EPICS Trend data in MDSplus

Many NSTX EPICS I/O points are stored in MDSplus 'eng_trend' trees using the shot number of YYYYMMDD. These points are acquired using the EPICS Channel Archiver. A daily job runs on nstxops to extract selected points from the Channel Archiver's data server and write them into daily trend trees. The data is nominally sampled once per minute but some signals are sampled more frequently.

One convenient method to view this data is with the NSTX Web Tools. In particular, the mdsCrossPlot and mdsList. Note that the x-axis is time, the units are

Each signal node must have a tag name defined for use by the Java program on the nstxops computer.
- The signal node has two child nodes.
  - The TIME node name and tag have a “_T” suffix.
  - The ALARM_STS node name and tag have “_STS” suffix.
The ENG_TREND tree is a child-tree of the NSTX_TREND tree.

An EPICS ArchiveViewer program can also be used to view and export(spreadsheet) the Channel Archiver's data (from the EPICS data store, not MDSplus).

EXAMPLE

For example these two signals are used for the NSTX Test Cell room temperature:

\ENG_TREND::NSTX_ROOMTMP
\ENG_TREND::NSTX_ROOMTMP_T

The first signal is the PV’s value; the second signal, having the _T appended, is the first signal’s timestamp value.

The timestamp value is in units of hours for that day (range 0 – 24).

• To plot the PV_value vs time, use the first signal for the ‘Y’ axis and the _T signal for the ‘X’ or time axis. o The web tool mdsCrossPlot can perform this operation. o http://nstx.pppl.gov/nstx/Software/WebTools/mdscrossplot.html

The timestamp value is in units of hours for that day (range 0 – 24).

Page last edited 06June2008 by Paul Sichta