Allen-Bradley 1771-DS PLC-5 Latching Input Module

The Allen-Bradley 1771-DS is a specialized 8-input Latching Input Module designed for the PLC-5 system. It is engineered to detect and latch high-speed pulses that occur too rapidly for a standard PLC-5 scan rate to capture. When a pulse is detected at an input terminal, the module sets a corresponding bit in the input image table during the next I/O scan.

Features

• 8-input latching capability for high-speed signal capture.
• Selectable pulse capture times: 0.1, 0.5, 1.0, 2.5, or 5.0 ms.
• Opto-electrical isolation of 1500V for signal integrity.
• Supports both master reset (all inputs) and individual input reset modes.
• Compatible with sensors featuring isolated pulse or gate outputs.

Applications

• High-speed signal capture for processes exceeding standard PLC-5 scan rates.
• Material handling systems requiring precise position or product presence detection.
• Packaging equipment and pick-and-place machinery.
• Custom machine tool manufacturing and textile assembly lines.

Technical Specifications

Installation Guidelines

• Slot Placement: The module can be installed in any I/O slot of a 1771 chassis, excluding the far-left slot reserved for the processor or adapter.
• Keying: To prevent incorrect module insertion, install keying bands on the backplane connector between pins 2 and 4, and between pins 18 and 20.
• Wiring: Connect field wiring to the appropriate field wiring arm (e.g., 1771-WH) before seating the module into the chassis.
• Handling: Always power down the I/O chassis before inserting or removing the module to prevent electrical damage or unexpected system behavior.

FAQs

What is the 1771-DS Module?

The 1771-DS is a Latching Input Module designed by Allen-Bradley for the PLC-5 system. It is an 8-input, rack-mountable module that operates within a 1771 I/O chassis, commonly used to capture fast pulses.

What are the input voltage levels?

Logic 1 is 10-27V DC, and Logic 0 is 0-5V DC.

What sensors are compatible?

It is designed for optical sensors with isolated pulse or gate outputs. The off-state leakage current of the sensors must not exceed 1mA @ 4V DC.

What is the modern replacement?

When upgrading from PLC-5 to ControlLogix (1756), users often replace it with high-speed modules like the 1756-IB16IF (Fast DC Input) or the 1756-IB16ISOE (Sequence of Events) to maintain fast response times.