Stored and nonstored formula channels

A formula channel of a service point can be configured as stored or non-stored. Both stored and non-stored formula channels honor formula changes at the time of evaluation.

The ability to establish stored virtual channels is a separate security permission from that of establishing virtual channels. If you feel you are lacking necessary UCE permissions, contact your system administrator.

Stored Formula Channels

Stored indicates that the formula channels are evaluated and results are stored in the database. With a stored channel, the application requesting data calls UCE, which computes the interval values for a specified time period for the calculated channel.  UCE also stores this data as an interval stream, like an actual measured value.  Whenever a program requests interval values for a stored calculated channel, UCE retrieves the previously stored values just as it would measured values.

When referencing a stored formula channel, UCE always loads the data that is in the database. If you set up a stored formula channel with a formula of A:1, even if service point A channel 1 has data for the requested time range, UCE cannot return results if IEE has no data for the stored formula channel. Until an aggregation process runs and stores the results of the formula into the database, the channel cannot be used by any applications.

Nonstored Formula Channels

Nonstored indicates that IEE does not store results in the database. Instead, it recomputes the value on the fly each time results are requested and passes those values to the requesting program.