Constant points are most commonly used to create a “virtual” point that looks like, and is treated, as if it were a measurement from an instrument or a register in a PLC.
Constant Tags are most frequently used for operator entry of values to calculation tags, scripts and third party software programs. Constant Tags are a holder of the value until another operator or script changes its value. Constant Tags usually have no input source other that changes by Operators and Scripts. However, DDE clients and 3rd Part API programs can change constant points (like any tag).
The WebAccess database can be configured to hold analog, digital, or text Constant Tags. A constant point is a user-defined value that can be independent of any control system device. Its value can be set to an initial value on start-up and changed during run-time operation. It also provides alarming, security, description and other features. It can be included in trends, displays, alarm summaries and reports.
Constant Tags are a Global Internal Tags: all clients, scripts and other tags will see the same value when reading this tag. Changes to the tag will be seen globally by all other clients, scripts and other tags.
The software license control file limits the number of Internal tags. The number of Internal Tags (Calculation + Accumulation + Constant) cannot exceed the number of IO tags in the license.
For detailed information see 4.7 Constant Tags.