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By adding OPC Client Driver tags to your application, you can communicate with OPC servers on your network, whether those are other VTScada applications, control equipment or other programs. The VTScada driver supports OPC DA 3.0
Driver Errors: To learn more about the cause of an error condition, refer to the Driver Summary Report and the Driver Error Report, both of which are available in the Reports page. The Show Stats button will also provide current and last error messages: Show Statistics Button Widget
Reference Notes:
The OPC interface allows for two-way communication, thus you can add both input and output tag types that exchange information with the OPC server through the OPC client drivers you configure.
OPC Client Driver I/O Addressing
OPC Classic Configuration - Technical information about the OPC Server configuration in VTScada.
The ID tab
The ID tab of every tag includes the same common elements: Name, Area, Description, and Help ID.
Name:
Uniquely identifies each tag in the application. If the tag is a child of another, the parent names will be displayed in a separate area before the name field.
You may right-click on the tag's name to add or remove a conditional start expression.
Area
The area field is used to group similar tags together. By defining an area, you make it possible to:
- Filter for particular tag groups when searching in the tag browser
- Link dial-out alarm rosters to Alarm tags having a particular area
- Limit the number of tags loaded upon startup.
- Filter the alarm display to show only certain areas.
- Filter tag selection by area when building reports
When working with Parent-Child tag structures, the area property of all child tags will automatically match the configured area of a parent. Naturally, you can change any tag's area as required. In the case of a child tag, the field background will turn yellow to indicate that you have applied an override. (Orange in the case of user-defined types. Refer to Configuration Field Colors)
To use the area field effectively, you might consider setting the same Area for each I/O driver and its related I/O tags to group all the tags representing the equipment processes installed at each I/O device. You might also consider naming the Area property for the physical location of the tag (i.e. a station or name of a landmark near the location of the I/O device). For serial port or Roster tags, you might configure the Area property according to the purpose of each tag, such as System or Communications.
You may define as many areas as you wish and you may leave the area blank for some tags (note that for Modem tags that are to be used with the Alarm Notification System, it is actually required that the area field be left blank).
To define a new area, type the name in the field. It will immediately be added. To use an existing area, use the drop-down list feature. Re-typing an existing area name is not recommended since a typo or misspelling will result in a second area being created.
There is no tool to remove an area name from VTScada since such a tool is unnecessary. An area definition will exist as long as any tag uses it and will stop existing when no tag uses it (following the next re-start).
Description
Tag names tend to be brief. The description field provides a way to give each tag a human-friendly note describing its purpose. While not mandatory, the description is highly recommended.
Tag descriptions are displayed in the tag browser, in the list of tags to be selected for a report and also on-screen when the operator holds the pointer over the tag’s widget. For installations that use the Alarm Notification System, the description will be spoken when identifying the tag that caused the alarm.
The description field will store up to 65,500 characters, but this will exceed the practical limits of what can be displayed on-screen.
This note is relevant only to those with a multilingual user interface:
When editing any textual parameter (description, area, engineering units...) always work in the phrase editor. Any changes made directly to the textual parameter will result in a new phrase being created rather than the existing phrase being changed.
In a unilingual application this makes no difference, but in a multilingual application it is regarded as poor practice.
Help Search Key
Used only by those who have created their own CHM-format context sensitive help files to accompany their application.
Server List
Select (or create) a named server list.
OPC Client Driver properties OPC tab
The OPC tab for the OPC Client driver tag properties folder consists of attributes used to identify and establish a connection to the control device to be associated with this driver. The OPC tab for an OPC Client driver is also used to identify the remote server node that the driver should use to transmit data.
OPC Server
The Server Prog ID field enables you to specify the program identifier (ProgID) for the OPC server to which you wish to connect. This will be a string of the form Manufacturer.OPC.ServerType.
Examples of a Server Prog ID are: Trihedral.VTSOPC.DA or Matrikon.OPC.Modbus.
The OPC Server vendor generally supplies the Server Prog ID. Refer to your OPC Server manufacturer's documentation for the correct details.
Remote Server Node
Use this field to specify the name of the workstation that is acting as the OPC server. The Remote Server Node field can be left blank in the event that the local workstation is the OPC server.
Analog Deadband (% of full scale)
Set a percentage by which analog values must change before a change in value is reported. If the percentage is 0, the updates will be event driven, occurring on each value change.
Hold
In the event of an interruption in communication, this option will cause the last good value to be held. You should use this option with caution because, unless there is another means to alert you to interruptions in communication, it will appear that a valid value is still being received.
Data Update Rate Controls
By default, data updates from OPC servers are sent to OPC clients only on change of value or quality, with the maximum rate at which the servers send the values to the clients set to a default of 1 second. This is the default time defined in the OPC standard. The following two settings allow the VTScada OPC Client driver to change this default behavior to meet application specific requirements.
Force Asynchronous Refresh
This option allows for an override to the default "send only on change" behavior and when selected will cause the VTScada OPC client to poll the OPC server for values at a fixed rate as defined in the individual I/O tag’s "Scan Interval" setting.
The default "send on change" behavior will still function when this option is selected. For example, if the I/O tag "Scan Interval" is set to 10 seconds, the server can still send values every second, but the setting will only act to force a refresh from the server every 10 seconds in addition to the update on change.
In some cases, use of this option this may cause excessive load on the OPC Server host as it services all of the data update requests, and should be used only when there is an application-specific need for time based updates versus the OPC standard of update on change.
Use Tag Scan Interval
If this option is selected, the VTScada OPC client driver will request that the server send the values to the client at a maximum update rate defined by the individual I/O tags’ "Scan Interval" instead of the default 1 second rate.
This feature affects only the rate at which the OPC Server updates tags in the VTScada OPC Client. The rate at which the OPC Server queries field devices depends on the server implementation and cannot be controlled from within VTScada.
If using this option, the client (VTScada) is updated with the current value at the end of each scan interval. If the value at the field device changes several times within that period, then even if those changes are read by the OPC Server, they are not sent to the client.
Accept Data Marked as
Values received by the OPC client tag are set to INVALID unless the attributes of the value are specifically set to GOOD (>= 0xC0). Use these options to accept values with other attributes as marked.
OPC Client Driver Tag Widgets
The following widgets are available to display information about your application’s OPC Client Driver tags:
