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Matrix Switch Modules 5
34980A User’s Guide 153
34933A Dual/Quad 4x8 Reed Matrix
Using program commands or the front panel of the 34980A, you can
configure the 34933A dual/quad 4x8 reed matrix module for differential
(2-wire) mode or single-ended (1-wire) mode.
The 34933A module contains 100
Ω in- rush resistors that are used to protect
the reed relays from reactive loads. If you have applications where in-rush
resistors interfere with measurements, connections are provided on the
terminal blocks for you to bypass the in-rush resistors that are located on the
columns. See the simplified schematics on page 155 and page 159.
However, if you choose to bypass the in-rush resistors, the life of the
reed relays that you bypass may be degraded.
Two-Wire Mode
To physically configure the module for 2-wire mode, use the 34933T-001
terminal block, or a compatible standard or custom cable. If using a standard
or custom cable, make sure you connect interlock pins 17 and 33 on the
Matrix 2 D-sub connector. Refer to the pinout drawing and table on
page 156.
In 2-wire mode, the 34933A module contains two matrices, each with 32
2-wire crosspoint non- latching reed relays organized in a 4-row by 8-column
configuration. Every row and column are made up of two wires each, a high
(H) and a low (L). Each crosspoint relay has a unique channel number
representing the row and column that intersect to create the crosspoint. For
example, channel 308 represents the crosspoint connection between row 3
and column 08 (all columns consisting of two digits; in this case the digits are
08). See the simplified schematic on page 155.
You can connect any combination of inputs and outputs at the same time.
However, only Matrix 2 in 2- wire mode of this module connects to the Analog
Buses. By closing channels 921 and 922 you can connect rows 5 and 6
respectively to the internal DMM of the 34980A mainframe for voltage and
resistance measurements.
In 2-wire mode, you can close no more than 20 channels simultaneously due
to power dissipation. 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.