Allen-Bradley 1771-IH 8-Channel DC Input Module

The 1771-IH digital DC input module delivers robust signal acquisition for industrial control systems. This Allen-Bradley component provides eight reliable input channels for your PLC-5 chassis. It operates on a DC power supply with a voltage range of 24 to 50 Volts DC. Engineers trust this module for its straightforward installation and dependable performance in demanding environments. Use the 1771-IH to monitor discrete sensors, limit switches, and selector switches effectively.

Step-by-Step User & Installation Guide

Mount the 1771-IH module directly into any standard 1771 I/O rack. You must ensure the rack power supply is off before installation. Slide the module firmly into the guided card tracks until seated properly. Secure the module using the top and bottom locking tabs. The module uses the 1771-WD wiring arm for all field wiring connections. This design allows for easy removal without disturbing terminal connections.

Connect your 24 to 48 Volt DC sourcing sensors to the wiring arm terminals. Each of the eight inputs corresponds to a specific terminal point on the arm. Verify that your input voltage meets the 10-60 VDC sink (source load) voltage category. The module provides a nominal input current of 8.4 mA at 24V DC. At 48V DC, that current rises to 20 mA. Always check the maximum on-state voltage of 10V DC for reliable signal detection.

Apply power to the rack after completing all wiring connections. Observe the eight red status indicators on the module faceplate. Each LED illuminates when its corresponding input channel is active. This visual feedback helps you verify correct wiring and sensor operation immediately. The module processes input signals with a typical on-delay of 15 ms. It features an off-delay of 20 ms for reliable signal transition detection.

Expert Technical Evaluation & Performance Review

The 1771-IH is a robust, rack-mountable digital input module for older PLC systems. Its design supports a wide DC operating range from 24 to 50 Volts. The module draws a backplane current of 74 milliamperes at 5V DC. This low current draw ensures minimal load on your chassis power supply. The module also provides an isolation voltage of 1500V AC RMS for robust signal integrity.

Signal delays are an important specification for time-critical applications. The module shows a typical on-state delay of 15 ms with a ±7 ms tolerance. The off-state delay is slightly longer at 20 ms with a ±9 ms tolerance. Engineers must account for these delays in their control logic timing. The maximum off-state current is only 0.7 milliamperes, minimizing false triggering risks.

Thermal management is excellent across the operating temperature range. The module operates safely from 0 to 60 degrees Celsius or 32 to 140 degrees Fahrenheit. Power dissipation ranges from a minimum of 0.4 Watts up to 8.1 Watts. Thermal dissipation scales from 1.3 BTU/hr to a maximum of 27.7 BTU/hr. These figures confirm the module runs cool even under full load conditions across eight active channels.