3.10
General 2-Terminal Measurement
For general voltage-stimulus measurement, use the 2-Terminal setting.
This measurement operates in
voltage mode
, where the voltage is adjusted and the current measured, and
current mode
, where the current is adjusted and the device voltage measured.
3.10.1
2-Terminal Measurement, Voltage Mode
This measurement is capable of sweeping from a negative to positive voltage while plotting the device current, so
that all quadrants are visible.
The total range of voltage is 30 volts, that is:
Stop voltage
−
Start Voltage
<
= 30
V
For example, the range could be set as
−
15
V to
+15
V, or
−
5
V to
+25
V.
(a) Control Settings
(b) Result
Figure 11: 2-Terminal Measurement, Voltage Mode
A typical measurement is shown in figure 11. The device under test is an arrangement of diodes: two of
1N4001 diodes in series, in parallel with a further three 1N4001 diodes in series. The result is a device with
approximately 1.4 volt threshold in one direction and a 2.1 volt threshold in the other direction.
This test is
voltage driven
. Testing a constant voltage device such as a diode or zener can easily result in a
measured current that exceeds the maximum current setting. In that case, a warning window will pop up. Reduce
the test voltage and then try the measurement again. For example, in the case of the diode array, a starting voltage
of -3 volts resulted in excessive current. The starting voltage was reduced to -1.8 volts, which allowed the analysis
to run to completion.
For a device with a very constant voltage drop - such as a zener with 6 volt or greater breakdown - it may be
necessary to use the
current mode
configuration. That configuration forces and controls the device current while
measuring the device voltage so there is less likelyhood of an over-current being triggered.
The connections are different for 2-terminal voltage and current mode. The instrument warns of this when
switching from voltage and current modes.
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