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Alarm events

EventNotificationReceived and the AlarmActivated family — alarm and event notifications from OPC UA event-notifier nodes. The right channel for operator-facing alarms with acknowledgement and audit.

OPC UA distinguishes data changes (a value moved) from events (something happened: a threshold was crossed, a condition fired, an alarm was raised). Events arrive as PhpOpcua\Client\Event\EventNotificationReceived. When the notification's payload matches a known alarm shape, the client also dispatches one of the specialised classes (AlarmActivated, AlarmDeactivated, LimitAlarmExceeded, …).

The fields shown below are the real fields on each class.

Note

Publish-driven. Events fire when something drives the publish loop. In managed mode with auto-publish, the daemon drives it for you. In direct mode, your code must call Opcua::publish(...).

Subscribing to events

Create a normal subscription, then attach an event-shaped monitored item to an event-notifier node (typically the Server node, ns=0;i=2253, or an alarm-area node):

php event subscription 
$sub = Opcua::createSubscription(publishingInterval: 1000.0);

Opcua::createEventMonitoredItem(
    subscriptionId: $sub->subscriptionId,
    nodeId:         'ns=0;i=2253',
    selectFields:   [
        'EventId', 'EventType', 'SourceNode', 'SourceName',
        'Time', 'ReceiveTime', 'LocalTime',
        'Message', 'Severity',
        'ConditionName', 'AckedState', 'ActiveState',
    ],
    clientHandle:   10,
);

selectFields is the list of event attributes you want each notification to carry. Server-side EventFilters (Severity > N, EventType = X) are configured via the createMonitoredItems() builder; see opcua-client docs for the filter API.

EventNotificationReceived — the generic class

php EventNotificationReceived 
namespace PhpOpcua\Client\Event;

final class EventNotificationReceived
{
    public function __construct(
        public OpcUaClientInterface $client,
        public int $subscriptionId,
        public int $sequenceNumber,
        public int $clientHandle,
        public array $eventFields,   // associative: field name => decoded value
    ) {}
}

$eventFields is keyed by the field name from your selectFields. There are no $eventId, $severity, $message, $sourceName, $isActive, $isAcked properties on the event — read them out of $eventFields:

$severity   = $event->eventFields['Severity']     ?? null;
$message    = $event->eventFields['Message']      ?? null;
$sourceName = $event->eventFields['SourceName']   ?? null;
$eventIdHex = bin2hex($event->eventFields['EventId'] ?? '');
$isActive   = (bool) ($event->eventFields['ActiveState'] ?? false);
$isAcked    = (bool) ($event->eventFields['AckedState'] ?? false);

Specialised alarm events

When EventNotificationReceived carries alarm-shaped fields, the client also dispatches one of these:

Class Extra fields (beyond $client)
AlarmEventReceived sourceName, message, severity, eventType
AlarmActivated subscriptionId, clientHandle, sourceName, severity, message
AlarmDeactivated sourceName
AlarmAcknowledged sourceName, acknowledger
AlarmConfirmed sourceName
AlarmShelved sourceName, shelved
AlarmSeverityChanged sourceName, oldSeverity, newSeverity
LimitAlarmExceeded subscriptionId, clientHandle, sourceName, limitState, severity
OffNormalAlarmTriggered subscriptionId, clientHandle, sourceName, severity

Note that LimitAlarmExceeded carries a single $limitState string (e.g. "HighHigh"), not limitName/limitValue pairs.

Listener — basic alarm record

php record alarm 
use Illuminate\Contracts\Queue\ShouldQueue;
use PhpOpcua\Client\Event\EventNotificationReceived;

class RecordAlarm implements ShouldQueue
{
    public string $queue = 'opcua-alarms';

    public function handle(EventNotificationReceived $event): void
    {
        $f = $event->eventFields;
        PlcAlarm::create([
            'event_id'    => isset($f['EventId']) ? bin2hex($f['EventId']) : null,
            'event_type'  => (string) ($f['EventType'] ?? ''),
            'source'      => $f['SourceName'] ?? null,
            'severity'    => $f['Severity'] ?? null,
            'message'     => $f['Message'] ?? null,
            'occurred_at' => $f['Time'] ?? null,
            'is_active'   => (bool) ($f['ActiveState'] ?? false),
            'is_acked'    => (bool) ($f['AckedState'] ?? false),
        ]);
    }
}

Routing to operators (using a specialised class)

Listening for AlarmActivated lets you skip the field unpacking for the most common case:

php alarm routing 
use Illuminate\Contracts\Queue\ShouldQueue;
use PhpOpcua\Client\Event\AlarmActivated;

class RouteAlarmToOperator implements ShouldQueue
{
    public string $queue = 'opcua-alarms';

    public function handle(AlarmActivated $event): void
    {
        if (($event->severity ?? 0) < 800) {
            return;
        }

        $operator = $this->findOperator($event->sourceName);
        if (!$operator) {
            return;
        }

        $operator->notify(new PlcAlarmRaised(
            source:   $event->sourceName,
            severity: $event->severity,
            message:  $event->message,
        ));
    }

    private function findOperator(?string $sourceName): ?User
    {
        return User::role('operator')
            ->whereHas('assignedLines', fn ($q) => $q->where('plc_source', $sourceName))
            ->first();
    }
}

PlcAlarmRaised is a Laravel Notification — it can dispatch to mail, Slack, broadcast, database, SMS, etc. See Integrations · Notifications.

