132 34980A User’s Guide
4 Low Frequency Multiplexer Switch Modules
34922A 70-Channel Armature Multiplexer
The high- density 34922A 70- Channel Armature Multiplexer (70- Ch Arm
MUX) is divided into two banks with 35 latching armature switches
(channels 1- 35 and 36- 70) in each. This module also contains eight
armature Analog Bus relays (channels 911- 914 and 921- 924), four on
each bank that can connect the bank relays to the system Analog Buses.
Through ABus1 and ABus2 you can connect any of the channels to the
internal DMM for voltage or resistance measurements. Refer to the
simplified schematic on page 133.
Using program commands or the mainframe front panel, you can control
each of the channel switches individually, and thus configure this module
in these modes:
• two independent 35- channel 2- wire MUXes. This configuration
requires neither using external wiring nor connecting through the
internal Analog Buses.
• one 35- channel 4- wire MUX. This configuration requires neither using
external wiring nor connecting through the internal Analog Buses.
For 4- wire resistance measurements, the instrument automatically
pairs channel n on Bank 1 with channel n+35 (Bank 2) to provide the
source and sense connections. Four- wire controls occur only when
doing 4- wire measurement operations through the internal DMM, such
as MEASure:FRESistance? or scanning a channel previously
configured as 4- wire.
• one 70- channel 2- wire MUX. You must use external wiring or connect
through the internal Analog Bus relays for this configuration.
For example, closing Analog Bus channels 913 and 923 connects
Bank 1 and Bank 2 through ABus3. Or, externally you can connect
COM1 to COM2 to create this configuration.
This module has capability to scan as many as 100 channels/second
using the internal DMM. With the automatic “break- before- make”
connection operation, you are assured that no two signals are connect to
each other during a scan. When using the module in a non- scanning
mode, you can close as many channels as you wish.
This module is interlock protected, which means whenever the D- sub
connector end of the modules is exposed, the Analog Bus relays
automatically open and disconnect from the Analog Bus. For more
information, refer to page 120 and page 134.
When the power is off, all channel relays maintain state, and the Analog
Bus relays open.
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