certain tag showing "uncertain" quality from graphic diagnotics
Sometime it did not happens few hours, sometime it happens once few minute continuously.
Found this issue only happen on a single page, i was then right click on the graphic to check the Diagnostics.
It shows certain tag with "Uncertain" Quality with First data (ms) about 1159ms.
Wish to know what will causes this error? As I check from the source, it is not direct from IO channel.
It come with some calculation with a tag created from block.
Voted best answer
The AC 800M OPC Server will set Uncertain data quality after a few missed MMS read scan intervals. Default is one scan every 500ms.
The reason why a MMS read fail can be many:
- Network problem
- Controller problem
- Controller application being downloaded
- Controller overload (>90% total CPU load)
- MMS transaction overload (too many transactions pulled by internal or external readers/writers, e.g. Process Panel 800, etc.)
- Lack of Task Tuning*
- OPC DA overload due to too many clients, too many OPC items subscribed or in use for non-cyclic reading (I call this undesired modus operandi for scanning) or writing, etc.
- A synchronous OPC client connecting directly to the AC 800M OPC server instead of routing it via the 800xA OPC DA framework. A synchronous client directly attached to an OPC server may suspend (=block!) the OPC server from catering other clients' requests / subscriptions. For this reason, always route synchronous clients via the 800xA OPC DA framework which will emulate a synchronous server while in the background use asynchronous methods to service it.
The controller log may contain additional details to why the AC 800M OPC server is unable to expedite MMS transactions with the controller.
Other OPC servers may set Uncertain quality for other reasons.