Acknowledgement

Acknowledging an alarm is an OPC UA method call. The real client API is call(NodeId|string $objectId, NodeId|string $methodId, array $inputArguments = []): CallResult:

php ack endpoint 
use PhpOpcua\LaravelOpcua\OpcuaManager;
use PhpOpcua\Client\Types\StatusCode;

class AcknowledgeAlarmController
{
    public function ack(Request $request, OpcuaManager $opcua): JsonResponse
    {
        $request->validate([
            'event_id' => ['required', 'string'],
            'comment'  => ['nullable', 'string', 'max:255'],
        ]);

        $eventId = hex2bin($request->input('event_id'));

        $result = $opcua->call(
            objectId: 'ns=0;i=2782',   // ConditionType
            methodId: 'ns=0;i=9111',   // Acknowledge
            inputArguments: [
                $eventId,
                ['locale' => 'en', 'text' => $request->input('comment', '')],
            ],
        );

        if (! StatusCode::isGood($result->statusCode)) {
            return response()->json([
                'error' => 'Ack failed: ' . StatusCode::getName($result->statusCode),
            ], 422);
        }

        PlcAlarmAck::create([
            'event_id' => $request->input('event_id'),
            'user_id'  => $request->user()->id,
            'comment'  => $request->input('comment'),
            'acked_at' => now(),
        ]);

        return response()->json(['status' => 'acked']);
    }
}

The server emits a follow-up AlarmAcknowledged (and an EventNotificationReceived with AckedState = true).

Audit chain

Every alarm and every ack is recorded. A 3-table schema does this cleanly:

Table Records
plc_alarms Alarm events (active, inactive)
plc_alarm_acks Acknowledgements
plc_alarm_chain Chain of state changes for a single event id

See Recipes · Alarm routing for the full migration and listener set.

Severity → routing

Severity Common usage Route
1 - 100 Info / diagnostic Database only
101 - 400 Low warning Database + UI banner
401 - 700 Warning Operator dashboard + Slack
701 - 900 Critical Slack + page on-call
901 - 1000 Emergency Page + phone tree

Configure the thresholds in config:

php config/alarms.php 
return [
    'severity_thresholds' => [
        'page'   => 900,
        'slack'  => 700,
        'email'  => 400,
        'record' => 0,
    ],
];

…and route in the listener:

php threshold routing 
use Illuminate\Contracts\Queue\ShouldQueue;
use PhpOpcua\Client\Event\AlarmActivated;

class RouteBySeverity implements ShouldQueue
{
    public function handle(AlarmActivated $event): void
    {
        $sev = $event->severity ?? 0;
        $thresh = config('alarms.severity_thresholds');

        if ($sev >= $thresh['page'])  { $this->page($event); }
        if ($sev >= $thresh['slack']) { $this->slack($event); }
        if ($sev >= $thresh['email']) { $this->email($event); }

        $this->record($event);
    }
    // ...
}

Broadcasting alarms to the UI

php alarm broadcast 
use Illuminate\Broadcasting\PrivateChannel;
use Illuminate\Contracts\Broadcasting\ShouldBroadcastNow;
use PhpOpcua\Client\Event\AlarmActivated;

class AlarmBroadcasted implements ShouldBroadcastNow
{
    public function __construct(
        public readonly ?string $source,
        public readonly ?int    $severity,
        public readonly ?string $message,
    ) {}

    public function broadcastOn(): PrivateChannel
    {
        return new PrivateChannel('plc.alarms');
    }
}

class BroadcastAlarmToUI
{
    public function handle(AlarmActivated $event): void
    {
        broadcast(new AlarmBroadcasted(
            source:   $event->sourceName,
            severity: $event->severity,
            message:  $event->message,
        ));
    }
}

Operator UIs (Livewire, Filament) subscribe to plc.alarms and update in real time.

Filters

Server-side filtering (via OPC UA EventFilter) is much cheaper than listener-side filtering — a noisy plant can emit thousands of low-severity events per minute and you do not want to deliver them all to PHP. See the createMonitoredItems() filter options in opcua-client for the exact API.

Last updated · 2026-05-25
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