BIHL+WIEDEMANN BWU1840 BWU1416 Retrofit-Compatible Safety Master

BIHL+WIEDEMANN BWU1840 BWU1416 Retrofit-Compatible Safety Master for Legacy AS-Interface Systems

The BIHL+WIEDEMANN BWU1840 and BWU1416 are ruggedized AS-Interface (AS-i) Safety Master modules engineered for demanding industrial environments where signal integrity, functional safety, and long-term availability are non-negotiable. These modules serve as the central safety communication backbone in AS-i network architectures, managing safe slave polling, safety monitor integration, and SIL 3 / PLe-compliant emergency stop and protective device circuits. For plant engineers and maintenance teams managing aging automation infrastructure, the BWU1840 and BWU1416 represent a proven, field-tested retrofit path that avoids the cost and risk of full PLC platform migration.

In legacy control systems built around AS-Interface generation 2 or early generation 3 topologies, the Safety Master is often the first component to reach end-of-life due to firmware obsolescence, connector wear, or discontinued vendor support. The BWU1840 and BWU1416 are designed to slot into existing AS-i network segments with minimal rewiring, preserving the original field device addressing, safety monitor configuration, and PLC program logic. This makes them a preferred choice for brownfield retrofit projects where downtime windows are measured in hours, not days.

Upgrade Compatibility Table

Retrofit Planning for Existing Automation Systems

Replacing a Safety Master in a live AS-Interface network requires careful pre-planning to protect both personnel safety and production continuity. Before removing the legacy BWU module, engineers should export the complete slave address configuration using the BIHL+WIEDEMANN BWConfig software or compatible AS-i Control Tools suite. This configuration file captures all 62 possible slave addresses, their assigned I/O profiles, and the safety slave pairing data that the safety monitor — typically a BWU3xx or BWU2xx series safety monitor — relies on to validate safe state transitions.

On the power side, the AS-i segment power supply must be verified to deliver sufficient current for the new module and all connected field devices. In many legacy installations, the original AS-i power supply — such as a BIHL+WIEDEMANN BWN series or equivalent 30V AS-i power supply — was sized for a smaller slave count. If the retrofit involves adding new AS-i safety slaves, such as additional BWU series safety I/O modules or third-party AS-i safety sensors, the power budget must be recalculated before commissioning.

For systems integrated with PROFIBUS DP networks, the Safety Master’s GSD file must be re-imported into the PLC engineering tool — typically Siemens STEP 7 or TIA Portal for S7-300 or S7-400 series controllers — to ensure the DP slave configuration matches the new module’s diagnostic and I/O data structure. In PROFINET environments, the GSDML file serves the same purpose. Engineers should also verify that the PLC’s DP master module, such as a Siemens CP 342-5 or CP 443-5, is configured with the correct baud rate and watchdog timeout for the AS-i gateway.

Terminal wiring for the BWU1840 and BWU1416 follows the standard AS-i two-wire topology. The yellow AS-i cable carries both power and data, while the black auxiliary power cable supplies 24 VDC to safety-relevant output devices. During the physical swap, technicians should label all terminal connections before disconnection and photograph the existing wiring layout. In control cabinets where space is constrained, the DIN rail mounting footprint of the BWU1840 and BWU1416 is compatible with standard 35mm rails, but adjacent modules — including AS-i repeaters, AS-i analyzers, or decoupling modules — should be checked for clearance.

HMI screens linked to AS-i diagnostic data, such as Siemens TP700 or TP1200 comfort panels running WinCC Flexible or WinCC Advanced, may display slave status, safety monitor state, or AS-i network health. After the module swap, these HMI screens should be validated to confirm that the diagnostic data tags still map correctly to the new Safety Master’s data interface. In some legacy projects, HMI tag addresses were hard-coded to specific DP slot offsets that may differ between BWU hardware revisions.

