1771-IH | Allen-Bradley 8-Channel 24-48V DC Digital Input Module

Product Introduction

The Allen‑Bradley 1771‑IH is a robust digital input module from the 1771 product family. It accepts DC signals from field devices such as proximity sensors, limit switches, and pushbuttons. This module operates with a supply voltage range of 24 to 50 Volts DC, covering the most common industrial control voltages. Its wide input range, from 10 to 60 Volts DC, provides excellent flexibility. The module mounts directly into a 1771 I/O rack, offering a space-efficient and reliable solution for your PLC‑5 system.

Technical Specifications

Input Characteristics

The 1771‑IH module provides eight (8) input channels, all configured as sink inputs for sourcing loads. This means the field device supplies the current to the module. The nominal input current measures 8.4 mA at 24V DC and increases to 20 mA at 48V DC. The maximum on-state voltage is 10V DC, ensuring reliable detection at lower thresholds. Conversely, the maximum off-state voltage is 4.5V DC. The off-state current stays below 1 mA, preventing false triggers. The input impedance ranges from 2.5 to 3K Ω in the on-state and 5 to 6K Ω in the off-state.

Power and Protection

This digital DC input module draws a backplane current of only 74 mA at 5V DC ±5%. This low draw makes it efficient for large systems with many modules. The module provides 1500V AC RMS isolation for one second. This protects the processor and backplane from voltage spikes and transients originating from field wiring. Power dissipation ranges from a minimum of 0.4 W to a maximum of 8.1 W. Thermal dissipation similarly ranges from 1.3 BTU/hr to 27.7 BTU/hr. These figures help you plan for proper heat management in your enclosure.

Performance and Speed

The 1771‑IH module processes input signals with predictable delays. The on-state signal delay (low to high) measures 15 ms with a tolerance of ±7 ms. The off-state signal delay (high to low) measures 20 ms with a tolerance of ±9 ms. For AC signals, the off-state delay is 24 ms with a ±10 ms tolerance. These delays provide sufficient response for most industrial control applications, including conveyor systems, packaging machinery, and material handling.

Mechanical and Environmental Parameters

Environmental Ratings

The Allen‑Bradley 1771‑IH operates reliably across a broad temperature range. It functions from 0 to 60 °C (32 to 140 °F). This makes it suitable for most indoor industrial environments. The module can withstand relative humidity levels from 5 to 95% non-condensing. It also meets standard shock and vibration requirements for rack-mounted industrial equipment. For storage, it tolerates temperatures from -40 to 85 °C.

Status Indicators

The module features eight red status indicators on its front panel. Each LED corresponds to one of the eight input channels. When an input is active (ON), its LED illuminates. This provides instant visual confirmation of field device status. These indicators simplify troubleshooting and system validation. You can quickly verify wiring and sensor operation without needing a programming terminal.

Installation and Configuration Guide

System Compatibility

The 1771‑IH module mounts into any standard 1771 I/O chassis. This compatibility covers a wide range of PLC‑5 systems. The module supports ½, 1, and 2-slot I/O addressing configurations. This flexibility allows system integrators to optimize rack space usage. Before installation, always power down the chassis. The module does not support Removal and Insertion Under Power (RIUP). Handle the module carefully to prevent electrostatic discharge damage.

Wiring with the 1771-WA Arm

This module requires the dedicated 1771‑WA wiring arm for field connections. This wiring arm enables quick module replacement without rewiring the field devices. For wiring, use solid or stranded copper wire with a gauge of 22 to 14 AWG. The insulation should have a rating of 75 °C or higher. Apply a torque of 0.8 to 1.0 Nm (7 to 9 lb-in) to the terminal screws. Ensure all field devices are DC-powered and comply with the 24-50V DC operating range. Never connect AC power sources to the inputs.

Packaging List

Your Allen‑Bradley 1771‑IH order will include the following items:

• (1) 1771-IH Digital DC Input Module

• (1) 1771-WA Wiring Arm

Note: The module and its accessories ship in protective anti-static packaging to prevent ESD damage during transit. All orders ship via FedEx, UPS, or DHL.

Frequently Asked Questions (FAQ)

Q1: What is the input voltage range for the 1771‑IH module?
This module operates with a nominal range of 24 to 50 Volts DC. However, it can detect signals as low as 10V DC as an ON state. The maximum off-state voltage is 4.5V DC. Never apply AC voltage to any input terminal.

Q2: What type of field devices work with the 1771‑IH?
The module accepts sink-type inputs. This means the field device must supply current to the module. Typical compatible devices include 24V DC proximity sensors, photoelectric sensors, pushbuttons, and selector switches that source current.

Q3: Which wiring arm does the 1771‑IH require?
This module uses the 1771‑WA wiring arm. This specific arm ensures proper signal termination. It also allows you to replace the module without disconnecting any field wiring, saving time during maintenance.

Q4: What is the signal delay of this input module?
The Allen‑Bradley 1771‑IH has an on-state delay of 15 ms (±7 ms). The off-state delay is 20 ms (±9 ms). For AC-type applications, expect a 24 ms (±10 ms) delay. These times are typical and account for filtering and debouncing.

Q5: How many inputs does the 1771‑IH module provide?
The module offers eight (8) input channels. Each channel has its own dedicated red status indicator on the front panel. This allows for easy monitoring of all connected field devices.