Allen-Bradley 1756-2WS ControlLogix Weigh Scale Module

The Allen-Bradley 1756-2WS, also cataloged as the 1756-2WS Dual-Channel Weigh Scale Module, serves as the primary ControlLogix I/O module utilized to execute dual independent strain-gauge signal acquisition across ControlLogix backplane platforms. Configured for load cell excitation and signal digitization in ControlLogix I/O chassis systems, the module provides direct electrical interface to Wheatstone bridge sensor arrays via two isolated measurement channels.

Within Allen-Bradley ControlLogix architecture, the module implements deterministic backplane communication with defined 5 VDC and 24 VDC power segmentation, enabling synchronized acquisition from up to eight 350 ohm load cells per channel.

Suffix Breakdown & Model Matrix

No officially published suffix segmentation exists for 1756-2WS. The identifier represents a fixed ControlLogix dual-channel weigh scale module variant within the 1756 I/O family.

Hardware Specifications

ControlLogix Backplane I/O Acquisition Behavior

Within the ControlLogix backplane architecture, the 1756-2WS performs synchronized analog acquisition using cyclic bus scheduling across the 5 VDC system rail. The module maintains dual-channel isolation logic, allowing independent scaling of strain-gauge bridge inputs without cross-channel interference. Backplane communication is executed via ControlLogix deterministic bus timing, supporting real-time load cell excitation monitoring and digital conversion alignment.

Frequently Asked Questions (FAQ)

Q: Does the 1756-2WS support hot-swap insertion in a live ControlLogix rack?
A: Yes, under ControlLogix system rules, the module supports hot-swap, but channel excitation should be disabled at application level before removal to avoid transient load cell excitation drift.

Q: How is backplane current distributed across the module?
A: The module draws 1.0 A from the 5 VDC backplane rail and a minor 0.0125 A from the 24 VDC auxiliary rail, with internal regulation separating signal conditioning and excitation circuitry.

Q: Can both channels operate independently with different load cell configurations?
A: Yes. Each channel operates as an independent measurement engine with separate Wheatstone bridge excitation and A/D conversion paths.

Field Installation Guidelines

• Ensure ControlLogix chassis power is fully removed before initial module insertion

• Verify backplane connector seating to avoid intermittent 5 VDC supply contact

• Maintain shield termination at single-point ground near PLC cabinet earth bar

• Route load cell wiring away from high-frequency switching conductors to reduce excitation noise coupling

• Observe torque and strain relief requirements on strain gauge cable entry points

• Ensure proper channel mapping configuration within ControlLogix Studio prior to energizing load cells