The ScadaLink Interface:

Configuring The ScadaLink Interface:

The ScadaLink interface is configured and tuned via the various options available under the ScadaLink menu item. For the purposes of this document, ScadaPhone's ScadaLink interface will be explored; other ScadaTEC products using the ScadaLink interface have very similar controls. In the following examples, we will explore each of the seven menu items listed in the pull down menu below the ScadaLink main menu item: Setup, Status, Scan Rate, Response Log, Discrete Representations, OPC Quality Options, and Server Startup Delay.

ScadaLink Setup Window:

All ScadaTEC products employing the ScadaLink interface need to be configured to connect with the appropriate server. This configuration is performed in the ScadaLink Setup window (which is accessible via the ScadaLink | Setup menu items).  Note that ScadaLink Setup window has a box labeled Interface Type which contains radio buttons to select the appropriate type of IPC to use to communicate with the SCADA Server.

Most SCADA software supports the industry standard OPC; however, some packages only support DDE or OLE. If you're not sure what type of IPC communication is supported by your SCADA software, you can browse the list of pre-configured servers by selecting the OPC radio button on the ScadaLink Setup window and then clicking on the blue text below the Selected Server Label (which reads "Intellution, Fix" in the example to the right). Clicking the blue label will display the server selection list corresponding to the selected Interface Type. For purposes of this example, click on the OPC radio button and then click the blue label.

The OPC Server List window comes pre-configured with link information for several popular SCADA packages. If your SCADA software is listed here, you only need to highlight its entry in the list and click the OK button.  If your SCADA package is not listed, you can add an appropriate entry by clicking the New menu item. Clicking either the New or Edit menu items opens the Edit OPC Server window.

The Edit OPC window contains two pieces of configurable information: the Name of the OPC server (for display and identification purposes) and the Service  (a.k.a. the Class Name) of the OPC server.  The Name field is not critical, it's just there to help the user to identify the server to be used (i.e. it is the text string that will be displayed in the OPC Server List window). The Service field is critical to making a ScadaLink connection; the Service string is used to make a Windows API call to establish the OLE/OPC conversation that will be used to transmit data between ScadaPhone and the SCADA server.  Each SCADA software package has a unique Class Name name which is registered within Windows. If you're not sure what your particular SCADA package's Class Name is, you need to consult the documentation for that package.

ScadaLink Status Window:

Once the ScadaLink interface has been configured, you can monitor its status by opening the ScadaLink Status window: The ScadaLink Status window updates at a very high rate of speed when a live connection is running, so it is virtually impossible to see the results of each and every transaction. However, the values shown on the Scan Rate line do provide useful feedback for system tuning. If your project is having problems retrieving data from only a few data points, you can examine the return value of each tag in the polling list by looking at the ScadaLink Response Log.

ScadaLink Scan Rate Window:

The rate at which ScadaPhone polls the SCADA server for tag values can be configured via the Adjust Scan Rate window. This window allows the system designer to adjust two parameters that control the polling:  The rate at which ScadaPhone will attempt to read values from the SCADA server. The number of tags to read during each interaction with the SCADA server. The purpose for these adjustments is to provide a means for optimizing ScadaPhone's update cycle time without monopolizing the CPU. In the example to the right, the settings indicate that ScadaPhone will read 3 tags from the SCADA server, wait 55 milliseconds, and then read again. In this example, ScadaPhone is reading 39 tags per second, which updates every tag in the polling list every 5.6 seconds (thus inferring that there are approximately 218 tags in the polling list).

ScadaLink Response Log:

The ScadaLink Response Log shows the response received for each tag in the ScadaLink polling list as well as a time stamp to indicate the last time this point was updated. This is useful to trace down problems with particular data points that are not being returned correctly from the SCADA server.  In some cases an error code or a blank may be returned. If this is the case, the tag name in the ScadaPhone tag database is probably not spelled correctly or there can be problems with character case (i.e. in some SCADA systems, "tag1" is not considered to be the same as "TAG1"). Another common error happens when tags are defined to be Discrete in ScadaPhone but they are actually defined as Analog in the SCADA system tag database. When this happens, ScadaPhone will alert you by displaying the Discrete Expected, Analog Received window:

If the Discrete Expected, Analog Received window appears, the only way to fix the problem is to switch ScadaPhone into Development mode and remove the offending tags from the Discrete's tab and move them to the Analogs tab.  In addition to the Analog/Discrete problem described above, another variety of ScadaLink response problems can arise if the ScadaLink is configured to use DDE and the SCADA server allows the system designer to assign non-standard string values to indicate True and False values for discrete tags. Intellution iFix provides a good example of this.

Discrete Representations:

In iFix, the system designer can specify any string to represent True and any string to represent False (e.g. "Running" can be assigned to True and "Stopped" can be assigned to False). If ScadaPhone is configured to use DDE to communicate with the SCADA server, these strings are returned when the tag is polled (an OPC connection typically returns "1" or "0"). Whenever ScadaPhone receives one of these non-standard responses, the Discrete Representations window is displayed. The Discrete Representations window provides a means for translating the non-standard responses into meaningful responses. In the example above, there are 3 non-standard responses listed. The first two are iFix error codes indicating that some of the tags in ScadaPhone's polling list are not valid; the third item is the string "STOPPED". In order to configure ScadaPhone to recognize "STOPPED" as being False, you must highlight "STOPPED" in the unrecognized response list, select the "FALSE, OFF, 0" radio button, and click the assign button. After assigning a value to "STOPPED", the Close button can be clicked to close this window.

OPC Quality Options:

Each time the ScadaLink interface polls an OPC server for a tag value, an additional "quality" attribute is returned along with the tag value. The quality attribute can be one of 3 values: Good, Bad, or Uncertain. This attribute conveys whether or not the SCADA server has had problems retrieving the tag value from field devices such as a PLC or other SCADA nodes via a network connection.  ScadaPhone can be configured to react to this attribute or to ignore this attribute. The OPC Quality Options window has 3 settings to determine whether or not ScadaPhone will update its tag value database based on the value of this quality attribute.

You may find it necessary to modify these settings if tag values in ScadaPhone are not being updated properly. By default, the ScadaLink interface ignores any tag value that has an OPC quality attribute less than Good; However, in some cases valid data can be returned with an attribute set to Uncertain or Bad. You can determine the quality that is being returned with each ScadaLink tag by examining the ScadaLink Response Log.

Server Startup Delay:

Once the ScadaPhone project has been completed and ScadaPhone is being put into service in the field, it is common practice to place a shortcut to ScadaPhone.exe in the Startup program group. This insures that in the event of a system shutdown, ScadaPhone will be launched when the computer has been restarted.  The only problem with launching ScadaPhone automatically is that, in most cases, ScadaPhone loads and starts running more quickly than the SCADA server software. If ScadaPhone attempts to open a link to the SCADA server before it has been completely initialized, the SCADA server may be disrupted to the point that it is unable to finish its start up process.

To combat this problem, the ScadaLink interface provides a configurable Server Startup Delay which tells ScadaPhone how long to wait before attempting a connection with the SCADA server. This delay allows the SCADA server to fully initialize and start running before ScadaPhone attempts to communicate with it. In order to properly configure this delay, you should launch you SCADA software and measure how long it takes to fully initialize and commence running. Once you've determined the length of time required for a full SCADA startup, configure ScadaPhone's Server Startup Delay to wait for that amount of time plus 10 seconds (to allow for variation).