Agilent Technologies L4400 User Manual
Page 117
L4421A 40-Channel Armature Multiplexer
4
L4400 User’s Guide
105
ABus1 and ABus2 you can connect any of the channels to a DMM for
voltage or resistance measurements. Refer to the simplified schematic on
ABus1 consists of three wires that are used for current and
voltage measurements. You cannot measure current and voltage
on ABus1 simultaneously.
You can control each of the channel switches individually, and thus
configure the instrument in these modes:
• two independent 20- channel 2- wire MUXes. This configuration
requires neither using external wiring nor connecting through the
internal Analog Buses.
• one 20- 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+20 (Bank 2) to provide the
source and sense connections. Four- wire controls require execution of
the ROUTe:CHANnel:FWIRe command or scanning a channel previously
configured as 4- wire.
• one 40- 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.
Low thermal offset voltage makes the L4421A ideal for low- level signal
switching. The 34921T optional terminal block provides a built- in
thermocouple reference junction that helps minimize errors due to
thermal offset when you measure thermocouples.
The L4421A has the capability to scan as many as 100 channels/second
using modern DMMs. With the automatic “break- before- make” connection
operation, you are assured that no two signals are connected 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 safety interlock protected, which means whenever the
D- sub connector end of the instrument is exposed, the analog bus relays
automatically open and disconnect from the analog bus. For more
information, refer to
and
.
When power is off, all channel relays maintain state, and the analog bus
relays open.
N O T E