The Larkin front end

[Eeyore]

Eeyore wrote
20 what, pushups? ....

I'd need to exercise a bit to do 20.

Mind you, I fancy my chances over Jim Thompson any day.

Graham

 

[mark]

Hello Jim,


There are various grades when simulating "truck". There is the smooth
glide along Interstate 80, then there is the not so smooth rumble from
Shannon Airport to Ballinsloe, and then there is the driver who tries to
find the "speed of least shaking" on a sastrugi track through the Sahara
desert.



After finishing a hi-rel module they showed me the impact tables where
it'll all be tested. Now I knew where that regular ka-bummmmph sound was
coming from. They raised the unit several feet and then let it drop onto
a concrete pad. Then again. And again. Every once in a while someone
would pour another layer. The concrete slowly became a pillar that drove
itself into the ground.

I'm going to have some 7,000G shock testing done real soon. That should be
really interesting to watch. Not often does one get to play with explosive
charges.
(I'm not doing it: a contract lab so should be safe)

M Walter

 

[SioL]

A ferrite bead won't do that.

Graham

Because?

SioL

 

[martin griffith]

I'd need to exercise a bit to do 20.

Mind you, I fancy my chances over Jim Thompson any day.

Graham

sorry, G, not going on that personal insult route.
Jim's probably ok in real life, the pics I saw of him, just a happy
family

I'll leave the insults to our Oz friend, who seems to be back on the
meds again,



martin

 

[Joerg]

Hello Mark,

I'm going to have some 7,000G shock testing done real soon. That should be
really interesting to watch. Not often does one get to play with explosive
charges.
(I'm not doing it: a contract lab so should be safe)

Do you remember that ad in an electronics magazine (in the days when
they still cut trees to be able to distribute them...) with a missile
test gone wrong? Big fireball, stuff flying, arrow pointing to a little
speck in all that flying debris: This is our XYZ supply, now
involuntarily airborne on its own. Then a totally mangled piece of metal
on a test bench: See, it still works!

 

[Eeyore]

sorry, G, not going on that personal insult route.
Jim's probably ok in real life, the pics I saw of him, just a happy
family

He called me fat though !

Just look at those pics !

Graham

 

[martin griffith]

He called me fat though !

Just look at those pics !

Graham

Nah, sorry not going there, as far as I'm concerned ( when sober)
personal comments/insults are not what I'm here for, I may dislike
what Mr.T votes for, but I'll try not to insult Jim personally, but it
can be difficult, can't it


martin

 

[John Larkin]

Hello John,



Wooden? Oh man. I hope it has at least a light-weight upper floor and
roof, for when the next big one hits. I remember a picture you posted
with a scarily mounted lifting crane.

Actually, the front/back/sides and support posts are concrete (old,
crappy concrete) and the roof and floors are wood. The front and back
are mostly glass, structurally useless. It *is* RF transparent. When
we bought it, we did a serious seismic upgrade: three huge poured
footings in the ground, steel frames all the way to the roof,
structural plywood on the floors and roof, and bazillions of brackets
and bolts. It cost a bundle.

It may be worthless after the big one, but at least maybe it won't
pancake and squash us all.

During an EMI job on an ultrasound machine they didn't really believe we
had shortwave radio interference. Until I asked them for the register
address that could change the Doppler CF and fiddled with it. The sound
of Big Ben was echoing through the engineering lab and the BBC World
Service news came out of the speakers...



Once I saw that from a plane taking off. Only the top stuck out after we
punched through the thick cloud layer. I could still bite myself that I
had left the camera in the baggage bin.

On some days, as seen from Twin Peaks, the fog is a solid layer on the
ground, and all you see is a few big buildings, like the pyramid, and
the GG bridge poking out, and a few steam plumes. Very cool.

John

 

[Eeyore]

Nah, sorry not going there, as far as I'm concerned ( when sober)
personal comments/insults are not what I'm here for, I may dislike
what Mr.T votes for, but I'll try not to insult Jim personally, but it
can be difficult, can't it

If he'd stop his own insulting behaviour......

He's simply on the receiving end of what *he* started.

Graham

 

[John Larkin]

Indeed, their lossiness is very handy.

Have you ever tried intentionally injecting modulated RF into a front end btw ?

Graham

Only from a nearby antenna. I have a set of the old tube GR unit RF
oscillators, from 10 MHz to about 2 GHz, and they output something
like a watt. So you can poke a banana lead in the connector as a
splash-everything antenna, or strip a bit of braid off a hank of coal
and make a more local source you can wave around. It's not
quantitative, but you can find resonances and do a rough before/after
comparison on things.

I've been meaning to buy a real EMI-type antenna, for crude
quantitative suceptability and emissions tests, but haven't got around
to that yet.

John

 

[John Larkin]

It sounds to me like we're comparing lossy low-pass filters to common-mode
chokes here. Isn't that kind of like apples and tomatoes?

I'm not comparing them. I figure RF can be common or differential, so
I just kill it all.

A common-mode choke has no ground connection, so can't block RF nearly
as well as a nice l-c-l-c filter nailed to the ground plane. The
diffamp input is just a few pF to ground, so RF can blast right
through a series choke. And without a ground, it won't help the ESD
situation either.

John

 

[John Larkin]

On Wed, 08 Nov 2006 08:28:34 -0800, John Larkin
[snip]

You're very polite, John.

