This website is no longer maintained. Its content may be obsolete. Please visit http://home.cern for current CERN information.
http://wikis/display/LHCOP/BPM+controls+status
Serious work in progress: concentration, writing to SDDS, re-publicaiton of capture data in place (Feb 2007) accessing 16 BPM crates in place in 7 & 8.
Demo first turn display here c/o Sandeep Bharade
See also concentration
The LHC orbit and trajectory acquisition system is based on a Wide Band Time Normaliser (WBTN) capable of processing the analogue signals from the pick-up at 40MHz. The resulting signal is transmitted via a fibre-optic link, treated, digitised using a 10-bit ADC and processed by a VME64x Digital Acquisition Board (DAB).
The VME64x acquisition chassis of the LHC orbit and trajectory system are
located in the SR buildings at each access point. The chassis is comprised
of a PowerPC, a TTC receiver and up to 18 Digital Acquisition Boards (DABs),
all linked via a custom AB/BDI VME64x backplane. Each DAB is capable of processing
the data from two WBTN mezzanine cards. A single WBTN mezzanine card receives
treats and digitises the pulse modulated signal sent by a single front-end
card, providing the DAB with a 40 MHz flow of 10-bit position data. The
DAB is capable of working in parallel in three different modes: orbit, capture
(or trajectory)
and post mortem. In orbit mode the incoming data is validated, calibrated
and summed for 20 ms to eliminate 50 Hz noise. The result is retrieved by the
PowerPC
which calculates the average orbit for each plane and corrects the result for
BPM geometrical non-linearity. This is repeated at 10 Hz, thus allowing the
possibility of a 1 Hz closed loop orbit feedback. At the same time the incoming
data is histogrammed to provide a standard deviation for each orbit reading.
In capture or trajectory mode the user is free to choose when, for which bunch(es)
and for how many turns the DAB stores the position data, while the post-mortem
mode stores the last 1000 orbits and 1000 turns in a circular buffer which
is frozen by the beam abort system.
Latency of around 1 second acceptable.
1. CMW request to "concentrator" including parameter list - subscribe.
2. Concentrator takes responsibility for issuing TTC request. Concentration of data will be done in LSA middle tier. Parameters to be established e.g. Batch/Bucket Number/Ring. Preloaded front-end settings will need to be invoked. Could well be a request automatically issued for each injection.
3. Concentrator subscribes (CMW) to all BPM crates and takes responsibility for pulling all BPM readings together and re-publishing.
. The same request (number of turns, bunches acquired, acq trigger) apply to all BPMs. Ie it is not possible to do different things on 2 BPMs on the same time. (we'll insist that this stays like this!)
. It is not possible to acquire every N turns, only consecutive turns are possible
. Multi turn acquisition is limited to up to 100000 turns on: - one user selected bunch OR - the beam average
Assume all acquisitions archived and logged.
Going to have to deal intelligently with the parts of the two rings in common, the various separation and crossing-angle bumps plus spectrometer magnet compensation etc.
Dedicated application