Keysight / Agilent / HP 34921A 40-Channel Armature Multiplexer with Low Thermal Offset

The Keysight 34921A is a 40-channel armature multiplexer module that routes analog signals with low thermal offset into the Keysight 34980A Multifunction Switch/Measure Unit. Built on latching armature relay technology, it delivers fast channel switching at up to 100 channels/second and accommodates both 2-wire and 4-wire measurement configurations. The module includes four additional fused current channels that route up to 1 A directly to the internal DMM, eliminating external shunt resistors for AC and DC current analysis.

– Technical Specifications

• Channel count: 40 × 2-wire channels (44 total with integrated current measurement channels)
• Switch voltage: Up to 300 V
• Switch current: 1 A
• Carry current: 2 A
• Scanning rate: Up to 100 channels/second
• Current measurement channels: 4 fused channels routing up to 1 A to internal DMM
• Relay type: Latching armature relays with relay counter
• Connectors: Standard 50-pin D-sub
• Terminal block: Optional 34921T with built-in thermocouple reference junction; supports up to 20 AWG (fewer than 100 connections) or 24 AWG (100+ connections)

– Key Features

• Low thermal offset characteristics for precision temperature and sensitive signal measurements
• Built-in thermocouple reference junction on terminal block for accurate temperature acquisition
• N:1 configuration support allows multiple channels to close simultaneously within each bank
• Expandable architecture: stack multiple MUX modules via analog buses to reach up to 560 × 2-wire or 640 × 1-wire channels per 34980A mainframe
• Mixed 2-wire and 4-wire operation within single module

– Typical Applications

• Multi-channel data acquisition and signal scanning
• Temperature measurement systems using thermocouples
• General-purpose signal routing and multiplexing
• AC/DC current and voltage measurement arrays

– Compatibility & Integration

The 34921A plugs directly into the 34980A mainframe and connects via analog buses to the internal DMM. SCPI programming enables full configuration and measurement control. External connections use standard 50-pin D-sub connectors paired with discrete terminal blocks or mass interconnect solutions.