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
-----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: Monday, June 20, 2011 11:04 AM
To: Hu, Yong
Cc: [email protected]
Subject: RE: radiation damage to electronics inside accelerator tunnel?
Just to add some of our experiences to the general discussion:
We've had problems with our absolute encoders fitted to our insertion
devices. These encoders are SSI devices.
In our case the encoders 'crash' when we suffer a beam dump.
We have yet to establish whether we will see long term radiation damage
of these devices. Some of them have been in the ring since 2005/2006.
I also understand that we see disruption of some readings from
Heidenhain incremental encoders during beam dumps.
Some comments from our internal discussions on the problem:
The failure modes:
The encoders fail during a beam dump and we are pretty sure that this is
as a result of a shower of particles disrupting the internal
electronics.
There are two failure modes, one where the encoder generates erroneous
position data and then recovers. The other is where the encoder stops
outputting a serial data stream and it requires a power cycle to
recover.
The investigation:
We investigated the fault with an oscilloscope to understand the fault
modes, and found the SSI output signals temporarily or permanently latch
up causing a full scale output to be read by the control device.
We investigated whether this could be as a result of an EMI problem
rather than as a result of the particles hitting the read-head and added
extra ground braiding.
We tried to add lead boxes around some of the encoders, but the results
of this were inconclusive.
Machine optics:
We found that with 'improving' machine optics, the problems decreased to
such an extent that it was agreed that we would stop investigating the
problem.
Other works:
We contacted the manufacturer and asked about relocating the read heads
away from the encoder body, but they were not keen on the investment in
time and money to solve a problem that only Diamond were seeing.
We stripped down an encoder to look at the parts inside and draw our own
conclusions about the internal design. There is a processor, FPGA and
some memory devices along with the optical components. It became clear
that these devices are more complicated than a standard incremental
encoder.
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Hu, Yong
Sent: 14 June 2011 20:42
To: [email protected]
Subject: radiation damage to electronics inside accelerator tunnel?
Hello All,
Did anyone have experience putting electronics, especially Moxa NPort
5110[1] and IFW Intelligent Filter Wheel[2], inside accelerator(Linac,
Booster, Storage Ring) tunnel? Any shielding required?
Thanks,
Yong
[1] http://www.moxa.com/product/NPort_5110.htm
[2] http://www.optecinc.com/astronomy/catalog/ifw/ifw.htm
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