🚀 go-pugleaf

Joerg wrote:
> 
> Joel Koltner wrote:
> > "Joerg" <invalid@invalid.invalid> wrote in message
> > news:7ai5luF1ur1mbU1@mid.individual.net...
> >> I usually spent a lot more time on the enclosures than on the electronics
> >> but the stuff is still working.
> >
> > Didn't anyone tell you that dovetail joints were optional? :-)
> >
> > Just kidding.  I can't imagine even you would have chiseled out dovetail
> > joints (since I'm thinking those dovetail jigs you use with a router didn't
> > exist for the casual home woodworker back then)...
> >
> 
> I didn't go that far but I polished and stained the corners until you
> couldn't really see where things butted up anymore.
> 
> Saw a contractor commercial lately about the Fein Multimaster. Drooling
> all over the place. Fein is "the" electric tool company in Germany, only
> the good stuff. You had to call a 1-800 number to find out the price and
> that should have been a dead give-away. Well, found it on the Internet,
> saw the prices of spare inserts and decided that I do not need it this
> urgently.
> 
> http://www.amazon.com/Fein-MultiMaster-FMM-250Q-Top/dp/B000U8S3QA


http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=67097


> > I built a small table (~2'x2'x1') for test equipment to live on not quite a
> > month ago.  I thoroughly enjoyed using a dado blade to cut a bunch of lap
> > joints, and verified the table could hold 300lbs.  Old boat anchors, here I
> > come!
> >
> 
> That's the other thing I built, or partially had built when I was around
> 15, size 6ft by 4ft and extremely sturdy (boat anchor proof). I made a
> drawing of the frame and asked my parents whether it was ok to get some
> metal stock, borrow a welding transformer and weld it in the garage. Oh
> no, no dice. So I went to the local HW store, a larger kind of mom and
> pop place. My classmates said they'd laugh at me there. The foreman took
> a look, "Yep, will be ready in two days, then we'll drive up there and
> chuck the frame over the hedge and you come down here to pay us the 70
> Deutschmarks". They didn't even want up front cash. Oh, now my chest
> swelled and I felt like an engineer. Until I glued the formica onto a
> panel that would become the top and I had it slightly skewed ...
> 
> --
> Regards, Joerg
> 
> http://www.analogconsultants.com/
> 
> "gmail" domain blocked because of excessive spam.
> Use another domain or send PM.


-- 
You can't have a sense of humor, if you have no sense!

John Larkin wrote:
> On Thu, 25 Jun 2009 14:37:54 -0700, Joerg <invalid@invalid.invalid>
> wrote:
> 
>> John Larkin wrote:
>>> On Thu, 25 Jun 2009 12:56:30 -0700, Joerg <invalid@invalid.invalid>
>>> wrote:
>>>
>> [...]
>>
>>>> Probably the litmus test for RF stuff like this is when people schlepp 
>>>> it to Otis Street and see if it can survive Sutro Tower.
>>> It's terrible here. Scope traces are gross fuzz, and all sorts of
>>> opamp front-ends like to rectify stuff.
>>>
>>> You should see the spectrum of a 10" clip lead.
>>>
>>> http://www.jimprice.com/sutro/tower1.jpg
>>>
>> Once I took off on a Europe flight out of SFO and the antenna top stuck 
>> out of the clouds while the rest of the tower was in the white. Picture 
>> perfect, and I had my camera in the overhead <aargh>. I could still bite 
>> myself, that opportunity never came again.
> 
> A couple of times I've been up on Twin Peaks and there was a sharply
> defined fog layer below. Only a couple of big buildings poke through,
> and a few plumes from power plants and such.
> 
> Sometimes the sun gets under the fog at sunrise/sunset. Cool.
> 
> ftp://jjlarkin.lmi.net/Kit1.JPG
> 

Nice. Would be even nicer without the attached city :-)

> 
>>
>>> We did do a useful simulation of a system that has a superconductive
>>> magnet/front end on one side of a room and some ADCs on the other
>>> side. We convinced ourselves that we need to go differential.
>>>
>> Yesterday I had my comeuppance WRT to the Instek GDS-2204 scope that I 
>> thought is so much better than Tektronix. In many ways it is, and also 
>> doesn't have the nasty conducted emissions on the probe cables. But when 
>> debugging 74MHz gear I could not figure out where a weird buzz was 
>> coming from. Until I turned off the scope ...
> 
> CPU clock maybe?
> 

Possibly. It even happens in standby power so maybe it's the SMPS in there.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

ehsjr wrote:
> Joerg wrote:
>> John Larkin wrote:
>>
>>> On Thu, 25 Jun 2009 19:50:09 GMT, Rich Grise <richgrise@example.net>
>>> wrote:
>>>
>>>> On Wed, 24 Jun 2009 22:01:51 -0700, John Larkin wrote:
>>>>
>>>>> On Wed, 24 Jun 2009 21:42:07 -0700, <castlebravo242@att.net> wrote:
>>>>>
>>>>>> "David L. Jones" <altzone@gmail.com> wrote in message 
>>>>>> news:h8B0m.53620$FI5.3564@newsfe12.iad...
>>>>>>
>>>>>>> Check out a rather unusual phenomenon you can see on your 
>>>>>>> oscilloscope in my latest blog (#14):
>>>>>>> http://www.alternatezone.com/eevblog/
>>>>>>> See if you can get it to happen on your scope!
>>>>>>> I'll offer a free subscription to my blog for the best screen 
>>>>>>> shot posted :->
>>>>>>>
>>>>>>> Oh, and the probe doesn't have to be shorted either.
>>>>>>
>>>>>> When I worked a Century Data we had a problem with our new reel to 
>>>>>> reel vaccuum column tape drive when ever someone would walk by the 
>>>>>> drive when it was reading it would get data errors. The problem 
>>>>>> was that the shield on the cable from the heads to the preamp was 
>>>>>> grounded on both ends.
>>>>>
>>>>> That's usually the best way to ground shields.
>>>>
>>>> When I was a kid, my brother built a Heathkit TOOB amp; in the low 
>>>> level
>>>> circuits, they only ever grounded one end of the shields.
>>>>
>>>
>>> Inside a steel chassis pan, it wouldn't matter. But then Heathkit was
>>> hardly an authority on signal management.
>>>
>>
>> Now wait a minute, they engineered darn good stuff. The old HW100/101 
>> transceivers were among the best ever made back in the tube days. 
>> Still got one. No noises or buzzes whatsoever and its performance in 
>> the vicinity of strong signals is stellar. The only not so good thing 
>> was the two rubber pulleys because they cooked out too fast, but you 
>> could keep a stash of them in the drawer.
>>
> 
> Brings back pleasant memories. I donated my HW101 to the Boy Scouts
> radio club many years ago. I wish I still had my HW 16 - lots of wee
> hours CW with that (my first) rig.
> 

At least you've got the memories, that's all that really counts. I 
donated my HW101 to a ham in former East Germany after the wall fell. 
Back then they didn't have the funds to buy western quality gear. I kept 
the older HW100 because that has a white-knuckle supply, direct 
rectification and Cockroft-Walton cascade from 230VAC mains. Plug it in 
the wrong way ... *BAM*. He got the good set, with original power supply 
and the whole thing looked hardly used, almost like new. He was really 
happy.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

