I've just read the latest OPC interface release note and have come across the trend advise function. I think I follow what it does but I just need clarification on 1 issue; does the PI server record the previous value as well as the new value so that PI data retrieved by Datalink will tie-up with what is shown on the trend?
Example; a plant data value changes from 1 to 10 (1, 10, 1, 10, 1, 10, etc) every 30 seconds. Normally this would give a sawtooth profile, but with trend advise I would get a stepped profile. So far so good. Normally (excluding the effects of exception and compression) the PI archive would store the original data profile (1, 10, 1, 10, 1, 10, etc) , but does the trend advise add extra data events to the PI archive to allow the PI trends to show the stepped profile, i.e. 1, 10, 10, 1, 1, 10, 10, 1, etc, when looking back at a trend over a number of hours/days/months, or is it just a live trend update function, that if you refresh the trend then you would get a sawtooth profile again?
Does my question make sense??