Wednesday
19th November 1997 - NISM & MISM alive!
From
John Storey......
Things are moving right along. Rodney Marks arrived last night,
ready to begin 12 months at the Pole. He'll be looking after
Abu, and already we've pressed him into service lugging things
around. Ev has been busy in the AASTO, and has been sending
messages back and forth to the AGO service crew.
Last
night we got *both* the nism and mism working. The mism was
easily able to detect Ant's hand when he leaned out the door
and waved at it. This not only proves that Ant is alive, but
also that he's warm-blooded. It also gives us great encouragement
that we will be able to leave two working instruments here
when we depart in a couple of weeks.
Firing
up the nism first, we were delighted to find that the Stirling-
cycle cooler switched on immediately, and everything just
worked the way it should. Scanning across the sky gives a
large variation in the amplitude of the signal we see (as
it should). The only problem is that the stepper motor doesn't
have enough grunt to consistently move the instrument - boy
do we have a surprise in store for it.
When
we last talked to the mism (in May), the chopper was refusing
to run above 500Hz. Naturally this was one of the first items
for discussion with it when we re-established contact last
night. Sure enough, 500 Hz. Tops. Maximum. This wouldn't matter
a whole lot except that the entire signal chain is tuned to
1kHz. Figuring that if the mism refused to be phase-locked
then we would refuse to be fazed, we plugged in the spare
chopper-driver board and the chopper immediately locked up
at a kHz, no argument.
This
delighted both Ant and me, as neither of us has any wish to
rip the optics box apart and mess with the chopper motor.
However I do take any electronics failure as a personal affront,
and the chopper driver board must have realised it was well
and truly for it.
The
"super" refuses to talk to the mism on the mism
port, so we're using the nism port instead. This might be
a software problem, or could be related to the fact that the
mism rs232 port is on a different board to the nism. Given
that the AFOS will not be running this year, a very simple
fix is to reassign port 1 to the mism.
The
next step was find out what when wrong with the original chopper-
driver board. (I am dismayed to find that not only is the
oscilloscope smarter than I am, but that the multimeter is
also ahead on points. It's a bright yellow you-beaut Fluke
meter, that Ant insisted I buy because it cost a lot of money.
When I tried to measure a voltage with the probes plugged
into the current socket, it beeped plaintively at me. I'm
not sure if this intelligence, or just instinct for self preservation.
Tomorrow I plan to hold it up in front of the mism and see
if it is alive, too.)
Anyway,
what was wrong with the chopper-driver board was that there
was a tiny little bit of grunge on the board, bridging between
two of the copper tracks. It was sufficiently conductive to
reduce the reference signal below the CMOS threshold, with
the result that the PLL simply ran at a random frequency close
to the middle of its range. We will need to talk to our normally
excellent electronics workshop about the hazards of leaving
grunge on the circuit board.
Actually,
we *had* intended to have all the boards made commercially
once the workshop had done the prototypes. I think I'm going
to vote for doing exactly that during 1998, especially in
view of the brown slime.
Speaking
of which, we ripped the nism off the roof of the AASTO and
sledded it across to the MAPO building. The inside of the
support bracket is covered in the last remnants of brown slime
(actually white slime, being aluminium). Because the nism
was exposed it acted as a big cryo-pump and is now covered
in more than its share of grunge. We'll clean it up tonight
and then fit the *new monster stepper motors* which Andre
tested in the lab and found to be all torque (*and* all action).
By
now we're fairly convinced that what hit the AASTO was a combination
of HF and HCl from the decomposing freon, plus H2SO4 from
the batteries. (Michelle thinks it was aliens, but she's wrong.
The aliens live at Old South Pole Station, and don't cause
any trouble as long as we invite them to Thanksgiving each
year, which we do. I've already been enlisted as a wine waiter
for the occasion). But I digress. The only really nasty in
the above list is HF, which gobbles up human flesh like an
offended alien. Paradoxically, it's *so* reactive that it's
very unlikely for any of it to be left in the AASTO - whatever
it landed on it will already have eaten and been thereby rendered
harmless (or so I believe).
Weather
is still very cold; still windy. They're scheduling 6 flights
a day to try to get the program back on schedule, but only
about half actually get here.
While
I'm typing this, Amnt is cleaning up the nism. That's why
this message is so long. When I finish I'm going to translate
it into French, then type it backwards in morse code, and
then go out and give Ant a hand.
Cheers,
John
 
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