held on a conveying means
2
such as a turntable, etc. at intervals of a fixed space and transported in the direction of the arrow intermittently.
FIG. 1
shows a continuous way of production. After a capacitor
1
has been fed at the feeding station S
IN
, preliminary charge takes place at a plurality of preliminary charging stations of S
p1
To S
p4
every time the conveying means
2
stops, and then a measuring voltage E[v] is applied at the measurement station S
M
and the insulation resistance is measured by a measuring apparatus
3
. After that, nonconforming capacitors are unloaded at the unloading station S
NG
for nonconforming articles and conforming capacitors are unloaded at the unloading station S
G
for conforming articles.
FIG. 2
shows a batch production. In the state that a plurality of capacitors
1
are held on a conveying means
2
, the conveying means
2
is stopped for a fixed period of time, and a voltage which is the same voltage as the measuring voltage Em is applied at a plurality of measurement stations of S
M1
To S
M5
for preliminary charge and at the same time the insulation resistance is measured by measuring apparatuses
3
. Further, reference numeral
4
represents a power supply of a rated voltage E[v], reference numeral
5
terminals for preliminary charge, and reference numeral
6
measurement terminals.
In the former case, because the electrodes of a capacitor are necessary to be made in contact with the terminals for preliminary charge many times, there is a disadvantage that the electrodes are likely to be damaged. Further, in the latter case, because preliminary charge is given to a number of capacitors
1
and they are measured at the same time, a large power supply unit is required. Furthermore, because multichannel measurements take place, many measuring apparatuses
3
are needed. Also, because one measuring apparatus
3
is switched for measurement, a complicated switching circuit is required. As a result, there was a drawback that the cost of equipment becomes high and the maintenance faces a difficulty.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to present a method of measuring insulation resistance of capacitors in which the number of contact of terminals with a capacitor is able to be reduced and a circuit necessary for measurement is able to be simplified.
In order to attain the above-mentioned object, in a first aspect of the present invention, a method of measuring insulation resistance that the insulation resistance is measured through a charging current flowing through a capacitor when preliminary charge takes place by applying a charge voltage Ep to the capacitor and then a measuring voltage Em is applied is characterized in that self-charge takes place in an open state during the time from the finish of the above-mentioned preliminary charge to the application of the measuring voltage Em.
Here, the principle of a method of measuring insulation resistance according to the present invention is explained. An equivalent circuit of a capacitor such as a ceramic capacitor is composed of capacitance C
0
, internal resistance r, insulation resistance R
0
, and the component of dielectric polarization (component of electrostatic absorption) D as shown in FIG.
3
. When a direct-current voltage is applied to such a capacitor, its charging characteristic is as shown in FIG.
4
. That is, the initial nonlinear charging characteristic A represents a region of charging capacitance C
0
. The linear charging characteristic C represents a region of charging the component of dielectric polarization D. The characteristic B represents a transition region between them. In
FIG. 4
, the vertical axis (current) and horizontal axis (time) are of a log scale.
Now, in
FIG. 4
, the charge is stopped in the course of the linear charging characteristic C and the capacitor is left in an open state, that is, without voltage applied. Then, after a fixed period of time, the charge is restarted. At this time, it has been found that, as shown by a broken line in
FIG. 4
, although the charging current value goes high once, the value is immediately stabilized on the linear charging characteristic C. After discussion of the phenomenon, the following reasoning was thought about by the present inventors. When charging is started initially, capacitance C
0
of a capacitor is charged by a charging voltage. But because it takes time to charge the component of dielectric polarization D, the component D is little charged at the initial step. While the charge is stopped, there is no flow of electric current to or from the outside because the capacitor is in an open state, that is, without voltage applied. During this time, charge (self-charge) of the component of dielectric polarization D by the electric charge in capacitance C
0
takes place, and this charge is in progress as if the first electric charge was not interrupted. Further, as capacitance C
0
is larger in capacitance than the component of dielectric polarization D, the charging voltage is lowered a little. When the charge is started again, because the charge of the component of dielectric polarization D has already progressed, it is thought that a little charge makes the capacitor stabilized in the desired charging characteristic C.
So, according to the present invention, by self-charge in an open state, that is, without voltage applied during the time from the finish of preliminary charge to the application of a measuring voltage, a capacitor is able to be charged without the electrodes of the capacitor making contact with the terminals many times for the purpose of preliminary charging. Furthermore, when a measuring voltage is applied to the capacitor, the self-charge of which has finished, it is possible to measure normal insulation resi

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