Handling Midnight Timestamps in the PI System

In the realm of industrial data systems, accurate timestamp management is crucial, particularly in systems like OSIsoft's PI System, where data accuracy can directly impact decision making and operational efficiency. However, handling timestamps that mark the transition from day to day—specifically midnight—can sometimes present challenges.

A common issue arises when dealing with external data sources that format midnight as 24:00:00 instead of the conventional 00:00:00. This discrepancy can lead to errors in the PI System, such as "argument out of range" exceptions, because PI’s DateTime data type does not support a 24:00:00 timestamp.

Understanding the Problem

The challenge usually surfaces in environments where data is periodically logged—for instance, every 15 minutes—and midnight is logged as 24:00:00. This format might seem intuitive within certain systems or rational from a human perspective as it indicates the end of a day, but it is not a time format that is supported by PI’s datetime handling functions.

For example, data arriving in the format "yyyyMMddhhmmss" might translate midnight of January 2nd, 2021, into the string "20210102240000", when it should be "20210103000000" for January 3rd, 2021, 00:00:00.

Solutions to the Midnight Timestamp Dilemma

Extracting and Reconstructing Time

To resolve this issue, the incoming timestamp should be manipulated to fit the supported format. The solution entails extracting the date and time portions separately from the timestamp string and then combining them back to form a valid DateTime object.

Step-by-Step:

1. Extract the Date and Time:

   • Use string manipulation functions to extract the date portion using a function like LEFT, that takes the first 8 characters of the timestamp for the date.
   • Similarly, extract the last 6 characters for the time using a RIGHT function.

2. Check for 24:00:00:

   • If the time portion is "240000", adjust it to "000000" and increment the date by one day.

3. Combine the Date and Time:

   • Combine the two components back into a single DateTime object, which can then be processed by the PI System.

Sample Code

Here's a simplified example of how this can be implemented in a PI UFL interface:

[FIELDS]
FIELD(2).NAME="Master_TimestampStr"
FIELD(2).TYPE="String"
FIELD(9).NAME="Master_Date"
FIELD(9).TYPE="DateTime"
FIELD(9).FORMAT="yyyyMMdd"
FIELD(10).NAME="Master_Time"
FIELD(10).TYPE="Time"
FIELD(10).FORMAT="hhmmss"

Master_TimestampStr=["*;(*);*;*;*;*;*;*;*"]

Master_Date = LEFT(Master_TimestampStr,8)
Master_Time = RIGHT(Master_TimestampStr,6)

IF Master_Time = "240000" THEN
    Master_Time = "000000"
    Master_Date = ADD_DAYS(Master_Date, 1)
ENDIF

Master_Timestamp = Master_Date + Master_Time

StoreInPI(TagName,,Master_Timestamp,Value1,0,,)

Conclusion

While encountering a midnight-as-24:00:00 issue might initially appear as a simple formatting hiccup, the implications can be significant in data accuracy and system function. By implementing a methodical approach to timestamp manipulation, users can effectively align their data influx with PI System’s requirements, ensuring smooth and error-free data logging.