Configured for direct field sensing execution in PLC-5 local and remote I/O chassis, the Allen-Bradley 1771-IA/C (1771-IA) Discrete Input Module provides direct physical/electrical execution by interfacing 120 VAC/VDC discrete field signals to the system processor.

Variant Matrix & Model Designations

• 1771-IA: Base 8-channel discrete input module operating within 120 VAC/VDC input voltage thresholds.

• 1771-IA/C: Revision C iteration featuring updated hardware component sourcing and standardized backplane contact plating.

• 1771-IA Series: Encompasses all functional hardware revisions (A through C) sharing identical field wiring arm connection assignments.

Electrical & Physical Specifications

Backplane Communication Velocity & Determinism

The module utilizes dedicated backplane logic circuitry to interface directly with the PLC-5 processor over the 1771 backplane bus structure. Channel status data is continuously mapped into the input image table during standard I/O scan sweeps. Internal optocouplers ensure isolated signal transfer, preventing high-voltage line transients from affecting backplane bus communication velocity or corrupting adjacent logic modules inside the rack enclosure.

Standard Package Contents

• 1 x Allen-Bradley 1771-IA/C Discrete Input Module

• 1 x Instruction sheet

Installation & Wiring Rules

• Key the 1771 chassis slot using plastic keying bands inserted between backplane pins 10 and 12, and pins 24 and 26.

• Disconnect all backplane and field power sources prior to inserting or removing the module from the rack.

• Utilize the 1771-WN wiring arm for field conductor terminations to allow module replacement without disturbing field wiring.

• Route AC input conductors separately from low-level DC analog or communication cables in dedicated wireways.

• Ensure all field wiring conduit connections meet local grounded raceway compliance standards.

System Technical FAQs

• What is the maximum backplane current draw for the 1771-IA/C module?

  The module draws a maximum of 75 mA from the 1771 backplane bus logic supply at 5 VDC.

• Can this input module accept both AC and DC field signal inputs?

  Yes, the hardware supports 87 to 138 VAC operating signals as well as 97 to 138 VDC discrete field inputs.

• What is the maximum allowable off-state current for AC inputs?

  The maximum off-state leakage current permitted without causing a false signal state trigger is 2.8 mA.

• Is hot-swapping permitted for this module during active system operation?

  No, removing or inserting the module under power can cause electrical arcing, backplane disruption, or processor faults.

• Which chassis types accept the 1771-IA/C hardware assembly?

  The module installs into standard 1771 universal I/O chassis, including 1771-AB through 1771-A4B system enclosures.

• What are the typical turn-on delay times for AC vs DC operational modes?

  Typical signal delay on transition is 24 (+/- 10) ms for AC inputs and 10 (+/- 4) ms for DC inputs.

• Does the module require an external logic power supply connection?

  No external logic supply is required; all internal control circuitry power is derived directly from the chassis backplane bus.

• How are field wiring connections made to the front of the unit?

  Connections terminate at an interchangeable 1771-WN field wiring arm that latches securely into the chassis frame.