The high-density 34924A 70-Channel Reed Multiplexer (70-Ch Reed MUX) is divided into two banks with 35 non-latching reed switches (channels 1-35 and 36-70) in each. 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. Through ABus1 and ABus2 you can connect any of the channels to the system DMM for voltage or resistance measurements.

Using program commands or the mainframe front panel, you can control each of the channel switches individually, and thus configure the 34924A in any of these modes:

• Two independent 35-channel 2-wire MUXes. This configuration requires neither using external wiring nor connecting through the internal Analog Buses.
• One 70-channel, 2-wire MUX. You must use external wiring or connect through the internal Analog Buses for this configuration.
• One 35-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 (source) with channel n+35 on Bank 2 (sense) to provide these connections. Four-wire controls occur only when doing 4-wire measurement operations through the internal DMM, or scanning a channel previously configured as 4-wire.

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.

In all modes, this module has capability to scan as many as 500 channels/second using the internal DMM. With the automatic “break-before-make” connection operation, you are assured that no two signals are connected to each other during a scan.

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 Bus.

Lifetime of relays is severely degraded as current or voltage goes up. If higher voltage is being switched, limits on source current are recommended.

When the power is off, all channel and Analog Bus relays open.

Terminal blocks

Two terminal blocks are available to facilitate wiring connections to the 34924A module:

• 34924T-001 (Option 001) - Terminal block with solder connectors
• 34924T-002 (Option 002) - Terminal block with screw connectors

For additional information on the 34924A, please see the document linked here beginning on page 25.

The chart below provides a brief overview of multiplexer modules for the 34980A.