Proliferating process control protocols (Exxon/TOG and OPC/Fieldcom, page 11, to name but two) got us thinking about the OSIsoft message format, OMF. A casual glance at an OMF message revealed that units of measure are handled in a cavalier fashion, as free text annotations in a ‘description’ field. In a short email exchange, we asked why, say, OPC-UA was not considered. We also asked how robustly OMF handles metadata like units of measure. A spokesperson told us ‘We do offer an OPC UA connection, if you want to use it, it’s all yours. But there are situations where someone may not want to reformat into OPC just to send data to the PI System. Here you can use OMF as an alternative.’ OSIsoft did not rise to our UoM bait!
On the metadata front, there are good reasons to go with OPC UA since it can handle units rigorously, with the EUInformation DataType. It also leverages the UNECE Recommendation N° 20 for a manufacturer’s equipment ID. Of course, the availability of a data field does not mean that it will necessarily contain any data! ‘Vanilla’ OPC by the way did not handle units very well. We will be continuing our investigation into metadata over the next few months. Your opinions and technical input are welcome – email@example.com.
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