[FUN] OPC for data transfer

[Stephen Mitschke]

> [FUN] Anyone putting different DCS's in the same control house?> Ian,> Jonas (Smar) wrote:> > "As mentioned by many OPC is an excellent way of integrating systems. The> existing DCS can be fitted with an OPC server. Although the OPC server is> not "native" to the DCS there are third party suppliers that have> developed> OPC server for most DCS. These servers typically run on dedicated Windows> NT computers fitted with the appropriate interface card. Many Fieldbus> hosts implement OPC servers as standard that can also be redundant in our> case".> > > I would be very interested to hear Jonas (and other) views on the benefits> of employing OPC rather than modbus. I understand that there is an OPC> version 2 now released. The benefits of employing OPC version 2 rather> than> modbus would also be of interest and whether employing OPC version 2 at> this point carries any risks. My understanding is that OPC version 2 can> transmit time stamped data (from safety system for example). Has this been> tried and tested.> > Karl.

[Stephen Mitschke]

> Dear Karl,> > 1. OPC DA (data access) v2 was released in February 1999 or possibly> earlier> so it is tried and tested. The HDA (historical data access) and A&E (alarm> and event) flavors of OPC are still version 1.> > 2. OPC products interoperability tested to v2 are already available.> > 3. Yes. OPC v2 technology supports time stamping.> > Are you asking which (Modbus or OPC) is better to link two dissimilar> systems (legacy and Fieldbus) together?> > A modern Fieldbus based system most likely has a built-in "native" OPC> server configured automatically when you build your control strategy. This> OPC server thus needs no manual configuration. Dated DCS do not have> "native" OPC and therefore require a third-party OPC server to be> configured, manually. Essentially you need to select and map the> parameters> you want to access using OPC. If you are lucky some may be done semi> automatically by converting from your DCS database. Then you need to link> the two OPC servers together using your OPC bridge software. This is a> drag> and drop operation, but it has to be done correctly and verified. I.e.> with> OPC there are a few steps involved. With OPC the data will be bridged> through one or more Windows PCs which you may or may not feel comfortable> with. All data converted to OPC can easily be used in all kinds of> software> too.> > If you use Modbus you need to configure the modern Fieldbus system to make> the variables of interest available as Modbus registers. You need to> configure the DCS or other system to convert the Modbus register data into> its own proprietary database. I guess the configuration burden is about> the> same. If the data also needs to go into software you may need to configure> an OPC server too anyway simply for display purpose.> > Forget about converting all fantastic FF information from the devices to> Modbus to bring into another system. It would be too much work. A modern> Fieldbus based system with a built-in "native" OPC server automatically> makes all information available easily for use in any OPC client software.> > I think OPC is ideal for brining data to operators. Between subsystems> Modbus may be a more direct approach.> > For the future ensure all your subsystems use FOUNDATION(tm) HSE. It may> take a while to convince all your package unit suppliers to adopt HSE so> start early. Adopting HSE as a single standard will make life easier for> package unit suppliers too.> > Jonas