2400 Series SourceMeter
®
User’s Manual
Ohms Measurements
4-9
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 available as a math
function (
Section 8
, “
Math operations
”).
The presence of thermal EMFs (V
EMF
) can adversely affect low-resistance measurement
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 sub-
tracts 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
Ω
=
∆
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.
NOTE
Manual offset-compensated ohms is also available as a math (FCTN) operation.
This math function allows you to specify both source values. For details, see
Section 8
, “
Offset-compensated ohms
.”
Enabling/disabling offset-compensated ohms
Offset-compensated ohms is enabled or disabled from the OFFSET COMPENSATION
option of the CONFIG OHMS menu as follows:
1.
Press CONFIG and then
Ω
to display the ohms configuration menu.
2.
Place the cursor on OFFSET COMPENSATION, and press ENTER.
3.
Place the cursor over ON (to enable compensation) or OFF (to disable compensa-
tion), and press ENTER.
4.
Use the EXIT key to exit the menu structure.
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