Agilent/Keysight 44421A

The Agilent/Keysight 44421A is a 20-channel guarded relay multiplexer assembly designed to switch analog signals from multiple transducers and sensors to the Keysight/Agilent 3497A Data Acquisition/Switch Unit or other connected instruments. Built with low thermal offset characteristics, this module excels in precision low-level measurement applications where signal integrity is critical. The assembly organizes 20 analog channels into two groups of 10, with each channel equipped with High, Low, and Guard relay lines for flexible signal routing and four-terminal resistance measurements.

Technical Specifications

• Channel Count: 20 analog signal channels organized in two decade groups


• Relay Configuration: Three relays per channel (High, Low, Guard lines)


• Switching Modes: Single channel closure per decade, random relay closure, incremental operation between programmable limits, dual-channel closure per assembly


• Input Impedance (Non-isolated): Minimum 19.5 kΩ


• Thermal Characteristics: Low thermal offset for precision low-level measurements


• Channel Configuration: Each channel supports optional filter or current shunt installation


• Reed Relay Switching: Enables fast, reliable analog signal multiplexing

Key Features

• Four-terminal resistance measurement capability when two channels (one per decade) are closed simultaneously


• Modular plug-in design for the 3497A mainframe


• Expansion capability to 900 total analog channels using multiple assemblies with HP 3498A Extender Chassis


• Guarded signal paths minimize crosstalk and maintain measurement accuracy across low-level signals

Typical Applications

• Strain gauge and bridge circuit measurement


• Resistance Temperature Detector (RTD) scanning


• Pressure sensor multiplexing


• Load cell signal acquisition


• Precision transducer data logging

Compatibility & Integration The 44421A integrates directly into the Keysight/Agilent 3497A Data Acquisition/Switch Unit. Systems can be expanded using the HP 3498A Extender Chassis to accommodate large-scale multi-channel measurement requirements. The module supports DC/AC voltage, 2-wire and 4-wire resistance, frequency, period, DC/AC current, and temperature measurements through compatible instrumentation.