DNP3 Event Classes — Prioritized Data Reporting
Key Takeaway
How DNP3 event classes organize data by priority — Class 0 for static data, Class 1/2/3 for event queues with configurable polling rates.
Quick Answer
DNP3 organizes data into four classes. Class 0 represents current static values (integrity data). Classes 1, 2, and 3 are event queues with configurable priority levels. The SCADA master polls each class on a separate schedule — Class 1 most frequently for alarms, Class 3 least frequently for status data.
Class Definitions
| Class | Type | Typical Content | Poll Rate |
|---|---|---|---|
| Class 0 | Static (current values) | All point current values | Integrity poll (infrequent) |
| Class 1 | Events (highest priority) | Critical alarms, safety events | 1-5 seconds |
| Class 2 | Events (medium priority) | Process values, measurements | 5-30 seconds |
| Class 3 | Events (lower priority) | Status changes, diagnostics | 30-120 seconds |
Integrity Poll
A Class 0 integrity poll retrieves all current static values from the outstation, providing a complete snapshot. This is typically run at startup and at longer intervals (5-30 minutes) to ensure master and outstation data are synchronized.
Event Poll
Class 1/2/3 event polls retrieve only queued change events since the last poll. This is much more bandwidth-efficient than polling all data repeatedly and is the primary data exchange mechanism during normal operation.
Assignment Strategy
- Class 1 — Alarms, safety shutdowns, and critical status changes that require immediate operator attention
- Class 2 — Process measurements (pressures, temperatures, flows) that change regularly and need timely reporting
- Class 3 — Equipment status, diagnostic flags, and non-critical information that can tolerate slower reporting
Frequently Asked Questions
A Class 0 poll retrieves all current static values from the outstation — a complete data snapshot. Run at startup and periodically (5-30 minutes) to ensure data synchronization.
Each data object on the outstation is assigned to Class 1, 2, or 3 in the device configuration. The SCADA master polls each class independently on its own schedule.