krw wrote:
> On Thu, 25 Jun 2009 18:00:52 -0700, Joerg <invalid@invalid.invalid>
> wrote:
> 
>> krw wrote:
>>> On Thu, 25 Jun 2009 17:13:00 -0700, Joerg <invalid@invalid.invalid>
>>> wrote:
>>>
>>>> Joel Koltner wrote:
>>>>> "Joerg" <invalid@invalid.invalid> wrote in message 
>>>>> news:7ai5luF1ur1mbU1@mid.individual.net...
>>>>>> I usually spent a lot more time on the enclosures than on the electronics 
>>>>>> but the stuff is still working.
>>>>> Didn't anyone tell you that dovetail joints were optional? :-)
>>>>>
>>>>> Just kidding.  I can't imagine even you would have chiseled out dovetail 
>>>>> joints (since I'm thinking those dovetail jigs you use with a router didn't 
>>>>> exist for the casual home woodworker back then)...
>>>>>
>>>> I didn't go that far but I polished and stained the corners until you 
>>>> couldn't really see where things butted up anymore.
>>>>
>>>> Saw a contractor commercial lately about the Fein Multimaster. Drooling 
>>>> all over the place. Fein is "the" electric tool company in Germany, only 
>>>> the good stuff. You had to call a 1-800 number to find out the price and 
>>>> that should have been a dead give-away. Well, found it on the Internet, 
>>>> saw the prices of spare inserts and decided that I do not need it this 
>>>> urgently.
>>> Fein is simply crazy expensive.  I looked at their routers over the
>>> weekend.  I wasn't impressed, for 4X what a Bosch or PC costs.  Bosch
>>> has a "Multi-Master type tool ("Multi-X", I think) that's a lot
>>> cheaper and looks just as good (Li-Ion battery, though).  A little
>>> lower down the line, Dremmel has a copy for $100ish.  If you want to
>>> go cheap, HarborFreight has one for $40.  The reports are decent,
>>> acknowledging that it's a $40 tool.  The only real complaint is that
>>> the blades loosen.  
>>>
>> The $40 version will be good enough for me.
> 
> But it's ugly orange.  ;-)  I think I'll spring for the Bosch.  I want
> to rip up some bamboo flooring and inlay a hearth in front of our
> fireplace.  I can't figure out another way to make the cuts against
> the wall.
> 

Look at the bright side: It could be worse. My Chinese meters here are 
bonbon-purple. Channel 3 on my DSO is bonbon-pink.

> 
>> I've used Fein drills, they 
>> are really top notch. I think grampa's drill in the garage is a Fein. 
>> About 100 years old, works like a champ.
> 
> I now have seven cordless drills (will likely give one to my son).  I
> just bought a little Bosch 12V Li-Ion to match the impact driver.  100
> years ago a cordless drill was a brace and bit.  ;-)


I am very impressed with the little Durafix single Li-Ion pistol-style 
electric screwdriver. $15. We had to build a large step box for our 
Rottie because he has trouble getting in and out of the car. The long 
deck screws were hard to turn but it muscled them in. Sure saved me a 
blister.

-- 
Regards, Joerg

http://www.analogconsultants.com/

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Use another domain or send PM.

John Larkin wrote:
> 
> At the receive (instrument) end, the ungrounded end of the coax shield
> becomes the hot side of a resonant "vertical" antenna. Any voltage
> there becomes 100% common-mode signal on the inner twisted pair.
> 
> What's wrong with a little current in the shield? The signal pair
> isn't affected. But volts, or tens of volts, of common-mode RF can be
> nasty.


   That's the reason you see lots of six inch wide copper bonding straps
in radio studios. They use one and a half inch straps to connect between
the equipment, and the bonding straps.


-- 
You can't have a sense of humor, if you have no sense!

"krw" <krw@att.bizzzzzzzzzzz> wrote in message 
news:m3f845t4q6m0otottpp8fph33kbo3egsak@4ax.com...
> But it's ugly orange.  ;-)  I think I'll spring for the Bosch.

The cordless one?  Or do they have a plug-in one now?

> I
> just bought a little Bosch 12V Li-Ion to match the impact driver.  100
> years ago a cordless drill was a brace and bit.  ;-)

We still used those back in industrial arts class in the mid-'80s since they 
didn't have enough electric drills to go around.  (I imagine they'd had them 
for decades!)

We had pretty good instructors... of the many demos they gave, I remember one 
where the guy said, "You want to know the difference between this cheap Black 
& Decker power drill here and this much-more-expensive Milwaukee?  Watch 
this?" -- Guy wraps his hand around the chuck on the B&D, hits the trigger 
with his other hand and... chuck doesn't turn, the drill just sitting them 
humming a bit.  "Don't try this with the Milwaukee!"

---Joel

On Thu, 25 Jun 2009 19:54:34 -0500, krw wrote:
> On Fri, 26 Jun 2009 00:23:28 GMT, Rich Grise <richgrise@example.net>
>>On Thu, 25 Jun 2009 17:13:00 -0700, Joerg wrote:
>>
>>> swelled and I felt like an engineer. Until I glued the formica onto a 
>>> panel that would become the top and I had it slightly skewed ...
>>
>>I guess nobody told you about the shims. ;-)
> 
> How do shims fix a skewed veneer?

You put the glue on the surface and let it dry, and lay thin pieces of
wood across it. Put the glue on the formica, let it dry, and lay it
on top of the shims. The shims have no glue, so don't stick. Line
the formica up, on top of the shims, and one by one take the shims 
out and let the formica stick to the surface.

I've seen it done on those "home improvement"-type TV shows. :-)

Cheers!
Rich

On Jun 24, 7:18 pm, "David L. Jones" <altz...@gmail.com> wrote:
> Check out a rather unusual phenomenon you can see on your oscilloscope in my
> latest blog (#14):http://www.alternatezone.com/eevblog/
> See if you can get it to happen on your scope!
> I'll offer a free subscription to my blog for the best screen shot posted
> :->
>
> Oh, and the probe doesn't have to be shorted either.
>
> Have fun.
> Dave.
> --
> ================================================
> Check out my Electronics Engineering Video Blog & Podcast:http://www.alternatezone.com/eevblog/


After watching your video, for some reason I was reminded of Starbuck
Flying and his computer adventures.  Aren't you glad he doesn't have a
scope?

:D

Michael

On Jun 26, 4:15 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Fri, 26 Jun 2009 22:22:22 GMT, ehsjr <eh...@NOSPAMverizon.net>
> wrote:
>
> >John Larkin wrote:
>
> ><snip>
>
> >> A couple of times I've been up on Twin Peaks and there was a sharply
> >> defined fog layer below. Only a couple of big buildings poke through,
> >> and a few plumes from power plants and such.
>
> >> Sometimes the sun gets under the fog at sunrise/sunset. Cool.
>
> >>ftp://jjlarkin.lmi.net/Kit1.JPG
>
> >Wow. You're making me drool.
>
> But a lot of the time we look out the kitchen window and see a wall of
> fog.
>
> John

I got this brilliant idea a few decades ago to watch the 4th of July
fireworks from Twin Peaks. Bad idea. The place is full of yahoos
shooting off their own fireworks. Should a fire break out, you are
screwed.

I did watch the Oakland Hill fire from Twin Peaks. I kid you not,
there was a group singing the Grateful Dead's "Fire on the Mountain",
over and over....

"Fred Abse" <excretatauris@invalid.invalid> wrote in message 
news:pan.2009.06.26.20.44.22.463914@invalid.invalid...
> On Fri, 26 Jun 2009 08:17:40 -0700, Joerg wrote:
>
>> Look at the bright side: It could be worse. My Chinese meters here are
>> bonbon-purple. Channel 3 on my DSO is bonbon-pink.
>
> When I was a lad, we called that color "Nipple Pink"
>
> ;-)
>

Thats not very PC Fred. These days we don't have nipples we have pediatric 
sustenance dispensers. 

