User Guide

Trends
8
What is Online/Offline Trend?
171
Siemens User Guide Version 2.1
A6V10415471_en_a_21
Building Technologies 2015-07-15
8.2 What is Online/Offline Trend?
Online Trend
Online trend records real-time values from your plant and displays them graphically
in a Trend View. The data values are sent to the trend application upon each
change of value. The measured values are temporary and can be stored for later
queries continuously in the Trend database (online Trendlog object). Online trends
can be used for real-time visualization of one or more process variables, usually for
the purposes of analysis or diagnosis.
Record Online Trend Data
Trend data are uploaded
continuously to the management
station and are not saved in the
automation station.
NOTE:
An uninterrupted site connection with the management station is required.
Measured values may be irretrievably lost when the site is interrupted during data
recording. Therefore, online trend is not well suited for long-term secure data
recording.
Offline Trend
Offline trend data is used for the longer-term storage and retrieval of historical data
for the analysis of entire plants or single processes. With offline trend, data is
recorded directly in the automation station. Users can retrieve data as needed or
automation stations can automatically upload the data. The data recording can be
prepared in advance using the engineering tool or you can create a Trendlog
object from the management station in the automation station (must be supported
by the subsystem).
Phase 1: Record Offline Trend Data
Trend data is saved locally to the
Trendlog object in the automation
station.
Phase 2: Upload Offline Trend Data
Trend data is uploaded if:
 The maximum buffer size is
reached.
 The number of defined
entries is reached.
 Manually triggered by the
management station.