Agilent Technologies Switch/Measure manual Simultaneously

4Low Frequency Multiplexer Switch Modules

34921A 40-Channel Armature Multiplexer with Low Thermal Offset

The 34921A 40- Channel Armature Multiplexer (40- Ch Arm MUX) is divided into two banks with 20 latching armature switches (channels

1- 20 and 21- 40) in each. This module also offers four additional fused relays (channels 41- 44) for making AC and DC current measurements with the internal DMM with no external shunts needed. These current channels feature “make- before- break” connections to ensure continuous current flow when switching from one current channel to another.

The current fuses are replaceable. Refer to the 34980A Service Guide for specific information about these fuses.

This module also contains nine armature Analog Bus relays (channels 911- 914, 921- 924, and 931), four on each bank that can connect the bank relays to the system Analog Buses and one that connects the current relays to the current input of the DMM. 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 104.

N O TE	ABus1 consists of three wires that are used for current and voltage
	measurements. You cannot measure current and voltage on ABus1
	simultaneously.

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 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 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 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.

102 34980A User’s Guide