Honeywell 05701-A-0284 System 57 Series

The Honeywell 05701-A-0284, also cataloged as the 05701-A-0284 Catalytic Sensor Drive, operates as a dedicated hardware component for conditioning and processing flammable gas signals within System 57 rack platforms.

Hardware Specifications

Process Control & Gas Detection Integration

The 05701-A-0284 acts as a specialized catalytic bead sensor interface card, executing signal conditioning and threshold evaluation directly at the hardware layer.

• Pellistor Bridge Driving: The module supplies a constant, regulated excitation current to external pellistor sensors. It continuously measures the millivolt imbalance of the Wheatstone bridge caused by gas combustion on the active element.
• 4-20 mA Loop and Channel Isolation: The input bridge signal is processed and converted into a standard 4-20 mA HART compatible analog output loop. Galvanic channel-to-channel isolation safeguards internal rack processing cards from field wiring faults and line surges.
• Local Alarm Relay Control: Houses configurable SPCO output relays to actuate local audible or visual alarms directly when combustible gas concentrations breach pre-defined Lower Explosive Limit (LEL) setpoints.

Frequently Asked Questions

• Q: How is the catalytic sensor drive current adjusted on this module?
• A: The bridge excitation current must be calibrated manually using the onboard potentiometers. Technicians must match the current exactly to the specifications of the connected catalytic sensor model to prevent thermal burnout of the active elements.
• Q: Can this card be inserted or removed under power (hot-swapping)?
• A: Yes, the card is physical-key rated for live slot insertion. However, pulling an active card will instantly open the associated 4-20 mA loop and any field trip circuits. Ensure the linked shutdown loops are placed in bypass before extraction.
• Q: How does the card signal a field sensor fault?
• A: In the event of a sensor open-circuit or short-circuit, the 05701-A-0284 drives its analog output down scale (typically below 3.0 mA) and energizes the dedicated fault relay to notify the supervisory DCS.

Field Installation Guidelines

• Excitation Voltage Verification: Before connecting the catalytic sensor field wiring, verify that the card's bridge voltage matches the sensor datasheet. Incorrect excitation voltage will permanently damage catalytic pellistors.
• Three-Wire Shield Termination: Field connections must utilize high-quality three-core shielded cabling. Terminate the cable shield at the system rack grounding bar only. Do not ground the shield at the sensor housing to avoid noise-generating ground loops.
• Firmware and Calibration Setup: Following hardware mounting, the sensor zero and span calibrations must be verified under stable ambient flow conditions using certified span gas mixtures.