Specifications
Main Properties
PlantScape Server and Client Configuration Guide 145
PlantScape uses “control confirmation” scans to ensure that controls are actually
performed by a controller. If a point parameter has a source and a destination
address, a parameter is scanned immediately after the value is changed. An alarm
is generated if the scanned value does not match the controlled value.
Source and destination addresses generally refer to locations within real
controllers. These addresses are known as hardware addresses.
The formats of hardware, source, and destination addresses depend on the type
of controller. Details about the format of these addresses can be found in the
Quick Builder online help for each controller.
It is also possible to address information in the server database, for example, the
parameter of another point. These are known as database addresses (see
page 179).
Point Scanning
Scanning is the process by which the server reads values from locations in
controllers, specified by the source addresses, and stores them in point
parameters.
The server uses the scanning process for status, analog, accumulator and access
points.
To minimize the load on the whole system, it is important to plan for and
implement an efficient scanning strategy. The two most common scanning
methods are:
• Periodic
•Exception
Periodic Scanning
Periodic scanning is the regular scanning of a point parameter at specified time
intervals.
You can choose from several scan periods, ranging from seconds to minutes, and
you can assign a different scan period to each input/output point parameter
when you configure each point. For example, if you assign a scan period of 15
seconds to the PV parameter of a point, the server scans the value in the
controller every 15 seconds.
When choosing a scan period, consider the following factors:
• Whether the controller automatically reports changes of state. If so, periodic
scanning might not be necessary (see “Exception Scanning” on page 146).
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