DE2404885A1 - Measurement of residual current on capacitors - with charging battery and voltage comparator and especially for electrolytic condensers - Google Patents

Abstract

A d.c. voltage is applied as a charging voltage to the capacitor in a first definite period. The capacitor is not disturbed during a subsequent second definite period, and when this period is over, the residual voltage still applied to the capacitor is compared with a component voltage proportional to the charging voltage. The second definite period can be kept shorter than the discharge time of the capacitor. The first period can be kept equal to the charging time of the capacitor or shorter than the charging time of the capacitor. A voltage comparator can compare the residual voltage and component voltage.

Description

Residual current measurement The invention relates to the measurement of residual currents on capacitors, especially on electrolytic capacitors.

In the case of electrolytic capacitors, in addition to the capacity, the nominal voltage and the dissipation factor, the residual current is one of the important values in data sheets are listed in a table and identify a respective capacitor.

The values of the residual current given in such tables are in each case Guide values, whereby the measurement conditions are usually given as these values sometimes change very strongly with operating time and temperature. In general such a measurement is performed after an operating time of 5 minutes at an ambient temperature of 20 ° C performed.

Sensitive ammeters are used for residual current measurements in the laboratory Use. For quality control measurements, for example in production for sorting capacitors lying within the residual current tolerances are such Devices cannot be used because they are very sensitive and expensive. Here is the residual current measurement usually carried out in a comparison with a residual current standard. It must but at least for each individual measurement after the DC voltage has been applied wait until the discharge current of the capacitor has decayed that far is that its value has fallen below that of the residual current to be measured.

The invention has set itself the task of showing a method by means of which a residual stream sorting in a shorter time and in a simple way can be made. Another object of the invention is to provide an arrangement to carry out such a method with a simple and inexpensive measurement setup to accomplish.

This object is achieved according to the invention in that the A DC voltage as a capacitor in each case in a first defined period of time Charging voltage is applied that in a subsequent second defined period of time leave the capacitor de-energized, and that after the second period of time has elapsed the residual voltage applied to the capacitor with one proportional to the charging voltage Partial voltage is compared.

It has been shown that a residual current constant k is defined leaves, which is proportional to the residual current IR and inversely proportional to the nominal capacity CN and the nominal voltage UN is: 1R k CN u CN With the internal resistance Usually of the capacitor as the quotient of the nominal voltage UN and the residual current IR the residual current constant k is represented as a reciprocal time constant: 1 1 k = ------ = CNR i The comparison used for the usual measurement of the residual current is therefore used IR <IR limit replaced by the comparison where MY is the time constant of the = voltage drop on the charged capacitor and N represents the comparison time constant. A residual current measurement is hereby greatly simplified.

According to a feature of the invention, the second is defined time period kept smaller than the discharge time of the capacitor.

This has the advantage that it is no longer necessary to wait for each individual measurement must be until the discharge current has fallen below the value of the residual current to be measured is; the individual measurement can be carried out much faster.

The arrangement according to the invention for performing the method is characterized in that the capacitor of a charging battery has a first Switch can be switched on and off and in its switched-off position via a second switch is arranged switchable to a voltage comparator.

With such an arrangement can be a very cheaper and easier Achieve measurement setup.

According to the invention is parallel to the capacitor and the charging battery arranged a voltage divider formed from two resistors, whose divider point is connected to the voltage comparator. It is beneficial to have a resistor to train the voltage divider changeable.

This means that the comparison voltage can be changed. The test setup can also be easily converted to other capacitor types; then only the measuring voltage has to be readjusted.

The invention is explained in more detail below with reference to the drawing; the figure shows the measurement setup for carrying out the method according to the invention.

The arranged between the measuring terminals 1 and 2 capacitor 3 in the Figure is by means of a toggle switch 4 in its switch position 4.1 one off the resistors 5 and 6 formed voltage divider connected in parallel. About one Switch 7 is a battery 8, which supplies the energy for charging the capacitor, switchable. In the switch position 4.2 of the changeover switch 4, the capacitor is connected via a switch 9 to a voltage comparator 10, to which also the divider point 11 of the voltage divider is connected. The electrical outlet of the voltage comparator 10 is connected to an electronic evaluation logic 12.

At time t = 0, switch 7 is closed; the toggle switch 4 is in its switch position 4.1 and the switch 9 is open 'the Capacitor 3 is charging. At a time t = a when the capacitor 3 has a certain Has reached the state of charge, which is a partial charge or the corresponds to full charge, the changeover switch 4 is in its switch position 4.2 brought. Then the capacitor 3 is from the battery 8 and the voltage divider 5, 6 and due to the open position of switch 9 also from the voltage comparator 10 separated. The capacitor 3 discharges through its own resistance depending on its magnitude more or less strong. At a time t = a + b the switch becomes 9 closed; the time t = a + b is shorter than the time of full discharge of the capacitor. When the switch 9 is closed, the remaining residual voltage is at the capacitor 3 in the voltage comparator 10 with the charging voltage of the battery 8 compared to the proportional voltage at the voltage divider point 11. This equivalent stress at the voltage divider point is adjustable by means of the changeable resistor 5. It is set so that it is within the residual current tolerances Capacitors result in a positive differential voltage in the comparator 10 or from the comparator 10 is displayed, for capacitors lying outside these tolerances a voltage zero alone or also voltage zero and negative values. The result of these voltage comparison values is processed electronically in the control logic so that subsequent sorting processes can be controlled with it.

List of Reference Numbers 22 measuring terminal 3 capacitor 4 changeover switch 4.1, 4.2 Switch position of the changeover switch 4 5, 6 Resistor 7 Switch 8 Battery 9 switch 10 voltage comparator 11 voltage divider point 12 evaluation logic 10 Claims

Claims (10)

Claims 1. Method for measuring residual currents on capacitors, in particular electrolytic capacitors that a DC voltage is applied to the capacitor in each case in a first defined period of time is applied as a charging voltage that is defined in a subsequent second Leave the capacitor de-energized for a period of time, and that after the end of the second Time span the residual voltage on the capacitor with one of the charging voltage proportional partial voltage is compared. 2.) The method according to claim 1, characterized in that the second defined period of time is kept smaller than the discharge time of the capacitor. 3.) Process according to claims 1 and 2, characterized in that that the first defined period of time is kept equal to the charging time of the capacitor will. 4.) Process according to claims 1 and 2, characterized in that that the first defined period of time is kept smaller than the charging time of the capacitor will. 5.) Method according to one of the preceding claims, characterized in that that the comparison of the residual voltage and the partial voltage with a voltage comparator is made. 6.) Arrangement for carrying out the method according to the preceding Claims, characterized in that the capacitor (3) is a charging battery (8) can be switched on and off via a first switch (4) and switched off in its Switch position (4.2) via a second switch (9) a voltage comparator (10) Is arranged switchable. 7.) Arrangement according to claim 6, characterized in that parallel to the capacitor (3) and the charging battery (8) one formed from two resistors (5, 6) Voltage divider is arranged, whose divider point (11) with the voltage comparator (10) is connected. 8.) Arrangement according to claim 7, characterized in that a resistor (5) of the voltage divider (5, 6) is designed to be variable. 9.) Arrangement according to claims 6 to 8, characterized in that that the charging battery (8) of the arrangement can be switched on via a further switch (7) is. 10.) Arrangement according to at least one of the preceding claims, characterized in that the voltage comparator (10) has an evaluation logic (12) is connected downstream for sorting the capacitors.