For systems using AS-i gateways to communicate with higher-level SCADA or DCS platforms — such as Honeywell Experion PKS or Yokogawa CENTUM VP — the gateway’s communication parameters, including station address, baud rate, and data consistency settings, should be documented before the swap and verified after commissioning. Signal isolators installed between the AS-i segment and the control room I/O marshalling panel should also be checked for compatibility with the new module’s output signal levels.

Downtime Control During System Migration

Minimizing unplanned downtime during a Safety Master replacement is the primary concern for maintenance teams operating continuous process lines or discrete manufacturing cells with tight cycle time requirements. The recommended approach is to perform the BWU1840 or BWU1416 swap during a scheduled maintenance window, with a pre-tested spare module on hand and the full slave configuration backup verified before the window opens.

The replacement sequence should follow a structured procedure: first, place the AS-i segment in a safe state by triggering the safety monitor’s muting or bypass function under controlled conditions; second, de-energize the AS-i power supply and disconnect the yellow and black AS-i cables from the legacy module; third, mount the new BWU1840 or BWU1416 on the DIN rail and reconnect all terminals per the documented wiring layout; fourth, restore power and use BWConfig or the AS-i Control Tools to upload the saved slave address configuration to the new module; fifth, perform a full safety function test — including emergency stop loop verification, light curtain response testing, and safety monitor reset — before returning the segment to automatic mode.

In multi-segment AS-i networks, where a single PLC controls multiple AS-i masters through a PROFIBUS or PROFINET backbone, only the affected segment needs to be taken offline. Other segments can continue operating, preserving partial production capacity during the maintenance window. This segmented approach is particularly valuable in large control cabinets housing multiple BWU Safety Masters alongside other automation components such as frequency inverters, motor starters, and I/O expansion modules.

NINERMAS supplies the BWU1840 and BWU1416 with pre-shipment functional testing completed and full test documentation included. Each unit is verified for AS-i communication integrity, safety relay output function, and power supply compatibility before dispatch. Combined with a 12-month warranty covering both parts and workmanship, this ensures that retrofit teams can proceed with confidence and that any post-installation issues are resolved without additional cost to the end user.

Retrofit Support FAQ

Q1: Is the BWU1840 a direct drop-in replacement for the BWU1416, or are there configuration differences?
The BWU1840 and BWU1416 share the same AS-Interface V3.0 Safety Master architecture and are functionally equivalent for most retrofit applications. However, specific firmware versions and communication interface options (PROFIBUS vs. PROFINET) may differ between part numbers. Always confirm the communication protocol variant required by your PLC backplane before ordering. NINERMAS can provide datasheet confirmation and pre-shipment verification upon request.

Q2: Do I need to reprogram the PLC after replacing the Safety Master?
In most cases, the PLC program logic does not require modification if the new BWU module is configured with the same slave address table and the GSD/GSDML file is re-imported correctly into the engineering tool. The safety monitor configuration — including safe slave pairing and output relay assignment — must be re-validated and re-commissioned according to the original safety function documentation. A full safety function test is mandatory before returning the system to production.

Q3: What is the lead time and warranty coverage for the BWU1840 and BWU1416?
NINERMAS maintains in-stock inventory of the BWU1840 and BWU1416 to support urgent retrofit and breakdown replacement requirements. Standard lead time for in-stock units is 3–7 business days for international shipment. Each unit is supplied with a 12-month warranty covering manufacturing defects and functional performance, supported by pre-shipment test documentation. Long-term supply commitments are available for customers managing multi-year spare parts programs.

Q4: Can the BWU1840 or BWU1416 operate with third-party AS-i safety slaves from other manufacturers?
Yes. The BWU1840 and BWU1416 comply with the AS-Interface Safety at Work specification, which defines interoperability between certified AS-i safety masters and safety slaves from different manufacturers. Field devices such as Pilz PSS safety relays, Schmersal AS-i safety switches, and Pepperl+Fuchs AS-i safety sensors can be integrated into a BWU-managed AS-i segment, provided each device holds a valid AS-i safety certification and is correctly addressed and paired in the safety monitor configuration.