|
Hello,
I thought I would add my own observations and questions about apparent
discontinuities in the data.
Attached is a short PDF showing the spatial pattern of just one such jump in
our data.
We have seen various types of jumps in the data, so allow me to use some
loose terminology. There is sometimes "popcorn" noise in a single
channel, which are isolated "pops" in the data, or sometime a bit
broader of a pulse looking pop (Note, you often have to switch off SSP to
confirm it is one channel, since SSP can make it look like multiple
channels). These are generally thought to be trapped flux and are generally
easily corrected by heating the channel.
Then there are SQUIDs that "unlock". We have had several people in
these emails say a sensor "saturates," but that sounds too EEG-like
to my ears. My crude understanding (I am not a SQUID electronics expert) is
that SQUIDs don't actually saturate, but rather, the feedback flux demands
become too great to maintain zero-flux in the coil, and the electronics
"unlock" their feedback operation. We see this effect when the
occasional truck passes directly by our room. Once a SQUID unlocks, the
subsequent data in that channel (and indeed, apparently adjacent channels)
are worthless until a reset command is manually issued, that restabilizes all
of the feedback operating points.
Then we have the phenomenon in the attached PDF, nearly identical to the one
that Gustavo Sudre posted earlier. We get this "pow" (better word?)
in a handfu of channels. The data return back to baseline shortly (because of
the highpass, presumably?), but still seem to be operational, i.e. a reset
does not seem required.
In the example I posted, it seems to be related to a tri-channel chip and
it's associated amplifier, but we see smaller pows in the adjacent
amplifiers, and not always all three channels. So if this is a spatial event,
why don't more channels see it?
One of my experts suggested that an RF event has occurred that only upsets
selected susceptible channels, i.e. it is spatially initiated, but an
electronic mishap. Is this a matter of tuning?
Conjectures by anyone on exactly what we are seeing? Is this "pow"
actually a simple flux jump that has not actually unlocked the electronics,
i.e. we're just in a new flux quanta but operating otherwise okay? How does
this discontinuity fit in with unlocked and unstable operation?
-- John
-------------------------
John C. Mosher, Ph.D.
[log in to unmask]
|
