User Manual

2400 Series SourceMeter
®
User’s Manual Relative and Math 8-5
This two-point measurement method is mathematically expressed as:
Offset-Compensated Ω = ∆V / ∆I where ∆V = V2 – V1 and ∆I = I2 – I1.
• V1 is the voltage measurement with the I-Source set to a specific level.
• V2 is the voltage measurement with the I-Source set to a different level
(typically zero).
• I1 is the current measurement with the I-Source set to a specific level.
• I2 is the current measurement with the I-Source set to a different level (typ-
ically zero).
You will be prompted to enter the two I-Source values, and the results is displayed
in ohms with the “Ω” symbol in the units field of the display.
Varistor alpha
This math formula is used to determine varistor alpha (α), an important parameter
that defines varistor characteristics. Alpha is defined as the logarithmic ratio of two
voltage measurement points on a non-linear V-I curve and is expressed as fol-
lows:
where:V1 is the voltage measurement at the first I-Source point.
V2 is the voltage measurement at the second I-Source point.
The log (x) function uses the absolute value of x.
When configuring this math function, you will be prompted to enter the two I-
source values. (See “Front panel math operations” later in this section.)
Voltage coefficient
High value or high-megohm resistors exhibit a change in resistance with a change
in applied voltage. This effect is known as voltage coefficient. The voltage coeffi-
cient is the percent change in resistance per unit change in applied voltage and is
defined as follows:
where:∆R = R2 - R1
∆V = V2 - V1
R1 is the resistance measurement at the first source point.
R2 is the resistance measurement at the second source point.
V1 is the voltage measurement at the first source point.
V2 is the voltage measurement at the second source point.
α
I2 I1⁄()log
V2 V1⁄()log
-----------------------------------=
Coefficient%
∆R
R2 ∆V×
-----------------------= 100%×