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Model 2790 SourceMeter
For front panel inputs, a banana plug generates a few microvolts. A clean copper conduc-
tor such as #10 bus wire is ideal for this application. For switching modules, use #20 AWG
copper wire to make connections. The leads to the Model 2790 may be shielded or
unshielded, as necessary. Refer to
Widely varying temperatures within the circuit can also create thermal EMFs. Therefore,
maintain constant temperatures to minimize these thermal EMFs. A shielded enclosure
around the circuit under test also helps by minimizing air currents.
The REL control can be used to null out constant offset voltages.
AC voltage offset
The Model 2790, at 5 digits resolution, will typically display 100 counts of offset on AC
volts with the input shorted. This offset is caused by the offset of the TRMS converter.
This offset will not affect reading accuracy and should not be zeroed out using the REL
feature. The following equation expresses how this offset (V
input (V
Displayed reading
Example: Range = 1VAC
Displayed reading
Displayed reading
The offset is seen as the last digit, which is not displayed. Therefore, the offset is negligible.
If REL were used to zero the display, the 100 counts of offset would be subtracted from V
resulting in an error of 100 counts in the displayed reading.
Current measurements (DCI and ACI)
The Model 2790 can make DCI measurements from 10nA to 3A and ACI measurements
from 1µA to 3A RMS.
klqb
®
Switch System Reference Manual
):
IN
(
)
2
=
V
IN
Offset
= 100 counts (1.0mV)
Input
= 100mV RMS
(
=
100mV
=
0.01V
= 0.100005 V
See the previous discussion about crest factor in
page
3-7.
"Shielding"
in
Appendix
(
)
2
+
V
OFFSET
)
(
)
2
2
+
1.0mV
6 –
(
×
)
+
1 10
V
D.
) is added to the signal
OFFSET
"Memory pattern scanning,"
3-13
,
IN
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