HARDY 1756-2WS Weigh Scale Module: ControlLogix-Compatible Weighing I/O for Industrial Process Control

Technical Dossier

Product Details And Specifications

HARDY 1756-2WS Series: Comprehensive Module Range and Technical Overview

The HARDY 1756-2WS is a dual-channel weigh scale module engineered for direct integration into the Allen-Bradley ControlLogix 1756 backplane. It is deployed across high-demand process industries including petrochemical refineries, nuclear fuel handling facilities, bulk chemical plants, cement manufacturing, and food-grade batching systems. The module eliminates the need for a standalone weight controller by embedding load cell signal conditioning, A/D conversion, and NTEP-certifiable weight data directly into the ControlLogix chassis. This architecture reduces panel footprint, eliminates serial communication latency, and allows weight data to be consumed natively by Logix ladder, function block, or structured text programs. Installed base spans North America, Europe, and Asia-Pacific, with documented deployments in continuous process environments requiring SIL-rated weight measurement and legal-for-trade compliance.

The Evolution of 1756-2WS Architecture

Hardy Instruments (acquired by Mettler Toledo in 2007) introduced the 1756-series weigh scale modules as a direct response to the industry shift from standalone weight controllers toward embedded, backplane-native I/O. Early Hardy weight controllers such as the HI 2110 and HI 3010 communicated via RS-232 or DeviceNet, requiring a dedicated serial interface module in the ControlLogix rack. The 1756-2WS eliminated this dependency by occupying a standard 1756 I/O slot and communicating over the ControlLogix backplane at full rack speed.

The original 1756-2WS revision supported C2 load cell technology (Hardy's patented second-generation C2 electronic calibration), allowing calibration without physical test weights — a critical feature for vessels in hazardous or inaccessible locations. Subsequent firmware revisions added WAVERSAVER® vibration rejection, which filters mechanical noise from conveyors, mixers, and vibrating feeders without sacrificing update rate. The module's architecture remained stable across ControlLogix platform generations (1756-L6x, 1756-L7x, 1756-L8x), maintaining backward compatibility with existing Studio 5000 / RSLogix 5000 Add-On Instructions (AOIs). As of 2024, the 1756-2WS is classified as a mature/end-of-active-development product. Mettler Toledo continues to supply replacement units and spare parts, but new feature development has migrated to the HI 6600 series platform. Long-term maintenance support for installed 1756-2WS systems remains available through authorized distributors and specialist spare parts suppliers.

1756-2WS Full Catalog & Functionalities (SKU List)

The following SKUs represent the core Hardy / Mettler Toledo 1756-platform and directly compatible weigh scale module range. Each entry reflects a verified, commercially documented part number.

1756-2WS: Dual-channel ControlLogix weigh scale I/O module, C2 & WAVERSAVER®
1756-1WS: Single-channel ControlLogix weigh scale module, C2 electronic calibration
HI 1756-2WS: OEM-labeled variant; functionally identical to 1756-2WS, Hardy catalog prefix
HI 1756-1WS: Single-channel OEM-labeled variant for ControlLogix platform
HI 6600-2WS: Next-generation dual-channel weigh scale module, successor platform
HI 6600-1WS: Next-generation single-channel weigh scale module
HI 3010: Standalone weight controller, RS-232/DeviceNet, predecessor to 1756-series
HI 2110: Panel-mount weight controller, analog output, legacy predecessor
HI 4050: Rate-of-change / flow rate weight controller, compatible with 1756 AOI
HI 4060: Batching/blending weight controller, multi-setpoint, standalone
HI 6300: Intrinsically safe weight transmitter, ATEX/IECEx rated
HI 6500: Weight/force measurement module, high-speed dynamic weighing
HI 2151/30WC: Compact weight controller, DIN-rail mount, Modbus RTU
HI 2151/30WS: Weight controller with serial output, legacy ControlNet interface
HI 9000MS: Multi-scale junction box with C2 diagnostics, field-mount
HI 215IT: Intrinsically safe weight transmitter, 4–20 mA analog output
HI 2160RC: Remote display/controller for Hardy weigh systems, panel-mount
HI 4050/30: Rate controller with 30-point linearization, process industry variant
1756-DHRIO: Allen-Bradley DH+ / Remote I/O bridge (required for legacy Hardy DeviceNet integration)

Sourcing Hard-to-Find & Obsolete 1756-2WS Parts

The 1756-2WS and its single-channel counterpart 1756-1WS are no longer in active production at Mettler Toledo's primary manufacturing line. Lead times through standard distribution channels can extend to 16–26 weeks for new-build units. DriveKNMS maintains a dedicated inventory of tested surplus, refurbished, and new-surplus 1756-2WS modules sourced from decommissioned process plant equipment, authorized liquidation, and controlled spare parts programs.

For facilities operating ControlLogix-based weigh systems with no near-term migration budget, DriveKNMS provides lifecycle extension support including: verified replacement units with full functional test documentation, firmware revision matching to existing installed base, and exchange programs that allow core return credit. All units are shipped with a test report referencing load cell input simulation, C2 calibration verification, and backplane communication integrity checks. Customers in the petrochemical, nuclear, and pharmaceutical sectors are supported under documented chain-of-custody procedures.

Quality Control for the 1756-2WS Range

The 1756-2WS presents specific test challenges due to its dual-function role as both an analog signal conditioner (load cell excitation and millivolt input) and a digital backplane I/O module. DriveKNMS applies a multi-stage test protocol to every unit processed:

Stage 1 — Backplane Communication Test: The module is seated in a live 1756 chassis with an L7x or L8x controller. RSLogix 5000 / Studio 5000 is used to verify module identity, firmware revision readback, and fault-free I/O tree registration.
Stage 2 — Load Cell Excitation Verification: Excitation voltage output (typically 10 VDC) is measured at the field wiring terminals under no-load and simulated load conditions using a precision resistive load cell simulator.
Stage 3 — A/D Conversion Accuracy: A calibrated millivolt source is applied across the signal inputs. Weight register values are read via the controller tag database and compared against reference values to verify A/D linearity within ±0.01% of full scale.
Stage 4 — C2 Electronic Calibration Cycle: A full C2 calibration sequence is executed using Hardy's documented procedure to confirm EEPROM write integrity and calibration data retention.
Stage 5 — WAVERSAVER® Filter Validation: Simulated vibration noise is injected via the signal input. Filter response is verified against Hardy's published attenuation specifications.
Stage 6 — Thermal Soak: Units are operated at elevated ambient temperature (50°C) for a minimum of 4 hours to screen for latent component failures prior to shipment.