Agilent Technologies Switch/Measure manual Four-Wire Mode, One-Wire Mode, Schematics on page 114

Low Frequency Multiplexer Switch Modules 4

Four-Wire Mode

This 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-Wire Mode

•two independent 40- channel 1- wire MUXes. This configuration requires neither using external wiring nor connecting through the internal Analog Buses.

•one 80- channel 1- wire MUX. You must use external wiring or connect through the internal Analog Bus for this configuration.

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.

In 1- wire mode, you can close no more than 40 channels simultaneously due to power dissipation. These channels are split 20 to a bank. For example, with one Analog Bus relay closed you can close up to a maximum of 39 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 connect 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. For more information, refer to page 96, and page 116 or page 119.

CAUTION	Because user-attached reactive loads and backplane parasitic
	capacitance may result in high in-rush currents, 100 Ω in-rush
	resistors protect the reed relays from damage and performance
	degradation. Therefore, you must consider these resistors when
	you are designing a measurement. Refer to the simplified
	schematics on page 114 and page 118.

34980A User’s Guide 113