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 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.

Enabling/disabling offset-compensated ohms

Offset-compensated ohms is enabled or disabled from the OFFSET COMPENSA-

TION option of the CONFIG OHMS menu.