The change_detect node

Emits new point-values only if different from the previous point.

  • Multiple fields can be monitored for change by this node.
  • If no fields are given, the complete data-item is compared to the last one.
  • If a reset_timeout is given, all previous values will be reset when no value is received within this amount of time. So that after the timeout the first data_item will be emitted.
  • For value comparison erlang's strict equals (=:=) is used, so 1.0 is not equal to 1.


%% detects any changes in data_items

%% detect changes in one field, with timeout
%% outputs at least the first data_item coming in after a 3 second timeout

%% detect changes in two fields, with timeout
|change_detect('data.State.Err', 'data.State.Msg')

% in-example json notation: 
% {"data": {"x": {"temp": 32.4564}, "y" : {"temp" : 31.15155}} }

|change_detect('data.x.temp', 'data.y.temp')


Parameter Description Default
[node] fields( string_list ) List of fields to monitor optional
reset_timeout( duration ) Previous values TTL 3h