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Alarms

Triggering

An alarm workflow begins when a monitored tag or expression meets a defined alarm condition. This condition might signal a value exceeding a limit, a rapid rate of change, or another system event. The system detects the condition and generates an alarm event.

Notification

The system sends out notifications based on the configuration of the associated AlarmGroup. These notifications can include visual alerts on operator screens, audible alarms, emails, text messages, or integration with external systems. Notifications target the appropriate personnel based on alarm priority and area.

Acknowledgment

Operators acknowledge alarms, indicating awareness of the issue. The AlarmGroup might require acknowledgment before certain actions occur or to silence audible notifications. Acknowledgment status is tracked within the system.

Resolution

Operators investigate and address the root cause of the alarm. This might involve corrective action, system adjustments, or equipment maintenance. Once the underlying issue is resolved, the alarm condition clears.

Clearing and Auto-Acknowledgment

When the alarm condition no longer exists, the alarm clears. Some alarms might clear automatically, while others might require manual clearing by an operator. The Alarms Module can also employ auto-acknowledgment timeouts, where an alarm automatically transitions to an acknowledged state after a set period if the operator has not taken action.

Logging and Audit Trails

The Alarms Module logs alarm events, acknowledgments, state changes, and any associated user actions. This log creates a comprehensive audit trail. It assists in troubleshooting, analyzing system performance, and ensuring compliance with any required standards or regulations.

Runtime Execution

Once the AlarmGroup and items have been configured, the Alarms Module can be executed to start monitoring the specified tags and conditions. During Runtime, the Alarms Module continuously evaluates the conditions of the AlarmItem and generates alarms when the conditions are met. The alarms are then added to the alarm database and can be visualized and acknowledged by the operators. The runtime behavior of the Alarms Module can be controlled through runtime attributes such as alarm logging level, acknowledge timeout, and alarm retention time.

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Alarm Lifecycle

State Machine

Each alarm item follows this state progression:

• Normal - Condition not met
  • → Active (condition triggered)
• Active - Condition met, not acknowledged
  • → Acknowledged (operator ack)
  • → Normalized (condition cleared)
• Acknowledged - Condition met, acknowledged
  • → Normal (condition cleared)
• Normalized - Condition cleared, not acknowledged
  • → Normal (operator ack)

State Transitions

csharp

// State transition events
OnActive()      // Normal → Active
OnAcknowledge() // Active → Acknowledged
OnNormalize()   // Active → Normalized
OnReturn()      // Any → Normal

Evaluation Process

Scan Cycle

The engine evaluates alarms in cycles:

1. Tag Value Update - Tag system notifies engine
2. Condition Check - Evaluate against limits
3. Deadband Verification - Apply time/value deadbands
4. State Evaluation - Determine state change
5. Event Generation - Create alarm event
6. Notification Dispatch - Trigger notifications

Multi-Threading

• Main Thread - Coordinates evaluation
• Evaluation Threads - Pool for condition checking
• Database Thread - Async logging
• Notification Threads - Parallel notification dispatch

Thread pool size: Min(CPU cores * 2, Active alarm count / 100)

Condition Evaluation

Standard Conditions

For each scan cycle:

IF (EvaluateCondition(TagValue, Limit))
  AND (NOT InDeadband())
  AND (EnableCondition == True)
  AND (Group.Enabled == True)
THEN
  TriggerAlarm()

Rate of Change

Special handling for RateOfChange:

CurrentRate = (CurrentValue - PreviousValue) / TimeDelta
IF (CurrentRate >= Limit)
  TriggerAlarm()

Sampling: Every 100ms for RateOfChange conditions

Deviation Alarms

Deviation = ABS(TagValue - Setpoint)
IF (Deviation > Limit + SetpointDeadband)
  TriggerAlarm()

Deadband Processing

Time Deadband

Prevents re-triggering within time window:

• Activation - Alarm triggers at T0
• Deadband Period - T0 to (T0 + TimeDeadband)
• Blocked - Cannot re-trigger during period
• Clear - After deadband expires

Value Deadband

Hysteresis to prevent chattering:

• Hi Alarm Example:
  • Trigger: Value >= 100
  • Clear: Value < (100 - Deadband)
  • Re-trigger: Value >= (100 + Deadband)

