Allen Bradley1771-ISDC (5 V) Multiplexer Input Module, 72 Contact Inputs, BCD Thumbwheel, 1771 I/O

Product Description

What this part is

Allen-Bradley 1771-IS DC (5 V) multiplexer input module. Product Type: multiplexed contact and BCD thumbwheel input module for the 1771 I/O platform. Function: reads the status of BCD thumbwheel switches and hard contact devices and returns the data to the processor data table by block transfer. Discrete Contact Inputs: up to 72. Thumbwheel Capacity: up to four 4-digit or six 3-digit BCD switches. Switch Supply Voltage: 5 V DC. Backplane Current: 800 mA. Mounting Type: 1771 I/O chassis, single slot. Unit Quantity: 1 Pc.

Decoding the designation

1771 — the Allen-Bradley 1771 I/O platform, the rack-based I/O family served by PLC-2, PLC-3 and PLC-5 processors.

IS — the DC (5 V) multiplexer input module within that platform.

Electrical data

Switch Supply Voltage: 5 V DC, supplied by the module. Switch Contact Current: 13 mA nominal per contact at 5 V DC. Backplane Current: 800 mA. Recommended Switch Rating: 8 to 14 mA at 5 V DC. Maximum On Resistance: 10 Ω including cable. Minimum Off Resistance: 10 kΩ. Logic: low-true, the enable lines grounding the inputs through a closed contact.

What these specs mean in practice

Discrete Contact Inputs: 72, arranged as nine banks of eight. One slot replaces up to nine discrete input modules and the ladder logic that would otherwise multiplex them, which is where the rack space and program savings come from.

Scan Time: 15.3 ms normal or 5.1 ms fast, user-selectable, with contact debouncing. Switch scanning runs independently of the processor I/O scan, so thumbwheel and pushbutton status is already in module memory when the block transfer arrives.

Thumbwheel Capacity: four 4-digit or six 3-digit BCD switches, one data table word per switch plus one diagnostic word. Operators set timer presets, counter presets and process setpoints directly on the panel and the values arrive as BCD digits.

Operating Modes: maintained contact, where status updates every scan, and momentary latched contact, where an off-to-on transition is captured and held. The latched mode catches a pushbutton or keyboard press between block transfers.

Memory Reset: automatic immediately after transfer, or by program logic after the done bit returns. Program reset suits remote I/O, where it guards the data across the transfer.

Backplane Current: 800 mA. The module powers the field switches itself, which is why its chassis draw is high for an input card and why it belongs in the rack power budget calculation.

Mounting data

Mounting Type: any Bulletin 1771 I/O chassis, single I/O slot. Terminations: 1771-WF field wiring arm, shipped with the module. Keying: backplane keying bands between 8 and 10, and between 26 and 28. Maximum Switch Cable Distance: 400 ft. Cable: shielded, 20 AWG or larger below 100 ft, 18 AWG to 400 ft. Maximum Cable Capacitance: 0.039 µF between wiring arm terminals. Operating Temperature: 0 to 60 °C (32 to 140 °F). Storage Temperature: −40 to 85 °C (−40 to 185 °F). Relative Humidity: 5 to 95 percent without condensation.

Quantity and configuration

Unit Quantity: 1 Pc. One multiplexer input module.

Interchange guidance

Manufacturer Status: discontinued. Part Number: 1771-IS. MPN Variants: 1771IS, 1771 IS, DUB. Hardware revision D and later carry a Part No. XXXXXXXX/D designation on the module nameplate. The earlier 1771-ISC is the predecessor catalogue number for the same function. On a Mini-PLC-2 controller the module pairs with the 1772-LN3 processor. Reference documentation: Rockwell publication 1771-2.35, DC (5V) Multiplexer Input Module Product Data.