YOKOGAWA ASS9262AT-1: CENTUM CS3000 DCS Analog Signal Sub-unit Board

Technical Dossier

Product Details And Specifications

YOKOGAWA ASS Series Technical Notes

The YOKOGAWA ASS series represents a family of analog signal sub-unit boards engineered for deployment within the CENTUM CS and CENTUM CS3000 Distributed Control Systems (DCS). These systems hold a dominant installed base across global heavy industries including petrochemical complexes, nuclear power facilities, crude oil refineries, LNG terminals, and continuous process manufacturing plants. The ASS-series boards function as the analog front-end interface layer between field instrumentation (transmitters, thermocouples, RTDs, control valves) and the CENTUM CS3000 controller backbone. Their role is critical: signal conditioning, isolation, and conversion at the I/O termination level. Facilities running CENTUM CS3000 architectures—many of which were commissioned between 1998 and 2012—continue to rely on ASS-series boards for both operational continuity and scheduled maintenance cycles. The global installed base of CENTUM CS3000 systems ensures sustained demand for ASS-series spare parts well into the 2030s.

The Evolution of ASS Series Architecture

The ASS series was introduced as part of YOKOGAWA's CENTUM CS platform in the mid-1990s, succeeding the earlier CENTUM-XL and MICRO-XL I/O termination architectures. The original CENTUM CS deployed ASS boards with parallel backplane communication, supporting analog input/output signal ranges of 4–20 mA DC and ±10 V DC. With the transition to CENTUM CS3000 (released circa 1998), the ASS series was refined to support enhanced noise immunity, improved channel isolation (channel-to-channel and channel-to-ground), and tighter signal accuracy tolerances (±0.1% of full scale). The CS3000 R3 revision further extended compatibility with HART-enabled field devices on select ASS input variants. Compatibility between CENTUM CS and CS3000 ASS boards is partial: mechanical form factor is shared, but firmware and bus protocol differences require verification before cross-generation substitution. As CENTUM CS3000 entered its mature/end-of-active-production phase (YOKOGAWA announced migration paths toward CENTUM VP from approximately 2008 onward), the ASS series transitioned from active catalog to long-term maintenance supply status. Facilities that have not migrated to CENTUM VP continue to require ASS boards as direct replacements, making lifecycle sourcing a primary procurement challenge.

ASS Series Full Catalog & Functionalities (SKU List)

The following SKUs represent verified, commonly deployed ASS-series boards within CENTUM CS and CS3000 installations. Classification follows functional role within the DCS I/O architecture:

Analog Input Sub-units (AI)

• ASS9262AT-1: 16-ch analog input sub-unit board, 4–20 mA, for CENTUM CS3000 field termination.
• ASS9262AT-2: 16-ch analog input sub-unit, voltage input variant, ±10 V DC signal range.
• ASS9262BT-1: 8-ch analog input sub-unit, high-density thermocouple/mV input, CS3000.
• ASS9262BT-2: 8-ch analog input sub-unit, RTD (Pt100) input, 3-wire configuration.
• ASS9261AT-1: 16-ch analog input sub-unit, standard current input, CENTUM CS compatible.
• ASS9261BT-1: 8-ch analog input sub-unit, thermocouple input, CENTUM CS generation.

Analog Output Sub-units (AO)

• ASS9263AT-1: 8-ch analog output sub-unit, 4–20 mA current output, CS3000 field termination.
• ASS9263AT-2: 8-ch analog output sub-unit, voltage output, ±10 V DC, CS3000.
• ASS9263BT-1: 4-ch analog output sub-unit, high-resolution 16-bit DAC, CS3000.
• ASS9261CT-1: 8-ch analog output sub-unit, CENTUM CS generation, current output.

Digital Input Sub-units (DI)

• ASS9264AT-1: 32-ch digital input sub-unit, 24 V DC dry contact, CS3000.
• ASS9264AT-2: 32-ch digital input sub-unit, 100–120 V AC wet contact input.
• ASS9264BT-1: 16-ch digital input sub-unit, high-voltage 220 V AC wet contact.

Digital Output Sub-units (DO)

• ASS9265AT-1: 16-ch digital output sub-unit, transistor output, 24 V DC, CS3000.
• ASS9265AT-2: 16-ch digital output sub-unit, relay contact output, 250 V AC/30 V DC.
• ASS9265BT-1: 8-ch digital output sub-unit, high-current relay, 5 A per channel.

Quality Control for the ASS Series Range

ASS-series boards present specific test challenges due to their multi-channel analog architecture and backplane bus communication interface. DriveKNMS applies the following verification protocol to all ASS-series units prior to dispatch:

• Visual inspection: PCB trace integrity, capacitor condition, connector pin alignment, and conformal coating assessment.
• Backplane bus communication test: Each board is seated in a CENTUM CS3000-compatible test rack and subjected to full bus enumeration and address response verification.
• Channel-by-channel analog accuracy test: All AI channels are verified against a calibrated signal source (Fluke 725 or equivalent) across the full 4–20 mA range. Accuracy tolerance: ±0.1% FS.
• Isolation resistance test: Channel-to-channel and channel-to-chassis isolation verified at ≥500 V DC, minimum 100 MΩ.
• Thermal burn-in: 24-hour powered soak at 40°C ambient prior to final inspection.
• Firmware version verification: Confirmed against YOKOGAWA's published CS3000 compatibility matrix.