Joel Koltner wrote:
> "Joerg" <invalid@invalid.invalid> wrote in message 
> news:7aii4kF1vcv49U1@mid.individual.net...
>> Saw a contractor commercial lately about the Fein Multimaster. Drooling all 
>> over the place.
> 
> I first saw the Fein Multimaster at the Portland Woodworking Show not that 
> long ago.  They were having a grand time demoing it -- and letting anyone who 
> cared to try it out themselves -- and it was *very* tempting.
> 
>> Well, found it on the Internet, saw the prices of spare inserts and decided 
>> that I do not need it this urgently.
> 
> There's been a lot of competition with it lately (apparently Fein's patent 
> expired?):
> 
> Rockwell: 
> http://www.amazon.com/Rockwell-RK5100K-Sonicrafter-20-Piece-Kit/dp/B001EYUGM8 
> (looks really good)
> Dremel: 
> http://www.amazon.com/Dremel-6300-01-120-Volt-Multi-Max-Oscillating/dp/B001FORC9C 
> (dunno)
> Habor Freight (!): 
> http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=65700 (you're 
> lucky if you get what you pay for?)
> 
> ...and there's always eBay for knock-off Fein inserts... (quality level... who 
> knows?)
> 
> Nice story about getting your workbench frame built.  I suspect that just 
> couldn't be done today, unfortunately. :-(
> 
> ---Joel
> 
> 

Interesting.  I was intrigued by this just last month and
meant to look into it:

Fein:
   www.4multimaster.com

-- 
Cheers,
James Arthur

On Jun 24, 7:18 pm, "David L. Jones" <altz...@gmail.com> wrote:
> Check out a rather unusual phenomenon you can see on your oscilloscope in my
> latest blog (#14):http://www.alternatezone.com/eevblog/
> See if you can get it to happen on your scope!
> I'll offer a free subscription to my blog for the best screen shot posted
> :->
>
> Oh, and the probe doesn't have to be shorted either.
>
> Have fun.
> Dave.
> --
> ================================================
> Check out my Electronics Engineering Video Blog & Podcast:http://www.alternatezone.com/eevblog/

His schematic of the scope probe and scope input are oversimplified to
the point of incorrectness.  Also, he ignored the low-pass nature of
the oscilloscope input, which might contribute to the clean
"sinusoidal" waveform.

In article <7716bb9f-f71a-43a4-bcb0-9847e42f58c3@i6g2000yqj.googlegroups.com>,
miso@sushi.com <miso@sushi.com> wrote:
>I got this brilliant idea a few decades ago to watch the 4th of July
>fireworks from Twin Peaks. Bad idea. The place is full of yahoos
>shooting off their own fireworks. Should a fire break out, you are
>screwed.

Oh come on, there's a huge reservoir up there.

I am amazed by the DIY fireworks at Dolores Park.  Much more fun than the
official shows.

Fred Abse wrote:
> On Fri, 26 Jun 2009 08:17:40 -0700, Joerg wrote:
> 
>> Look at the bright side: It could be worse. My Chinese meters here are 
>> bonbon-purple. Channel 3 on my DSO is bonbon-pink.
> 
> When I was a lad, we called that color "Nipple Pink"
> 
> ;-)
> 

Well, I got meeself a lass and married her so I can't say that never no 
more :-)

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

David DiGiacomo wrote:
> In article <7716bb9f-f71a-43a4-bcb0-9847e42f58c3@i6g2000yqj.googlegroups.com>,
> miso@sushi.com <miso@sushi.com> wrote:
>> I got this brilliant idea a few decades ago to watch the 4th of July
>> fireworks from Twin Peaks. Bad idea. The place is full of yahoos
>> shooting off their own fireworks. Should a fire break out, you are
>> screwed.
> 
> Oh come on, there's a huge reservoir up there.
> 
> I am amazed by the DIY fireworks at Dolores Park.  Much more fun than the
> official shows.


We had this here, yesterday (photo is from last year though), top view 
from a friend's deck:

http://goldcountryimages.static.adqic.com/uploads/inline/1213875563_8746.jpg

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Sun, 28 Jun 2009 15:49:19 -0500, david@slack.com (David DiGiacomo)
wrote:

>In article <7716bb9f-f71a-43a4-bcb0-9847e42f58c3@i6g2000yqj.googlegroups.com>,
>miso@sushi.com <miso@sushi.com> wrote:
>>I got this brilliant idea a few decades ago to watch the 4th of July
>>fireworks from Twin Peaks. Bad idea. The place is full of yahoos
>>shooting off their own fireworks. Should a fire break out, you are
>>screwed.
>
>Oh come on, there's a huge reservoir up there.
>
>I am amazed by the DIY fireworks at Dolores Park.  Much more fun than the
>official shows.

I used to live on 16th street, across from the mission, when the area
was still a real dump, and cheap... a 3 room flat for $315. Now the
whole area has gotten trendy and expensive, and Dolores Park is a
weekend flesh market. Cool.

Been to The Monk's Kettle? That have 20 exotic beers on tap and make a
different pot pie every day.

But Joseph Schmitt will be shut down soon. Boycott Hershey's!

John

On Jun 28, 1:49 pm, da...@slack.com (David DiGiacomo) wrote:
> In article <7716bb9f-f71a-43a4-bcb0-9847e42f5...@i6g2000yqj.googlegroups.com>,
>
> m...@sushi.com <m...@sushi.com> wrote:
> >I got this brilliant idea a few decades ago to watch the 4th of July
> >fireworks from Twin Peaks. Bad idea. The place is full of yahoos
> >shooting off their own fireworks. Should a fire break out, you are
> >screwed.
>
> Oh come on, there's a huge reservoir up there.
>
> I am amazed by the DIY fireworks at Dolores Park.  Much more fun than the
> official shows.

The road can't handle much traffic unles things have changed. I
haven't brought a car to SF in a few years. Too much hassle. I do
recall the official fireworks being more like an  "impressionistic"
painting.

One of the better 4th of July displays I saw was in Las Vegas. I was
at the Paradise Hilton. From the parking garage, you could see their
fireworks and displays all around town. The top level was packed with
people, so I guess this is a common way to watch the events. I'm sure
the Stratosphere is packed for the 4th.

On Sun, 28 Jun 2009 12:45:41 -0700 (PDT), Richard Henry
<pomerado@hotmail.com> wrote:

>On Jun 24, 7:18�pm, "David L. Jones" <altz...@gmail.com> wrote:
>> Check out a rather unusual phenomenon you can see on your oscilloscope in my
>> latest blog (#14):http://www.alternatezone.com/eevblog/
>> See if you can get it to happen on your scope!
>> I'll offer a free subscription to my blog for the best screen shot posted
>> :->
>>
>> Oh, and the probe doesn't have to be shorted either.
>>
>> Have fun.
>> Dave.
>> --
>> ================================================
>> Check out my Electronics Engineering Video Blog & Podcast:http://www.alternatezone.com/eevblog/
>
>His schematic of the scope probe and scope input are oversimplified to
>the point of incorrectness.  Also, he ignored the low-pass nature of
>the oscilloscope input, which might contribute to the clean
>"sinusoidal" waveform.

Scope vertical amps don't ring.

John

On Jun 28, 6:03 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Sun, 28 Jun 2009 12:45:41 -0700 (PDT), Richard Henry
>
>
>
> <pomer...@hotmail.com> wrote:
> >On Jun 24, 7:18 pm, "David L. Jones" <altz...@gmail.com> wrote:
> >> Check out a rather unusual phenomenon you can see on your oscilloscope in my
> >> latest blog (#14):http://www.alternatezone.com/eevblog/
> >> See if you can get it to happen on your scope!
> >> I'll offer a free subscription to my blog for the best screen shot posted
> >> :->
>
> >> Oh, and the probe doesn't have to be shorted either.
>
> >> Have fun.
> >> Dave.
> >> --
> >> ================================================
> >> Check out my Electronics Engineering Video Blog & Podcast:http://www.alternatezone.com/eevblog/
>
> >His schematic of the scope probe and scope input are oversimplified to
> >the point of incorrectness.  Also, he ignored the low-pass nature of
> >the oscilloscope input, which might contribute to the clean
> >"sinusoidal" waveform.
>
> Scope vertical amps don't ring.

That was not my point.  The limited low-pass band of the input
amplifier and sampling circuit will either completely filter out
higher-frequency components, or will alias them down.  If you are
seeing a nice sinusoidal waveform on an oscillioscope whose
fundamental frequency is close to the frequency limit of the scope,
chck it with a higher-frequency device.

