File name 5991-2332EN English _ 2013-07-24 _ PDF 424 KB c20141007 .pdf
Achieve Accurate Two Wire
Resistance Measurements with the
Keysight 34923A & 34924A Multiplexers
This Application Note outlines a method for minimizing the channel path resistance and increasing the accuracy for 2-wire
resistance measurements with the 34923A and 34924A reed relay multiplexer modules for the 34980A Data Acquisition
unit. This method has the additional beneit of allowing the use of all channels for resistance measurements as in the
traditional two wire resistance measurement technique.
The 34923A and 34924A multiplexers have 100 ohm current limiting resistors, as well as backplane relays, PC board trace
and internal connector resistances that contribute an offset plus some additional errors to 2-wire resistance measure-
ments. The following is a proposed solution to address this issue.
Four wire resistance measurements provide the highest
accuracy by eliminating all internal path resistance and
DUT lead resistance from the result. Typically, this requires
two channels for each measurement. We offer an alter-
native technique, detailed in this application note, which
eliminates the internal path resistance from PC board
traces and additional relays in the measurement path.
Figure 1. 34980A Multifunction Switch/Measure System
Figure 2. 34923A 40/80 Channel Reed Multiplexer for the 34980A.
Figure 3. 34924A 70 Channel Reed Multiplexer for the 34980A.
The 40 2-wire channel 34923A topology (Figure 4 below), a 4-wire measurement up to the point where analog bus-
shows 100 ohm (+/- 5%) current limiting resistors which ses 1 and 2 join, just before the channel relays, shown by
are in the measurement path to the 34980A Multifunc- the red circles in Figure 4. This is done by coniguring the
tion Switch/Measure built-in DMM for 2-wire resistance DMM for 4-wire resistance with no channel list and closing
measurements. The contact resistances of the backplane backplane relays 911 and 912. Instead of using the scan
relays as well as the PC board and connectors (not shown) commands, we recommend using the low level open and
are also in the path. The same applies to the 70 2-wire close commands to deine the coniguration and make the
channel 34924A. The traditional method for eliminating measurement. Backplane relays 911 and 912 are closed for
these resistances is by using a 4-wire resistance measure- scanning bank 1 channels and backplane relays 921 and
ment. That method requires two channels per measure- 922 are closed for scanning bank 2 channels. As a result,
ment and reduces the total number of measurement the only