6-18 Keysight B2900 User’s Guide, Edition 5Function DetailsMath ExpressionThis function is effective for reducing measurement errors in low resistancemeasurements.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 avaristor’s non-linear I-V characteristics curve, and CURR[c][1] and VOLT[c][1] arethe data at the another point.VOLTCOEF Calculates voltage coefficient using the following formula.VOLTCOEF = (RES[c][1]-RES[c][0]) / (RES[c][1] * (VOLT[c][1]-VOLT[c][0]))* 100 %where, RES[c][0] and RES[c][1] are the resistance measurement data at the first andsecond measurement points, respectively, and VOLT[c][0] and VOLT[c][1] are thevoltage measurement data at the first and second measurement points, respectively.The voltage coefficient is known as the ratio of the fractional change for a resistorwhose resistance varies with voltage.Resources Used in the ExpressionsThe following resources can be used in user-defined math expressions.• Reserved variablesThe variables listed in Table 6-2 are reserved for reading the channel output ormeasurement data.Scalar variable is used for spot measurement data.Vector (array) variable is used for sweep measurement data.• Math operatorsThe following operators are available.• Arithmetic operators: +, -, *, /, ^, see Table 6-3• Elementary functions: ln, log, sin, cos, tan, expThe functions log and ln perform the operation after calculating the absolutevalue. So if a negative value is specified, they do not cause an error but calculateas a positive value. For example, log(-10) results in log(10)=1.
