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112 34980A User’s Guide
4 Low Frequency Multiplexer Switch Modules
34923A 40/80-Channel Reed Multiplexer
The 34923A 40/80-Channel Reed Multiplexer (40/80-Ch Reed MUX) is
divided into two equal banks of non-latching reed switches. 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. You can connect any of the channels to the
internal DMM through ABus1 and ABus2 for voltage or resistance
measurements.
Using program commands or the mainframe front panel, you can control
each of the channel switches individually, and configure this module for
differential (2-wire or 4-wire) or single-ended (1-wire) mode. Refer to
the simplified schematics on page 114 and page 118.
If you are using an optional Agilent 349xxT terminal block to connect
your DUT to this module be sure to use the terminal block that
corresponds to your module configuration. Use the 34923T-001 terminal
block for 2-wire or 4-wire configuration. Use the 34923T-002 terminal
block for 1-wire configuration. Refer to drawings on page 117 and
page 120.
You can confirm the mode in which your module is configured by using
the SYSTem:CTYPe? <slot number> program command. This command
returns the identity of the plug-in module in the specified slot.
Two-Wire Mode
• two independent 20-channel 2- wire MUXes. This configuration
requires neither using external wiring nor connecting through the
internal Analog Buses.
• one 40-channel, 2-wire MUX. You must use external wiring or connect
through the internal Analog Buses for this configuration.
In 2-wire mode, you can close no more than 20 channels simultaneously
due to power dissipation. These 20 channels are split 10 to a bank.
However, note that Analog Bus relays count half as much as channel
relays in that total. For example, with one Analog Bus relay closed, you
can close up to a maximum of 19 channel relays. If you try to close more
than the allowed number of channels, you will receive an error message.
NOTE
Whenever you change from 2- or 4-wire mode to 1-wire mode, or the
reverse, you must cycle power on the 34980A for the configuration
to take effect.