Hello
I am subscribing to multiple items with code below. When I use the item values just for showing on my apps screen there is no much problem. But in some cases I need to draw some curve with the data. As I know the OPC DA server is checking every X ms's (in my case 100ms) the value of the related item and sends the data just when it has changed. When I have multiple items then it is often the case that I get totaly different amount of items after the total subscription period (let's say 60 seconds). In this case I have to take programaticaly measures to detect when exactly , which item has not changed (by checking the timestamps)
I have following question regarding that point:
1) Is it not possible to get in the defined subsription cyle (100ms) everytime the data, whether it has changed or not. Is such a subscription possible?
2) If 1) is not possible: Is it possible to get an information of the subscription cycle? I mean when I get a lot of data from multiple items, I can pair them just reg. their timestamps. Does the OPC DA server has also an information in which subscription cycle the data was send? (let's say in the first 1.cycle,2.cyle,3.cycle....) In this case I could monitor the cycles, and when an item value is not included in that cycle, I would say, OK it has not changed.
client.SubscribeMultipleItems(
new[] {
new DAItemGroupArguments(ip, "OPC.IwSCP.1", item_array[0], 100, null),
new DAItemGroupArguments(ip, "OPC.IwSCP.1", item_array[1], 100, null),
new DAItemGroupArguments(ip, "OPC.IwSCP.1", item_array[2], 100, null),
new DAItemGroupArguments(ip, "OPC.IwSCP.1", item_array[3], 100, null)
});