Foxboro FBM218 — 8-Channel Analog Output Module

Model Series: FBM218 — 8-Channel Analog Output

Technical Specifications:

• Channel Count: 8 channels
• Output Signal Type: 4–20 mA (2-wire, loop-powered) or 1–5 VDC
• Output Resolution: 12-bit D/A converter
• Accuracy: ±0.2% of full scale
• Load Impedance (4–20 mA): 0 to 600Ω
• Isolation: 1500 VDC channel-to-bus
• Update Rate: 100 ms (all channels simultaneous)
• Operating Temperature: 0°C to 60°C (32°F to 140°F)
• Power Consumption: < 3.0 W
• Dimensions: Standard FBM form factor — 105mm x 130mm x 30mm

Structure Features:

• 8 output terminal pairs on the front face
• Backplane edge connector with gold-plated contacts
• Per-channel LED indicators for output status, active signal, and fault
• DIP switches for output type (4–20 mA / 1–5 VDC) and fail-safe mode selection

Function Features:

• Simultaneous update of all 8 output channels at 100 ms intervals
• Output tracking — outputs follow setpoint during bumpless controller transfers
• Fail-safe configuration per channel:
  • Hold Last Value
  • Go to Zero (4 mA / 0 VDC)
  • Go to Full Scale (20 mA / 5 VDC)
• Open-loop (burnout) detection — alerts controller if output circuit is broken
• Per-channel enable/disable via software command

Working Principle:
The I/A Series controller sends digital setpoint values over the backplane bus to the FBM218. The module’s 12-bit D/A converter transforms each value into an analog signal. An output driver circuit with current regulation generates the 4–20 mA loop signal (or voltage output). Isolation transformers (1500 VDC rating) separate the bus-side digital logic from the field-side analog outputs.

Advantage Highlights:

• Per-channel fail-safe selection ensures safe plant state during any failure mode
• 1500 VDC isolation provides robust protection against field-side electrical faults
• Simultaneous update (100 ms) eliminates inter-channel timing skew — critical for multi-valve control loops
• Open-loop detection enables predictive maintenance of output circuits

Applicable Industries:

• Process Control
• Oil and Gas
• Chemical Manufacturing
• Power Generation
• Pulp and Paper

Installation Requirements:

• Mount on FBM207B or FBM207C terminal base module
• For 4–20 mA outputs: total loop current = 8 channels × 20 mA = 160 mA maximum — ensure loop power supply is rated accordingly
• For 1–5 VDC outputs: use shielded cable with shield grounded at controller end only
• Torque terminal screws to 0.5–0.8 Nm

Usage Notes:

• Configure fail-safe action for each channel before system startup — this is a safety-critical setting
• Do not exceed 600Ω total loop resistance for any 4–20 mA output channel
• Verify module address matches the controller configuration before applying power
• Perform output calibration (zero and span) for each channel using Foxboro Configuration Software prior to commissioning
• The FBM218 is functionally equivalent to FBM214 in channel count but represents a distinct hardware revision with updated diagnostics — verify part number compatibility with existing system configuration