Keithley 6430 Instruction Manual page 338

17-28 SCPI Command Reference
NOTE The log and ln operations are performed on the absolute value of the specified num-
ber. For example, log (100) = 2 and log (-100) = 2.
Expressions are evaluated according to the following precedence rules:
1. Enclosed by parentheses
2. Unary operators (+ and -)
3. ^ (exponentiation)
4. * (multiplication) and / (division)
5. + (addition) and - (subtraction)
6. Left to right.
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 cur-
rent measurement. Conversely, if configured to Source I Measure V, the cur-
rent 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 volt-
age measurement (not the programmed V-Source value). Conversely, if con-
figured 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 measured
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)
After a calculation is configured and enabled, the results are displayed when
source-measure operations are performed. See :STATe. Use the :data? com-
mand to send the results to the computer.
Vectored math
By incorporating vectors, you select which readings to use for the math cal-
culation. After all programmed source-measure operations are completed,
the math calculation(s) are performed using readings indicated by the speci-
fied 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 readings.
Since the SourceMeter is programmed to perform 10 source-measure opera-
Calculate power using voltage measurement
and I-Source value.