Experimental Physics and
Industrial Control System

<[email protected]> · Mon, 20 Jun 2011 15:03:54 +0000

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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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System