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stabilize in a reasonable amount of time. See the section on the constant voltage
mode for effects on ranges and accuracy.
It will take a short while for the internal circuitry and the DUT to stabilize after
applying the bias voltage. The time is primarily determined by the RC time
constant of the source resistance and the capacitor under test, plus the internal
AC coupling capacitor of 0.47
F. During this time, the reading on the meter may
change if it is continuously triggered. In this case, the initial readings should be
disregarded. If this is a problem, use the triggered mode (simply wait a short time
before triggering) or increase the settling time. See the section on measurement
rate for information on how to set the settling time. In addition, the capacitance of
some capacitors will slowly drift after a change in DC voltage.
Internal Bias
To apply the 2.0V DC internal bias voltage to the capacitor under test, first verify
that the capacitor is connected to the test fixture with correct polarity (positive to
the right). Press the
INT
key to apply the bias voltage. After a second or two, the
reading should be stable. Before removing it from the fixture, press the
INT
key a
second time to switch off the bias in order to discharge the capacitor.
External Bias
The meter has rear panel connectors to allow an external bias voltage of up to
+40 VDC to be applied across the capacitor under test. This supply must be
floating (neither side connected to ground) and must be current limited to less
than 250mA. A linear supply is recommended (instead of a switching supply).
The supply should be well filtered, to remove ripple from the bias voltage.
Connections to the bias supply are made on the rear panel with two banana jacks.
The red jack is the positive side of the supply and the black, the negative. There
is an internal diode within the unit to prevent a negative voltage from being
applied. The bias supply lines are fused with a 250mA fuse on the rear panel,
next to the banana jacks. If the meter does not yield stable readings when the
external bias switched is on, check this fuse. If the bias supply is connected
backwards, there is a good chance that the bias supply fuse will blow. Provisions
are needed to discharge the bias voltage from the capacitor under test before
removing it from the fixture. In general, external switches or discharging resistors
should be provided along with the bias supply to ensure safe operation.
To apply an external bias voltage, ensure that the bias supply is connected
correctly. Verify that the capacitor is installed with the correct polarity in the test
fixture (positive to the right). Next press
EXT
button to apply the bias voltage.
After a second or two, the reading should be stable. After the measurement is
complete, discharge the capacitor under test before removing it from the fixture.
For occasional nonproduction use with small capacitors (<500 µF) and low
bias voltages (<20 VDC), the meter can discharge the capacitor internally. Press
the
EXT
button to switch off the bias. The capacitor will then discharge through
the meter in the same manner as the internal bias.