Siemens SIWAREX WP321 7MH4601-1AA01 Electronic Weighing Modules - FC-RUSIO-3224

Technical Dossier

Product Details And Specifications

Siemens SIWAREX WP321 Series Technical Notes

The Evolution of SIWAREX WP321 Architecture

The SIWAREX WP321 was introduced as part of Siemens' broader SIWAREX product family, which traces its origins to the early 1990s with the SIWAREX M and SIWAREX U series — standalone weighing transmitters with serial interfaces. The WP321 represented a structural shift: rather than operating as an independent instrument, it was architected as a plug-in module for the SIMATIC S7-300 backplane, communicating via the S7 internal bus. This integration model allowed process engineers to configure, calibrate, and monitor weighing functions directly from STEP 7 or TIA Portal without a separate HMI or communication gateway.

Early WP321 variants supported up to four strain-gauge load cells (350 Ω) with a combined cable resistance tolerance of up to 40 Ω. Subsequent hardware revisions expanded diagnostic capabilities, added support for SIWATOOL W PC software for remote parameterization, and improved EMC shielding for use in high-interference environments. The module's firmware architecture uses a dedicated weighing processor independent of the S7 CPU, ensuring that weighing tasks are not affected by CPU scan cycle variations — a critical requirement in legal-for-trade applications.

As the SIMATIC S7-300 platform entered its end-of-life phase (Siemens announced discontinuation of S7-300 hardware in 2023, with support extending to 2028), the SIWAREX WP321 series transitioned into a maintenance and spare parts lifecycle. The functional successor for new installations is the SIWAREX WP371, designed for the SIMATIC ET 200SP platform. However, the WP321 remains the only compatible module for existing S7-300 and ET 200M installations, making long-term spare parts availability a critical operational concern for plant maintenance teams.

SIWAREX WP321 Full Catalog & Functionalities (SKU List)

The following SKUs represent the verified SIWAREX WP321 product range. Each entry reflects a distinct hardware configuration or approval variant within the series:

7MH4601-1AA01: SIWAREX WP321 weighing module, 1-channel, for S7-300/ET 200M, non-trade approved, standard version.
7MH4601-1AB01: SIWAREX WP321, 1-channel, OIML R76 legal-for-trade approved, Class III, up to 3000e.
7MH4601-1AC01: SIWAREX WP321, 1-channel, NTEP legal-for-trade approved, Class III, for North American markets.
7MH4601-2AA01: SIWAREX WP321 with extended temperature range (-25°C to +60°C), non-trade approved.
7MH4601-2AB01: SIWAREX WP321 extended temperature, OIML R76 approved, for outdoor/harsh environment installations.
7MH4610-1AA01: SIWAREX WP321 replacement module kit, includes calibration certificate and SIWATOOL W license.
7MH4615-1AA01: SIWAREX WP321 spare module, factory-calibrated, for direct swap in certified installations.
7MH4650-1AA01: SIWAREX WP321 connection module for ET 200M IM 153-x interface, passive backplane adapter.
7MH4660-1AA01: SIWAREX WP321 shielding and grounding kit for 4-wire load cell connection.
7MH4660-2AA01: SIWAREX WP321 shielding kit for 6-wire load cell connection with sense lines.
7MH4900-1AA01: SIWATOOL W software license for WP321 parameterization, calibration, and diagnostics via PC.
7MH4900-2AA01: SIWATOOL W software upgrade package, adds batch reporting and audit trail functions.
7MH4601-1AA01-Z: SIWAREX WP321 with factory-specific customization (Z-option), per customer specification.
7MH4601-1AB01-Z: SIWAREX WP321 OIML-approved with Z-option customization for special load cell configurations.
7MH4601-1AA01 (Repair Exchange): Siemens-certified repair exchange unit for 7MH4601-1AA01, tested to OEM specification.

Sourcing Hard-to-Find & Obsolete SIWAREX WP321 Parts

Q: Can you support multi-unit or repeat RFQ requests?
A: Yes. Send the model list, target quantity and destination so DRIVEKNMS can review sourcing options and quote the requirement as a project RFQ.

Quality Control for the SIWAREX WP321 Range

The SIWAREX WP321 module integrates a dedicated weighing processor, internal A/D converter, and S7 backplane bus interface — three subsystems that require independent verification during any refurbishment or pre-sale testing process. DriveKNMS applies the following test protocol to all WP321 units:

Backplane bus communication is verified using a SIMATIC S7-300 test rack with IM 360/361 interface modules, confirming correct module identification, parameter read/write, and cyclic data exchange. The internal A/D converter is tested against a calibrated load cell simulator across the full input range (0–30 mV/V), verifying linearity, zero stability, and span accuracy to within ±0.01% of full scale. Legal-for-trade variants (OIML/NTEP) are additionally checked for seal integrity and calibration certificate validity. Firmware version is read and logged; modules with outdated firmware are updated using SIWATOOL W prior to dispatch where applicable. Final functional test includes simulation of overload, underload, and cable break conditions to confirm diagnostic output behavior matches Siemens specification.