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128 34980A User’s Guide
4 Low Frequency Multiplexer Switch Modules
Four-Wire
• one 20-channel 4- wire MUX. This configuration requires using neither
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+20 (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-Wire
• two independent 40-channel 1- wire MUXes. This configuration
requires neither using external wiring nor connecting through the
Analog Bus relays.
• one 80-channel 1-wire MUX. You must use external wiring or connect
through the Analog Bus relays for this configuration.
Interlock Protection
This module is interlock protected, which means whenever the D-sub
connector end of the modules is exposed, the Analog Bus relays
immediately open and disconnect from the Analog Buses. For more
information, refer to page 96.
Overvoltage Protection
This module also features high voltage detection (< 100 V) and current
limiting circuitry to protect the FET relays. This circuitry senses current
flows from input overvoltages. These overvoltages may come from either
the MUX input or from the Analog Buses. In addition, each channel is
also protected from input overvoltages with a resistor.
When overvoltage is detected, all relays (Analog Bus and FET) are
opened. While in the overvoltage state, any attempts to close any Analog
Bus or FET switch, results in an error status response from the module.
Once in the overvoltage state, you must restore normal module operation
with one of these actions:
• using the SYSTem:CPON <slot> command. This affects only the
module specified.
NOTE
Because all bank relays supply only HI signals, you can apply a
LOW signal through COM1 L or COM2 L when you are making
2-wire resistance measurements in 1-wire mode.