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5-24 Ratio and Delta
To check measurement repeatability, you may wish to perform more than one Delta
measurement at each current amplitude. In Figure 5-11 , the SourceMeter outputs five bipolar
steps for each amplitude. The result will be five Delta measurements for each amplitude. When
configuring the custom sweep, ±10µA would be assigned to the first 10 points of the sweep,
±20µA would be assigned to the next 10 points, and ±50µA would be assigned to the last 10
points. Therefore, the custom sweep in
Figure 5-11 would be made up of 30 points (P0 through
P29).
The procedure to use the SourceMeter and Model 2182 to perform Delta measurements is
provided in “ Delta measurement procedure using a SourceMeter .” That procedure (presented
earlier in this section under “ Delta ”) uses a 2-point custom sweep and will have to be modified
for this application as follows:
• This application uses two Model 2182s. Therefore, both nanovoltmeters must be
configured exactly the same.
• In Step 3 of the procedure, change the Trigger Count to equal the number of points in the
custom sweep. For example, if using the 30-point custom sweep in
Figure 5-11 , set the
Trigger Count to 30.
• In Step 5, assign current values to the sweep points. For the example 30-point sweep, the
current values for points P0 through P29 are shown in
Figure 5-11 .
• In Step 7, enable line synchronization on both Model 2182s. To access control, press
SHIFT and then LSYNC.
NOTE Optimum synchronization among all instruments is achieved when Model 2182 line
synchronization is enabled, and autozero is disabled. Autozero cannot be disabled
from the front panel of the Model 2182. When controlling this application over the
bus, use the following commands for the Model 2182s:
:SYSTem:LSYNc:STATe ON Enable 2182 Line Synchronization
:SYSTem:AZERo:STATe OFF Disable 2182 Autozero
Autozero should only be disabled for short periods of time. After performing a sweep,
re-enable Autozero. For details on Autozero, see
Section 2 .
• In Step 9, set the buffers of both Model 2182s to store the Delta readings. If performing
a 30-point sweep, set both buffers to store 30 Delta readings.
Log sweep — If your test requires currents that span two or more decades, you can configure
the SourceMeter to output a log sweep. The 30-point sweep in Figure 5-11 is confined to the
10µA-100uA decade. If, for example, you want to expand the sweep to span three current
decades, the next 30 sweep points would be used for the 100µA, 200µA, and the 500µA
amplitudes. The last 30 sweep points would be used for the 1mA, 2mA, and 5mA amplitudes.
The I-V data points can then be graphed using a logarithmic/linear scale.