226 Keysight B2980B User’s Guide, Edition 1
Function Details
Math Expression
VARALPHA Calculates varistor alpha using the following formula.
VARALPHA = log(CURR[c][1] / CURR[c][0]) / log(VOLT[c][1] / VOLT[c][0])
where, CURR[c][0] and VOLT[c][0] are the measurement data at a point on a
varistor’s non-linear I-V characteristics curve, and CURR[c][1] and VOLT[c][1] are
the data at the another point.
Resources Used in the Expressions
The following resources can be used in user-defined math expressions.
• Reserved variables
The variables listed in Table 5-3 are reserved for reading the measurement
data of voltage source output.
Scalar variable is used for spot measurement data.
Vector (array) variable is used for sweep measurement data.
• Math operators
The following operators are available.
• Arithmetic operators: , , *, /, ^, see Table 5-4.
• Elementary functions: ln, log, sin, cos, tan, exp
The functions log and ln perform the operation after calculating the absolute
value. So if a negative value is specified, they do not cause an error but
calculate as a positive value. For example, log(10) results in log(10)=1.
• Math variables
You can use maximum 32 variables in the math expressions. To use the math
variables, see “Math Variable Dialog Box” on page 178.
The math variables listed in Table 5-5 have already been defined for the
predefined math expressions in B2980. The predefined math variables are not
cleared by the power off and on operations. At power-on or resetting (by the
*RST command or the device clear), 0 is set for all predefined math variables.
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