Settings Tab

OPC Data Access Source System

You have created a source system that is based on the OPC DA standard. See also: Basic Concepts of OPC and OPC DA Source System.

To make the settings for the OPC DA source system, select the OPC DA source system in the Plant Connectivity Management Console and click on the Settings tab.

For the information you need to enter, use the following table:

OPC DA Settings
Field	Description
Acquisition Mode	Specifies whether, in the case of a tag query, PCo is to obtain the value of the queried tag from the OPC server synchronously or asynchronously in the query process.
Force Flat Namespace	If you choose the setting On, a flat namespace is created. In this case, all hierarchy information is removed from the namespace of the OPC DA server and stored at root level. Note The setting Force Flat Namespace is only possible for OPC DA 2.05a.
Use Vendor Filter	If your source system supports the OPC specification 3.0, you can use this setting to specify that the source-system-specific filter method is used during browsing and not the general filter method that applies to all source systems. To do so, choose the setting On. When you enter the filter string, you need to adhere to the syntax specified by the software maker of your source system.
Synchronous Read Source	This field is only used in the query process. You can make the following settings: From Device With this setting, the tags are read directly from a device. From Cache With this setting, the tags are read from the cache of the OPC DA server. This setting results in better performance.
Acceptable Data Quality	With this setting, you define the OPC data quality of a tag that is to be allowed. When a tag is read out of the OPC source system, the data quality of the tag is also provided and can be taken into account accordingly. Example For example, you have set the data quality in PCo to Good. The OPC server checks the PCo settings and only sends tags with the appropriate data quality, meaning that a tag with poor data quality is not transferred to PCo in this case. The following data quality settings are possible: Any Quality This is the default setting. This setting means that the data quality of a tag is not taken into account. Good If you choose the Good setting, only tags with good data quality are used. If the data quality is poorer (Uncertain or Bad), PCo issues an error message. Uncertain If you choose the Uncertain setting, only tags with the data quality Good or Uncertain are accepted. If the data quality is poor, PCo issues an error message. Bad If you choose the Bad setting, PCo also accepts tags with poor data quality. Error The OPC server sets the data quality of a tag to Error if the call has failed. The effect of the Error setting is that tags with incorrect data quality are also accepted by PCo.
Browsing Mode (DA 2.05a)	The browsing mode specifies the internal technique with which the hierarchical namespace of an OPC DA 2.05a server is to be browsed. The following settings are possible: Absolute Path This is the default setting. With this setting, the direct path is given internally during browsing and the system goes directly to the desired hierarchy node. Relative Path You must only use this setting if browsing is not successful using the default setting. This can occur on servers that do not quite conform to the OPC specification during browsing. With this setting, each level in the namespace is browsed. It is not possible to skip a level. Example If you are using an RSLinx server, you need to use the Browsing Mode Relative Path setting.

In the following area, you make the settings for a group of tags. These settings then apply to all tags of this group on the OPC server.

Group Settings
Field	Description
Name	Name of an OPC-server-internal group of tags. This group comprises all tags specified for a certain agent instance on the Subscription Items tab. You can choose any name for the group.
Update Rate	Indicates the rate at which the OPC server is to send values to PCo. If you specify 100 milliseconds, for example, the OPC server is to send values to PCo every 100 milliseconds.
Deadband	Limit value for filtering out measurement values. Here you can enter a percentage to define the bandwidth in which the value of a tag must at least change before the OPC DA source system reports the value to PCo as changed. Example You have defined a minimum and a maximum value for a specific tag on the OPC server. The percentage that you enter here in the Deadband field is applied to the difference between the minimum and maximum value. For example, on the OPC server, you have specified for the tag that a tag value is to be between 0 and 100. With a deadband of 10%, the tag value must now change down or up by 10 compared to the last reported value so that a notification is sent from the OPC server. If a tag value is 50 and changes to 52, no notification is sent. If the tag value changes later to 58, a notification is still not sent. Only when the tag value reaches 60 is a notification triggered from the OPC server.