User Manual

4-8 Ohms Measurements 2400 Series SourceMeter
®
User’s Manual
Offset-compensated ohms
NOTE For the Model 2430, the following offset-compensated ohms method is
not valid in the Pulse Mode. However, offset compensated ohms is avail
-
able as a math function (Section 8, “Math operations”).
The presence of thermal EMFs (V
EMF
) can adversely affect low-resistance mea-
surement accuracy. To overcome these unwanted offset voltages, use the offset-
compensated ohms measurement method.
In general, this method measures resistance (V/I) at a specific source level and
then subtracts a resistance measurement made with the source set to zero. With
the source set to zero, the source level is V
EMF
. Thus, the resistance contributed
by the presence of V
EMF
is eliminated.
This two-point measurement method is mathematically expressed as:
Offset-Compensated = V / I where V = V2 – V1 and I = I2 – I1.
V1 is the voltage measurement with the source set to a specific level.
V2 is the voltage measurement with the source set to zero.
I1 is the current measurement with the source set to a specific level.
I2 is the current measurement with the source set to zero.
For auto ohms, the SourceMeter will select the appropriate current source level
and voltage measurement range. For manual ohms, first select the appropriate
source (V or I) value while the output is off. When the source is turned on, the
output will cycle between the programmed value and zero (0A or 0V) to derive the
offset-compensated ohms measurement.
Enabling/disabling offset-compensated ohms
Offset-compensated ohms is enabled or disabled from the OFFSET COMPENSA-
TION option of the CONFIG OHMS menu.