Richard Henry wrote:
> On Jun 28, 6:03 pm, John Larkin
> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>> On Sun, 28 Jun 2009 12:45:41 -0700 (PDT), Richard Henry
>>
>>
>>
>> <pomer...@hotmail.com> wrote:
>>> On Jun 24, 7:18 pm, "David L. Jones" <altz...@gmail.com> wrote:
>>>> Check out a rather unusual phenomenon you can see on your
>>>> oscilloscope in my
>>>> latest blog (#14):http://www.alternatezone.com/eevblog/
>>>> See if you can get it to happen on your scope!
>>>> I'll offer a free subscription to my blog for the best screen shot
>>>> posted :->
>>
>>>> Oh, and the probe doesn't have to be shorted either.
>>
>>>> Have fun.
>>>> Dave.
>>>> --
>>>> ================================================
>>>> Check out my Electronics Engineering Video Blog &
>>>> Podcast:http://www.alternatezone.com/eevblog/
>>
>>> His schematic of the scope probe and scope input are oversimplified
>>> to the point of incorrectness. Also, he ignored the low-pass nature
>>> of the oscilloscope input, which might contribute to the clean
>>> "sinusoidal" waveform.
>>
>> Scope vertical amps don't ring.
>
> That was not my point.  The limited low-pass band of the input
> amplifier and sampling circuit will either completely filter out
> higher-frequency components, or will alias them down.  If you are
> seeing a nice sinusoidal waveform on an oscillioscope whose
> fundamental frequency is close to the frequency limit of the scope,
> chck it with a higher-frequency device.

I've seen the same (or similar) result with a higher bandwidth (300MHz) 
scope, so the vertical bandwidth limit has nothing to do with it. The 
TDS-220 is just the one I happened to have available at the time. I filmed 
some comment on this extra stuff but it didn't make the cut.

Dave.

-- 
================================================
Check out my Electronics Engineering Video Blog & Podcast:
http://www.alternatezone.com/eevblog/

Joerg wrote:
> ehsjr wrote:
> 
>> krw wrote:
>>
>>> On Fri, 26 Jun 2009 20:04:30 GMT, ehsjr <ehsjr@NOSPAMverizon.net>
>>> wrote:
>>>
>>>
>>>> krw wrote:
>>>>
>>>> <snip>
>>>>
>>>>>
>>>>> Fein is simply crazy expensive.  I looked at their routers over the
>>>>> weekend.  I wasn't impressed, for 4X what a Bosch or PC costs.  Bosch
>>>>> has a "Multi-Master type tool ("Multi-X", I think) that's a lot
>>>>> cheaper and looks just as good (Li-Ion battery, though).  A little
>>>>> lower down the line, Dremmel has a copy for $100ish.  If you want to
>>>>> go cheap, HarborFreight has one for $40.  The reports are decent,
>>>>> acknowledging that it's a $40 tool.  The only real complaint is that
>>>>> the blades loosen.
>>>>
>>>>
>>>> Where do you get reports on the Harbor Freight stuff?
>>>> I'd like to be able to see what others think about what
>>>> I might buy - like their 12' sliding compound miter saw.
>>>
>>>
>>>
>>> I have their 10" SLCS.  For $100 it's not bad at all.  I just bought
>>> it to cut 2x4s and it does that very well.  I did some molding with it
>>> in my last house, too.  I'll likely replace it with a better saw in
>>> the next year or so, though.
>>>
>>> As far as discussions of these things, rec.woodworking is likely the
>>> best place.  There are a lot of tool snobs there too, but also a lot
>>> of information.
>>>
>>>
>>>> Sometimes they're good for power tools that will be used
>>>> infrequently.  The stuff I've bought from them for light
>>>> use has never disappointed - but I haven't used it either
>>>> under harsh conditions or extensively.
>>>
>>>
>>>
>>> I don't have too many HF power tools, but a few.  You really have to
>>> be careful.   The above SLCS is fairly good (it's weak on compound
>>> miters).  I've looked at their wet saw and would have bought it if I
>>> knew about it before I bought mine.  OTOH, I have a couple of cordless
>>> drills that are just so bad that I don't even count them.
>>
>>
>> Thanks for the info on the saw.  My use would be like yours,
>> primarily rough carpentry. I have a bunch of decorative
>> "garden ties" to replace, and the 12" saw will handle them.
>>
>> I have a $24 1/2" hammer drill from them - flawless for the
>> few times I've used it.  The cordless 9.6V is pretty much
>> useless, except for maybe drilling a couple of holes in
>> a project box.  I love their cheap $2.99 meters for monitoring
>> stuff, and as a source of LCD displays for projects. ...
> 
> 
> 
> How do you wire up the LCD? Just the bare glass or did you find a trick 
> to get into their blob chip?
> 
> [...]
> 

I wish I could get into the blob, just as a matter of
interest.  I doubt it would be work the effort, though.
Displays don't cost that much to make it worthwhile.
The simple hack is to just use the thing on the meter
PC board - you can saw away what you don't need.
The last one I hacked used the whole meter, minus the
switching, just to monitor a supply voltage. There was plenty
of room inside the supply cabinet so I just soldered leads
to the input and did a little surgery on the front panel
so yo could see the LCD.  I had a little DC-DC converter
that provided the 9V for the meter. The supply ramps the
voltage up slowly between set points over time, and the built
in meter provides a way to watch the progress without
needing to connect an external meter each time.

Ed

On Sat, 27 Jun 2009 15:35:55 -0700, Joerg wrote:
> Rich Grise wrote:
>> On Thu, 25 Jun 2009 19:54:34 -0500, krw wrote:
>>> On Fri, 26 Jun 2009 00:23:28 GMT, Rich Grise <richgrise@example.net>
>>>> On Thu, 25 Jun 2009 17:13:00 -0700, Joerg wrote:
>>>>
>>>>> swelled and I felt like an engineer. Until I glued the formica onto a 
>>>>> panel that would become the top and I had it slightly skewed ...
>>>> I guess nobody told you about the shims. ;-)
>>> How do shims fix a skewed veneer?
>> 
>> You put the glue on the surface and let it dry, and lay thin pieces of
>> wood across it. Put the glue on the formica, let it dry, and lay it
>> on top of the shims. The shims have no glue, so don't stick. Line
>> the formica up, on top of the shims, and one by one take the shims 
>> out and let the formica stick to the surface.
>> 
>> I've seen it done on those "home improvement"-type TV shows. :-)
> 
> With a fresh can of Henkel Pattex glue the shims may never come out again.

Well, then I guess using Henkel Pattex glue isn't all that great an idea. ;-)

Use just plain ol' ordinary common off-the-shelf "contact cement", and
let it DRY before you start placing the shims. Come to think of it,
when I was a video game tech, the shipping guy used to do it to the
sides of video games when they'd convert a cabinet from one game to
another.

Cheers!
Rich

Michael A. Terrell wrote:
> John Larkin wrote:
>> At the receive (instrument) end, the ungrounded end of the coax shield
>> becomes the hot side of a resonant "vertical" antenna. Any voltage
>> there becomes 100% common-mode signal on the inner twisted pair.
>>
>> What's wrong with a little current in the shield? The signal pair
>> isn't affected. But volts, or tens of volts, of common-mode RF can be
>> nasty.
> 
> 
>    That's the reason you see lots of six inch wide copper bonding straps
> in radio studios. They use one and a half inch straps to connect between
> the equipment, and the bonding straps.
> 

Same in this here lab :-)

-- 
Regards, Joerg

http://www.analogconsultants.com/

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On Thu, 25 Jun 2009 12:39:08 -0700, John Larkin wrote:

> On Thu, 25 Jun 2009 13:48:35 -0400, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>John Larkin wrote:
>>> On Wed, 24 Jun 2009 21:42:07 -0700, <castlebravo242@att.net> wrote:
>>> 
>>>> ... was reading it would get data errors. The problem was that the
>>>> shield on the cable from the heads to the preamp was grounded on both
>>>> ends.
>>> 
>>> That's usually the best way to ground shields.
>>> 
>>Depends.  With floating transducers and shielded twisted pair, it's best
>>to ground the shield only at the transducer end.  That way any
>>capacitive imbalance doesn't produce any currents, because the shield is
>>at the transducer's idea of ground.
>>
>>
> At the receive (instrument) end, the ungrounded end of the coax shield
> becomes the hot side of a resonant "vertical" antenna. Any voltage there
> becomes 100% common-mode signal on the inner twisted pair.
> 
> What's wrong with a little current in the shield? The signal pair isn't
> affected. But volts, or tens of volts, of common-mode RF can be nasty.
> 
I think half of us are talking about low-noise audio frequencies, and
half of us are talking about RF. The way I heard it, you leave one end
unshielded for audio preamps and stuff, but ground both ends for RF;
I think it has to do with wavelength and, well, propagation
characteristics. Of course, the thing that was drummed into me while
they were teaching me this was "GROUND LOOPS!". :-)

