Metso AO4H

Product Overview

AO4H is a rack-mounted industrial analog output module designed for Metso distributed control systems, dedicated to converting digital control bus signals into standard analog current signals to drive field actuators including control valves, proportional regulators, variable frequency drives and positioners. It provides isolated multi-channel analog output for heavy process industrial closed-loop control.
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Description

Technical Specifications

  1. Channel Quantity: 4 independent analog output channels
  2. Output Signal Standard: 4–20 mA DC current loop
  3. Load Resistance Max: 750 Ω per single channel
  4. Power Supply: 24 VDC ±10% system backplane power supply
  5. Resolution: 16-bit digital-to-analog conversion
  6. Output Accuracy: ±0.05% full scale range (FSR) at 25 °C
  7. Temperature Drift: ≤0.0015% FSR / °C
  8. Galvanic Isolation: 2500 VAC isolation between backplane bus and field output channels; channel-to-channel isolation 500 VDC
  9. Communication Bus: Metso proprietary internal DCS backplane bus, compatible with Metso main controller racks
  10. Response Time: ≤120 μs full range output adjustment
  11. Operating Temperature Range: -20 °C to +70 °C
  12. Storage Temperature Range: -40 °C to +85 °C
  13. Protection Class: IP20 (indoor cabinet installation only)
  14. Dimension: 130 mm (H) × 35 mm (W) × 115 mm (D)
  15. Net Weight: 0.32 kg

Functional Features

  1. Full channel independent calibration via DCS human-machine interface without hardware disassembly
  2. Built-in open-circuit detection for each 4–20 mA loop; fault flag uploaded to controller bus
  3. Configurable fail-safe output mode: hold last value, set 4 mA minimum, set 20 mA maximum, user-defined fixed current
  4. Anti-surge protection for field wiring: TVS diode array suppresses voltage spike up to 36 VDC
  5. Digital filter adjustable bandwidth (0.1 Hz – 100 Hz) to eliminate field signal noise
  6. Hot-swap compatible; module replacement without full rack power cut-off
  7. Onboard LED status indicators: power, bus communication, channel fault

Working Principle

The main DCS controller transmits digital setpoint data via the rack backplane bus to AO4H’s onboard FPGA processor. The FPGA distributes digital values to four independent 16-bit DAC chips. Each DAC converts digital data to analog voltage, which drives a precision current output circuit to generate stabilized 4–20 mA loop current. Isolation transformers separate low-voltage control logic from high-interference field wiring to block ground loop noise. Onboard monitoring circuits continuously sample loop current; abnormal resistance or open circuit triggers digital fault signal upload to the master controller.

Material Composition

  1. Housing: Flame-retardant black ABS plastic, UL94-V0 fire rating
  2. Main PCB: FR-4 high-temperature fiberglass circuit board with tin-lead-free plating
  3. Isolation Components: Epoxy-sealed pulse isolation transformers
  4. Terminal Block: Nylon PA66 insulated screw terminals, copper alloy conductive cores
  5. Heat Dissipation: Passive aluminum alloy heat sink attached to power regulation chips

Structural Characteristics

  1. Standard 35 mm DIN rail rack insertion structure, left-side backplane gold-plated contact pins
  2. Front panel integrated detachable 12-pin field wiring terminal block
  3. Vertical layered PCB layout: isolation layer separates bus logic area and field output circuit area
  4. All electronic components surface-mount assembled for compact volume
  5. Integrated mechanical locking buckle to prevent vibration-induced module loosening

Advantage Highlights

  1. SIL 2 safety integrity level certified for critical process control loops
  2. Ultra-low temperature drift maintains precision in wide ambient temperature fluctuations
  3. Channel-independent isolation eliminates cross-talk interference between multiple field actuators
  4. Hot-swap design reduces production downtime during module maintenance
  5. Unified calibration software integrated into Metso DCS native platform, no third-party configuration tools
  6. Robust surge protection adapts to mining, pulp and paper heavy electromagnetic interference environments

Applicable Industries

Mining mineral processing, pulp & paper manufacturing, oil & gas upstream/downstream, chemical continuous process, power plant boiler control, metallurgy smelting, water & wastewater treatment plant

Installation Requirements

  1. Install only inside IP54 or higher industrial control cabinet; avoid direct dust, moisture and corrosive gas exposure
  2. DIN rail vertical mounting; maximum cabinet internal operating temperature shall not exceed 70 °C
  3. Field wiring shielded twisted pair cable mandatory; cable shielding single-point grounded at cabinet terminal strip
  4. Maximum field wiring length limited to 1000 meters for 4–20 mA signal loops
  5. Maintain minimum 20 mm vertical clearance between adjacent IO modules for passive heat dissipation

Usage Precautions

  1. Strictly prohibit applying voltage exceeding 30 VDC to analog output terminals; permanent circuit damage occurs
  2. Do not install in cabinet areas with rapid temperature cycling exceeding 10 °C per minute
  3. Calibrate all output channels every 12 months for precision-critical control loops
  4. When replacing modules, confirm DCS controller offline permission to avoid sudden actuator displacement
  5. Store spare modules in low-humidity environment with desiccant; avoid long-term storage above 60 °C
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