Eeyore/Graham IS stupid AND ignorant ;-)

...Jim Thompson

Well, at least he does let his emotions interfere with his thinking.

John

Sno-o-o-o-ort ;-)

...Jim Thompson

Wasn't meant to be a joke, actually. One of the hardest things to do
in this business is to not let your emotions distort your perceptions
or screw up your judgements.

John

 

[Jim Thompson]

On Wed, 08 Nov 2006 10:34:26 -0700, Jim Thompson

On Wed, 08 Nov 2006 08:28:34 -0800, John Larkin
[snip]

You're very polite, John.

Eeyore/Graham IS stupid AND ignorant ;-)

...Jim Thompson

Well, at least he does let his emotions interfere with his thinking.

John

Sno-o-o-o-ort ;-)

...Jim Thompson

Wasn't meant to be a joke, actually. One of the hardest things to do
in this business is to not let your emotions distort your perceptions
or screw up your judgements.

John

Yep. Probably my worst short-coming, or maybe it's a long-coming ;-)
.... I tend to be persistently difficult and don't let clients push me
into a quick crappy solution... makes some of them angry with me :-(

...Jim Thompson

 

[Joerg]

Hello Jim,

... I tend to be persistently difficult and don't let clients push me
into a quick crappy solution... makes some of them angry with me :-(

Does that happen a lot? Maybe I was lucky. The only time someone tried
to push me was about the mechanical part of a machine and I told them I
wouldn't be able to work for them then. So they did it my way but nobody
became too grumpy about that.

 

[Richard The Dreaded Libertarian]

Yep. Probably my worst short-coming, or maybe it's a long-coming ;-)
... I tend to be persistently difficult and don't let clients push me
into a quick crappy solution... makes some of them angry with me :-(

I am resolute. You are stubborn. He is a pig-headed fool. ;-)

Cheers!
Rich

 

[John Larkin]

On Wed, 08 Nov 2006 08:28:34 -0800, John Larkin



The load cell based weigh scales used for mixing semiconductor gasses
at Praxair have a 100 kg capacity with 1 mg resolution - 8 digits. The
plant manager claimed that they were the most accurate scales in
existence. I didn't get the linearity spec, but I would be surprised
if it was worse than 7 digits, as linearity is the only thing that
counts in this application and cost is nearly irrelevant. Some
processes require dopants mixed to concentrations as low as 200 ppb
(in multiple dilution steps), where once mixed it is impossible to
verify mixing accuracy with any existing instrument. If you can come
up with a mass spectrometer that can measure dopant and impurity
concentration with a few ppb accuracy (as opposed to the few tens of
ppb now available) you could probably sell at least one to every
semiconductor gasses plant in existence. All 3 of them IIRC .

A good load cell is amazing. Some of the weighing cells are totally
insensitive to torque. You can bolt a platform to the top of the cell
and put a weight anywhere on it, and it always weighs the same. I
didn't think that was possible until I saw it myself.

Have you looked at the TI ADS1232/4 - looks pretty good for moderate
accuracy load cell weighing, as does the older and more available
AD7730 (I am still waiting for my ADS1232 eval board to arrive,
ordered several months ago). I intend to put it in the load cell with
only a few cm of strain gage leads inside the shielded load cell
enclosure, with filtering then only required on the power leads to a
precision linear regualtor also inside the load cell enclosure.

We've been using the AD7793 lately, and it's very nice. It has a bunch
of gain ranges down to something like +-25 mV, and it seems good to
about 1 uv stability. Of course, a load cell deserves a really good
diffamp ahead of a CMOS ADC for extreme results.

If you use the same source for load cell excitation as drives the ADC
reference, all sorts of nasties cancel out, but you probably knew
that.

John

 

[John Larkin]

I'm going to have some 7,000G shock testing done real soon. That should be
really interesting to watch. Not often does one get to play with explosive
charges.
(I'm not doing it: a contract lab so should be safe)

M Walter

We did some big engine-room control consoles for the Navy LHA ships.
We had to send them up to a quarry pond in Vermont where they bolted
them into a barge and then set off charges in the water. The
high-speed film was impressive... indicator lenses flying off into the
air and such. They used some sort of magnesium flares to illuminate
the scene for the fast cameras, and that caught some of our stuff on
fire, but they didn't count that as a failure.

John

 

[[email protected]]

If he'd stop his own insulting behaviour......

He's simply on the receiving end of what *he* started.

Graham

An eye-for-an-eye and everyone's blind.

Best wishes,
James Arthur

 

[[email protected]]

On Wed, 08 Nov 2006 08:28:34 -0800, John Larkin


You're very polite, John.

Eeyore/Graham IS stupid AND ignorant ;-)

Not stupid, just stubborn, stubborn as ... a mule. And perhaps a
little overly resistant to real data.

I don't get the controversy over the beads--kill the real RF, let the
diff amp handle the rest. Seems simple enough.

Doesn't explain where all that energy is going in my little
switcher--57% efficiency, and I can't find the loss. Dang it.
(inductor suspected)

James Arthur

 

[xray]

or strip a bit of braid off a hank of coal
and make a more local source you can wave around.

I assume that your coal was actually coax. My coal never came with a
braid.

Spelling shouldn't count much here, but it threw me off when I read it.

I've been wavin' 'round a coal wand, all the live long day.