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Description
Application ScenariosA 600 MW coal-fired unit running Bailey INFI 90 on the balance-of-plant side hit a rack-space squeeze during a retrofit that added 56 new motor-status points (circuit-breaker auxiliary contacts from the 6 kV switchgear + local ISOL/READY pushbutton statuses from the pulverizer lube-skids). The main MFC rack was full—adding a second full-size DI card would have meant a new baseplate, new power feed, and a week of loop-check. Instead, the instrumentation lead dropped an ABB NDSM05 into a satellite card rack daisy-chained off the MFC’s slave bus, landed all 56 points on the 64-channel spread, and configured the MFC as master to poll the NDSM05 in 10 ms groups. The “default” switch on the NDSM05 was set to “last-state-hold” so that a lost master comms wouldn’t false-trip the ESD annunciator bits. Commissioning took one afternoon; the plant avoided a second MFC baseplate and kept the loop-check within the outage window. Six months later during a storm-induced PCU reboot, the NDSM05 held its DI states exactly as configured—no spurious breaker-status alarms flooded the annunciator.
Parameter
| Main Parameters | Value/Description |
|---|---|
| Product Model | ABB NDSM05 |
| Manufacturer | ABB (Bailey INFI 90 / Net 90 lineage) |
| Product Category | Digital Slave Input Module |
| System Compatibility | ABB Bailey INFI 90 / Net 90 DCS |
| Digital Input Channels | 64 CH, 24 V DC nominal (±20%) |
| Input Type | Dry contact or voltage-driven (5 kΩ typ. input impedance) |
| Channel Isolation | Optical isolation, 150 V RMS channel-to-channel & channel-to-system logic |
| Response Time | < 5 ms (signal change → backplane update) |
| Propagation Delay | 25–100 µs (low↔high / high↔low, per DSM05 baseline) |
| Power Supply | 5 V DC ±5% (module logic from backplane), 24 V DC (110 supply, 21.6–26.4 V) |
| Current Consumption | ~757 mA @ 5 V typ. (logic), plus I/O load |
| Power Dissipation | ~6 W typical (4.6 W logic + 1.0 W I/O + 5.0 W 24 V I/O buffer, per DSM05 baseline) |
| Surge Withstand | IEEE 472-1974 (IEEE SWC) on input channels |
| Mounting | Bailey system card rack (single-slot) or 35 mm DIN rail |
| Operating Temperature | 0 °C to +60 °C |
| Storage Temperature | -20 °C to +85 °C |
| Humidity | 5%–95% RH, non-condensing |
| Dimensions (H×W×D) | 140 × 80 × 210 mm |
| Weight | Approx. 1.2 kg |
| Certifications | CE / CSA / UL / RoHS |
Technical Principles and Innovative Values
- Innovation Point 1: Master-Slave Polling over INFI 90 Backplane. The NDSM05 has no intelligence of its own—it’s a “queried” slave. The MFC/PCU (master) periodically polls groups of eight DI channels, reads the group state, and the NDSM05 echoes it back over the backplane. This offloads the MFC’s scan—instead of the MFC debouncing 64 contacts itself, the NDSM05 buffers them and the master picks up fresh group-states every backplane cycle. The front-panel green “STATUS” LED confirms healthy master-slave handshake; red STATUS + lit group-signal LEDs flags a default event.
- Innovation Point 2: Per-Channel Optical Isolation + IEEE 472 Surge Rating. Each of the 64 DI channels is galvanically isolated from system logic and from each other (150 V RMS channel-to-channel, 150 V RMS channel-to-system). Combined with IEEE 472 surge-withstand compliance on the input side, the NDSM05 shrugs off the induced transients that ride long tray-runs from 6 kV switchgear auxiliary contacts—common in power-plant retrofit racks where the slave sits 40 m from the breaker yard.
- Innovation Point 3: Configurable Default Behavior on Master Loss. The NDSM05 carries a module-level configuration switch (documented in the DSM05/NDSM05 instruction) that tells the slave what to do if the master disappears: either drive all outputs (where applicable on sibling DSM variants) to a preset safe state, or hold the last-known state. On the NDSM05 (input-only), this manifests as how the group-status LEDs present during a backplane loss and whether the slave continues echoing last-known DI states to a recovering master. For ESD-adjacent DI (valve-limit confirms, emergency-pushbutton latches), setting this right avoids false-clearing annunciator bits during a PCU reboot.
