Description
Foxboro FBM211 | 16-Channel 0 to 20 mA Input Module
Product Introduction
When a DCS cabinet is packed with conventional 4–20 mA transmitters, channel density and signal integrity become practical engineering constraints—not brochure specifications. The Foxboro FBM211 addresses that job with sixteen analog current-input channels in a standard 200 Series Fieldbus Module architecture.
Each FBM211 channel accepts a 2-wire analog signal, including conventional 4–20 mA transmitters, self-powered 20 mA sources, and properly configured supervised digital inputs. The module converts the field signals for communication across the redundant 2 Mbps module Fieldbus, while its analog input application provides configurable conversion timing and rate-of-change processing.
The important distinction is channel architecture. The FBM211 provides 16 independent input channels, but the inputs are group isolated in groups of eight, not individually galvanically isolated from one another. They are isolated from ground and module logic. That distinction matters when replacing modules in mixed-ground, multi-transmitter cabinets.
For engineers working on an existing Foxboro installation, the current Schneider Electric specification identifies the module hardware as RH914TN, superseding the older P0914TN designation. The current product specification is PSS 41H-2S211, Rev D, dated May 2025.
FBM211
Key Technical Specifications
- Module: FBM211
- Function: 0 to 20 mA analog input
- Number of channels: 16
- Input type: 20 mA DC analog input
- Input range: 0 to 20.4 mA DC
- Per-channel current limit: 33 mA
- Accuracy: ±0.03% of span, including linearity
- Accuracy temperature coefficient: ±50 ppm/°C
- Input impedance: 61.9 Ω nominal
- A/D conversion: Multiplexed Sigma-Delta converter
- Integration period: Software configurable
- Common-mode rejection: >100 dB at 50/60 Hz
- Normal-mode rejection: >35 dB at 50/60 Hz
- Analog update capability: New readings every 100 ms
- HART compatibility: Yes
- Fieldbus: Redundant 2 Mbps module Fieldbus
- Power input: 24 VDC +5% / -10%, redundant
- Maximum consumption: 7 W at 24 VDC
- Maximum consumption with all inputs at 20.4 mA using internal power: 11 W
- Maximum heat dissipation: 3 W at 24 VDC
- Module operating temperature: -20 to +70°C (-4 to +158°F)
- Storage temperature: -40 to +70°C (-40 to +158°F)
- Relative humidity: 5–95%, noncondensing
- Contamination rating: ISA S71.04 Class G3
- Module weight: Approximately 284 g (10 oz)
- Dimensions: 102 × 45 × 104 mm
- Height including mounting lugs: 114 mm
- Termination cable distance: Up to 30 m (98 ft)
- Termination cable: 37-pin male D-subminiature
- Module part number: RH914TN
- Legacy part number: P0914TN
These specifications are taken from Schneider Electric’s current FBM211 product specification.
Signal Architecture and Application
The is primarily intended for 2-wire analog transmitter applications. A conventional 4–20 mA transmitter fits naturally into the architecture, but the published input range extends from 0 to 20.4 mA, giving the control system additional signal space beyond the nominal process range.
The module uses a multiplexed Sigma-Delta converter shared across the input channels. New analog readings can be produced every 100 ms, while the integration period is software configurable to average the converted values and reduce process noise and power-line-frequency interference.
That filtering behavior should be considered during control-loop migration. A transmitter can be electrically healthy while an excessively long integration period introduces additional apparent process lag. When tuning PID loops or evaluating logic execution timing, distinguish between the field transmitter response, FBM conversion/integration, controller scan behavior, and final output processing.
HART Compatibility
The input channels meet the impedance requirements for a HART high-impedance device and can operate in a HART loop without interfering with HART communication between the field transmitter and handheld communicator.
There is one important Foxboro-specific detail: when a FoxCom or HART transmitter is used with the , Schneider specifies a 200 Ω in-line resistor, RH902VY, installed in series with the transmitter. Do not assume that every legacy termination arrangement can be transferred unchanged simply because the nominal signal remains 4–20 mA.
