OPCIS Groups

Each group represents a connection to an OPC server. As such, more groups result in higher CPU utilization. All tags in an OPCIS belong to a group, which is represented by an OPC Group Facility. An OPC Group Facility can be used to monitor a variety of OPC server and OPC Group statistics. By default, all tags in an OPCIS belong to the group named OPCDEFAULTGROUP. This group is created automatically; on startup the OPCIS creates a facility named OPCDEFAULTGROUP and a set of status tags that represent information about the OPC connection.

Note: If the facility type for an OPCIS group is blank, the OPCIS will automatically update the facility type to OPC_FAC and updates from the OPC server will occur. If the facility type for an OPCIS group is set to any string other than "OPC_FAC", all point tags associated with that group will be disabled. This functionality is logged in the OPCIS log file under "MAX_TRACE" log settings.

For more information about status tags, see the following subsections:

OPC Group Definition Point

One of the tags in an OPC Group Facility is referred to as the OPC Group Definition tag; it has a UDC of SYOPCGDEF, which is a system UDC. 

Point configuration attributes for the OPC Group Definition tag define the information about the group, while the value of the tag defines the update rate of a group. The group point attributes described below will take precedence over OPC service configuration file keyword settings.

The point configuration fields that have special meaning for an OPC Group Definition tag are General 1, Table Driven 1, Table Driven 2, Table Driven 3, and External ID. These fields are configured on the Application and Point Reference pages of the point configuration record:

Field PNT Page Description

General 1

Application

Use the General 1 data field to configure application-specific properties for a particular point. The value can be free-form text up to a maximum of 20 characters.

Group Rollup Filter Definition

Use the General 1 data field to specify a group rollup filter definition. You can use facility attributes or group node attributes.

Use the General 3 data field to reference a Group Service (GRP) attribute if the filter definition exceeds 20 characters.

For more information about uses for these properties, see Filtering a Group Rollup.

OPCIS Points

Many OPC servers initialize tags to a sentinel value (for example, -9999.99) that does not represent a true tag value. Set the General 1 data field to a numeric value that should be ignored. When a tag with this value is received from the external OPC Server, it is marked as unreliable, but the value will be discarded and the previous value is retained.

For more information about OPC Group Definition tags, see OPCIS Groups.

SVCMON Points

For more information, see Validating the SVCMON.

Table Driven 1

Application

Use the Table Driven 1 data field to configure application-specific properties for a particular point. The table entry is from the TRS.CMT1 table.

OPCIS Points

The Table Driven 1 data field has special meaning for an OPC Group Definition tag. It can be used to indicate what to do with the value of an OPC tag with OPC Quality flags that indicate an error. That is, how is the value of the real-time record in the OPCIS updated when unreliable data is returned from an external OPC Server.

Select a value from the drop-down menu or click … to select or configure an entry. Two default options are supported: store the value or ignore the value. The default behavior is to mark it as unreliable and save the value from the external OPC Server.

  • If set to OPCIS Store Unreliable Value (OPCBADSTR) and a value with a bad OPC quality is read from the OPC Server, the value will be stored. When the value is stored, the UNRELIABLE status bit is set and the timestamp is updated.
  • If set to OPCIS Ignore Unreliable Value (OPCBADIGNR) and a value with a bad OPC quality is read from the OPC Server, the value will be discarded and the previous value is retained. When the previous value is retained, the UNRELIABLE status bit is set and the timestamp is updated.

Normal point processing will occur to determine if the updated real-time record is sent to the VHS, and since either the status bits or the value have changed, the record will be sent to the VHS. However, if the UNRELIABLE status bit was previously set, then neither the value nor status bits will have changed and so no new record will be sent to the VHS.

For more information, see OPCIS Groups.

SVCMON Points

For more information, see Validating the SVCMON.

Table Driven 2

Application

Use the Table Driven 2 data field to configure application-specific properties for a particular point. The table entry is from the TRS.CMT2 table.

