Maximum Send Time

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Maximum send time, also known as Output heartbeat, is a mechanism for forcing output network variables to be updated over the network. It specifies the time interval in seconds between updates to the network variable whether or not its value has changed. For example, setting the output heartbeat to 60 seconds ensures that the output network variable is updated and transmitted to bound input network variables once every 60 seconds.

This setting also allows a network variable to provide an “I’m OK” output that can be used by destination devices to ensure the originating device is still healthy.

Setting output heartbeat to zero disables this feature, that is, the output network variable is updated, within the constraints of minimum send time and send on delta, only when its value changes.

SCPTmaxSendTime is the configuration property for output heartbeat. The default value for output heartbeat is 300 seconds, with the following exceptions:

The Scheduler functional block has a default output heartbeat set to 60 seconds.

Real Time Clock functional block network variables have no output heartbeat.