Application Scenarios
A 350 MW coal-fired power plant was upgrading its boiler rear-pass temperature monitoring, which involved 84 thermocouple points across the superheater, reheater, and economizer sections. Originally wired through barrier-type cold-junction compensators and analog input cards, the arrangement suffered from drift and required frequent re-calibration. The instrumentation team replaced the old I/O with six ABB 57120001-HZ (DSAI 155) boards installed in an S100 I/O rack connected to the Advant Controller 160. Each DSAI 155 acquired 14 differential TC signals with built-in cold-junction compensation referenced to the rack’s ambient sensor. Post-commissioning, the DCS displayed linearized °C values directly—no external scaling required—and the plant’s annual loop-check report showed a 60% reduction in temperature-loop calibration deviations. When one channel flagged an “open circuit” via the module’s wire-break diagnostic, the technician identified and repaired a loose TC connection before any process upset occurred, demonstrating the operational value of the 57120001-HZ‘s embedded diagnostics.
Parameter
| Main Parameters | Value/Description |
|---|---|
| Product Model | 57120001-HZ (DSAI 155) |
| HW Version / Code | 2668 184-143/1 |
| Manufacturer | ABB (Advant OCS / Symphony™ Plus — S100 I/O Series) |
| Product Category | Thermocouple / Analog Input Board (AI Module) |
| Number of Channels | 14 differential input channels, independently configurable |
| Input Signal Types | Thermocouple J, K, T, E, R, S, B, N; optionally mV or 4–20 mA via ext. transmitter |
| A/D Resolution | 16-bit |
| Accuracy | ±0.1 °C typical (K-type TC); ±0.05 % FS for linear signals |
| Cold Junction Comp. | On-board precision CJC sensor, auto-compensated per channel group |
| Isolation | Channel-to-system & channel-group isolation, typ. 500 V–2500 V AC (dep. on rack) |
| Update / Scan Time | Meets process control real-time requirements; typ. 100–500 ms for all channels |
| Power Supply | 5 V DC / 24 V DC via S100 backplane (typ. consumption ≈ 1.8 W) |
| Operating Temp. | 0 °C to +55 °C (32 °F to 131 °F), some sources cite -25 °C to +70 °C for extended |
| Dimensions (approx.) | 324 × 225 × 22.5 mm (L × W × H), standard S100 Eurocard format, single slot |
| Diagnostics | Per-channel open-wire detection, over-range flag, module status LED (RUN/ERR) |
| Hot-Swap | Supported in live S100 rack (with redundant power / proper system config) |
Technical Principles and Innovative Values
The ABB 57120001-HZ (DSAI 155) applies decades of ABB process measurement expertise to simplify temperature data acquisition:
- Innovation Point 1 — Integrated Cold-Junction Compensation & Linearization: Each DSAI 155 contains a calibrated temperature sensor on the board to measure the terminal-block temperature, automatically applying CJ correction and polynomial linearization for each TC type in firmware. This removes the need for external compensation boxes and manual curve-fitting in the control logic.
- Innovation Point 2 — 14 Differential High-Impedance Inputs with 16-bit Sigma-Delta ADC: Unlike lower-resolution multiplexed designs, the module uses a precision sigma-delta converter per channel group with digital filtering, delivering ±0.1 °C repeatability on TC loops even in electrically noisy switchgear rooms.
- Innovation Point 3 — Open-Circuit / Wire-Break Detection: The module continuously monitors input impedance. A broken TC wire or loose terminal produces an immediate diagnostic alarm (“Sensor Failure”) distinguishable from a valid high-temperature reading—preventing false trips or incorrect process actions.
- Innovation Point 4 — S100 Backplane DMA & Hot-Swap Support: Data is exchanged with the Advant / Symphony Plus controller via the S100 bus using direct memory access, minimizing scan overhead. In systems with proper rack power, the 57120001-HZ can be extracted and replaced live; the new board auto-loads its configuration from the controller database on insertion.
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