Offset-compensated ohms
The presence of thermoelectric EMFs (V
EMF
) can adversely affect low-resistance measurement
accuracy. To overcome these unwanted offset voltages, you can use offset-compensated ohms.
Offset-compensated ohms measurements can be performed on the 1 Ω, 10 Ω, 100 Ω, 1 kΩ, and
10 kΩ ranges for the four-wire ohm measure function. It cannot be done on the two-wire ohm
measure function.
The various instrument operations, including offset-compensated ohms, are performed on the input
signal in a sequential manner.
For a normal resistance measurement, the Series 3700A 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.
Enable or disable offset-compensated ohms
Offset-compensated ohms is an attribute that can be set for the 4-wire ohms measure function. To
enable or disable it from the front panel:
Figure 70: Enabling offset-compensated ohms
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