Timestamp hierarchical logs
In Compact HMI 800 application I'm using a log configuration to several flows of liquid. The log configuration consists of both direct and hierarchical logs. The problems are the timestamps of the logged values.
For example a direct value taken each hour can have a timestamp of 06:34:50,
the timestamp of a hierarchical value taken once every 24 hour can vary between 00:00 and 01:00, and the timestamp of both direct and hierarchical logs taken each half hour can vary so it is not always e.g 08:30.
Can these timestamp be controlled? since I intend to use this to log the volume of liquid to Excel. The volume is measured with a PLC and the variable is set to zero during the night.
Also are these timestamps influenced by Dayligt savings time?
You are correct.
A Basic History hiearchical log with a Min Time of 24 hours will align on midnight, UTC.
According to the OPC HDA standard, aggregated time stamps align to the start of the interval, i.e. an hourly Time Average made from a primary log's minute values from 23:00 through 23:59 will be stored with the time 23:00 (start of interval) *not* midnight which might be the expected since the average is not "ready" until midnight.
Calculating offsets, etc with respect to local time, DST, etc. is a very complicated matter - hence most historians I've come across store data on UTC with no DST. Local time offset incl DST is added by the client (e.g. a Trend Display or DataDirect plugin).
I don't think you can change this behavior - your report code need to adapt for this, e.g. reading hourly values instead of daily values or try getting your PLC to zero on UTC time, not local time.