Experimental Physics and
Industrial Control System

Mohan Ramanathan <[email protected]> · Tue, 21 Jun 2011 08:31:40 -0500

Folks:

I been watching the stories of these radiation damage.

Let me give you all my perspective of what we saw long long time ago at APS and we have managed to handle these problems.

At APS we operate at 7.0 GeV.  The ID's we used had SSI based absolute encoders.  These encoders have CCD in them.  Its a know fact that CMOS has problem with neutron damage.
We started installing shielding of encoders and even then the absolute linear encoders started dying ( I am talking of back in 1995-2000 time frame).  At that time we started looking at alternate encoder and we started using virtual absolute encoders.  These are based on transistor and diodes.  We have since shielded most of the encoders and have had good luck since.

We also were the once to use smart servo motors back in 2000 time frame and ran in severe problem with damage to electronics resulting in motor run offs.
Most of the problem were related to neutron damage.

mohan

On Jun 20, 2011, at 2:21 PM, Rarback, Harvey M. wrote:

> 	Folks,
> 
> Let me add another data point to the vulnerability of SSI encoders inside the beam tunnel near beam height.  We've had *seven* unrecoverable TR Electronics LT Series failures as well as a few Hall effect limit switch failures at SPEAR.  Shielding with ~1 cm of Pb seems to have fixed (or slowed down?) the failure rate.
> 
> Potentiometers and LVDTs inside the tunnel make a great deal of sense.
> 
>                               --Harvey
> ----
> Harvey Rarback                   phone: (650)926-3963
> SLAC National Accelerator Lab    fax:   (650)926-4100
> 2575 Sand Hill Road              home phone: (650)560-9111
> Menlo Park, CA 94025             [email protected]
>                                 http://ssrl.slac.stanford.edu/~rarback
> 
>    "Always tell the truth, that way you don't have to keep track."
>                             Pogo
> 
> 
>> -----Original Message-----
>> From: [email protected] [mailto:tech-talk-
>> [email protected]] On Behalf Of Hu, Yong
>> Sent: Monday, June 20, 2011 9:24 AM
>> To: [email protected]; Josh Stein; Richard Farnsworth;
>> [email protected]; [email protected]
>> Cc: [email protected]
>> Subject: RE: radiation damage to electronics inside accelerator tunnel?
>> 
>> Thanks a lot for all of you sharing experiences and giving suggestions
>> which are really helpful for me to convince our Diagnostics Group to
>> re-design cabling and shielding.
>> 
>> Regarding position measurement encoder, we're going to use Potentiometer
>> and LVDT with stepper motor for beam diagnostics (slits, scrapers,
>> etc.). We think these kinds of analog encoders might have better
>> resistance to EMI and radiation.
>> 
>> Yong
> 
> 

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Mohan Ramanathan						Senior Beamline Engineer
[email protected]						Advanced Photon Source
(630)-252-3773 (off)/(630)-822-5625(Cell)	Argonne National Laboratory
(630)-252-7187 (FAX)					Argonne, IL 60439
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System