1771-IG | Allen-Bradley 8-Channel PLC-5 TTL Input Module

Product Introduction

The Allen‑Bradley 1771‑IG is a specialized digital input module that belongs to the 1771 product family. It serves as a critical interface between TTL-compatible field devices and your PLC‑5 processor. This module accepts 5 Volt DC signals from encoders, BCD interfaces, and other digital sensors. It then converts these signals into the logic levels the processor requires for data table updates. Consequently, it provides a direct and efficient method for bringing high-speed digital signals into your control system.

Technical Specifications

Input Characteristics

The 1771‑IG module offers eight (8) digital input channels, each designed for 5V DC TTL logic. The operating voltage range spans from 5.0 to 5.3 Volts DC, ensuring compatibility with standard TTL devices. When an input energizes, the module detects this state change in less than 1 millisecond. This rapid response makes the module ideal for high-speed counting or position feedback applications. For the off-to-on transition, the typical signal delay is 20 milliseconds, while the AC signal delay measures 24 milliseconds.

Power Requirements

This TTL input module requires two separate power sources to function correctly. First, it draws a backplane current of 122 milliamperes from the 1771 I/O chassis. Second, you must provide a separate 5V DC customer supply for the TTL signal transmission. The module allows a maximum customer supply current of 500mA per module. This dual-power design ensures that the field signals remain isolated from the backplane logic. Additionally, the module has a maximum power dissipation of 3.3W and a thermal dissipation of 11.3 BTU/hr.

Mechanical and Environmental Parameters

Isolation and Protection

The Allen‑Bradley 1771‑IG incorporates optoelectrical isolation to protect the system circuits from electrical transients. This feature enhances the reliability of your PLC‑5 system in noisy industrial environments. Moreover, the module includes an input filtering feature that actively reduces electrical noise. This prevents false triggering and ensures stable reading of TTL signals. The module also features a conformal coating on its circuit board, which protects against moisture, dust, and chemical contaminants.

Environmental Ratings

This 1771 digital input module operates reliably across a wide range of conditions. It functions within a temperature range of 0 to 60 °C. For storage, it can withstand temperatures from -40 to 85 °C. The module tolerates a relative humidity of 5 to 95% non-condensing. Its shock resistance measures 15 G while operating and 30 G when non-operating. These ratings make it suitable for most industrial automation applications.

Installation and Configuration Guide

System Compatibility and Mounting

The 1771‑IG module mounts directly into any standard 1771 I/O chassis that contains a PLC processor. It supports ½, 1, and 2-slot I/O addressing configurations, offering flexibility for system design. For proper slot identification, use keying bands between pins 34 and 36 for the upper connector. For the lower connector, place them between pins 4 and 6. The module's front panel includes eight status indicators. These LEDs provide visual confirmation of active TTL voltages on each input channel.

Wiring with the 1771-WC Arm

The 1771‑IG module uses the dedicated 1771‑WC wiring arm for all field terminations. This wiring arm allows you to replace the module without disconnecting individual field wires. For field 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. Remember that this module only works with DC voltage. Do not connect any AC voltage sources to its inputs.

Packaging List

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

• (1) 1771-IG Digital DC Input Module

• (1) 1771-WC 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 voltage range for the 1771-IG module?
This module specifically operates with 5V DC TTL signals. The acceptable input voltage range is 5.0 to 5.3 Volts DC. Never apply AC voltage or higher DC voltages to the inputs, as this will damage the module.

Q2: What type of power supply does the 1771‑IG require?
The module requires two power sources. The 1771 backplane provides the first source, drawing 122mA. You must also supply a separate 5V DC power source for the TTL signal transmission, with a maximum of 500mA per module.

Q3: Can I replace the 1771‑IG module without disconnecting the wiring?
Yes, you can. The module uses the 1771‑WC wiring arm. This design lets you remove the module from the chassis while leaving all field wiring securely attached to the arm. This simplifies maintenance and reduces downtime.

Q4: What is the response time of this input module?
The Allen‑Bradley 1771‑IG provides a very fast response. When an input turns on, the signal delay is less than 1 millisecond. This speed makes it suitable for TTL interfaces and BCD encoders that require quick detection.

Q5: How does the 1771‑IG protect against electrical noise?
The module uses two key protection methods. First, it has optoelectrical isolation that separates the field inputs from the backplane logic. Second, it includes an input filtering feature that reduces the impact of electrical transients and noise.