Cheers!
Rich

On Tue, 30 Jun 2009 17:27:21 GMT, Rich Grise <richgrise@example.net>
wrote:

>On Thu, 25 Jun 2009 12:39:08 -0700, John Larkin wrote:
>
>> On Thu, 25 Jun 2009 13:48:35 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>John Larkin wrote:
>>>> On Wed, 24 Jun 2009 21:42:07 -0700, <castlebravo242@att.net> wrote:
>>>> 
>>>>> ... was reading it would get data errors. The problem was that the
>>>>> shield on the cable from the heads to the preamp was grounded on both
>>>>> ends.
>>>> 
>>>> That's usually the best way to ground shields.
>>>> 
>>>Depends.  With floating transducers and shielded twisted pair, it's best
>>>to ground the shield only at the transducer end.  That way any
>>>capacitive imbalance doesn't produce any currents, because the shield is
>>>at the transducer's idea of ground.
>>>
>>>
>> At the receive (instrument) end, the ungrounded end of the coax shield
>> becomes the hot side of a resonant "vertical" antenna. Any voltage there
>> becomes 100% common-mode signal on the inner twisted pair.
>> 
>> What's wrong with a little current in the shield? The signal pair isn't
>> affected. But volts, or tens of volts, of common-mode RF can be nasty.
>> 
>I think half of us are talking about low-noise audio frequencies, and
>half of us are talking about RF. The way I heard it, you leave one end
>unshielded for audio preamps and stuff, but ground both ends for RF;
>I think it has to do with wavelength and, well, propagation
>characteristics. Of course, the thing that was drummed into me while
>they were teaching me this was "GROUND LOOPS!". :-)
>
>Cheers!
>Rich

Audio: if one end of a shield is disconnected, the delta-voltage (60
Hz, RF, esd spikes) between chassis is greater. If the signal is
single-ended, that increases noise directly. If differential, it
increases common-mode noise.

Why would you want to do that?

A 60-Hz (and RF, and ESD) "ground loop" can result from different
boxes being plugged into different outlets which have some 60 Hz
difference voltage (or form a relative antenna for RF.) Connecting the
shield on both ends shorts out some or most of this difference voltage
and REDUCES the effect of the "ground loop" on the signal.

Whoever did the drumming was passing on folklore.

John

Rich Grise wrote:
> On Thu, 25 Jun 2009 12:39:08 -0700, John Larkin wrote:
> 
>> On Thu, 25 Jun 2009 13:48:35 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>> John Larkin wrote:
>>>> On Wed, 24 Jun 2009 21:42:07 -0700, <castlebravo242@att.net> wrote:
>>>>
>>>>> ... was reading it would get data errors. The problem was that the
>>>>> shield on the cable from the heads to the preamp was grounded on both
>>>>> ends.
>>>> That's usually the best way to ground shields.
>>>>
>>> Depends.  With floating transducers and shielded twisted pair, it's best
>>> to ground the shield only at the transducer end.  That way any
>>> capacitive imbalance doesn't produce any currents, because the shield is
>>> at the transducer's idea of ground.
>>>
>>>
>> At the receive (instrument) end, the ungrounded end of the coax shield
>> becomes the hot side of a resonant "vertical" antenna. Any voltage there
>> becomes 100% common-mode signal on the inner twisted pair.
>>
>> What's wrong with a little current in the shield? The signal pair isn't
>> affected. But volts, or tens of volts, of common-mode RF can be nasty.
>>
> I think half of us are talking about low-noise audio frequencies, and
> half of us are talking about RF. The way I heard it, you leave one end
> unshielded for audio preamps and stuff, but ground both ends for RF;
> I think it has to do with wavelength and, well, propagation
> characteristics. Of course, the thing that was drummed into me while
> they were teaching me this was "GROUND LOOPS!". :-)
> 

Trouble is, since we moved from Alexander Graham Bell's wall phone (with 
crank) to cell phones RF frequently turns into audio after getting into 
such single-end shielded cables. All it takes is an opamp with bipolar 
input structure.

Of course, with a good old tube amp you'll continue to be fine :-)

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

John Larkin wrote:
> On Tue, 30 Jun 2009 17:27:21 GMT, Rich Grise <richgrise@example.net>
> wrote:
> 
>> On Thu, 25 Jun 2009 12:39:08 -0700, John Larkin wrote:
>>
>>> On Thu, 25 Jun 2009 13:48:35 -0400, Phil Hobbs
>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>> John Larkin wrote:
>>>>> On Wed, 24 Jun 2009 21:42:07 -0700, <castlebravo242@att.net> wrote:
>>>>>
>>>>>> ... was reading it would get data errors. The problem was that the
>>>>>> shield on the cable from the heads to the preamp was grounded on both
>>>>>> ends.
>>>>> That's usually the best way to ground shields.
>>>>>
>>>> Depends.  With floating transducers and shielded twisted pair, it's best
>>>> to ground the shield only at the transducer end.  That way any
>>>> capacitive imbalance doesn't produce any currents, because the shield is
>>>> at the transducer's idea of ground.
>>>>
>>>>
>>> At the receive (instrument) end, the ungrounded end of the coax shield
>>> becomes the hot side of a resonant "vertical" antenna. Any voltage there
>>> becomes 100% common-mode signal on the inner twisted pair.
>>>
>>> What's wrong with a little current in the shield? The signal pair isn't
>>> affected. But volts, or tens of volts, of common-mode RF can be nasty.
>>>
>> I think half of us are talking about low-noise audio frequencies, and
>> half of us are talking about RF. The way I heard it, you leave one end
>> unshielded for audio preamps and stuff, but ground both ends for RF;
>> I think it has to do with wavelength and, well, propagation
>> characteristics. Of course, the thing that was drummed into me while
>> they were teaching me this was "GROUND LOOPS!". :-)
>>
>> Cheers!
>> Rich
> 
> Audio: if one end of a shield is disconnected, the delta-voltage (60
> Hz, RF, esd spikes) between chassis is greater. If the signal is
> single-ended, that increases noise directly. If differential, it
> increases common-mode noise.
> 
> Why would you want to do that?
> 
> A 60-Hz (and RF, and ESD) "ground loop" can result from different
> boxes being plugged into different outlets which have some 60 Hz
> difference voltage (or form a relative antenna for RF.) Connecting the
> shield on both ends shorts out some or most of this difference voltage
> and REDUCES the effect of the "ground loop" on the signal.
> 

Unless the shield slowly commences a faint red glow, followed by some 
"amperage scent" wafting through the room ...

Seriously, I've seen that happen.


> Whoever did the drumming was passing on folklore.
> 

Yup. OTOH that provides a good business opportunity 8-D

-- 
Regards, Joerg

http://www.analogconsultants.com/

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Use another domain or send PM.

