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<HTML>
<HEAD>
<TITLE>Chopper Control</TITLE>
</HEAD>
<BODY>
<H1>Chopper Control</H1>
<P>
FOCUS is equipped with a Dornier Chopper system running two choppers:
a disk chopper and a fermi chopper. In most situations the diskchopper is
in slave mode. This means his speed is a predefined ratio of the
speed of the fermichopper. Furthermore, there is a phase difference between
the two choppers in order to allow for the fligh time of neutrons
between choppers.
</P>
<p>
The program handling RS-232 requests at the chopper control computer
is rather slow. This would slow the SICS server to unacceptable
levels, if any request would be handled through the RS-232 interface. In order
to cope with the problem, the SICS server buffers chopper
information. This information is updated any minute if not set otherwise.
</p>
<p>
The chopper system control is divided into several distinct objects: There
is the actual chopper controller which mainly serves for answering
status requests. Then there are a couple of virtual motors which
represent the four modifiable parameters of the chopper control
system. These can be driven through the normal <a
href="drive.htm">drive</a> command. The commands understood by the
chopper controller object are:
<dl>
<DT>choco list
<DD>prints a listing of all known chopper parameters.
<DT>choco name
<DD>print only the value of parameter name. Possible values for name
can be extratcted from the list printed with choco list.
<DT>chosta
<DD>This command procedure prints a status listing of the chopper
system in a nicely formatted stefan-happy form.
</dl>
The following virtual motor variables exist for the chopper system.
<dL>
<DT>fermispeed
<DD>fermi chopper speed
<DT>diskspeed
<DD>disk chopper speed. Note, that driving this parameter while the
chopper system is in synchronous mode will throw an error condition.
<DT>phase
<DD> The phase difference between the two choppers.
<DT>ratio
<DD>The ratio of fermi to disk chopper speeds.
<DT>updateintervall
<DD>The update intervall for the buffering of chopper data. Units are
seconds. Setting to low values here will compromise the responsiveness
of the SICS server.
</DL>
Each of the variables kindly prints its current value when given as a
command. Modifying values happens through the normal drive
command. For instance the command:
<pre>
drive fermispeed 10000
</pre>
will drive the fermi chopper to 10000 RPM eventually and if no problem occurs.
Please check your input carefully for all chopper commands.
Dornier has provided no way to stop an erraneous command in its software. So, if you intend to run the chopper to 1000 RPM and mistyped it as 10000 then
you'll wait for 20 minutes until the chopper is at speed!
</p>
</BODY>
</HTML>