Offset-Compensated Ohm Calculations; Power Calculations - Keithley 2461 Reference Manual

Model 2461 Interactive SourceMeter® Instrument Reference Manual

Offset-compensated ohm calculations

The presence of thermoelectric EMFs (V
accuracy. To overcome these offset voltages, you can use offset-compensated ohms if you are
making 4-wire resistance measurements on ranges up to 100 kΩ.
Instrument operations, including offset-compensated ohms, are performed on the input signal in a
sequential manner.
For a normal resistance measurement, the Model 2461 sources a current (I) and measures the
voltage (V). The resistance (R) is then calculated as (R=V/I) and the reading is displayed.
For offset-compensated ohms, two measurements are performed: one normal resistance
measurement, and one using the lowest current source setting.
The offset-compensated ohms reading is then calculated as follows:
V is the voltage measurement with the current source at its normal level.
1
V is the voltage measurement using the lowest current source setting.
2
I is the current measurement with the source set to a specific level.
1
I is the current measurement with the source set to zero.
2
This 2-point measurement process and reading calculation eliminates the resistance contributed by
the presence of V
When the source is turned on, the output cycles between the programmed value and zero (0 A or
0 V) to derive the offset-compensated ohms measurement.

Power calculations

Power readings are calculated from the measured current and voltage as follows:
Where:
P is the calculated power
V is the measured voltage
I is the measured current
2461-901-01 A/November 2015
EMF
.
EMF
Section 4: Source-measure considerations
) can adversely affect low-resistance measurement
4-21