Schneider AS-B875-111 Modicon 984 Analog Input Module

Description

Key Technical Specifications

These specifications are consistent across available Modicon 800/984 technical documentation.

Product Introduction

The Schneider Electric Modicon AS-B875-111 is a legacy analog input module for Modicon 800 Series and 984-class PLC I/O systems. It converts voltage and current process signals into digital values and can be configured for either 8 differential or 16 single-ended inputs.

Its main technical distinction is the combination of 14-bit resolution, multiple bipolar and unipolar input ranges, and selectable channel configuration. This makes it useful when maintaining an existing 984/800-series installation where the original I/O architecture must be retained. Schneider documentation also identifies the AS-B875-111 in legacy B800-to-X80 migration documentation, so verify the migration wiring carefully before substituting a modern module.

AS-B875-111

AS-B875-111

Installation & Configuration Guide

Stage 1: Pre-Installation Preparation — Approximately 5–10 Minutes

⚠️ Safety First: Notify operations, place the controlled process in a safe state, and follow the site’s lockout/tagout procedure before removing the module. Do not assume this legacy I/O module is hot-swappable.

Tools Required:

• ESD wrist strap
• Appropriate screwdriver
• Digital multimeter
• Wire labels
• Smartphone or camera for configuration photographs

Data Backup:

1. Confirm the exact replacement number: AS-B875-111.
2. Record the PLC rack and slot position.
3. Photograph the existing terminal wiring before disconnecting anything.
4. Record the existing channel configuration.
5. Save the current PLC application and configuration where applicable.
6. Record any diagnostic indications before shutdown.

Stage 2: Removing the Old Module — Approximately 5 Minutes

1. Remove the module cover or front access components as applicable.
2. Label every field wire before disconnecting it.
3. Disconnect the terminal connector without pulling on individual conductors.
4. Release the module’s mechanical retaining mechanism.
5. Pull the module straight out of the rack.
6. Inspect the mating connector and rack area for contamination, bent contacts, or physical damage.

⚠️ Keep the removed AS-B875-111 beside the replacement until commissioning is complete. The terminal arrangement and channel configuration are useful references during troubleshooting.

Stage 3: Installing the Replacement — Approximately 5–10 Minutes

1. Put on the grounded ESD wrist strap before handling the replacement board.
2. Confirm that the replacement marking reads AS-B875-111.
3. Verify that the terminal connector and mechanical keying correspond to the existing installation.
4. Install the module into the correct rack slot.
5. Seat the module fully without forcing it.
6. Reconnect the terminal connector.
7. Verify every wire against the photographs and wiring documentation before applying power.

The AS- supports both 8 differential and 16 single-ended configurations. The distinction matters during wiring because the terminal assignment changes with the selected configuration.

Self-Check:

• Correct AS- model
• Correct rack slot
• Terminal connector fully seated
• Wiring verified
• Channel configuration verified
• ESD precautions maintained

Stage 4: Power-On & Testing — Approximately 10 Minutes

1. Check the supply rails with a multimeter before powering the rack.
2. Power the rack according to the site’s approved startup procedure.
3. Observe the module status indication.
4. Check the PLC’s I/O diagnostic information.
5. Verify that each configured analog channel reports a plausible value.
6. Apply a known test signal where practical.
7. Compare the PLC value against the calibrated input source.
8. Return field devices to normal operation only after the I/O checks pass.

Schneider Electric specifically documents the AS- ACTIVE LED behavior: a rapid flash indicates initialization, while a slow flash indicates that at least one input is out of range.

Troubleshooting Note: If the ACTIVE LED continues flashing slowly after startup, check the field signal range and channel configuration before assuming the replacement module is defective.

Frequently Asked Questions (FAQ)

Can the AS- be hot-swapped?

Do not treat it as a hot-swappable module unless the specific rack architecture and OEM documentation explicitly permit live removal. For a legacy Modicon 800/984 installation, the safer replacement procedure is to place the process in a safe state and remove power according to the site’s LOTO procedure.

What type of signals does the AS- accept?

It accepts multiple voltage and current ranges, including 4–20 mA, 0–20 mA, ±20 mA, 1–5 VDC, 0–5 VDC, ±5 VDC, 0–10 VDC, and ±10 VDC.

Is the AS- an 8-channel or 16-channel module?

It supports 8 differential inputs or 16 single-ended inputs, with the configuration being user selectable. Do not assume that a replacement module can simply be wired according to an 8-channel diagram without checking the existing configuration.

What resolution does this module provide?

The AS- provides 14-bit analog-to-digital resolution. Published specifications also list ±0.1% accuracy and ±0.05% linearity.

Is the AS- obsolete?

It is a legacy Modicon product, and current third-party lifecycle listings identify it as discontinued. That does not mean it cannot be sourced, but available units may come from surplus, used, or refurbished inventory.

Can I replace it with a modern Schneider Electric analog input module?

Potentially, but do not treat it as a drop-in substitution. Schneider documentation includes an AS–to-Modicon X80 migration path, but the wiring map and receiving module configuration must be checked carefully.

Will I receive a genuinely new AS-?

That depends on the seller’s actual inventory. Legacy modules are available in different conditions, including factory-sealed, new surplus, used, and refurbished. The exact condition, revision, accessories, and test status should be confirmed before purchase rather than inferred from the product number alone.