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Q: What OPC servers are supported by these controls - will my OPC server work ?
A:
You may use these controls with any OPC server that supports the OPC Data Access 1.0 or 2.x interfaces. The ActiveX controls will detect either interface and use the most current interface found on the OPC server. Although Software Toolbox offers a variety of OPC servers, it is in no way a requirement to use our OPC servers with these products.
Q: Does the Plot Pack support OPC capabilities ?
A:
Not at this time in the first release (Sept. 10, 2001) - we will be adding this capability in Fall 2001.
Q: Does the Strip Chart support OPC capabilities ?
A:
No - you should use the Plot Pack component when it's new version is released with OPC client capabilities added. Due to architectural restrictions in the design of the Strip chart, it is not practical to add OPC client capabilities to the Strip Chart control.
Q: I don't want the control to write when properties change - how can I disable the writes ?
A:
You have a few options now and in the future. At this time, you will need to make the item in your OPC server read only so that when we attempt to
Q: What happens to any error messages or item quality data from the OPC server that gets sent
back to your control when the OPC server sends back an item value update ?
A:
At this time we do not pass back the Quality and Timestamp data to you through the ActiveX controls. We are working on some methods to provide this data to you so that you can use the data as you see fit.
Q: My OPC server is sending back raw units of analog data and I need to scale them to
engineering units - what can I do ?
A:
You should see if your OPC server supports scaling in the OPC server and if so, you should go reconfigure the item in the OPC server so that our control receives the scaled data. We are planning to add scaling capabilities to our controls in a subsequent release in Fall 2001.
Q: My OPC server doesn't appear to support item browsing - what do I do ?
A:
You can type in the item name on the OPC tab on the properties page - it is not necessary to use our item browser (obviously it is easier if your OPC server supports it though).
Q: I am having DCOM connection problems when I try to connect to a remote machine
A:
Setting up a DCOM connection between two computers requires that you carefully setup the security on both machines and also setup the DCOM configuration settings. We have a tutorial on this subject that will help you in this.
Q:
Can I have multiple properties connected to different OPC items on the same ActiveX control ?
A: Yes - you use the Add button on the OPC tab on the properties page to bring up the properties dialog, choose another property, then connect that property to additional OPC items on an OPC server..
Q: Can I connect different properties on the same ActiveX control to items on different OPC
servers ?
A: Yes - you use the Add button on the OPC tab on the properties page to bring up the properties dialog, choose another property, then connect that property to additional OPC items. The OPC Server selection is independent on each and every property that you connect. We would caution you that each OPC server connection, by the very nature of the connection, will consume computing resources and that if you had too many different server connections on a single control, particularly if the OPC servers were remote, you will see slow startup for your application as our control goes out and sets up the connection with each OPC server at initialization.
Q: I want to add or change OPC item connections through code instead of through your property
pages - can I do that ?
A:
Yes you can. Using the OPCItemAdd method and the SetOPCItem.... and GetOPCItem.... methods, you can programmatically add items to an instance of the control.
Q: If I disable the auto-connect, how do I then in code tell the object to connect to the OPC
server ?
A:
You can enable any items through code using the OPCItemActivate method. You call the OPCItemActivate method and pass in the index number of the OPC item (in the list of items you have connected through the properties page). We will be adding a method that will let you make a simple method call to determine the index # of the property you are activating by simply passing in the property name. For now, as long as you are not adding and deleting bound properties all the time, a general rule would be to go to the OPC tab on the properties page, and the bound properties shown in your list of connections will be indexed 0,1,2,etc. starting at the top and working down the list. If you added the connections through code then you will already have the index in your code from when you called the OPCItemAdd method, which returns to your code the index number of the item added.
Q: I have picked a computer and am trying to bring up the list of available OPC servers but
nothing happens.
A:
You likely have an issue with your DCOM configuration settings. We suggest you review our DCOM configuration tutorial to see if you have things setup properly. This can even happen on a local machine where the OPC client and server are on the same machine if your DCOM settings are not properly configured.
Q: Can I use the controls in Front Page/Internet Explorer
A:
Although we have supported this container with our existing Instrumentation ActiveX controls for some time now, we are still doing testing of our OPC capabilities in this container (9/12/2001) and will revise this FAQ when we have a sample program and application note available and have completed our testing with this container.
Q: When your controls read data, are you using Synchronous or Asynchronous calls to the OPC
server ?
A:
We use the Asynchronous subscription read mechanism in the OPC specifications. This means that when our control initializes, it connects to the OPC server, advises the OPC server of the Item(s) it is interested in receiving updates for, and gives the OPC server a pointer to the DataChange interface on our OPC client control. The OPC server then will make a call back to our ActiveX control whenever it has changed data. This method eliminates polling between our controls and the OPC server which helps maintain good performance.
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