Hi,

On the operator station there is a mounted plant hierarchy of the production system. I am wondering how does the operator station fill in/read the values from the production system?

Is it that there is a process (qcom? ) on the operator station that reads the whole or part of the production systems database and fills in the local mounted db? if thats the case, at what frequency the values are read from the production systems' rt db?
Thanks,
Shahzad.

Hi Shahzad,

A volume in a process station is cache mounted in the operator station. This means that when you for example look at the object tree in the runtime navigator, requests about children and siblings are sent to the process station. The information in the latest requests is stored in a cache and before the request is sent, the cache is searched. This communication is performed by the nethandler, rt_neth.

When you open a graph and display the value of an attribute, or open an object in the navigator, there is another mechanism called subscription. The subscription is set up by the nethandler, and the timer monitor, rt_tmon, in the process station will continously send the current value of the attribute with a specific interval. The interval is unique for each subscription and depends of for example the scantime of the graph. There is though an optimization of the subscription pakets so it's not sure you will get exactly the reqeusted interval.

When you set a value from the operator station, a specific set request is sent, so this is done instantly.

/Claes

Thanks this explains it well.