SRS SIM925 Four-Wire Multiplexer

The SRS SIM925 Octal Four-Wire Multiplexer is an eight-channel switching module designed for low-level signal applications requiring precise Kelvin-lead measurements. It routes signals across eight input channels with four-wire per-channel architecture, accommodating optional sense-lead buffering or functioning as a standard 4-pole/8-throw switch. The module integrates into the SIM900 Mainframe or operates standalone with user-supplied ±15 V and +5 V power.

A clock-stopping architecture minimizes digital noise during switching, preserving signal integrity for sensitive analog measurements.

Technical Specifications

• Input channels: 8 plus 1 bypass channel


• Series resistance: 2.0 Ω maximum


• Isolation resistance: >10 GΩ typical


• Input capacitance: <60 pF on selected channel; <25 pF between selected and unselected channels; <25 pF on unselected channels


• Maximum switching capacity: 10 mA @ 10 VDC


• Thermal EMF: <10 µV typical


• Bias current: 5 pA typical


• Switching speed: 50 ms maximum


• Bandwidth: 1 MHz typical


• Switching logic: Break-before-make (default); Make-before-break available via remote interface


• Maximum voltage to earth: ±15 V per terminal

Key Features

• Break-before-make switching minimizes transient artifacts and cross-talk


• Four-wire Kelvin configuration supports precision resistance and impedance measurements


• Clock-stopping eliminates switching-induced noise on sensitive channels


• Cascadable architecture enables expansion to larger switching matrices


• Front-panel and remote control for manual and automated operation


• DB-37 front-panel connector; DB-9 rear connectors for bypass and common output

Typical Applications

• Multi-channel resistance and RTD measurements


• Automated temperature sensor characterization


• Low-level analog signal routing and switching


• Integration with lock-in amplifiers for signal recovery


• Kelvin-lead switching in precision test systems

Compatibility & Integration Designed for the SIM900 Mainframe ecosystem, the SIM925 pairs with the SIM921 AC Resistance Bridge, SIM922A Diode Monitor, and SIM923A RTD Monitor. Communication routes through the mainframe's RS-232 or optional GPIB interface. Multiple SIM925 modules cascade for expanded switching networks.