Keithley 2461 Reference Manual

Model 2461
Interactive SourceMeter® Instrument Reference Manual Section 4: Source-
measure considerations
2461-901-01 A/November 2015 4-21
Offset-compensated ohm calculations
The presence of thermoelectric EMFs (V
EMF
) can adversely affect low-resistance measurement
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
1
is the voltage measurement with the current source at its normal level.
V
2
is the voltage measurement using the lowest current source setting.
I
1
is the current measurement with the source set to a specific level.
I
2
is the current measurement with the source set to zero.
This 2-point measurement process and reading calculation eliminates the resistance contributed by
the presence of V
EMF
.
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

Keithley 2461 Specifications

General

Maximum Current	7 A
Power	100 W
Resolution	6.5 digits
Source Measure Unit (SMU)	Yes
DC Voltage	100 V
Maximum Voltage	100 V
Display	5-inch capacitive touchscreen
Connectivity	USB, GPIB
Software	TSP
DC Current	7 A
Current Source Range	0 to 7 A
Voltage Measurement Range	100 mV to 100 V
Current Measurement Range	10 nA to 7 A
Voltage Measurement Resolution	100 nV