A Distributed Feedback System for Rapid Stabilization of Arbitrary Process Variables Page: 3 of 3
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4 FUTURE DIRECTIONS
4.1 Additional Lock Types
The remaining slow lock types in use at Jefferson Lab
will be integrated into the Generic Lock Server
architecture. For this to happen the architecture must be
extended to allow MIMO lock types. It must also allow
for locks that must be calibrated at runtime like the Orbit
Locks and locks that use the on-line accelerator model
server for calibration like the Energy Locks.
4.2 Server Security
Access to all CEBAF IOC's is controlled through CA
security. To function, the Generic Lock Server must run
with a user ID that is allowed to write to the IOC's.
However, because it is designed to be flexible, the CDEV
Generic Server has no built-in security model. This means
that any user connected to the accelerator network can
write to the virtual attributes of the lock devices and
create a lock that writes to any channel in the system,
effectively circumventing CA security. Plugging this
loophole is a top development priority. A security layer
will be added to the lock server allowing writes only by
specific groups of users from specific machines. In the
longer term, it would be useful if the attributes of a lock
would inherit the security of the lock's output channel.
4.3 PID Auto-tuning
Determining appropriate gains for PID controllers is a
non-trivial task. To make the PID Lock class more usable
by non-experts it would be very desirable to have a means
to automatically characterize the closed loop transfer
function and determine appropriate PID gains for
optimum stability, if they exist. Many such algorithms
exist . If one can be found that is sufficiently general, it
might be integrated into the lock server architecture or
could exist as a separate process, making it more useful
for tuning EPICS CPID records as well.
4.4 Dynamic Linking
The very low degree of coupling among the various
lock and server classes means that it is not necessary to
statically link the lock classes with a server. Following the
model that CDEV uses with its service classes, the code
for individual lock types could be dynamically loaded as
needed. This would allow completely new types of locks
to be added to a running server without even restarting it,
much less rebuilding it.
4.5 Expanding the Lock Namespace
One limitation imposed by CDEV is that all device
names must be declared in static Device Definition
Language (DDL) files that are used by clients to map
device names to the appropriate services and servers.
Thus, although new locks can be created in the server
with arbitrary names, clients canno find them unless they
use names pre-declared in a common DDL file. This
prohibits the use of descriptive device names for
dynamically created locks. A dedicated client like the
Generic Lock GUI could be designed to dynamically
discover the lock names, but th y would still not be
available to general purpose clients like archivers.
CDEV can be configured to fall through to a particular
service when a device name is not found in the DDL file.
For many sites that use CDEV with EPICS, this default is
configured to use CA. The Portable CA Server (PCAS)
 suggests a way to make fully dynamic virtual
devices. A PCAS could be set p to host the virtual
device/attribute pairs needed by such devices.
Recognition of the need for the
and the PID Locks as well
implementation grew out of man
members of the Jefferson Lab Opi
Beam Applications Team, especial]
Generic Lock Server
as ideas for their
discussions with the
rations Group and the
y Yves Roblin.
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Developing Device Control Applications",
Proceedings of ICALEPCS95, Chicago.
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Industrial Control System Arc itecture: Past, Present,
and Future", Proceedings of ICALEPCS93, Berlin.
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K. S. White and S. Withersppon, "Using Servers to
Enhance Control System Capability", Proceedings of
PAC 1999, New York.
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"Design and Implementation of a Slow Orbit Control
Package at Thomas Jefferso i National Accelerator
Facility", Proceedings of PAC 1997, Vancouver.
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for Energy and Beam Stabili nation , Proceedings of
ICALEPCS99, Trieste, Italy.
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Lebedev, "Empirically Ietermined Response
Matrices for On-line Orbit a d Energy Correction at
Thomas Jefferson National Accelerator Facility",
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Client-Server Applications'', Proceedings of
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2nd ed., pp.375-389, Addison-Wesley, 1995.
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Bevins, Brian. A Distributed Feedback System for Rapid Stabilization of Arbitrary Process Variables, article, November 1, 2001; Newport News, Virginia. (digital.library.unt.edu/ark:/67531/metadc715963/m1/3/: accessed February 22, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.