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Represents a numeric input network variable in the program.
The NvInputFanIn can be used in place of NvInputNumeric, in situations requiring a “fan-in” binding, where multiple output network variables are bound to the input network variable. Fan-in (or many-to-one) bindings are used when many controllers need to send information to a single controller, such as would occur with a number of VAV box controllers communicating their space temperature or air flow back to a single air handling unit controller.
Each NvInputFanIn block maintains a memory table of received values from its bound source network variables. The source network variables can be any general purpose or point status network variable, but they must all be of the same network variable type.
In the memory table, the incoming network variable values are stored together with the source device’s subnet:node address. The subnet:node address is the device’s LonTalk address, assigned by the network management tool when the device is commissioned.
As each network variable in the group is updated, the table is accessed and the value is stored in the table location associated with the source subnet:node address and marked as new. If there is no entry in the table for that subnet:node address and there is an unused table location, then both the subnet:node address and the value are stored in that location.
Meanwhile, a background scan is performed periodically and marks new values as old and old values as invalid. The background scan reads the whole table at a rate of one pass every 400 seconds. This scan period guarantees that a value remains valid (marked as either new or old) for 400 to 800 seconds before being marked invalid. The scan period was chosen to ensure that the values of incoming network variables are always valid, when using the default network variable heartbeat of 300 seconds or less.
The network variable type and associated format can be changed by selecting ‘Change NV Type’ from the SmartTag.