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<== Date ==> <== Thread ==>

Subject: Re: Controls & Physics
From: "Steven M. Hartman" <hartmansm@ornl.gov>
To: Korhonen Timo <Timo.Korhonen@psi.ch>, Michele Joyce <erb@jlab.org>
Cc: "tech-talk@aps.anl.gov" <tech-talk@aps.anl.gov>
Date: Tue, 23 Mar 2010 09:30:26 -0400
Korhonen Timo wrote:

The calculations are put into a layer of EPICS records that uses the hardware layer records as inputs and outputs.
Basically we work(ed) together with the physicists and translate(d) some of the most used applications into epics
templates; those have then bunches of calcout records for the formulas and other stuff to distribute/concentrate the values
as needed. One can achieve quite neat results with epics records....
Once this is done, the physics parameters are available for all applications. For changing the parameters you then need
just a simple screen - medm panel for instance.
Of course, all this can also be done using a server. I think however that the implementation in the records has paid off.

That is similar to the approach I took. PVs for beam energy (MeV), quad focusing strength (m^-2), betatron tune shift, orbit correction (mrad), undulator K/gamma, etc. are the PVs which are available at the operator interface layer (e.g. medm). The logic for translating this to engineering units (e.g. power supply Amps) is all contained in the EPICS database layer. In most cases, it is not a one-to-one mapping. For instance, the betatron tune shift knob drives 9 families of quadrupoles involving 16 (if I recall correctly) power supplies. The wiggler knob drives even more power supplies with built in feed-forward compensation for orbit shifts and tune shifts. And the beam energy knob touches nearly every magnet power supply (with the quadrupoles, for instance, maintaining the same effective focusing strength for the different energy beam).


Within the EPICS database, it is basically an ao record for a high-level parameter, a bunch of calc, calcout and fanout records, breakpoint records (for non-linear mapping), and then to ao records to drive the hardware, with event records used for synchronization.


-- Steven Hartman hartmansm@ornl.gov || 865-466-6473

References:
Controls & Physics Steiner, Mathias
Re: Controls & Physics Korhonen Timo
Re: Controls & Physics Michele Joyce
Re: Controls & Physics Korhonen Timo

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