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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

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