Ion Chamber Instruments

["Peter J. Chiaro Jr" <chiaropjjr@ornl.gov>]

I would like to provide some additional information for this discussion.
There were a few statements regarding various models of ion chambers that
need to be clarified.

The Eberline RO-20 and the Bicron RSO-50E are five range instruments that
were to, or could, take the place of two other instrument models for each
company.  The other models were the RO-2 and RO-2A, and the RSO-5 and
RSO-50 for Eberline and Bicron respectively.  The magnetic arm mechanism
was part of the RO-2 series as well as the RSO5 and 50.  It is not part of
either the 20 or 50E.  The RO-2 series and RSO5 and 50 each had four
ranges, 0-5, 0-50, 0-500, 0-5000 mR/hr for the 2 and 5, and a factor of ten
higher for the 2A and 50.
The magnetic arm would activate reed switches located on the base of the
ion chamber to place the high range resistor in circuit or switch the unit
into zero mode.  The Eberline arm was stiff and would sometimes attach
itself to the frame of the unit.  The Bicron arm was more flexible and was,
in my opinion, designed somewhat better.  The mount was on a post that
didn't bend up or down.  Unfortunately, there was only one bumper on one
side of the throw of the switch that allowed the arm to bend until it
stopped activating the reed switch.
The 20 and 50E designs did not make use of a magnetic arm and added a
range, each covering both ranges of the other instruments.  Both new
designs had their problems.  The 50E had stability problems that some had
observed, others hadn't.  The 20 was initially somewhat erratic and more
temperature sensitive, but with cooperation of the manufacturer, we were
able to have that worked out.  I can talk in more detail off-line since we
did a substantial amount of testing and evaluation using the Environmental
Effects Laboratory at ORNL.  Additional information can also be found at
"http://www.ic.ornl.gov/centers/ite/hpinfo.htm.";

As a member of the DOE-HPIC and co-chair, I would also like to clarify a
statement made regarding tests performed by DOE contractors.  Testing was
primarily to ANSI42.17A, not the extreme testing of 42.17C.  The
instruments selected did not have minimal problems.  Substantial problems
did exist.  One of the models was supposed to be de-selected due to these
problems.  At this time, I believe most have been cleared up through the
efforts of individual facilities and the vendors.

 

Peter J. Chiaro Jr
Instrumentation and Controls Division
P.O. Box 2008
Oak Ridge National Laboratory
Oak Ridge, TN  37831-6004
(423)576-4598
(423)574-1249 (fax)
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