删除未改变值的消息
问题
如果您希望当消息的有效载荷值自上一条消息以来未发生变化时删除该消息。例如，您有一个传感器以固定间隔发送开关状态，而您只希望知道值何时发生了变化。
解决方案
使用 RBE 节点（按异常报告）来阻止消息，除非其值已更改。
示例
[{"id":"6079638d.df403c","type":"inject","z":"ac14500e.2c57d","name":"","topic":"","payload":"0","payloadType":"num","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":90,"y":1500,"wires":[["87129503.c7b358"]]},{"id":"87129503.c7b358","type":"rbe","z":"ac14500e.2c57d","name":"report-by-exception","func":"deadband","gap":"","start":"","inout":"out","property":"payload","x":300,"y":1520,"wires":[["5e2ffc27.c61dd4"]]},{"id":"5e2ffc27.c61dd4","type":"debug","z":"ac14500e.2c57d","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","x":510,"y":1520,"wires":[]},{"id":"2dc49f96.3070c","type":"inject","z":"ac14500e.2c57d","name":"","topic":"","payload":"1","payloadType":"num","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":90,"y":1540,"wires":[["87129503.c7b358"]]}]
讨论
RBE 可用于删除消息，除非其值已更改。这对于检测变化很有用。
如果正在检查的属性是数字，则该节点还可以配置一个阈值，以确定值必须改变多少才能使消息传递下去。
