To Next Page

To Previous Page

Dry circuit testing

Many low resistance measurements are made on contact devices such as switches and relay

contacts. The purpose of these tests is to determine whether oxidation has increased the

resistance of the contacts. If the voltage across the contacts during the test is too high, the

oxidation will be punctured and render the test meaningless.

Dry circuit testing limits the voltage across the DUT to 20mV or less.

NOTE This function is only available in four-wire ohms.

Offset compensation

Offset compensation is used to compensate for voltage potential, such as thermal offsets,

across the device under test. In offset compensation, a full-scale source current is applied to the

resistance being measured during part of the measurement cycle. Figure 2-7 shows the measure-

ment cycle. During the ﬁrst half of the measurement cycle, the reduced source current is applied

and the voltage being measured is any thermal EMFs present in the circuit plus the voltage

across R

with the reduced source current:

During the second half of the measurement cycle, the full-scale source current is on, and the

total voltage measured includes the voltage drop across the resistor and any thermal EMFs. This

is deﬁned as follows:

Offset compensation is available up to 100MΩ. However, compensation is only being used

on the 10KΩ and lower ranges. An ’o’ will ﬂash on the display if offset compensation is turned

on and measuring 100KΩ and higher ranges, indicating offset compensation has no effect.

Since the thermal EMF voltage is measured during the ﬁrst and second half of the cycle, it

can be subtracted from the voltage measurement made during the ﬁrst half of the cycle. The

result is the offset-compensated voltage measurement:

Therefore,

EMF

SFS

– V=

EMF

SFS

+()V

EMF

+()–=

SFS

–()=

SFS

–

-------------------------=

2-26 Basic Measurements

Keithley 2010 User Manual

Other manuals for Keithley 2010