All PI Systems support digital states in two ways:
· if a numeric or string point value is not usable, the point value can be a digital state indicating the nature of the problem.
· you can define digital points whose only valid values are digital state codes.
In both cases, each digital state code translates to a specific string. The strings come from the digital state table and are maintained by the PI System.
The PI-API function pipt_digstate can be used to obtain the digital state string given the code. This function works for all PI Systems.
PI for OpenVMS
The PI System for OpenVMS maintains a single digital state table, containing the digital state codes and the corresponding state strings. The total number of possible digital state codes is site-specific. The codes are negative numbers, starting at -1. Values for a given digital point must be in a contiguous range of digital state codes. The start and end of this range must be specified when the point is created.
Digital state codes from the same table are used as values of numeric points when the data is bad or unusable. OSI Software sets aside ranges of digital state codes to indicate common data collection problems.
PI for Windows NT and UNIX
In PI for Windows NT and UNIX, it is possible to organize digital states into separate sets. When defining digital points, you assign a specific state set to the point. The digital point can hold codes from this state set, or the system set.
The system set holds generic digital states useful for many points, such as "Shutdown" and "Bad Input." The system set has a set number of zero. When a numeric or string point has a bad or unusable data value, you can add a digital state code from the system set only.