On Tue, 30 Jun 2009 11:38:10 -0700, Joerg <invalid@invalid.invalid>
wrote:

>John Larkin wrote:
>> On Tue, 30 Jun 2009 17:27:21 GMT, Rich Grise <richgrise@example.net>
>> wrote:
>> 
>>> On Thu, 25 Jun 2009 12:39:08 -0700, John Larkin wrote:
>>>
>>>> On Thu, 25 Jun 2009 13:48:35 -0400, Phil Hobbs
>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>> John Larkin wrote:
>>>>>> On Wed, 24 Jun 2009 21:42:07 -0700, <castlebravo242@att.net> wrote:
>>>>>>
>>>>>>> ... was reading it would get data errors. The problem was that the
>>>>>>> shield on the cable from the heads to the preamp was grounded on both
>>>>>>> ends.
>>>>>> That's usually the best way to ground shields.
>>>>>>
>>>>> Depends.  With floating transducers and shielded twisted pair, it's best
>>>>> to ground the shield only at the transducer end.  That way any
>>>>> capacitive imbalance doesn't produce any currents, because the shield is
>>>>> at the transducer's idea of ground.
>>>>>
>>>>>
>>>> At the receive (instrument) end, the ungrounded end of the coax shield
>>>> becomes the hot side of a resonant "vertical" antenna. Any voltage there
>>>> becomes 100% common-mode signal on the inner twisted pair.
>>>>
>>>> What's wrong with a little current in the shield? The signal pair isn't
>>>> affected. But volts, or tens of volts, of common-mode RF can be nasty.
>>>>
>>> I think half of us are talking about low-noise audio frequencies, and
>>> half of us are talking about RF. The way I heard it, you leave one end
>>> unshielded for audio preamps and stuff, but ground both ends for RF;
>>> I think it has to do with wavelength and, well, propagation
>>> characteristics. Of course, the thing that was drummed into me while
>>> they were teaching me this was "GROUND LOOPS!". :-)
>>>
>>> Cheers!
>>> Rich
>> 
>> Audio: if one end of a shield is disconnected, the delta-voltage (60
>> Hz, RF, esd spikes) between chassis is greater. If the signal is
>> single-ended, that increases noise directly. If differential, it
>> increases common-mode noise.
>> 
>> Why would you want to do that?
>> 
>> A 60-Hz (and RF, and ESD) "ground loop" can result from different
>> boxes being plugged into different outlets which have some 60 Hz
>> difference voltage (or form a relative antenna for RF.) Connecting the
>> shield on both ends shorts out some or most of this difference voltage
>> and REDUCES the effect of the "ground loop" on the signal.
>> 
>
>Unless the shield slowly commences a faint red glow, followed by some 
>"amperage scent" wafting through the room ...
>
>Seriously, I've seen that happen.

Yup. I've seen some ghastly wiring, some done by licensed
electricians.

The most 60 Hz I've experienced (between outlet ground pins, in an
office building) was a few volts RMS, and plenty stiff. Messed up some
printer signals pretty good.

The real way to pipe signals around is fiberoptics. A kilovolts of
common-mode is no problem.

Hey, time for our engineering meeting; Japanese food today!

John

On Tue, 30 Jun 2009 11:15:06 -0700, John Larkin wrote:
> 
> Audio: if one end of a shield is disconnected, the delta-voltage (60
> Hz, RF, esd spikes) between chassis is greater. If the signal is
> single-ended, that increases noise directly. If differential, it
> increases common-mode noise.
> 
> Why would you want to do that?

Because that's what it said to do in the instructions that came with
the kit.

Cheers!
Rich

John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

>On Tue, 30 Jun 2009 11:38:10 -0700, Joerg <invalid@invalid.invalid>
>wrote:
>
>>John Larkin wrote:
>>> On Tue, 30 Jun 2009 17:27:21 GMT, Rich Grise <richgrise@example.net>
>>> wrote:
>>> 
>>>> On Thu, 25 Jun 2009 12:39:08 -0700, John Larkin wrote:
>>>>
>>>>> On Thu, 25 Jun 2009 13:48:35 -0400, Phil Hobbs
>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>> John Larkin wrote:
>>>>>>> On Wed, 24 Jun 2009 21:42:07 -0700, <castlebravo242@att.net> wrote:
>>>>>>>
>>>>>>>> ... was reading it would get data errors. The problem was that the
>>>>>>>> shield on the cable from the heads to the preamp was grounded on both
>>>>>>>> ends.
>>>>>>> That's usually the best way to ground shields.
>>>>>>>
>>>>>> Depends.  With floating transducers and shielded twisted pair, it's best
>>>>>> to ground the shield only at the transducer end.  That way any
>>>>>> capacitive imbalance doesn't produce any currents, because the shield is
>>>>>> at the transducer's idea of ground.
>>>>>>
>>>>>>
>>>>> At the receive (instrument) end, the ungrounded end of the coax shield
>>>>> becomes the hot side of a resonant "vertical" antenna. Any voltage there
>>>>> becomes 100% common-mode signal on the inner twisted pair.
>>>>>
>>>>> What's wrong with a little current in the shield? The signal pair isn't
>>>>> affected. But volts, or tens of volts, of common-mode RF can be nasty.
>>>>>
>>>> I think half of us are talking about low-noise audio frequencies, and
>>>> half of us are talking about RF. The way I heard it, you leave one end
>>>> unshielded for audio preamps and stuff, but ground both ends for RF;
>>>> I think it has to do with wavelength and, well, propagation
>>>> characteristics. Of course, the thing that was drummed into me while
>>>> they were teaching me this was "GROUND LOOPS!". :-)
>>>>
>>>> Cheers!
>>>> Rich
>>> 
>>> Audio: if one end of a shield is disconnected, the delta-voltage (60
>>> Hz, RF, esd spikes) between chassis is greater. If the signal is
>>> single-ended, that increases noise directly. If differential, it
>>> increases common-mode noise.
>>> 
>>> Why would you want to do that?
>>> 
>>> A 60-Hz (and RF, and ESD) "ground loop" can result from different
>>> boxes being plugged into different outlets which have some 60 Hz
>>> difference voltage (or form a relative antenna for RF.) Connecting the
>>> shield on both ends shorts out some or most of this difference voltage
>>> and REDUCES the effect of the "ground loop" on the signal.
>>> 
>>
>>Unless the shield slowly commences a faint red glow, followed by some 
>>"amperage scent" wafting through the room ...
>>
>>Seriously, I've seen that happen.
>
>Yup. I've seen some ghastly wiring, some done by licensed
>electricians.
>
>The most 60 Hz I've experienced (between outlet ground pins, in an
>office building) was a few volts RMS, and plenty stiff. Messed up some
>printer signals pretty good.
>
>The real way to pipe signals around is fiberoptics. A kilovolts of
>common-mode is no problem.

I wish... I'm working on interfacing a current sensing coil from a
welding transformer. During welding there is a couple of hundred volts
everywhere. This project starts to give me a headache :-)

