Capacitor leakage measurement method
Capacitor is that almost all electrical devices are used on the main device. Capacitor leakage resistance is being tested in a number of electrical characteristics. Leakage resistance is often referred to as "IR" (Insulation Resistance, insulation resistance), to "Meg - micro Act" means. In other cases, leakage may be expressed as a particular voltage (usually voltage) under the leakage current.

Capacitor leakage by applying a fixed voltage to the capacitor and measuring the resulting current measured. Leakage current will decay exponentially with time, so Before measuring current, voltage must be applied to a known time period (dwell time).

For statistical purposes, to test a certain number of capacitors to generate useful data. For testing, we need an automatic switching system.

Figure 1 shows a capacitor leak test system, which uses a Keithley 6517A electrometer type / source, 7158 Small current C-scan cards and switch cards, such as 7111-S or 7169A. Card is installed in the 7002 switch hosts.

Figure 1, capacitor leakage test system

In the test system, a set of switches (7111-S-type or 7169A model) was used to test the voltage applied to each capacitor. In the normally closed position, the capacitor is connected to one end of the circuit LO. When the switch is touched, the capacitor is connected to a voltage source. Touch switch is usually interlaced (for example, an interval of 2 seconds), resulting in leakage measurement before each capacitor can be charged the same time period. If the maximum test voltage of 110 V or less, you can use the 7111-S-type switch card; Otherwise, you can use the 7169A switching card test up to 500 V voltage. If you have more than 500 V applied voltage, the rating should be used with the appropriate switch.

The second set of switches (7158 model) after a suitable time to smooth each capacitor will be connected to Picoammeter dollars. Please note that the capacitor is switched to picoamp dollars before it is connected to the circuit the LO. This makes the leakage flow in the charging device can be continuously flow.

For this application, a single instrument provides low current voltage source and measurement functions. 6517A-type displays resistance or leakage, and provides up to 1000 VDC voltage, it is particularly suitable for this application.

In the tested capacitor, the voltage source should be set to zero. Sometimes in the capacitor before removing from the test fixture, it must discharge. Note that in Figure 1 the capacitance (C) through the normally closed relay contacts to form a discharge path. Synchronized test sequences are as follows:

Static - 7169A for the normally closed relay, 7158 relay is normally closed.

Applied voltage (dwell time) - 7169A relay connected to the normally open contact, relay 7158 remains normally closed.

Measuring current - 7169A relay remains in the normally open position, 7158 is connected to normally open relay contacts.

Discharge capacitor - 7169A relay connected to the normally closed contacts 7158 connected to the normally closed relay contacts.

As the 7169A-type C-type switch isolation switch on the card remain in the current measurement period is energized, all from the switch card with any offset current measurement is irrelevant.

Capacitor in series with the resistor (R) is the test system is an important component. It limits the charging current of each capacitor and the capacitor short circuit protection relays. In addition, the resistor also limits the exchange gain feedback ammeter. In general, when the source capacitance increases, the noise gain will increase. The resistor will limit the gain is finite. Reasonable limit is to make the RC time constant of 0.5 to 2 seconds. And electrometer (pA) of the HI terminal is biased diode in series play a limited role of the exchange gain.

A "coaxial three column-BNC" converter (7078-TRX-BNC type) is used to connect the 6517A to a 7158-type switch cards. Capacitor through the 7158 low-noise coaxial cable connected to the switching card. You can use insulated wire to 7111-S switch card connected to the capacitor. 7169A-type cable connector is connected.

Summary

Based on the capacitance measurement technique of leakage in the capacitor leakage measurement, in measurements for statistical purposes, to test a certain number of capacitors to generate useful data. For testing, we need an automatic switching system. That is what we call the capacitors leak test system. In this paper, systematic analysis of this capacitor leakage test system technical parameters, the reader can learn the system from which information