SmartSwarm 300 Series
:
78
In SmartWorx Hub, when you select this Event type on an Input or a Coil, no further configuration is required.
However, if it is selected on an Input Register or a Holding Register, an additional field appears at the top of the
table:
In the “Change by” field, you may enter a percentage value. The MQTT publish will only be triggered if the
enriched register value has changed by
more
than this value. The default value is 0%, which means that ANY
change will constitute a trigger event.
The following example shows a register that usually has a numeric value of 100, but with occasional deviations.
The red annotations show when MQTT publishes will be triggered, assuming that a Change rule is applied, with
“Change by” = 0%:
Note that we get only 13 MQTT messages, as opposed to 68 if we had used a Read rule.
For analog data it probably does not make sense to create a Change rule with “Change by” = 0%, as process noise
will inevitably cause the least-significant bits to change all the time. This will trigger a lot of MQTT publishes, which
may lead to a large cellular bill. The “Change by” field can be used to reject noise.
Continuing the example above, if we apply a Change rule with “Change by” = 10% we can reduce the number of
MQTT messages from 13 to 4:
