The Velocity Selector
The velocity selector is a turbine rotating at high speed. This turbine
annihilates all neutrons which do not manage to travel through the
turbine in a time intervall defined by the rotation speed of the turbine.
Thus neutrons in a certain speed range (energy range) are selected. The
distribution of neutrons is also dependent of a tilt angle between the
rotation axis of the turbine and the neutron beam. A high speed device like
a velocity selector has to account for gyroscopic forces when moving the
device. In praxis this means that the selector must be stopped before the
tilt angle can be changed. Furthermore there are forbidden areas of rotation
speeds. In these areas the velocity selector is in destructive resonance with
itself or its bedding. The command set for a velocity selector is defined
below. The name of the velocity selctor object is assumed to be nvs.
- nvs rottolerance par
- Sets or requests the tolerance the rotation speed may have before an
error is issued.
- nvs list
- Displays rotation speed and tilt angle of the velocity selctor.
- nvs add min max
- This command adds a forbiden region between min and max to the list
of forbidden regiosn of the velocity selector. These values are usually
configured in the configuration file.
- nvs rot = newval tilt = newval
- This command sets a new tilt angle and/or rotation speed for the
velocity selector. Either one or both of the keywords tilt or rot may be
given, followed by a number.
- nvs interrupt val
- Requests or sets an interrupt value. This interrupt will be issued when
an error on this velocity selector ocurred. With a parameter a new value
is set, without the current value is printed.
- nvs userrights val
- Requests or sets a userright value. This userright value defines
who may drive this velocity selector. With a parameter a new value
is set, without the current value is printed.
- nvs tilttolerance val
- Requests or sets a tilttolerance value. This parameter defines the
permissable tolerance for the tilt motor. With a parameter a new value
is set, without the current value is printed.
- nvs rotinterest
- Enables printing of status messages about the current state of the
selector when it is driven.
- nvs loss
- Starts a loss current measurement on the velocity selector and prints the
result.
- nvs forbidden
- Prints a list of forbidden speed regions for this selector.
- nvs status
- Prints a status summary of the velocity selector.
The commands described so far cover the actual handling of the velocity
selector. During a measurement users might want to use further functions
such as:
- Monitor the rotation speed of the velocity selector.
- Log the rotation speeds of the velocity selector.
- Initiate error handling when the velocity selector fails to stay within
a predefined tolerance of rotation speeds.
Now, these are tasks usually connected with sample environment devices. Now,
the SICS programmers have been lazy. Moreover they wanted to avoid
duplicating code
(and bugs). Consequently, they tricked the velocity selector to be a
sample environment device as well. This means besides the actual velocity
selector object (in this case called nvs) there exists another object for
monitoring the velocity selector. The name of this device is the name of the
velocity selector object with the string watch appended. For example if the
velocity selector has the SICS name nvs, the monitor object will be
nvswatch. The commands understood by the watch object are fully decribed in
the section about sample environment devices.
Please note, that all driving commands for the watch object have been
disabled. Driving can only be achieved through the velocity selector object.