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------

Nico Coesel wrote:
> John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
> 
>> On Tue, 30 Jun 2009 11:38:10 -0700, Joerg <invalid@invalid.invalid>
>> wrote:
>>
>>> John Larkin wrote:
>>>> On Tue, 30 Jun 2009 17:27:21 GMT, Rich Grise <richgrise@example.net>
>>>> wrote:
>>>>
>>>>> On Thu, 25 Jun 2009 12:39:08 -0700, John Larkin wrote:
>>>>>
>>>>>> On Thu, 25 Jun 2009 13:48:35 -0400, Phil Hobbs
>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>>> John Larkin wrote:
>>>>>>>> On Wed, 24 Jun 2009 21:42:07 -0700, <castlebravo242@att.net> wrote:
>>>>>>>>
>>>>>>>>> ... was reading it would get data errors. The problem was that the
>>>>>>>>> shield on the cable from the heads to the preamp was grounded on both
>>>>>>>>> ends.
>>>>>>>> That's usually the best way to ground shields.
>>>>>>>>
>>>>>>> Depends.  With floating transducers and shielded twisted pair, it's best
>>>>>>> to ground the shield only at the transducer end.  That way any
>>>>>>> capacitive imbalance doesn't produce any currents, because the shield is
>>>>>>> at the transducer's idea of ground.
>>>>>>>
>>>>>>>
>>>>>> At the receive (instrument) end, the ungrounded end of the coax shield
>>>>>> becomes the hot side of a resonant "vertical" antenna. Any voltage there
>>>>>> becomes 100% common-mode signal on the inner twisted pair.
>>>>>>
>>>>>> What's wrong with a little current in the shield? The signal pair isn't
>>>>>> affected. But volts, or tens of volts, of common-mode RF can be nasty.
>>>>>>
>>>>> I think half of us are talking about low-noise audio frequencies, and
>>>>> half of us are talking about RF. The way I heard it, you leave one end
>>>>> unshielded for audio preamps and stuff, but ground both ends for RF;
>>>>> I think it has to do with wavelength and, well, propagation
>>>>> characteristics. Of course, the thing that was drummed into me while
>>>>> they were teaching me this was "GROUND LOOPS!". :-)
>>>>>
>>>>> Cheers!
>>>>> Rich
>>>> Audio: if one end of a shield is disconnected, the delta-voltage (60
>>>> Hz, RF, esd spikes) between chassis is greater. If the signal is
>>>> single-ended, that increases noise directly. If differential, it
>>>> increases common-mode noise.
>>>>
>>>> Why would you want to do that?
>>>>
>>>> A 60-Hz (and RF, and ESD) "ground loop" can result from different
>>>> boxes being plugged into different outlets which have some 60 Hz
>>>> difference voltage (or form a relative antenna for RF.) Connecting the
>>>> shield on both ends shorts out some or most of this difference voltage
>>>> and REDUCES the effect of the "ground loop" on the signal.
>>>>
>>> Unless the shield slowly commences a faint red glow, followed by some 
>>> "amperage scent" wafting through the room ...
>>>
>>> Seriously, I've seen that happen.
>> Yup. I've seen some ghastly wiring, some done by licensed
>> electricians.
>>
>> The most 60 Hz I've experienced (between outlet ground pins, in an
>> office building) was a few volts RMS, and plenty stiff. Messed up some
>> printer signals pretty good.
>>
>> The real way to pipe signals around is fiberoptics. A kilovolts of
>> common-mode is no problem.
> 
> I wish... I'm working on interfacing a current sensing coil from a
> welding transformer. During welding there is a couple of hundred volts
> everywhere. This project starts to give me a headache :-)
> 

Try differential transfer, shielded twisted pair or Twinax soldered to 
the burden resistor, from there to your measurement box, place a 2nd 
signal transformer there. Make sure the twisted pair is source- and/or 
end-terminated properly, usually 100-120ohms. And never, never use this 
connection as the burden resistor even if there is a fire extinguisher 
at hand ...

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Joerg <invalid@invalid.invalid> wrote:

>Nico Coesel wrote:
>> John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>> 
>>> On Tue, 30 Jun 2009 11:38:10 -0700, Joerg <invalid@invalid.invalid>
>>> wrote:
>>>
>>>> John Larkin wrote:
>>>>> On Tue, 30 Jun 2009 17:27:21 GMT, Rich Grise <richgrise@example.net>
>>>>> wrote:
>>>>>
>>>>>> On Thu, 25 Jun 2009 12:39:08 -0700, John Larkin wrote:
>>>>>>
>>>>>>> On Thu, 25 Jun 2009 13:48:35 -0400, Phil Hobbs
>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>>>> John Larkin wrote:
>>>>>>>>> On Wed, 24 Jun 2009 21:42:07 -0700, <castlebravo242@att.net> wrote:
>>>>>>>>>
>>>>>>>>>> ... was reading it would get data errors. The problem was that the
>>>>>>>>>> shield on the cable from the heads to the preamp was grounded on both
>>>>>>>>>> ends.
>>>>>>>>> That's usually the best way to ground shields.
>>>>>>>>>
>>>>>>>> Depends.  With floating transducers and shielded twisted pair, it's best
>>>>>>>> to ground the shield only at the transducer end.  That way any
>>>>>>>> capacitive imbalance doesn't produce any currents, because the shield is
>>>>>>>> at the transducer's idea of ground.
>>>>>>>>
>>>>>>>>
>>>>>>> At the receive (instrument) end, the ungrounded end of the coax shield
>>>>>>> becomes the hot side of a resonant "vertical" antenna. Any voltage there
>>>>>>> becomes 100% common-mode signal on the inner twisted pair.
>>>>>>>
>>>>>>> What's wrong with a little current in the shield? The signal pair isn't
>>>>>>> affected. But volts, or tens of volts, of common-mode RF can be nasty.
>>>>>>>
>>>>>> I think half of us are talking about low-noise audio frequencies, and
>>>>>> half of us are talking about RF. The way I heard it, you leave one end
>>>>>> unshielded for audio preamps and stuff, but ground both ends for RF;
>>>>>> I think it has to do with wavelength and, well, propagation
>>>>>> characteristics. Of course, the thing that was drummed into me while
>>>>>> they were teaching me this was "GROUND LOOPS!". :-)
>>>>>>
>>>>>> Cheers!
>>>>>> Rich
>>>>> Audio: if one end of a shield is disconnected, the delta-voltage (60
>>>>> Hz, RF, esd spikes) between chassis is greater. If the signal is
>>>>> single-ended, that increases noise directly. If differential, it
>>>>> increases common-mode noise.
>>>>>
>>>>> Why would you want to do that?
>>>>>
>>>>> A 60-Hz (and RF, and ESD) "ground loop" can result from different
>>>>> boxes being plugged into different outlets which have some 60 Hz
>>>>> difference voltage (or form a relative antenna for RF.) Connecting the
>>>>> shield on both ends shorts out some or most of this difference voltage
>>>>> and REDUCES the effect of the "ground loop" on the signal.
>>>>>
>>>> Unless the shield slowly commences a faint red glow, followed by some 
>>>> "amperage scent" wafting through the room ...
>>>>
>>>> Seriously, I've seen that happen.
>>> Yup. I've seen some ghastly wiring, some done by licensed
>>> electricians.
>>>
>>> The most 60 Hz I've experienced (between outlet ground pins, in an
>>> office building) was a few volts RMS, and plenty stiff. Messed up some
>>> printer signals pretty good.
>>>
>>> The real way to pipe signals around is fiberoptics. A kilovolts of
>>> common-mode is no problem.
>> 
>> I wish... I'm working on interfacing a current sensing coil from a
>> welding transformer. During welding there is a couple of hundred volts
>> everywhere. This project starts to give me a headache :-)
>> 
>
>Try differential transfer, shielded twisted pair or Twinax soldered to 
>the burden resistor, from there to your measurement box, place a 2nd 
>signal transformer there. Make sure the twisted pair is source- and/or 

I already went for a differential input. Solves most of the problems,
but not all but I'm pretty sure the inputs where overdriven as well. I
fixed that, but didn't field-test it. A 2nd signal transformer won't
fly because the pulses may be quite long (up to 100ms). 

The problem is that nobody seems to know what the pulses look like
exactly. The transformer is pulsed by a 1000Hz PWM signal. This makes
me assume the current sensor sees pulses as well. But the shape
probably depends on the induction in the welding circuit while
carrying many kA...

>end-terminated properly, usually 100-120ohms. And never, never use this 
>connection as the burden resistor even if there is a fire extinguisher 
>at hand ...

That might be worth something to explore. The burden resistor (1k is
specified) is now on the measurement board itself. I'd like to keep it
there though to keep the installation procedure easy. The wiring in
the test setup is pretty short (2 meters) but bad (not twisted,
unshielded). I'll order some shielded twisted pair tomorow. I already
figured this must be part of the problem.

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------

Nico Coesel wrote:
> Joerg <invalid@invalid.invalid> wrote:
> 
>> Nico Coesel wrote:

[...]

>>> I wish... I'm working on interfacing a current sensing coil from a
>>> welding transformer. During welding there is a couple of hundred volts
>>> everywhere. This project starts to give me a headache :-)
>>>

Recipe against headache in cases like this: Proper matching of literally 
everything, shielding, a glass or two of Beerenburger.


>> Try differential transfer, shielded twisted pair or Twinax soldered to 
>> the burden resistor, from there to your measurement box, place a 2nd 
>> signal transformer there. Make sure the twisted pair is source- and/or 
> 
> I already went for a differential input. Solves most of the problems,
> but not all but I'm pretty sure the inputs where overdriven as well. I
> fixed that, but didn't field-test it. A 2nd signal transformer won't
> fly because the pulses may be quite long (up to 100ms). 
> 

100msec? Is it a DC welder? Anyhow, 100msec is feasible if you use a 
small doorbell transformer, the kind with two compartments where you can 
scrap one of them out with wire cutters and without having to 
disassemble the core. Calculate it so it's well under the saturation 
limits at 10Hz. Commercial current transformers can also go that low if 
you use one that's totally oversized for your current.

