404A790H27
June 08, 2026

404A790H27

The 404A790H27 is a 16‑channel isolated digital output relay module designed by Emerson (formerly Westinghouse) for Ovation™ / WDPF / Q‑Line DCS platforms. As an enhanced variant in the 404A790 series, it provides dry‑contact switching for critical industrial loads, featuring hot‑swap capability, comprehensive on‑board diagnostics, and full channel‑to‑backplane isolation for high‑reliability process control applications.

Description

1. Product Introduction

The 404A790H27 is a 16‑channel isolated digital output relay module designed by Emerson (formerly Westinghouse) for Ovation™ / WDPF / Q‑Line DCS platforms. As an enhanced variant in the 404A790 series, it provides dry‑contact switching for critical industrial loads, featuring hot‑swap capability, comprehensive on‑board diagnostics, and full channel‑to‑backplane isolation for high‑reliability process control applications.

2. Technical Specifications

  • Channels: 16 independent isolated relay outputs (NO/COM, dry contact)

  • Contact Rating: 250 VAC / 30 VDC; 10 A (resistive) / 5 A (inductive)

  • Isolation:

    • Channel to backplane: 1500 VAC, 1 minute

    • Channel to channel: 500 VAC, 1 minute

  • Power Supply: 24 VDC ±10% (from DCS backplane)

  • Current Consumption: Max 250 mA

  • Power Dissipation: ≤ 6 W

  • Relay Lifespan:

    • Mechanical: 10,000,000 cycles

    • Electrical (full load): 100,000 cycles

  • Response Time: ≤ 10 ms

  • Operating Temperature: 0 °C to +55 °C

  • Storage Temperature: −20 °C to +70 °C

  • Relative Humidity: 5%–95%, non‑condensing

  • Key Features: Hot‑swappable; fail‑open on power/communication loss

  • LED Indicators: Green (PWR), Red (FAULT), Yellow (CH1–CH16 status)

  • Physical: Single‑slot module; approx. 220 × 30 × 250 mm, 1.2 kg

3. Application Fields

  • Power Generation: Thermal/nuclear power plant auxiliary control, interlock protection, valve/pump motor control.

  • Petrochemical: Solenoid valves, transfer pumps, emergency shutdown (ESD) devices.

  • Water Treatment: Dosing pumps, drain valves, mechanical screens, aeration equipment.

  • General Process Industries: Metallurgy, pulp & paper, cement, and other high‑reliability discrete control applications.

4. Installation & Wiring

  1. Ensure the DCS cabinet is de‑energized before installation.

  2. Insert the module into an available I/O slot; the backplane connector engages automatically.

  3. For hot swap, verify the system permits online replacement (Ovation/WDPF compatible).

  4. Field Wiring:

    • Connect load devices to NO (Normally Open) and COM terminals per channel.

    • Maintain isolation between field wiring and backplane cabling.

  5. Secure all connections; avoid over‑torqueing terminals.

5. Operation & Diagnostics

  • Power‑on: Green PWR LED illuminates when 24 VDC is supplied.

  • Channel Status: Yellow LED = output ON; LED off = output OFF.

  • Fault Indication: Red FAULT LED = detected fault (e.g., communication loss, overcurrent, or relay failure).

  • Diagnostics: The module reports channel‑level status to the DCS for alarm and maintenance logging.

6. Maintenance & Safety

  • Preventive Maintenance: Inspect connections annually; test relay contacts for wear.

  • Safety:

    • Disconnect all power before servicing.

    • Do not exceed rated contact voltage/current.

    • Operate within specified temperature/humidity limits.

7. Product Status

  • Lifecycle: End‑of‑Life (EOL); original manufacturing discontinued.

  • Availability: Refurbished and used units offered as spare parts; typical warranty 6–12 months.

  • Compatibility: Fully compatible with Ovation, WDPF, and Q‑Line DCS systems.


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