Allen-Bradley 1771-NOC N-Series Analog I/O Module

Product Overview

The Allen-Bradley 1771-NOC is an N-Series 8-channel isolated analog current output module for PLC-5 systems. It provides high-resolution 0–25 mA current sourcing outputs with 14-bit resolution (3.20 µA/bit), making it ideal for precise control of pneumatic positioners, valve actuators, and legacy 4–20 mA instrumentation loops in process control applications.

Key Specifications

• Module Type: N-Series Analog Output
• Number of Outputs: 8 isolated current outputs
• Output Type: Current sourcing
• Output Range: 0–25 mA
• Resolution: 3.20 µA/bit (approximately 14-bit)
• Output Impedance: >1 MΩ
• Backplane Current: 2.9 A (at 20 mA/output); 3.3 A (at 25 mA/output)
• Power Dissipation: 5.5 W at 5 VDC
• Data Format: BCD or natural binary
• Update Time: 25 ms maximum
• Offset Drift: ±1 µA/°C
• Gain Drift: ±50 ppm/°C
• Output Overvoltage Protection: 140 VAC RMS continuous
• RTP Compatibility: 1771-RTP3 (fused) / 1771-RTP4 (unfused)
• Wiring Arm: 1771-WH
• Operating Temperature: 0–60 °C
• Storage Temperature: −40–85 °C
• Humidity: 5–95% non-condensing

Features & Benefits

• Extended 0–25 mA Range: Supports standard 4–20 mA loops plus extended range for specific pneumatic positioners and legacy devices
• High 14-Bit Resolution: 3.20 µA/bit enables smooth, step-free control signals minimizing valve hunting
• Isolated Outputs: Channel-to-channel isolation reduces ground loops and improves measurement integrity
• Programmable Reset Values: Each channel configurable for safe shutdown conditions
• Flexible RTP Options: Compatible with fused (1771-RTP3) or unfused (1771-RTP4) remote terminal blocks
• Robust Protection: 140 VAC RMS continuous overvoltage protection safeguards output circuitry

Applications

• Pneumatic valve positioner control
• Analog loop current instrumentation
• Proportional control in process industries
• Variable speed drive analog references
• Damper and actuator positioning

Installation Guide

1. Chassis Power Verification: Ensure the 1771 chassis power supply can deliver 3.3A at 5VDC for full-load operation. This is a high-current module.
2. RTP Selection: Choose 1771-RTP3 (fused) for applications requiring individual channel fuse protection, or 1771-RTP4 (unfused) for simplified wiring.
3. Module Installation: Insert the 1771-NOC into the 1771 chassis slot. Attach the 1771-WH wiring arm for field connections.
4. Field Wiring: Connect current loop devices to the RTP terminals. Verify loop impedance is compatible with the >1 MΩ output impedance specification.
5. Configuration: Set data format (BCD or natural binary) and programmable reset values per application requirements via PLC-5 programming software.
6. Calibration Check: Verify output accuracy across the 0–25 mA range using a calibrated current meter before commissioning.

FAQ

Q: Can the 1771-NOC output voltage signals?
A: No. The 1771-NOC is strictly a current sourcing module (0–25 mA). For voltage output (e.g., 0–10V), select a different 1771-N series module rated for voltage output.

Q: Why does this module draw so much backplane current?
A: The 1771-NOC sources current directly from the backplane to drive field loads. At full 25 mA per channel, it draws up to 3.3A. Ensure your power supply is adequately sized.

Q: What is the difference between 1771-RTP3 and 1771-RTP4?
A: 1771-RTP3 includes individual channel fuses for protection; 1771-RTP4 is unfused for applications where external protection is provided.

Q: Is the 0–25 mA range compatible with standard 4–20 mA devices?
A: Yes. The 0–25 mA range fully encompasses the 4–20 mA standard. Program your output scaling accordingly in the PLC-5 processor.

Selection Tips

• Critical: Verify chassis power supply capacity (3.3A at 5VDC max) before installing this module
• Confirm field devices accept 0–25 mA current signals; some devices are limited to 4–20 mA
• Select fused RTP (1771-RTP3) for safety-critical applications
• Consider loop impedance and cable length to ensure signal integrity
• For new installations, evaluate ControlLogix 1756-OF8I or CompactLogix analog output modules