Echelon LNS - Manual (Page 234)

LNS Programmer's Guide 220
ByVal nvMonitorPoint As Object, _
ByVal dataPoint As Object, _
ByVal srcAddress As Object)
If nvMonitorPoint.Tag = "Room Thermometer" Then
roomTemp = dataPoint.FormattedValue
End If
End Sub
Note that by using the
OnNvMonitorPointUpdateEvent
event as described in this
section, you will receive the events through the LNS Object Server. You can use the
ILcaNvMonitorPointListener interface to receive the events directly from the
network variable monitor point, which may be more efficient. You can only use this
technique if your development environment supports multi-threading. For more
information on this, see Tracking Monitor Point Updates on page 228.
The Implicit Bound Network Variable Monitoring Scenario
In the implicit bound monitoring scenario, LNS implicitly creates a connection from each
monitored output network variable in the monitor set to the corresponding network
variable monitor point. Every time the value of an output network variable on a device is
updated, the device will send a network variable update to LNS through the appropriate
connection. LNS will then report the update to the LNS client application via the
OnNvMonitorPointUpdateEvent
event, as with the polled network variable monitoring
scenario. The network variable connections created by LNS are “invisible” connections,
meaning that you will not see the connections in any of the hub or target collections, and
the connections do not use any network variables on the Network Service Device.
NOTE: Network variable monitor points in temporary monitor sets cannot be
automatically bound by LNS to the monitoring node. As a result, you can only use the
implicit bound network variable monitoring scenario with permanent monitor sets.
Bound monitoring is most efficient when your application needs to be notified
immediately when the value of the network variable changes, but the value may not
change very frequently (for example an alarm or failure condition notification). You will
receive updates sooner using this method than the polled network variable monitoring
method, because your application will be notified of network variable updates as soon as
they occur. When using polled network variable monitoring, you will only receive
OnNvMonitorPointUpdateEvent
events at the rate specified by the
PollInterval
property.
To use implicit bound monitoring, follow these steps:
1. Create a monitor set and add monitor points for the network variables
you want to monitor. For more information on these tasks, see Creating
Monitor Sets on page 194, and Managing Monitor Sets on page 195.
2. When you set the monitoring options for the monitor set, set the
UseBoundUpdates
property to
True
to enable implicit bound monitoring.
Note that it is possible for polled and bound monitoring to take place
simultaneously. Set the
SuppressPollingIfBound
property to
True,
or set the PollInterval property to 0, to ensure that only bound
monitoring takes place.
3. Make sure that you set the
ThrottleInterval
property appropriately.
This property should be set to 0 if you want to be sure that network
variable update events are fired for each update.