1756-PLS Allen-Bradley Programmable Limit Switch Module

Allen-Bradley 1756-PLS ControlLogix Programmable Limit Switch Module

Product Introduction

The 1756-PLS from Allen‑Bradley is a dedicated Programmable Limit Switch Module for the ControlLogix platform. It monitors machine position through an Allen‑Bradley resolver. Once the position reaches preset limits, the module energizes or de‑energizes its outputs accordingly. This function replaces mechanical limit switches in many applications.

For instance, you can use the 1756-PLS in rotary tables, press machines, or packaging equipment. It provides 16 single-ended inputs (10‑31.2V DC) and 16 outputs (10‑31.2V DC, 1A per output). Outputs are arranged in 4 groups of 4, each with separate power and common. This grouping gives you flexibility for different load requirements.

Additionally, the Allen-Bradley 1756-PLS supports three operation modes. It occupies three contiguous slots in a ControlLogix chassis. You can configure low limit and high limit setpoint positions easily through the control software.

Technical Specifications

• Manufacturer: Allen‑Bradley

• Series: ControlLogix

• Module Type: Programmable Limit Switch

• Inputs: 16 single-ended (10‑31.2V DC)

• Outputs: 16 (10‑31.2V DC, 1A max per output)

• Output grouping: 4 groups of 4 outputs with separate power/common

• Input grouping: 4 groups of 4 inputs with separate commons

• Operation modes: 3 contiguous slots in chassis

• Backplane current (5V): 1000 mA

• Backplane current (24V): 125 mA

• Power dissipation: 25.7 W at 30°C, 21.3 W at 60°C

• Thermal dissipation: 6.35 BTU/hr (nominal DC), 9.56 BTU/hr (max DC)

• Off-state voltage (max): 5V DC

• Off-state current (max): 1.5 mA

• On-state current: 3‑10 mA

• Removable Terminal Blocks: 3 x RTB (1756‑TBSH or 1756‑TBNH)

• Dimensions: 5.51 x 4.41 x 5.71 inches

Environmental Ratings

• Operating temperature: 0°C to 60°C (32°F to 140°F)

• Storage temperature: -45°C to 60°C

• Operating humidity: 0‑95% non‑condensing

• Enclosure: None (open-style)

• UPC: 10612598172594

Installation & Important Warnings

First, ensure the ControlLogix chassis is powered off before installing the 1756-PLS. Insert the module into three contiguous slots as required. Then, connect field-side wiring using the three RTBs (1756‑TBSH or 1756‑TBNH).

Critical warning: Do not remove the Allen-Bradley 1756-PLS from the chassis while power is applied. Doing so may cause message commands to commit configuration errors. Input data and output data can also be affected. Furthermore, removal under power may cause the module to lose its previous configuration.

Another important note: An electric arc can occur when inserting or removing any module while backplane power is on. This arc can damage the module or adjacent components. Therefore, always disconnect power before installation or removal.

Packaging List

• 1 x 1756-PLS Programmable Limit Switch Module

• 1 x quick reference guide

• RTBs are sold separately (1756‑TBSH or 1756‑TBNH)

• No certificate or warranty documents included

Shipping Methods

We ship worldwide using Fedex, UPS, or DHL. Tracking number provided within 24 hours.

Frequently Asked Questions (FAQ)

1. Does the 1756-PLS work with any resolver brand?
It is designed specifically for Allen‑Bradley resolvers. Third‑party resolvers may not provide compatible signals.

2. How many slots does the 1756-PLS occupy in the chassis?
It requires three contiguous slots. This is fixed by the module's operation mode and hardware design.

3. Can I mix input and output voltages on the same module?
No. Both inputs and outputs operate at 10‑31.2V DC. You cannot connect AC signals or higher DC voltages to the Allen-Bradley 1756-PLS.

4. What happens if I exceed 1A per output?
Each output has a maximum rating of 1A. Exceeding this may blow the internal protection or damage the output circuit. Use external relays for higher loads.

5. How do I configure low and high limit setpoints?
Use RSLogix 5000 or Studio 5000 software. The 1756-PLS appears in the I/O configuration tree. From there, you set position-based limits for each output channel.