DataChangeFilter

概述

OPC UA Part 4 §7.17 DataChangeFilter 让客户端告诉服务端何时 push 数据, 减少 Publish 流量:

• Trigger — 触发条件 (Status / StatusValue / StatusValueTimestamp)
• DeadbandType — 死区类型 (None / Absolute / Percent)
• DeadbandValue — 死区数值

API

类 / 字段	类别	读写	说明
DataChangeFilter(trigger, deadband_type, deadband_value)	类	—	过滤器
sub.add(node_id, attr, sampling_ms, mode, queue_size, discard_oldest, filter)	方法	写	带 filter 的重载

相关结构:

class DataChangeTrigger(IntEnum):
    STATUS                 = 0   # 仅 StatusCode 变化
    STATUS_VALUE           = 1   # StatusCode 或 Value 变化 (默认)
    STATUS_VALUE_TIMESTAMP = 2   # 任一变化

class DeadbandType(IntEnum):
    NONE     = 0   # 无死区
    ABSOLUTE = 1   # 绝对死区
    PERCENT  = 2   # 百分比死区 (基于 EURange)

代码示例

from opcua import (
    DarraOpcUa, AttributeId, MonitoringMode,
    DataChangeFilter, DataChangeTrigger, DeadbandType
)

with DarraOpcUa("opc.tcp://localhost:4840") as ua:
    ua.connect()

    sub = ua.create_subscription(publishing_interval_ms=100)

    # 1) 绝对死区 0.5
    filter1 = DataChangeFilter(
        trigger=DataChangeTrigger.STATUS_VALUE,
        deadband_type=DeadbandType.ABSOLUTE,
        deadband_value=0.5,
    )
    mi1 = sub.add("ns=2;s=Temp", AttributeId.VALUE, 100,
                  MonitoringMode.REPORTING, 1, True, filter1)

    # 2) 百分比死区 2%
    filter2 = DataChangeFilter(deadband_type=DeadbandType.PERCENT, deadband_value=2.0)
    mi2 = sub.add("ns=2;s=Flow", AttributeId.VALUE, 100,
                  MonitoringMode.REPORTING, 1, True, filter2)

    # 3) 仅 Status 变化
    filter3 = DataChangeFilter(trigger=DataChangeTrigger.STATUS)
    mi3 = sub.add("ns=2;s=Comm.Status", AttributeId.VALUE, 200,
                  MonitoringMode.REPORTING, 1, True, filter3)

    @sub.on_data_changed
    def on_dc(args):
        print(f"[mi={args.client_handle}] {args.value.value} ({args.value.status})")

实现说明

• Stack 不支持时 SDK graceful 降级:
  • 仍调底层 add 注册 MI, filter 失效, 数据全量上报
  • filter 缓存到本地, 重连/重建时仍可还原
  • 推一条 Diagnostic Warn 事件
• Percent 死区依赖目标节点的 EURange Property

最佳实践

• 模拟量首选 Absolute, 例如 0.5°C
• 大量程信号用 Percent
• 数字量不需 filter
• 死区不要太大, 经验 0.1%-2%

跨语言对照

C#	Python	Java	C++	Rust	C
DataChangeFilter	DataChangeFilter	DataChangeFilter	DataChangeFilter	DataChangeFilter	DarraUa_DataChangeFilter

下一步

• EventFilter
• Add Monitored Items