Termination and Field Wiring
field wiring is routed through DIN-rail-mounted termination assemblies. The termination assembly provides the physical interface between sixteen 2-wire analog input signals and the FBM.
Two primary termination arrangements are documented:
- RH916JT / P0916PQ: Uses a customer-supplied external DC power supply for field-device loop power.
- RH916BT / P0916BU: Uses the FBM auxiliary +24 VDC power supply for field-device loop power.
The current specification lists Polyamide termination assemblies for -20 to +70°C operation, while the PVC versions have a more restrictive -20 to +50°C temperature range. Termination cables are available in polyurethane/PVC and LSZH constructions, with lengths up to 30 m.
For replacement work, identify the existing TA and cable before ordering only the module. A correct module paired with the wrong termination arrangement can turn a straightforward spare-part replacement into a cabinet rework.
Isolation and Safety
The uses 16 group-isolated channels, with each group containing eight channels. The channels are not individually galvanically isolated from one another, although the input circuitry is galvanically isolated from ground and module logic.
Schneider specifies a 600 VAC withstand test for one minute between the group-isolated channels and earth. This should not be confused with a permissible operating voltage.
Do not use the 600 VAC withstand figure as an input-voltage rating. Schneider specifically warns that the channels are not intended for permanent connection to hazardous-voltage circuits, and connection above 30 VAC or 60 VDC violates the stated electrical safety requirements.
Redundant Fieldbus and Replacement Architecture
The communicates with its associated Fieldbus Communications Module or Field Control Processor through the redundant 2 Mbps module Fieldbus.
Both Fieldbus paths, A and B, are supported. If one communication path becomes unsuccessful or the system switches paths, the can continue communicating over the active path.
The module also receives redundant independent DC power through the 200 Series baseplate. This architecture is important when planning migration or replacement work because the is not simply a stand-alone 16-channel current-input card; its baseplate, termination assembly, Fieldbus architecture, power distribution, and controller configuration all form part of the installation.
Supervised Digital Input Capability
One less obvious capability is supervised digital input monitoring.
With suitable external resistors, an channel can monitor a dry field contact while simultaneously checking field-loop continuity. The system can distinguish conditions such as contact open, contact closed, field wiring open, and wiring shorted to ground or between the loop conductors.
The published example uses different current levels to distinguish these states:
- Contact open: approximately 3 mA
- Contact closed: approximately 6 mA
- Field wiring open: 0 mA
- Certain wiring-short conditions: approximately 16 mA
This is useful for legacy alarm, permissive, and interlock circuits where simple binary sensing is insufficient and line-fault supervision is required.
Global Sourcing & Live-Test SOP
For procurement, surplus replacement, or cross-border sourcing, the should be handled as a configuration-sensitive DCS I/O module—not as a generic 16-channel analog card.
1. Inbound Verification
- Confirm the exact front-label designation: .
- Cross-check the hardware identifier against RH914TN and the legacy P0914TN designation.
- Record serial number, revision markings, manufacturing labels, and visible module condition.
- Inspect the Fieldbus connectors, baseplate interface, termination connector, and enclosure for corrosion, impact damage, contamination, or rework.
- Trace OEM paperwork and commercial documentation where available.
- Compare label typography, connector condition, fasteners, PCB exposure, and enclosure markings for counterfeit or previously reworked hardware.
2. Live Simulation
Recommended bench testing should use a controlled 0–20 mA source rather than an arbitrary transmitter.
Verify representative points such as:
- 0 mA
- 4 mA
- 12 mA
- 20 mA
Check the corresponding controller-side engineering values and confirm that all sixteen channels respond correctly.
For a higher-confidence acceptance test, simulate multiple channels simultaneously and verify that the measured values remain stable under load. A calibrated current source is preferable to using a handheld multimeter as the primary signal generator.
3. Diagnostics
Check:
- Module LED status
- Fieldbus path A communication
- Fieldbus path B communication
- Input channel diagnostics
- Controller recognition
- Configuration download
- Analog value stability
- Rate-of-change behavior
- Integration-time configuration
- HART loop behavior where applicable
If HART functionality is part of the application, verify the actual loop
