Mr JP,
I think you are right there is a need for a simple software package that would enable you to configure a simple data display which could be accessed from any PC with a web browser - your laptop, my laptop, anyone's desktop. Anywhere.
As you know, OPC is pretty much the standard way of getting the data between PLCs and SCADA/HMI. OPC servers are available for all the well known PLC brands, and most of the HMI/SCADA packages have OPC server built in to expose their tag databases. Assuming the data your are interested is available in one or more of those OPC servers, the OPC data can be read/written via the web. Our OPC client ActiveX toolkit OPCWare Client Developer includes several samples that you can refer to for OPC web interfaces. These samples demonstrate how you can use our product to accomplish what you described.
In simple terms, there are two ways to read/write OPC data over the web with OPCWare Client Developer. The first is through the web server, the second is through the web client.
To do this the first way, through the web server, you can use ASP pages, which run on the web server itself, so you don't need to have any OPC software installed on the web clients - you only need the OPCWare Client Developer OCX in one location - on the web server itself. This is a thin client configuration, and does not rely on DCOM to get the data to and from the web clients, just HTTP. You only need to worry about DCOM if the OPC server is not on the web server PC, and even then, you only need to worry about a single DCOM connection. If you could put the OPC server on the web server, this would totally eliminate DCOM. In any case, there is no DCOM between the web server and web client.
The second alternative is a rich client (or fat client), where you run the ActiveX at each web client and embed VBScript or JavaScript in the HTML on the client side. Assuming the OPC server is not located on the web client PC, this always relies on DCOM, and you also have the additional overhead of installing the ActiveX runtime on each client PC. You do get more functionality in this way, but at the expense of extra administration effort, and DCOM/firewall/security issues.
So the simplest configuration is definitely the ASP method, and I would recommend that.
You only need to install OPCWare Client Developer on the web server, no other software is required, apart from the OPC server(s) of course. You do not have to purchase an expensive SCADA or HMI package, plus you do not need to purchase add ons. You do need to have knowledge of ASP programming in order to configure the web server as an OPC client using OPCWare Client Developer, but most webmasters will have adequate ASP skills.
Sorry if this got a little long or sounds complicated, but it is simple really (I hope!).
Regards,
Neil Kingston
Data Layers