2400 Series SourceMeter
®
User’s Manual SCPI Command Reference 18-31
The readings used for the calculation depend on how the SourceMeter is
configured. If configured to Source V Measure I, the voltage reading for
the calculation will be the source value, and the current reading will be
the current measurement. Conversely, if configured to Source I Measure
V, the current reading will be the source value, and the voltage reading
will be the voltage measurement.
Measure readings take priority over source readings. Thus, if configured
to Source V Measure V, the voltage reading for the calculation will be
the voltage measurement (not the programmed V-Source value). Con-
versely, if configured to Source I Measure I, the current reading for the
calculation will be the current measurement.
The result of a calculation using a reading that is not sourced or mea-
sured will be the invalid NAN (not a number) value of +9.91e37. For
example, using a current reading in a calculation for Source V Measure
V will cause a NAN result.
Example using Source I Measure V configuration:
:calc:math (volt * curr) Calculate power using voltage measurement
and I-Source value.
After a calculation is configured and enabled, the results are displayed
when source-measure operations are performed. (See “:STATe <b>,”
page 18-33.) Use the :data? command to send the results to the
computer.
Vectored math
By incorporating vectors, you select which readings to use for the math
calculation. After all programmed source-measure operations are com-
pleted, the math calculation(s) are performed using readings indicated
by the specified vectors.
Vector numbers are enclosed in brackets ([]), and start at 0. Thus, vector
0 is the first reading in the array, vector 1 is the second reading in the
array, and so on. The largest vector number in the expression defines the
vector array size.
For example, assume the SourceMeter is programmed to perform 10
source-measure operations, and the following vectored math calculation
is used:
(volt[3] - volt[9])
The above expression defines a vector array that is made up of 10 read-
ings. Since the SourceMeter is programmed to perform 10 source-
measure operations, the calculation will yield one result every 10 SDM
cycles. The fourth voltage reading (vector 3) and the 10th voltage read-
ing (vector 9) are used for the calculation.
Now assume that the SourceMeter is configured to perform 20 source-
measure operations. Since the vector size is still 10, two 10-reading
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