OPCIS Points

The Table Driven 2 data field has special meaning for an OPC Group Definition tag. It can be used to specify whether the OPC server is to retrieve data from the cache or the device. This applies to all synchronous communication. This attribute provides the functionality of the OPC_SYNC_IO configuration file keyword at the group level.

Select a value from the drop-down menu or click … to select or configure an entry. Two default options are supported: sync data via the cache or sync data via the device.

  • If set to OPCIS Sync IO via Cache (OPCSYNCCCH), the OPCIS will sync IO via the cache
  • If set to OPCIS Sync IO via Device (OPCSYNCDEV), the OPCIS will sync IO via the device.

For more information, see OPCIS Groups.

Table Driven 3

Application

Use the Table Driven 3 data field to configure application-specific properties for a particular point. The entry is from the TRS.CMT3 table.

OPCIS Points

The Table Driven 3 data field has special meaning for an OPC Group Definition tag. It can be used to define the type of communication between the OPCIS and the OPC server. This attribute provides the functionality of the OPC_IO_TYPE configuration file keyword at the group level.

Select a value from the drop-down menu or click … to select or configure an entry. Two default options are supported: asynchronous callbacks or synchronous IO.

  • If set to OPCIS Asynchronous IO (OPCIOASYNC), the OPCIS will use asynchronous callbacks, since asynchronous IO is not supported by the OPCIS.
  • If set to OPCIS Synchronous IO (OPCIOSYNC), the OPCIS will use synchronous IO.

For more information, see OPCIS Groups.

External ID

Point reference

The External ID property can be used to specify the server and machine name for the OPC group when linking points to an external OPC server. The format is: server_name=<server>; machine_name=<machine>

 

The External ID field has special meaning for an OPC Group Definition tag, see OPCIS Data Points and OPCIS Groups for more information.

The value of the OPC Group Definition tag indicates the OPC group update rate:

Note: Deleting an OPCIS group's SYOPCGDEF point causes that group to use the default group settings from the .cfg file.

Custom OPC Groups

Custom OPC groups can be created. Each has its own configuration and update rate.

Example

In the example below there are two groups: the default group and a group named OPC30SEC. The default group has an update rate of 60 seconds. This rate is based on the OPCIS configuration. The OPC30SEC group has an update rate of 30 seconds. This rate is based on the value of the OPC Group Definition tag (MYSITE.OPCIS::OPC30SEC.SYOPCGDEF).

Custom OPC Groups example

Custom OPC Groups

The update rate of a group can be changed in runtime by issuing a setpoint command to the Group Definition Tag. See OPCIS System UDCs for more information about creating these tags.

OPC Group Write Queue Size

Another tag in an OPC Group Facility is the OPC Group Write Queue Sz tag; it has UDC of SYOPCWQS, which is a system UDC. 

The value of the OPC Group Write Queue Sz point represents the current number of items in the OPC write queue, which queues requests to write values to the associated OPC server.

As with the OPC Group Definition point, the General 1 data field on the Application page of the point configuration record carries special meaning for this tag and defines information about the group. The General 1 data field is used to control the maximum write queue size of the OPC group to which the point is added.

The default value is 1000. Set the General 1 data field to another numeric value to change the size of the queue. Every change to the point will be logged in the OPCIS.

OPC Group Status Tags

Upon startup, the OPCIS creates three Group Status tags to monitor group activity. The facility of the tag is in the format SITE_SERVICE (for example, MYSITE_OPCIS). The UDCs are described in the table below.

UDC UDC Name Description Point Type

SYOPCSGAC

OPC Groups Active

Number of groups active in the OPCIS.

Analog Input

SYOPCSGCT

OPC Group Count

Number of groups defined in the OPCIS.

Analog Input

SYOPCSGNC

OPC Groups Not Connected

Number of groups not connected in the OPCIS.

Analog Input

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