A device the controller expects to be present has stopped responding. Any control loop that depends on it is driven to its safe state.
| At a glance | |
|---|---|
| Code | 100 |
| Shown as | Device Disconnected |
| In the alarm list | The device’s name, then Disconnected — for example Conductivity Probe Disconnected (upcoming firmware) |
| Severity | Warning |
| Category | 1xx — Device / bus |
| Clears | Automatically, when the device responds again |
| LED | Health light, red dropout |
If the Power light is blinking red, stop and fix that first. A power fault (600) cuts power to the Modbus port, which makes every device on that bus stop responding at once. The disconnection is real, but the cause is upstream — and it will clear on its own once input power recovers.
The giveaway is several devices dropping simultaneously. One device failing is a device problem; all of them failing together is almost always power or bus wiring.
| Cause | What to look for |
|---|---|
| Input power fault | Multiple devices lost at once; Power light blinking red. See 600. |
| Loose or damaged cable | A single device affected. Often intermittent with vibration. |
| Bus wiring problem | Modbus polarity, missing termination, or a star topology instead of a daisy chain. |
| Device lost its own supply | Externally powered devices have their own failure modes. |
| Address or configuration change | A device replaced or re-addressed no longer matches what the controller expects. |
| Electrical noise | Long unshielded runs near variable-frequency drives corrupt bus traffic. |
| Weak WiFi signal | Wireless devices only. The device is too far from the controller, or behind metal. |
| Failed device | Least common, but it happens. |
Before you start: Safety. Isolate power before touching terminals.
1. Note how many devices dropped. One, or several? That single observation separates a device fault from a power or bus fault.
2. If several dropped: use the pattern — see Troubleshooting device connections. Check input power (600) and the bus trunk before looking at any individual device.
3. If one dropped:
Each kind has its own troubleshooting table: Modbus, Wireless, IO-Link.
4. Check what changed. Devices rarely fail spontaneously. Recent work in the panel, a replaced sensor, or a new drive installed nearby are all more likely than a random failure.
5. Confirm recovery. The device reappears and this alarm clears. The loop resumes automatically.
Control loops that need it report Control Inoperable (230) and are held in their safe state — they do not run on stale readings. Restoring the device clears both alarms.