How can LON communications be throttled in MNL-800 controllers?


Too much LON communications traffic can cause LON communications errors.

Product Line

TAC I/A Series


MNL-800 controllers on LON network


Sending output LON SNVT values too frequently or more often than reasonably needed.


There are a series of NCI (configuration) objects that control the transmission and reception of these data values on the LON network.
One of four NCI objects (nciSndHeartBeatA, B, C or D) are assigned to each NVO object in the application program. This value regulates the periodic LON transmission queuing of the NVO object values for each binding.
One of four NCI  objects (nciRcvHeartBeatA, B, C or D) are assigned to each NVI object in the application program. This value regulates the fallback timeout for each NVI object value. If a value is not received via the binding in this time period, the NVI object value will revert to its application defined default value.

In an MNL-800 controller, there are two additional NCI objects that are used to regulate the flow of data onto the LON network.
The nciMinOutTime object is used to throttle the transmission of all data values queued to be sent via bindings over the LON network. This NCI object sets the transmission time interval between each NVO value being sent on the network. The important fact here is that the product of the number of bound NVO values times this interval (nciMinOutTime) must be LESS than the shortest nciSndHeartBeatX (X=A, B, C or D) interval.

For example, if the Send HeartBeat is set to the default of 120 seconds and there are 60 NVO SNVTs bound from this controller, the nciMinOutTime must be set to a value of less than 2 seconds.  The recommendation for setting this SNVT value one half the shortest nciSntHrtBr divided by the number of NVO SNVTs bound from the controller.  

The nciMinPropTm object is used to regulate the transmission queuing of changing bound NVO object values. This timer acts as a time based filter to prevent a rapidly changing NVO value, such as a constantly changing temperature, from overwhelming the communication capacity of the LON network. Typically this value is set to a value of 1 to 5 seconds.

Additional information can be found in Chapter 6 of the WorkPlace Tech Tool 4.0 Engineering Guide (F-27254).

This section is provided to give the reader a basic understanding of bound LON communications, as applied to LON controllers in general.
Data communications across a LON network is accomplished by using a LON Network management tool to create a binding between a device with a data source (NVO object) and one or more devices with data receivers (NVI objects) in other LON controllers. The device containing the data source will send the bound data value at a periodic rate, as defined by the associated SendHeartBeat NCI object, and whenever the value of that object changes. If the NVI object does not receive a value from the sender (bound NVO object) within a specified time period, as defined by the associated ReceiveHeartBeat NCI object, the NVI object will use a local fallback value until such time as it receives a new value via the binding.