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--- ezeio2:expref:start [2020-11-03 21:03] – johpar
+++ ezeio2:expref:start [2022-11-16 23:33] – [Field expressions] andreh
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 ===== Expressions =====
-{{indexmenu_n>700}}
+{{indexmenu_n>900}}
 Within the configuration of an ezeio, mathematical expressions are used to produce a value/result for "Fields", "Alarms" and "Conditions". This powerful tool can produce mathematical and logical results using multiple constants and/or variables from the available resources on an ezeio. Expressions can be as simple as the constant "1" to indicate True/ON or as complex as necessary.
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 Since we are looking for kW-hours, we need to divide the momentary power with 36000 (3600 seconds in an hour, and we are re-evaluating 10 times per second).
+=== Example: Signal filter ===
+If data from a register (or other field) includes a lot of noise and needs to be filtered over time, a simple field expression can be used to implement a IIR filter function:
+<code javascript>( f(THIS)*99 + r(1,1) )/100</code>
+Knowing that the expression evaluated 10 times per second, we are keeping 99% of the value, and adding 1% from the signal every 100ms. Thus the response time for this filter is about 7s for a 3dB (50%) response.
 ==== Reverse expressions ====