Configured for 4-20 mA current signal acquisition in the PLC-5 I/O chassis, the Allen-Bradley 1771-NIS/A (1771-NIS Analog Module) provides eight isolated analog input channels with module-supplied loop power. The module is part of the 1771 N-Series high-resolution analog I/O family and interfaces with PLC-3, PLC-5, and PLC-5/250 systems through block-transfer communication. Rockwell Automation lists the 1771-NIS as discontinued effective May 31, 2017.

Model and Revision Information

The base catalog number is 1771-NIS. Available revisions identified in the supplied material are 1771-NIS/A, 1771-NIS/B, and 1771-NIS/C. These suffixes identify hardware revisions rather than different input functions.

Rockwell Automation documentation identifies the 1771-NIS as an 8-channel isolated current-input module with a 4-20 mA range. The Rockwell selection documentation lists a 2.9 A backplane current value, while the older 1771 system selection material also identifies the module as requiring approximately 2.4 A in the system configuration data. For rack power calculations, the module-specific published maximum of 2.9 A should be used.

PLC-5 Backplane and Signal Interface

The 1771-NIS is an intelligent block-transfer analog module rather than a simple discrete input card. Analog channel data is transferred between the module and the PLC controller through the 1771 I/O backplane.

Key electrical characteristics include:

• 8 isolated current-input channels.
• 4-20 mA nominal measurement range.
• Module-supplied loop power for compatible two-wire transmitters.
• 20-30 VDC loop-power source.
• 330 nA/bit resolution with 16-bit unipolar conversion.
• Maximum input impedance of 300 Ohm.
• 24 VDC overvoltage protection.
• 9 Hz input bandwidth.
• High and low signal processing functions are supported through module configuration.

The module is specified for use with a 1771 Remote Termination Panel. Rockwell documentation identifies the 1771-RTP4 as the applicable RTP for the 1771-NIS.

Industrial Control Interface Characteristics

The 1771-NIS belongs to the Allen-Bradley PLC-5 industrial control architecture. Its analog values are processed locally and exchanged with the PLC through block-transfer operations.

The supplied configuration information indicates that the module can use Natural Binary or scaled data representation. Digital filtering and channel configuration are handled through the module configuration block rather than through discrete I/O addressing.

For PLC-5 rack design, the 2.9 A maximum backplane load must be included in the chassis power calculation. The 12 W module dissipation also contributes to the thermal load inside the I/O chassis.

Ordering Information

• 1 x Allen-Bradley 1771-NIS Analog Input Module
• 1 x Compatible 1771 PLC-5 I/O chassis installation position
• 1 x 1771-RTP4 Remote Termination Panel, when required by the field wiring arrangement
• 2 x Compatible cable assemblies may be required for RTP connection; published compatible cable examples include 1771-NC6 and 1771-NC15.
• Manuals, cables, RTPs, and other accessories are not assumed to be included unless specifically listed with the supplied item.

Installation and Wiring Notes

Chassis Installation

• Install the module in a compatible 1771 I/O chassis slot.
• Verify that the chassis power supply can support the module's backplane current requirement.
• Include the module's power dissipation when calculating rack thermal loading.
• Power to the I/O chassis should be removed before installing or removing the module.
• Verify the module revision against the existing PLC-5 application before replacement.

Analog Loop Wiring

• Use shielded instrumentation wiring appropriate for 4-20 mA signals.
• Separate low-level analog wiring from high-current motor and power conductors.
• Maintain consistent signal polarity throughout the transmitter loop.
• Terminate cable shields according to the plant grounding standard.
• Avoid creating unintended shield ground loops.
• Verify transmitter loop voltage against the module-supplied loop-power specification before commissioning.

RTP Connection

• Use the specified remote termination arrangement for the 1771-NIS.
• Verify cable type and cable length before installation.
• Confirm terminal assignments against the applicable 1771-NIS documentation.
• Do not apply field wiring directly to an incompatible terminal assembly.

Frequently Asked Questions

• How many analog inputs does the 1771-NIS provide?

  It provides 8 isolated current-input channels. Each channel is intended for analog current measurement within the module's specified input range.

• What signal does the 1771-NIS measure?

  The primary signal range is 4-20 mA. The published extended measurement range is 0.1-21 mA.

• Does the module provide loop power?

  Yes. The module supplies loop power for compatible field transmitters. The specified loop-power source is 20-30 VDC.

• What is the backplane current requirement?

  Published documentation lists a maximum backplane current of 2.9 A. This value should be included when calculating 1771 chassis power capacity.

• What resolution is available on the analog inputs?

  The input conversion is specified as 16-bit unipolar resolution with approximately 330 nA/bit for the current-input channels.

• Can the 1771-NIS be hot-swapped?

  Do not assume hot-swap capability. The 1771 system installation procedure requires chassis power to be removed before inserting or removing an I/O module.

• Which remote termination panel is specified?

  The 1771-RTP4 is identified for the 1771-NIS. Compatible cable assemblies are required when using the remote termination arrangement.

• Which PLC platforms can interface with the module?

  The 1771-NIS interfaces with PLC-3, PLC-5, and PLC-5/250 controllers that support the required block-transfer operation.