Logging of Supervisory Data at Bessy

Third generation light sources are facilities requiring ultimate beam stability. Typically component design tries to suppress well known perturbations. During operations a crucial element of the control system is the logging of all signals that might be suited to identify unknown sources of performance degradation. As soon as correlatable data are available it is feasible to plan detailed additional measurements, characterize the systems involved and design appropriate countermeasures (e.g. feedback, component redesign). In this paper the status of the data archiving system in use at BESSY is described. Planned developments and ideas are sketched. 1 SCOPE AND PRIORITIES At dedicated measurements parameters are stepped intentionally and the resulting effects on other parameters are recorded and evaluated. In contrast the precautionary measure of logging parameters relevant for operational conditions into certain archives has no specific application in mind. Mostly the data are never extracted and analyzed. But if a certain interruption, a slow drift or any other unexpected behavior of the machine has to be analyzed the logged data become invaluable and should be sufficiently complete to contain a clue to the explanation or at least a hint on what should be examined more thoroughly. 1.1 Data of Interest A vast amount of parameters is required to describe the operation condition of a light source. The basic configuration is given by the strength of all beam guiding, kicking and wiggling fields as well as by the status and performance of the accelerating and damping elements. With stored beam all signals from the diagnostic system become relevant: beam intensity and lifetime, orbit displacements, source point size and shape, etc. Environmental variables like vacuum in the beam pipe, temperature profiles and variations, performance of the cooling systems strongly influence operation conditions. Delivered beam quality also depends on operational modes like fill pattern, status of feed-back systems etc. Frequently changes in the accelerator performance are due to not-intended operator actions or caused by spontaneous and volatile events typically captured by an alarm system. Funded by the Bundesministerium für Bildung, Wissenschaft Forschung und Technologie and by the Land Berlin Email: [email protected] 1.2 Format and Groupings Differences between various commonly used recording modes are basically substantiated by the meaningful frequencies of data gathering. The adaptive way of storing date with a fixed, sufficiently high frequency during periods of rapid changes and switching to the recording of monitor events notifying the occasional occurrence of a change is for most signals a universal compromise [1]. In addition snap-shot files are needed for comparison and reload of different accelerator settings. Reading with useradjustable frequency is needed for online visualized stability monitoring and trending. Short term history buffers help to mediate a quick overview of the present status. Event capturing facilities are used to document (transient) alarms and operator actions. Run book entries hold data measured by hand or comments and observations. Natural structure for a grouping of the various signals to record with one or the other method is given by the device classes the monitored equipment belongs to. 1.3 Latencies Acceptable latencies between data recording and viewing vary strongly with the application. For ‘online’ trend analysis the latency should be negligible, for long term statistical analysis data latency is no issue. 2 ARCHIVING MODES AND TOOLS At BESSY a couple of signal logging facilities are in use. They cover most of todays needs but do not share a common data format and are thus not suited for combined correlation analysis. 2.1 Snapshot Files One of the central working horses for the operation is a save/restore tool that allows to keep particular well characterized accelerator set-ups and return to these states by reloading the appropriate data sets[2]. Focus of this tool is given to the flexibility of hierarchical, partial, additive and filtered selection of data subsets for storing, comparison, reload and export. File-sets control the bundling of data gathering and hold the data. They reflect device hierarchies, are easily adaptable to changes in the equipment collections and allow to be systematically backwards corrected if e.g. hardware changes require the use of new units. Today a thousand of files describe ‘good’ states and can be analyzed with respect to operational changes. International Conference on Accelerator and Large Experimental Physics Control Systems 431 International Conference Accel rator and L rge Experim ntal Physics Control Systems, 1999, Trieste, Italy