Friday, January 7, 2011

Data acquisition challenges: Non-technical barriers to acquisition

I'm trying to figure out a systematic way of integrating building data from the Seimens BMS in Sutardja Dai Hall. I'm about 90 minutes from dialing into a meeting to talk to Siemens engineers and I figured i'd write a quick blog post on my notes for OPC. The notes are actually based on this pdf.

OPC stands for OLE for Process Control (too many TLAs! --Three Letter Acronyms). OLE stands for Object Linking and Embedding. It's used to read/write value to/from sensors and controllers. For my StreamFS system, i'm interested is collecting as many data streams from physical data sources (from various large sensor deployments) and integrating them into a single system. So lets look a little closer at OPC.

OPC is a software processes that run over client-server connections between a computer and gateway -- the front-end machine that receives all the deployment data. The gateway receives and sets values from the sensors that are attached to it. The machine is typically connected to the gateway via ethernet or serial. In SDH, a serial connection is used. Serial connections are bandwidth limited in comparison to ethernet. Typically the range of serial bandwidth is between 128 Kbps and 8 Mbps, depending on the type of serial cable that's used. I do not know what the available bandwidth in SDH is in the serial installed. According to a meeting we had a few weeks ago, there is a 300-object download limit per sampling period on the Seimens system -- we assumed this was because of the serial connection, however, we were informed that through OPC, we can attain all the objects from all the sensors. So the bottleneck cannot be because of the serial connection. It must be a topological bottleneck through the Seimens root server. OPC, must bypass the root to avoid the bottleneck. (There's also a push to upgrade from serial to ethernet, but if the bottleneck is topological, ethernet won't help!).

The OPC server can be accessed by either using the serial interface or the TCP/IP interface. I'm not sure if it's depending on the connection to the gateway server. When setting up the server, it must have the same address and process name as the gateway program.

The main set of questions that come out of this short overview for the Siemens folks are:

1) Is the bottleneck topological?
2) Do we need to purchase Siemens OPC?
3) Can we access the deployment information bus and send control signals to sensors from the web interface? What documentation should we look at to learn more about that interface?
4) How does the web interface compare with OPC?
5) What's the security model? How can we gain read/write access? Who manages/sets the security policy?

These conversations with Siemens have been dragging for months. It's incredible how little information we get from them phone call after phone call. They are clearly trying to protect their business by being vague. You can't really blame them, but it's very frustrating as a researcher trying to do some science!

No comments:

Post a Comment