Echelon LNS - Manual (Page 228)

LNS Programmer's Guide 214
You can also call the
Disable()
method on a specific
NvMonitorPoint
or
MsgMonitorPoint
object. This will override subsequent calls to the
MonitorSet
object's
Enable()
method. In other words, if you call the
Disable()
method on a
monitor point named
Point A
, and then call the
Enable()
method on the monitor set
containing
Point A
,
Point A
would not be enabled, but all other monitor points in the
monitor set that have not been explicitly disabled would be. Once you have disabled a
monitor point with the
Disable()
method, you can only re-enable it by calling the
Enable()
method on the monitor point, or by closing and re-opening the monitor set it
belongs to.
Once a monitor set or monitor point has been opened and enabled, you can use it for
monitor and control operations. For guidelines on how you can use network variable
monitor points, see Using Network Variable Monitor Points on page 214. For guidelines
on how you can use message monitor points, see Using Message Monitor Points on page
224.
Using Network Variable Monitor Points
This section describes four ways that you can use network variable monitor points to
monitor the values of the network variables on your devices:
• Explicitly Reading the Monitor Point. In this scenario, the application
explicitly reads network variable values individually. This method is
most efficient if network variable values need to be read infrequently and
unpredictably. For more information on this, see Explicitly Reading and
Writing Network Variable Monitor Points on page 215.
• Polled Monitoring. This method is most efficient when the value of a
network variable must be checked regularly, but the application does not
need to know immediately if the value changes (for example, outside air
temperature). In this scenario, LNS periodically polls the value of the
monitor points in the monitor set and reports them to your application
via the
OnNvMonitorPointUpdateEvent
event. For more information
on this, Polled Network Variable Monitoring on page 217.
• Implicit Bound Monitoring. This method is most efficient when you are
monitoring a network variable whose value will change infrequently, but
your application will require immediate notification when the value does
change (for example an alarm or failure condition notification). For more
information on this, see The Implicit Bound Network Variable Monitoring
Scenario on page 220.
• Explicit Bound Monitoring and Control. In this scenario, network
variables are explicitly created on the Network Service Device used by
the monitor and control application, and bound to network variables on
the devices in your network. This method allows the implementation of
fan-in monitoring, which is the process of connecting two or more output
device network variables with a single host input network variable. For
more information, see The Explicit Bound Network Variable Monitoring
and Control Scenario on page 221.
There are two ways you can use network variable monitor points to control the value of a
network variable:
• Explicitly Writing the Monitor Point. In this scenario, the application
explicitly writes network variable values individually, one at a time. This