HARDY HI 1756 Modules: HI 1756-WS

Technical Dossier

Product Details And Specifications

HARDY HI 1756 Series: Comprehensive Module Range and Technical Overview

The HARDY HI 1756 series represents a purpose-built family of weigh scale and process control modules designed for direct integration into the Allen-Bradley ControlLogix 1756 backplane. Deployed across global heavy industry — including petrochemical refineries, nuclear fuel processing facilities, bulk material handling terminals, and continuous process chemical plants — the HI 1756 platform provides deterministic weight measurement within a standard PLC chassis, eliminating the need for standalone weight controllers and reducing panel footprint. Its adoption in safety-critical and high-throughput environments has made it a long-cycle asset with multi-decade installed base presence.

The Evolution of HI 1756 Architecture

The HI 1756 series was introduced by HARDY Instruments (now part of Roper Technologies) as a direct response to the industry shift toward integrated PLC-based weighing, replacing discrete analog weight transmitters and standalone junction boxes. Early revisions of the HI 1756-WS communicated via the ControlLogix backplane using explicit messaging; subsequent firmware generations introduced implicit I/O and producer/consumer messaging for real-time weight data exchange at scan rates compatible with high-speed batching applications.

The architecture centers on a 24-bit analog-to-digital converter front end, C2 electronic calibration (eliminating the need for physical test weights in many applications), and WAVERSAVER® vibration rejection — a HARDY-proprietary digital filter that isolates true load cell signal from structural vibration common in industrial environments. Compatibility spans ControlLogix L6x, L7x, and L8x processor families, with EtherNet/IP and DeviceNet communication variants addressing different plant network topologies. As the ControlLogix platform itself has evolved through multiple chassis generations, the HI 1756 module's form factor and backplane interface have remained stable, making it a long-term spare parts commitment for end users.

HI 1756 Full Catalog & Functionalities (SKU List)

The following SKUs represent the documented HI 1756 product range. Modules are classified by primary function:

Weigh Scale / Analog Input Modules

• HI 1756-WS: Single-channel weigh scale module for ControlLogix; C2 calibration, WAVERSAVER® filter, 24-bit ADC
• HI 1756-2WS: Dual-channel weigh scale module; two independent scale inputs in single 1756 slot
• HI 1756-WS/A: Revision A weigh scale module; early production variant with legacy firmware baseline
• HI 1756-WS/B: Revision B; updated ADC reference circuit and improved EMI rejection
• HI 1756-WS/C: Revision C; current production baseline with enhanced diagnostics and Studio 5000 AOI support
• HI 1756-WS-EIP: EtherNet/IP-enabled weigh scale module; standalone network node capability independent of backplane processor

Junction Box / C2 Calibration Interface

• HI 215IT: Intrinsically safe C2 junction box; interfaces load cells to HI 1756-WS in hazardous area installations
• HI 6110: C2 summing card; combines up to 8 load cell signals for multi-point scale configurations
• HI 6020: Analog junction box; passive summing for non-C2 load cell arrays

DeviceNet Communication Variants

• HI 1756-WS/DN: DeviceNet adapter variant; integrates weigh data onto DeviceNet network segment
• HI 1756-DNIO: DeviceNet I/O module for HARDY weigh systems; discrete I/O expansion for batching control

Remote I/O & Expansion

• HI 1756-RIO: Remote I/O interface module; bridges legacy RIO network to ControlLogix chassis
• HI 1756-WSSAFE: SIL-rated weigh scale module variant; designed for functional safety applications per IEC 61511

Accessories & Ancillary Hardware

• HI 1769-WS: CompactLogix-compatible weigh scale module; same WAVERSAVER® and C2 technology in 1769 form factor
• HI 1734-WS: POINT I/O weigh scale adapter; distributed weigh node for POINT I/O systems
• HI 4050: Panel-mount weight controller; standalone alternative for non-PLC-integrated applications
• HI 3000: Weigh scale transmitter; DIN-rail mount, 4–20 mA output, predecessor to HI 1756 platform

Sourcing Hard-to-Find & Obsolete HI 1756 Parts

Several HI 1756 revision variants — particularly HI 1756-WS/A and HI 1756-WS/B — have been discontinued by HARDY and are no longer available through authorized distribution channels. Plants operating legacy ControlLogix L6x or L7x systems with these modules face a sourcing gap: the newer HI 1756-WS/C revision may require firmware and AOI updates that are not feasible during a planned maintenance window.

DriveKNMS maintains a dedicated inventory of tested surplus and refurbished HI 1756 series modules, sourced from decommissioned plant assets and verified against original HARDY factory specifications. Our stock covers both current-production and end-of-life revision codes, enabling like-for-like replacement without requiring system reconfiguration. For plants requiring long-term maintenance agreements covering the full HI 1756 installed base, DriveKNMS provides multi-year supply commitments with documented traceability.

Quality Control for the HI 1756 Range

The HI 1756-WS and its variants present specific test challenges due to their mixed analog front-end and digital backplane interface. DriveKNMS applies a structured verification protocol to all HI 1756 units prior to shipment:

• Backplane communication test: Module is seated in a live ControlLogix chassis and verified to enumerate correctly under RSLogix 5000 / Studio 5000 environment
• ADC linearity verification: A calibrated load cell simulator applies known millivolt signals across the full input range; output is compared against HARDY factory calibration data
• C2 calibration bus integrity: The C2 serial interface is exercised to confirm electronic calibration capability without physical weights
• WAVERSAVER® filter response: Dynamic signal injection confirms filter coefficients are intact and vibration rejection is within specification
• Thermal soak: Units are operated at elevated ambient temperature for a minimum of 4 hours to screen latent component failures
• Firmware revision documentation: Revision code is recorded and disclosed to the customer prior to shipment