3721 TRICONEX Analog Input Module

‌Invensys 3721 Series Troubleshooting Guide‌

‌1. Preliminary Checks‌

• Verify power supply: 24VDC ±10% (measure at terminal block)
• Check LED indicators:
  • Green (PWR): Steady = Normal
  • Red (FLT): Flashing = Module error
• Confirm I/O wiring integrity (min. 22AWG shielded cable)

‌2. Diagnostic Procedure‌

graph TD
A[FLT LED Status] --> B{Pattern?}
B -->|1 Flash| C[Channel 1 Fault]
B -->|2 Flashes| D[Channel 2 Fault]
B -->|Continuous| E[Module Failure]
C/D --> F[Check field device load]
E --> G[Replace module]

‌3. Common Fault Resolution‌

• ‌Open Circuit‌: Verify field device resistance (<50Ω)
• ‌Short Circuit‌: Disconnect loads, measure insulation (>1MΩ)
• ‌Communication Error‌:
  • Cycle power to baseplate
  • Verify PROFIBUS DP termination (SW1=ON for end node)

‌4. Advanced Diagnostics‌

• Use Foxboro I/A Tools software:
  bashCopy Code
  

  dcli -c "read 3721.diag" # Retrieves detailed error log

• Check backplane voltage (5.1V±2% at test point TP3)

‌5. Maintenance Notes‌

• ESD protection required during handling
• Firmware updates via PCMCIA slot (v4.2+ recommended)
• MTBF: 250,000 hours (IEC 61709)

3721 TRICONEX PDF
3721‌

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