Experimental Physics and
Industrial Control System

"Steven M. Hartman" <[email protected]> · Thu, 21 Oct 2010 11:21:39 -0400

Silver wrote:
 I need to implement a function for insertion device like this:

Read a two-dimensions table file from the disk, which is values for gap positions and Correction coil power supplies (one gap value corresponding to 4 power supply value). If a gap position is set from the operator, four power supplies will be set automatically.

I want to use SNC language to do this, for reading the data from disk, use an asub record for it. Is it ok? Is there any better ways? Did anyone finish this job before?
Any suggestions are appreciated.

I did something very similar a few years back. I used lookup
tables (breakpoint tables) as a feed forward for non-linear tune
compensation for an insertion device (wiggler). The feed forwards,
based on wiggler 'K', drove 9 quad families (about two dozen power
supplies including series main coils and trims) to compensate for
the non-linear betatron tune shifts from the wiggler. (With
another feed forward implemented in a similar manner to compensate
for orbit shifts.)
The ai and ao records included in base support a breakpoint table
facility which may be adequate for your needs. But this conversion
is to/from RVAL (which is an int) and VAL (which is a double). I
hacked a bpt record (based on the ai record) which used the break
point table functions included in base to do double to double
conversions for my needs. In this way, everything was done in the
EPICS database (no sequencer, no subroutine records, etc).
Note that in base >= 3.14.9, breakpoint tables must be monotonic
by default. There is a flag to over-ride this requirement which
must be used when using the breakpoint table in this type of
compensation which likely needs a non-monotonic lookup table.
--
Steven Hartman
[email protected] || 865-466-6473

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System