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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Input Channels | 4 isolated and independent |
| Output Channels | 4 isolated and independent |
| Input Range (each) | 0 to 20.4 mA dc |
| Output Range (each) | 0 to 20.4 mA dc |
| Accuracy (Input & Output) | ±0.05% of span |
| Output Load (Maximum) | 735 Ω |
| Compliance Voltage | 18.6 V nominal at 20 mA |
| Isolation | 600 V ac for 1 minute (channel-to-channel and channel-to-ground) |
| Communication | Redundant Fieldbus |
| Power Supply | 26 to 42 V dc (redundant) |
| Power Consumption | 14 W maximum |
| Heat Dissipation | 12 W maximum |
| Output Settling Time | 100 ms (10–90% step to within 1%) |
| Operating Temperature | 0 to 60 °C (32 to 140 °F) |
| Relative Humidity | 5 to 95% non-condensing |
4. Product Introduction
The Foxboro FBM04 is a combined 0–20 mA analog input/output interface module from the original I/A Series 100 Series Fieldbus Module family. It provides four isolated analog input channels and four isolated analog output channels in a single module.
Each input accepts a 2-wire 4–20 mA transmitter or a self-powered 0–20 mA source. Each output drives an external load up to 735 Ω and produces a 0–20 mA signal. Channels are galvanically isolated from each other and from ground. The module communicates over the redundant Fieldbus to the control processor. While this is legacy 100 Series hardware, many plants still rely on it; the modern functional equivalent is the FBM204 (or FBM244 for HART support). This unit is supplied as New Original / New Surplus stock for direct replacement.
- FBM04
- FBM04
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| Input channel reads zero or open | Open field wiring or failed transmitter | ✅ High | Measure loop current at input terminals | Verify transmitter power and wiring first |
| Output channel stuck or no current | Open load, shorted wiring, or failed output driver | ✅ High | Measure voltage/current at output terminals with known load | Check load resistance (≤735 Ω) and wiring |
| All channels offline | Fieldbus communication failure or power issue | ✅ High | Check redundant Fieldbus LEDs and 26–42 V supply | Confirm both Fieldbus legs and power supplies |
| Output current incorrect | Calibration drift or incorrect configuration | ✅ Medium | Force known percentage and measure actual mA | Re-calibrate or verify configuration parameters |
| Intermittent channel errors | Loose termination block or poor contact | ✅ High | Reseat connector block; inspect pins | Clean and re-torque field terminations |
| Module not recognized by CP | Wrong address or failed module | ❌ Low | Verify rotary address switches and status LEDs | Swap with known-good module if available |
If symptoms persist, capture module status LEDs, Fieldbus diagnostics from the control processor, and photos of the termination block, then contact technical support.
6. Frequently Asked Questions (FAQ)
Q: What is the modern replacement for the FBM04? A: For non-HART devices the functional equivalent is the FBM204 (4 input + 4 output, channel-isolated). For HART support use the FBM244. Termination Assembly Adapters allow reuse of existing field wiring.
Q: Are the channels isolated? A: Yes. All eight channels (4 AI + 4 AO) are galvanically isolated from each other and from ground (600 V ac withstand).
Q: What is the maximum load the outputs can drive? A: 735 Ω. Compliance voltage is approximately 18.6 V at 20 mA.
Q: Why is the price lower than a factory-new unit from Schneider Electric? A: This is New Original / New Surplus stock—genuine Foxboro parts that have never been installed in a running system. Units ship with a 1-year warranty after functional verification.
Q: Can I hot-swap the FBM04? A: In most I/A Series installations the module can be removed and inserted under power following proper procedures, but always follow site lockout and the specific mounting structure guidelines.
Q: Does it support HART? A: No. The original FBM04 is analog-only. HART capability requires later modules such as the FBM244.
Q: What is the typical lead time and warranty? A: Units are normally in stock for same- or next-day shipment. All modules carry a 1-year warranty against defects in materials and workmanship.
