5-28 Model 2790 SourceMeter
®
Switch System User’s Manual
I-source readback
This readback circuit measures the actual current that is flowing in the test circuit through
the DUT (bridgewire or shunt bar). It is used to verify that the programmed current level
of the I-source is being used in the tests.
NOTE I-source readback is only accurate to 1%. It is only intended as a verification
and not a high accuracy measurement.
The I-source readback circuits are shown in Figure 5-13. Figure 5-13A shows how to
measure the current for the bridgewire test, while Figure 5-13B shows how to measure
the current for the shunt bar test.
In both circuits, the Model 2790 DMM measures the voltage across the 1Ω resistor
(V
MEAS
). Readback current (I
RB
) is then calculated using Ohms Law (I
RB
= V
MEAS
/ 1Ω).
Make sure to open all channels before closing the appropriate channels for I-source read-
back. When finished, make sure to again open all channels.
The mX+b calculation can be used to read the I-source current in amps by setting “m” to
1.0 and “b” to 0.0:
Front panel operation: Press SHIFT > press MATH > select mX+B > set M to +1.0 > set
B to 0.0 > select UNITS: A
Remote programming: CALC:FORM MXB
CALC:KMAT:MMF 1.0
CALC:KMAT:MBF 0.0
CALC:KMAT:MUN ‘A’
CALC:STAT ON
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