Glossary
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- actuator
-
This is the generic term for a device which feedback uses to control
the beam. Examples are an XCOR (horizontal correction magnet) and PHAS
(a phase shifter controlled via a PAU)
- BPM
-
Acronym for Beam Position Monitor. This device determines the position
of the beam. A Processing module connected to it (BPMP) converts the
analog voltages to digital values which can be read by the micro
- calibration
-
A procedure by which all the actuators of a feedback loop are varied and
the changes of the states are recorded. In control theory jargon this
is called identification. It is done to directly measure some of the
transfer matrix elements used in the design of a loop.
- feedback loop
-
The necessary hardware and software needed to stabilize a number of
states. Some number of sensors and actuators will be needed to do this.
- gold orbit
-
The values of all the measurements used by a feedback loop
typically recorded at a time when
the accelerator is in a good (golden) state that you want to maintain.
These values can be used as offsets to be subtracted
from the present feedback measurements. In this way a feedback loop
can be set to maintain a particular saved setup.
- launch loop
-
This is the most common type of feedback loop. It controls the launch
of the beam from one part of the accelerator to another. The states
controlled are the horizontal and vertical position and angle and
sometimes the energy. Some loops do this for a single beam and others
do it for both electrons and positrons. The sensors used are BPMs.
- measurement
-
The result of reading a sensor. A typical measurement is the value of
the beam position.
- plant
-
This is the generic control theory term for the device being
controlled by a feedback loop. In our case this is the accelerator and
the description of it includes a lot of transfer matrix elements and
any dynamics of the actuators such as a finite slew rate or LR time constant.
- ring buffer
-
This contains data (such as measurements or states) recorded for each
pulse of the accelerator for the last few hundred pulses. It is also
sometimes used to refer to a plot of this data. It is used for
diagnostic purposes to check the response of a loop.
- robust
-
An adjective describing a desirable feature of a feedback loop. A loop
is robust if it keeps working properly even if the real plant is
different than that which was used to design the loop. Examples of
things which could be different are the time response of an actuator
and the values of transfer matrix elements.
- sensor
-
A device which is used to make a measurement for a feedback loop.
Examples are a BPM which measures the beam position and a profile
monitor which measures the size of the beam.
- states
-
Numbers used to describe the present state of a system. The estimates
of the states for
pulse are calculated from the state estimates
for pulse and the measurements
for pulse . Examples of states are the horizontal position and
angle of the beam at a point, the beam energy, the energy spread, and
an estimate of the present magnetic field of a corrector.
Next: About this document
Up: Fast Feedback Users Guide
Previous: Feedback status shows
SLAC Controls Software
Fri Nov 4 11:34:56 PST 1994