1771-DR | Allen-Bradley | PLC-5 I/O Module

Product Overview

The Allen-Bradley 1771-DR is a digital input module for PLC-5 1771 I/O systems. It provides discrete signal acquisition with defined ON/OFF current thresholds and input impedance characteristics for reliable detection of field device states in industrial control applications.

Key Specifications

• On-State Current (min): 5 mA
• Off-State Current (max): 2.5 mA
• Input Impedance: 22 kΩ
• Isolation: Channel-to-backplane isolation
• Platform: PLC-5 / 1771 I/O
• Mounting: 1771 chassis

Features & Benefits

• Defined Current Thresholds: Clear 5 mA ON / 2.5 mA OFF current specifications ensure reliable signal detection
• Moderate Input Impedance: 22 kΩ input impedance is compatible with a wide range of field devices
• Isolated Inputs: Channel-to-backplane isolation protects controller from field-side electrical disturbances
• Standard 1771 Form Factor: Compatible with all 1771-series I/O chassis for easy integration

Applications

• General-purpose discrete input interfacing
• Switch and contact status monitoring
• Relay output feedback detection
• Legacy PLC-5 system maintenance

Installation Guide

1. Chassis Installation: Insert the 1771-DR into a compatible 1771-series I/O chassis slot.
2. Field Device Verification: Confirm field devices can deliver at least 5 mA ON-state current into a 22 kΩ load.
3. Wiring Connection: Use the appropriate 1771 wiring arm for field terminal connections.
4. Signal Verification: Measure OFF-state current to ensure it does not exceed 2.5 mA when the device is inactive.
5. Status Check: Power up and verify input response matches field device states.

FAQ

Q: What is the input impedance of the 1771-DR?
A: The module presents approximately 22 kΩ input impedance to field devices.

Q: What are the ON/OFF current thresholds?
A: The module requires a minimum of 5 mA for ON-state detection and guarantees OFF-state for currents below 2.5 mA.

Q: Is the 1771-DR compatible with dry contact switches?
A: Dry contacts require a voltage source in series. Verify the contact circuit can deliver sufficient current (5 mA min) when closed.

Selection Tips

• Calculate field circuit current with the 22 kΩ load to ensure reliable ON-state detection
• Verify OFF-state leakage current does not exceed 2.5 mA
• For new designs, evaluate ControlLogix or CompactLogix digital input modules with similar specifications