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Keysight Technologies
Achieve Accurate Two Wire
Resistance Measurements with the
Keysight 34923A & 34924A Multiplexers
Application Note
Introduction
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.
Abstract
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.
02
Proposed Solution
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 extraneous resistances in the path are the chan-
channels by half. With the traditional 2-wire resistance nel relays, the terminal block trace resistance, and the
measurement, the DMM measurement (MEAS) and sense lead resistance to the DUT. The channel relays are reed
(SENS) lines are connected in the DMM, as shown in relays with very low and repeatable contact resistance.
Figure 4 on the previous page. The backplane relays, the The backplane relays, the 100 ohm current limiting resistor
current limiting resistor and the backplane trace resis- and the backplane and DMM input relay resistances are
tance are included in the measurement path. The resit- all removed because a 4 wire resistance measurement is
stance these obstacles induce can be removed by making being made through these components of the path.
Figure 4. 34923A 40 channel reed multiplexer.
03
The trade-off is speed. This is because low level open and
CONF:FRES configures the DMM for 4-wire
close commands must be used rather than the traditional
resistance independent of the channels
scan commands. With traditional 2-wire resistance scanning
being used
with the 34923A/24A, the maximum speed is 530 ch/sec
across two banks using the fastest settings - 60Hz power line ROUT:OPEN (@1921,1922)
frequency - using LAN sockets. With this close-measure- ROUT:CLOS (@1911,1912)
open method, the speed is reduced to 93.6 ch/sec. With the
default settings including autorange and autozero on, NPLC For i=1 to 20,
1, default channel delay and display on, the speed is 27.3 A = 1000 + i
ch/sec with traditional scanning and is 5.1 ch/sec with the
pseudo 4-wire close-measure-open method. ROUT:CLOS (@,A,)
The 34980A command sequence for this measurement for READ?
the 40 channel 34923A module can easily be extended to the
34924A by simply increasing the loop count, as indicated at Read the DMM 4-wire resistance value
right. for channel 1000 + i.
Scanning shorted channels with this method will typically ROUT:OPEN (@,A,)
show < 1 ohm resistance on each channel. This and the DUT
lead resistance can usually be measured and then removed End loop
from the result using the built-in y = mx + b scaling function ROUT:OPEN (@1911,1912)
of the 34980A, thus providing accurate 2-wire resistance
ROUT:CLOS (@1921,1922)
measurements approaching the accuracy of the 4-wire resis-
tance technique. For I = 1 to 20,
A = 1020 + i
Conclusion
ROUT:CLOS (@,A,)
This method achieves a much more accurate 2-wire resis- READ?
tance measurement scanning when using either the 34923A
or the 34924A reed relay multiplexer modules. ROUT:OPEN (@,A,)
End loop
Ordering information
Model Description
Mainframe - holds up to 8 plug-in modules
34980A Multifunction switch/measure mainframe Comes standard with "DMM" option, BenchLink data logger software,
user guide on CD-ROM, power cord and quickstart package.
34832A BenchLink data logger pro software Upgrade your complimentary software package to add limit checking and
decision making for more complex applications.
Multiplexer modules Module connectors Optional terminal blocks, cables, connector kits
34923A 40/80 channel reed multiplexer 2- 50 pin Dsub, Male 3492xT Terminal block with screw connectors
Y1135A - 1.5 m 50-pin M/F Dsub cable
Y1136A - 3 m 50-pin M/F Dsub cable
Y1139A - 50-pin female solder cup connector kit
34924A 70 channel reed multiplexer 2- 78 pin Dsub, Male 3492xT Terminal block, option 001 for solder con-
nections, option 002 for screw connectors
Y1137A - 1.5 m 78-pin M/F Dsub cable
Y1138A - 3 m 78-pin M/F Dsub cable
Y1140A - 78-pin female solder cup connector kit
04
05 | Keysight | Achieve Accurate Two Wire Resistance Measurements with the Keysight 34923A & 34924A Multiplexers - Application Note
Software Information
For more information on Keysight
Technologies' products, applications or
Supported Systems Microsoft Windows 98 SE/NT/2000/XP services, please contact your local Keysight
Software drivers IVI-C and IVI-COM for Windows NT/2000/XP Labview office. The complete list is available at:
Compatible programming Keysight VEE Pro, Keysight T&M toolkit (requires Visual Studio.NET) www.keysight.com/find/contactus
tools and environments National Instruments Test Stand, Measurement Studio, LabWindows/
CVI, Labview, Switch Executive Americas
Microsoft Visual Studio.NET, C/C++, Visual Basic 6 Canada (877) 894 4414
Brazil 55 11 3351 7010
Keysight IO Libraries Version 14 or greater
Mexico 001 800 254 2440
United States (800) 829 4444
Keysight BenchLink data logger software
Asia Paciic
Operating system Windows 2000 SP4, XP SP2 Australia 1 800 629 485
Controller Recommended: Pentium