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TN AppSvr165 Understanding Application Server IO Scan Modes

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Description

This guide from InSource will help you understand the scan modes in application server when talking to IO. The options are:

 

Active

ActiveAll

ActiveonDemand

 

 

  • Author: Mike Viteri
  • Published: 11/9/2015
  • Applies to: Application Server

 

 

Details

The differences between the scan modes are listed below

 

Active

  • Items are deleted and added to the scan group as requested (referenced) by the clients. 
  •  Items that exist when a scan mode change occurs are not deleted unless the previous mode was  ActiveAll and the items are no longer referenced. 
  • The Active scan mode polls all points that are referenced, whether active or inactive. 
  •  In Active scan mode an attribute is always in the active state. When the last reference to the attribute is unregistered/unadvised, the attribute is deleted. 

 

ActiveAll

 

  • Scanning is continuous and dynamic attributes are never removed when unsubscribed.  
  • Items are activated by client requests, but continue to exist even after the client are not interested in them anymore. 
  • Items are not removed when the scan mode changes. 
  • The scan group polls the field device for all points irrespective of whether they are currently active, inactive, or even subscribed to by items.

 

ActiveOnDemand

 

  • When the scan mode is configured as ActiveOnDemand, attributes that are not actively being referenced by any client or object are made Inactive and are not scanned. 
  • New Items are deleted and added to the scan group as requested (referenced) by clients. 
  • Items that exist when a scan mode change occurs are not deleted unless the previous mode was ActiveAll and the items are no longer referenced. 
  • ActiveOnDemand scan mode polls the field device for currently active items only. Inactive items are not scanned. 

 

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