Foxboro FBM203C P0922UD I/A Series RTD Input Module

Foxboro FBM203C P0922UD RTD Input Fieldbus Module

The Foxboro FBM203C P0922UD, also cataloged as the FBM203C RTD Input Module, operates as a dedicated hardware component for low-resistance temperature signal acquisition within Foxboro I/A Series and Foxboro Evo DCS platforms. Configured with eight channel-isolated resistance temperature detector (RTD) input channels, the module accepts 2-wire or 3-wire copper RTD inputs across a 0 to 30 ohm measurement span. The board utilizes individual sigma-delta A/D converters per channel to digitize resistance measurements for transmission over the redundant Module Fieldbus.

Hardware Specifications

Process Control and Signal Isolation

Galvanic isolation across all eight input channels prevents ground loops and suppresses high-frequency noise interference between field instruments and the internal DCS backplane. Operating in parallel with 4-20 mA HART loop protocol instruments in common cabinet termination layouts, the module delivers dedicated 0.54 mA sensor excitation current per channel to minimize self-heating in low-resistance copper RTDs. Onboard thermal management keeps internal power dissipation under 3 W, while internal cold junction compensation (CJC) principles and high common-mode noise rejection (>125 dB at 50/60 Hz) maintain 16-bit measurement stability across shifting ambient conditions.

Frequently Asked Questions

Q: How does the 0 to 30 ohm range on the FBM203C differ from standard FBM203 modules? A: The FBM203C variant is specifically scaled for 0 to 30 ohm resistance spans to optimize measurement resolution and accuracy when interfacing with 10 ohm copper RTD sensors.

Q: What sensor wiring configurations are supported by the termination assemblies? A: The module supports both 2-wire and 3-wire RTD wiring connections, where 3-wire configurations allow the module to compensate for lead-wire resistance across field cables up to 30 m in length.

Q: How does independent A/D conversion on each channel affect signal processing? A: Each channel features its own dedicated sigma-delta A/D converter, enabling continuous, parallel sampling of all eight RTD inputs without multiplexing delays or channel switching noise.

Field Installation Guidelines

Mount the module assembly onto its designated slot on the 200 Series FBM baseplate, pressing evenly until the mechanical retention clips snap into position. Ensure cabinet main supply power is completely de-energized or isolated prior to connecting interface cables to the 37-pin D-subminiature baseplate connector. Connect a 14 AWG copper bonding strap from the baseplate grounding stud directly to the main cabinet earth bus to maintain low-impedance grounding.

Route field RTD signal cables through dedicated wiring channels, maintaining separation from high-voltage AC lines to prevent magnetic noise coupling. Terminate individual cable overall shields at the termination assembly shield rail using a single earth ground connection to avoid ground loop current paths. Technicians must wear a grounded ESD wrist strap whenever handling unmounted circuit modules or making adjustment jumper changes on termination assemblies.