Combined Deadbands

Both time AND value must be satisfied:

CanRetrigger = (TimeSinceLastAlarm > TimeDeadband) 
            AND (ValueChange > ValueDeadband)

Database Operations

Write Queue

Asynchronous database writes:

• Queue Size: 10,000 events (configurable)
• Batch Size: 100 events per write
• Flush Interval: 1 second or when batch full

Event Types Logged

• Alarm Active - Condition triggered
• Alarm Acknowledged - Operator acknowledgment
• Alarm Normalized - Condition cleared
• Alarm Return - Return to normal
• Configuration Change - Runtime modifications

Database Schema

sql

AlarmEvents (
  EventID BIGINT PRIMARY KEY,
  Timestamp DATETIME,
  TagName VARCHAR(255),
  AlarmGroup VARCHAR(100),
  AlarmArea VARCHAR(255),
  EventType INT,
  Value FLOAT,
  Limit FLOAT,
  Message TEXT,
  UserName VARCHAR(100),
  AckTime DATETIME
)

Notification Pipeline

Dispatch Sequence

1. Group Notification - Check NotificationMethod
2. Sound Alert - Play configured sound
3. Visual Update - Update display elements
4. Script Execution - Call custom methods
5. External Systems - API calls/integrations

Priority Handling

High-priority alarms bypass queue:

Priority >= 900: Immediate dispatch
Priority 500-899: High priority queue
Priority 100-499: Normal queue
Priority < 100: Low priority queue

Performance Optimization

Evaluation Strategies

Lazy Evaluation:

• Only evaluate on tag change
• Skip disabled alarms
• Cache unchanging conditions

Batch Processing:

• Group related alarms
• Evaluate in parallel
• Single database transaction

Memory Management

• Alarm Pool: Pre-allocated alarm objects
• Event Buffer: Circular buffer for events
• Cache Size: Last 1000 evaluations
• String Interning: Reuse message strings

CPU Optimization

• Condition Caching: Store compiled expressions
• SIMD Operations: Vectorized limit checks
• Thread Affinity: Pin threads to cores

Startup Sequence

1. Load Configuration - Read alarm definitions
2. Initialize Database - Connect and verify schema
3. Compile Conditions - Pre-compile expressions
4. Cache Warmup - Load recent alarm states
5. Apply Disable Time - Suppress per settings
6. Begin Evaluation - Start scan cycles

Shutdown Sequence

1. Stop Evaluation - Halt new scans
2. Process Queue - Complete pending evaluations
3. Flush Database - Write all events
4. Save State - Cache current states
5. Close Connections - Cleanup resources

Advanced Configuration

Engine Tuning Parameters

Access via configuration file:

xml

<AlarmEngine>
  <ThreadPoolSize>16</ThreadPoolSize>
  <EvaluationInterval>100</EvaluationInterval>
  <DatabaseBatchSize>100</DatabaseBatchSize>
  <QueueSize>10000</QueueSize>
  <CacheSize>1000</CacheSize>
  <UseParallelEvaluation>true</UseParallelEvaluation>
</AlarmEngine>

Runtime Metrics

Monitor engine performance:

csharp

var metrics = @Alarm.Engine.Metrics;
int evaluationsPerSec = metrics.EvaluationRate;
int queueDepth = metrics.QueueDepth;
double avgEvalTime = metrics.AverageEvaluationTime;
int activeThreads = metrics.ActiveThreadCount;

Troubleshooting

High CPU Usage:

• Reduce evaluation frequency
• Optimize complex conditions
• Increase deadband values
• Check for alarm storms

Database Lag:

• Increase batch size
• Optimize connection string
• Check database performance
• Archive old data

Memory Growth:

• Reduce cache size
• Check for memory leaks
• Monitor queue depth
• Clear old events

Missed Alarms:

• Verify evaluation interval
• Check thread pool size
• Review condition logic
• Monitor system resources

Best Practices

1. Size thread pool appropriately - 2x CPU cores typical
2. Use deadbands effectively - Prevent evaluation storms
3. Optimize conditions - Simple expressions evaluate faster
4. Batch database writes - Reduce I/O overhead
5. Monitor queue depth - Indicates processing bottlenecks
6. Regular maintenance - Archive and optimize database
7. Profile before optimizing - Measure actual bottlenecks

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