Honeywell RM7850A1019 Relay Module

The Honeywell RM7850A1019 serves as the primary RM7850A Burner Control Unit utilized to execute flame safeguard sequencing, pre-ignition logic, and airflow validation across 7800 Series platforms. Operating on a nominal line voltage of 120 VAC at 50/60 Hz, this microprocessor-based control module manages interrupted pilot types and intermittent second-stage pilot valve timing. It incorporates user-selectable airflow check switches, a mandatory 15-second post-purge cycle, and hardwired lockout interlock inputs to ensure safe light-off and continuous operational monitoring in industrial burner assemblies.

Hardware Specifications

4-20 mA HART & Channel-to-Channel Isolation Profiles

The Honeywell RM7850A1019 integrates high-integrity channel-to-channel isolation between its low-voltage logic circuitry, external 4-20 mA HART loop interfaces, and line-voltage output contacts. To prevent signal distortion from nearby motor drives or transformers, the onboard signal conditioning circuit isolates optical, flame rod, or UV detector inputs from backplane noise. Relay output channels controlling safety shutoff valves and ignition transformers maintain physical galvanic separation from internal microprocessors, ensuring deterministic lockout response times upon flame failure or system trip events.

Frequently Asked Questions

Q: What happens if the user-selectable airflow check switch fails to prove closed during start-up?

A: If the airflow switch input does not close within the specified pre-ignition timing window, the module aborts the light-off sequence and initiates a safety lockout condition, requiring a manual reset before re-attempting ignition.

Q: Can the RM7850A1019 module be removed or inserted while the wiring subbase is powered?

A: No. The 120 VAC main power source must be completely de-energized prior to inserting or removing the module to prevent electrical arcing across terminal pins and to avoid un-sequenced relay actuation.

Field Installation Guidelines

1. Mount the subbase vertically within a protective NEMA enclosure to allow proper natural convection cooling across the housing and internal power dissipating components.
2. Route low-voltage flame sensor wires in separate grounded metallic conduits away from line-voltage ignition transformer leads to prevent inductive noise pickup; ensure standard 5-thread engagement for all threaded NPT conduit fittings.
3. Align the RM7850A1019 connector guide rails with the subbase socket, push firmly to seat all pins, and tighten side lock screws to ensure subbase ground continuity before applying 120 VAC line power.