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.
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
Model
1771-DS
Inputs
8
Input Voltage (Logic 1)
10 to 27V DC
Input Voltage (Logic 0)
0 to 5V DC
Nominal Input Current
20mA @ 27V DC
Max Off-State Current
1mA @ 4V DC
Backplane Current
375mA typical
Isolation
1500V Opto-electrical
Operating Temperature
0 to 60 degC
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.
