Keithley 6514, Instruction Manual

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4-14 Amps Measurements
Capacitor leakage current
Figure 4-7 shows how to measure the leakage current for a capacitor. The magnitude of the
leakage is dependent on the type of dielectric and the applied voltage. A resistor and a diode are
used to limit noise for the measurement.
For this test, a fixed bias voltage is to be applied to the capacitor for a specified time to allow
the capacitor to fully charge (current decays exponentially with time). The leakage current is
then measured. After the measurement, the voltage source is set to output 0V for a specified time
to allow the capacitor to discharge.
Cable insulation resistance
NOTE
For this test, Model 6514 uses the source voltage, measure current method to
determine resistance. Once a current measurement is performed, resistance can be
calculated.
Figure 4-8 shows how to measure the insulation resistance of a cable. The resistance of the
insulator between the shield and the inner conductor is being measured. The cable sample should
be kept as short as possible to minimize input capacitance to the ammeter.
For this test a fixed bias voltage is applied across the insulator for a specified time to allow
the charging effects of cable capacitance to stabilize. The current is then measured. Cable resis-
tance (R) can then be calculated as follows:
R = V/I
where; V is the sourced bias voltage
I is the measured current
230
V-Source
A
+
-
6514
Ammeter
HI
LO
HI
LO
Equivalent Circuit
Figure 4-7
Connections; capacitor
leakage current test
230
V-Source
A
+
-
6514
Ammeter
HI
LO
HI
LO
Cable
Resistance
Equivalent Circuit
Figure 4-8
Connections; cable
insulation resistance
test