5. ADVANCED OPERATION
This section will provide the user with a guide to:
two-, three- and four-terminal connections
measurement of very small capacitors
measurement of very small inductors
measurement of iron-cored and ferrite inductors
5.1 Two-, Three- and Four-Terminal Connections
The meter has four front panel BNC sockets for screened cable connections to the device under
test (DUT). In each case the outer connection provides the screening and the inner is the active
connection. The outer pair of panel connectors carries the signal source (YELLOW) and current
return (BROWN) signals, while the inner pair serves to monitor the actual voltage at the DUT,
excluding any voltage drops arising in the source and return leads. With Kelvin clip leads or the
four-terminal component fixture 1EV1006, screened four-terminal connections are made
automatically to the DUT.
If the impedance being measured is greater than 1kΩ, four-terminal connections are not
necessary, the S/C trim facility being used to remove the effect of series lead impedance.
For low impedances, the main advantage of four-terminal connections is to reduce the effect of
contact resistance variations at the DUT.
If the DUT has a large area of metal not connected to either of its measured terminals (e.g. a
screen or core), this should be separately connected to ground using the green clip lead; but if
there is a relatively large unscreened conducting surface which is connected to one of its
measured terminals (e.g. an air-spaced tuning capacitor), this should be connected to the
YELLOW signal source lead to minimize noise pick-up.
5.2 Measurement of Very Small Capacitors
For best accuracy when measuring small value capacitors it is necessary to perform an O/C trim
(see section 4.3.1) at the frequency to be used for the measurement and to ensure that the
measurement leads are not moved between the trimming and the measurement.
When measuring surface-mount or leadless capacitors with the two-terminal SMD tweezers,
part no. 1EVA40120, the cam should be used to set the jaw spacing of the tweezers to the width
of the DUT when performing the O/C trim so that the residual capacitance of the tweezers is
trimmed out.
5.3 Measurement of Very Small Inductors
The meter measures the difference between the inductance of S/C trimming and the inductance
of the DUT. Stable measurement lead arrangements are essential for low inductance
measurements; the use of the four-terminal component fixture, part no. 1EV1006, is
recommended for leaded components. When using this fixture, S/C trim (see section 4.3.1) is
achieved by placing a wire across the jaws:
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