Echelon LNS Bedienungsanleitung PDF herunterladen (Seite 231)

LNS Programmer's Guide

217

2. Acquire a DataPoint object to use to write the value of the network

variable monitor point. Then, set the value of the DataPoint object and

call the Write() method. LNS will update the value of the network

variable being monitored with the new value.

Set MyDataPoint = MyNvMonitorPoint.DataPoint

MyDataPoint.FormattedValue = “75.0 1”

MyDataPoint.Write()

NOTE: If the AutoWrite property is set to True, you do not need to call

the Write() method in this step.

Polled Network Variable Monitoring

In the polled monitoring scenario, LNS periodically polls the values of the monitor points

and reports the values using the OnNvMonitorPointUpdateEvent event. 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 when the value changes (for example,

outside air temperature).

To use polled monitoring, you must first 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. Note that

when you set the monitoring options, the PollInterval property determines the rate at

which LNS will poll the value of each network variable being monitored.

Once you have created a monitor set and established a poll interval, you can open and

enable the monitor set, or a group of monitor points within the set. When you open and

enable the monitor set, make sure that the doPoll parameter is set to True. This will

enable polled monitoring for all monitor points on the monitor set. For more information

on how to open and enable monitor sets, see Opening and Enabling Monitor Sets on page

213.

You can stop polled monitoring for an entire monitor set by calling the Disable()

method on the monitor set (this will stop all monitoring). Or, you can stop polled

monitoring by calling the Enable() method with the doPoll parameter set to False

(this will leave monitoring enabled). In this case, polling will not be enabled for that

monitor point, even if it is enabled for the monitor set, until you call Enable() method

on the NvMonitorPoint object with the doPoll parameter set to True.

Once polling for a network variable monitor point has been enabled, your application will

be informed of the result of each poll via the OnNvMonitorPointUpdateEvent event. If

you only want your application to be informed when the value of a network variable

monitor point changes, set the ReportByException property to True when you set the

monitoring options for the set or point.

The OnNvMonitorPointUpdateEvent event includes three parameters: the

NvMonitorPoint object whose value is being reported, a DataPoint object containing

the value of the NvMonitorPoint, and a SourceAddress object that you can use to

identify the device containing the network variable.

Echelon does not recommend using the SourceAddress object to identify the network

variable, since source addresses may change, and translating from a source address to an

application device may be time consuming. A more efficient alternative is to set the

NvMonitorPoint object’s Tag property to a value you can use to identify the network

variable and source device associated with the monitor point when you create it.

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