Description
Product Introduction & Engineering Value
The FBM237 provides eight independently isolated 0-20 mA DC analog output channels. Each channel is galvanically isolated from the others and from ground. The module can be installed as a single unit or paired with a second FBM237 and a Redundant Adapter so that both modules share one Termination Assembly and independently drive the same output values.
When configured for redundancy, each module continuously attempts to hold its assigned output current. Fail-safe behavior is selectable: non-redundant operation supports Hold or Fallback per channel; redundant operation falls back to 0 mA on a per-channel basis if required. The module communicates with the FCP over the standard 2 Mbps Module Fieldbus and is suitable for Class G3 harsh environments.
Technical Specifications
| Parameter | Value |
|---|---|
| Output Channels | 8, channel-isolated |
| Output Range | 0 to 20.4 mA DC |
| Accuracy (includes linearity) | ±0.05% of span (0.1 mA to 20 mA) |
| Temperature Coefficient | ±50 ppm/°C |
| Resolution | 13 bits |
| Maximum Output Load | 750 Ω |
| Output Processing Delay | 30 ms maximum |
| Fail-Safe Options | Non-redundant: Hold or Fallback per channel; Redundant: Fallback to 0 mA |
| Power Supply | 24 V DC +5% / –10% (redundant) |
| Power Consumption | 7 W maximum |
| Heat Dissipation | 5 W maximum |
| Operating Temperature | –20 to +70 °C (–4 to +158 °F) |
Field Application & The “Trench” Experience
A Gulf Coast olefins plant needed reliable 4-20 mA outputs for eight critical control valves on a cracked-gas compressor anti-surge system. Two FBM237 modules were installed as a redundant pair sharing one Termination Assembly. During a subsequent power-supply disturbance on one module, the second module continued driving the correct currents with no process impact. The failed card was replaced online the following shift without interrupting the outputs.
Typical niche applications:
- Redundant 0-20 mA drive for anti-surge and recycle valve positioners on high-speed compressors
- Isolated analog outputs to I/P transducers and electronic positioners on a multi-effect evaporator train
- Critical final-element control on a continuous polymerization reactor where single-module failure is unacceptable
FBM237
FBM237
Transparency SOP: QA & Testing
Each unit is powered on a dual 24 V supply and verified for Fieldbus communication. All eight channels are driven across the 0-20 mA range against a calibrated load while accuracy and isolation are confirmed. Fail-safe behavior is tested in both single and (when applicable) redundant configurations. The module then undergoes an elevated-temperature soak while continuous output stability is monitored. Only units that pass the full sequence are released.
The Veteran’s Tech Trap Guide
⚠️ Redundant pairs share the field connector. When two FBM237 modules are paired, the corresponding output channels are connected together at the Termination Assembly and are therefore not isolated from each other. Do not assume full channel-to-channel isolation remains between the two modules in a redundant pair.
PRO TIP: Confirm the exact fail-safe configuration required by the process before loading the application program. Non-redundant and redundant modes handle Fallback differently; an incorrect setting can drive outputs to zero unexpectedly during a module fault.
⚠️ Output load and compliance voltage. The maximum load is 750 Ω. Long cable runs or high-impedance loads can push the module out of compliance at 20 mA. Always calculate the total loop resistance including the field device.
Dynamic FAQ
Q: Can the FBM237 be used as a single module or only in pairs? A: It is redundant-ready. It can operate as a single module or as a redundant pair when installed with a second FBM237 and the appropriate Redundant Adapter.
Q: What is the fail-safe behavior in redundant mode? A: In redundant configuration the outputs fall back to 0 mA on a per-channel basis if required by the application program settings.
Q: What is the maximum load the outputs can drive? A: 750 Ω maximum per channel.
Q: Is field calibration required? A: No. The module and Termination Assembly leave the factory calibrated. No field adjustment is required or possible.
Q: Are New Surplus units original Foxboro product? A: Yes. Units are original OEM material that have passed full output accuracy, isolation, and (where applicable) redundant failover testing.
Q: What warranty is provided? A: 12-month warranty against defects in materials and workmanship from the date of shipment for both New Surplus and fully tested refurbished units.
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