Unless the input diff-amp has a huge common mode range even for fast 
stuff such as spikes I am not sure you can do it without another 
transformer at the receiving end. Or rather, I've seen cases where it 
didn't work.


> The problem is that nobody seems to know what the pulses look like
> exactly. The transformer is pulsed by a 1000Hz PWM signal. This makes
> me assume the current sensor sees pulses as well. But the shape
> probably depends on the induction in the welding circuit while
> carrying many kA...
> 

If it's fed 1kHz then 1kHz should come out.


>> end-terminated properly, usually 100-120ohms. And never, never use this 
>> connection as the burden resistor even if there is a fire extinguisher 
>> at hand ...
> 
> That might be worth something to explore. The burden resistor (1k is
> specified) is now on the measurement board itself. I'd like to keep it
> there though to keep the installation procedure easy. ...


Not good. Increases noise, big time, because the cable is mismatched 
because even regular cord won't have a Z of 1000ohms. And if the cable 
ever comes off ... tungggg ... phssssss ... *PHUT*


>                                               ... The wiring in
> the test setup is pretty short (2 meters) but bad (not twisted,
> unshielded). I'll order some shielded twisted pair tomorow. I already
> figured this must be part of the problem.
> 

Ook niet zo goed. In an environment like this you can't work without 
shielded twisted pair, definitely not across two meters. That's like 
trying to listen to a Mozart concerto on a Harley-Davidson.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Tue, 30 Jun 2009 11:55:56 -0700, John Larkin wrote:
> 
> Hey, time for our engineering meeting; Japanese food today!
> 
Can you get decent yakisoba in SFO? I also like plain ol' ordinary
fried rice, but I can make that at home; I wish I had the recipe
that the Java Curry Shop in Shinjuku used - best curry I've ever
had! :-)

Yes, Japanese curry. :-)

Thanks!
Rich

Joerg <invalid@invalid.invalid> wrote:

>Nico Coesel wrote:
>> Joerg <invalid@invalid.invalid> wrote:
>> 
>>> Nico Coesel wrote:
>
>[...]
>
>>>> I wish... I'm working on interfacing a current sensing coil from a
>>>> welding transformer. During welding there is a couple of hundred volts
>>>> everywhere. This project starts to give me a headache :-)
>>>>
>
>Recipe against headache in cases like this: Proper matching of literally 
>everything, shielding, a glass or two of Beerenburger.

Shielding sounds doable. The Beerenburger is out of the question
though :-)

>>> Try differential transfer, shielded twisted pair or Twinax soldered to 
>>> the burden resistor, from there to your measurement box, place a 2nd 
>>> signal transformer there. Make sure the twisted pair is source- and/or 
>> 
>> I already went for a differential input. Solves most of the problems,
>> but not all but I'm pretty sure the inputs where overdriven as well. I
>> fixed that, but didn't field-test it. A 2nd signal transformer won't
>> fly because the pulses may be quite long (up to 100ms). 
>> 
>
>100msec? Is it a DC welder? Anyhow, 100msec is feasible if you use a 
>small doorbell transformer, the kind with two compartments where you can 
>scrap one of them out with wire cutters and without having to 

Yup. It's a DC welder. I already tried a small mains transformer but
that doesn't work out very well in a test. Besides that would exceed
budget and space constraints.

>Unless the input diff-amp has a huge common mode range even for fast 
>stuff such as spikes I am not sure you can do it without another 
>transformer at the receiving end. Or rather, I've seen cases where it 
>didn't work.

I think I have a pretty decent diff-amp. It can handle about 800V p-p
common mode.

>> That might be worth something to explore. The burden resistor (1k is
>> specified) is now on the measurement board itself. I'd like to keep it
>> there though to keep the installation procedure easy. ...
>
>
>Not good. Increases noise, big time, because the cable is mismatched 
>because even regular cord won't have a Z of 1000ohms. And if the cable 
>ever comes off ... tungggg ... phssssss ... *PHUT*

The cord coming off doesn't seem to be a problem. All similar systems
I've seen so far have the burden resistor on the measurement board,
not on the welding transformer. But I'll try it anyways. The old ways
are not necessarely the best ways :-)

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------

John Larkin wrote:
> 
> Yup. Once people get fixated on "ground loops" they are forever lost
> to reason.


   There is a fairly mindless thread about ground loops on
news:sci.electronics.repair right now.


-- 
You can't have a sense of humor, if you have no sense!

"Nico Coesel" <nico@puntnl.niks> wrote in message 
news:4a4e83ad.2781589312@news.planet.nl...
> The cord coming off doesn't seem to be a problem. All similar systems
> I've seen so far have the burden resistor on the measurement board,
> not on the welding transformer. But I'll try it anyways. The old ways
> are not necessarely the best ways :-)

Every CT I've built has had the resistor as close to the transformer (i.e., 
on it) as possible.  I've had quite awful results putting the resistor on 
any kind of length.  Come to think of it, that may be more due to the 
resistor itself having length, which would be a problem.  Still, better safe 
than sorry...

'Course, I wind my own, encapsulated in masking tape, so embedding a burden 
resistor is no big deal.  ;o)

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms 

Tim Williams wrote:
> 
> "Nico Coesel" <nico@puntnl.niks> wrote in message
> news:4a4e83ad.2781589312@news.planet.nl...
> > The cord coming off doesn't seem to be a problem. All similar systems
> > I've seen so far have the burden resistor on the measurement board,
> > not on the welding transformer. But I'll try it anyways. The old ways
> > are not necessarely the best ways :-)
> 
> Every CT I've built has had the resistor as close to the transformer (i.e.,
> on it) as possible.  I've had quite awful results putting the resistor on
> any kind of length.  Come to think of it, that may be more due to the
> resistor itself having length, which would be a problem.  Still, better safe
> than sorry...
> 
> 'Course, I wind my own, encapsulated in masking tape, so embedding a burden
> resistor is no big deal.  ;o)
> 
> Tim



 'Course, I wind my own, encapsulated in masking tape, so embedding a
burden
> resistor is no burden.  ;o)


-- 
You can't have a sense of humor, if you have no sense!

Nico Coesel wrote:
> Joerg <invalid@invalid.invalid> wrote:
> 
>> Nico Coesel wrote:
>>> Joerg <invalid@invalid.invalid> wrote:
>>>
>>>> Nico Coesel wrote:
>> [...]
>>
>>>>> I wish... I'm working on interfacing a current sensing coil from a
>>>>> welding transformer. During welding there is a couple of hundred volts
>>>>> everywhere. This project starts to give me a headache :-)
>>>>>
>> Recipe against headache in cases like this: Proper matching of literally 
>> everything, shielding, a glass or two of Beerenburger.
> 
> Shielding sounds doable. The Beerenburger is out of the question
> though :-)
> 

I liked this stuff ;-)


>>>> Try differential transfer, shielded twisted pair or Twinax soldered to 
>>>> the burden resistor, from there to your measurement box, place a 2nd 
>>>> signal transformer there. Make sure the twisted pair is source- and/or 
>>> I already went for a differential input. Solves most of the problems,
>>> but not all but I'm pretty sure the inputs where overdriven as well. I
>>> fixed that, but didn't field-test it. A 2nd signal transformer won't
>>> fly because the pulses may be quite long (up to 100ms). 
>>>
>> 100msec? Is it a DC welder? Anyhow, 100msec is feasible if you use a 
>> small doorbell transformer, the kind with two compartments where you can 
>> scrap one of them out with wire cutters and without having to 
> 
> Yup. It's a DC welder. I already tried a small mains transformer but
> that doesn't work out very well in a test. Besides that would exceed
> budget and space constraints.
> 

A doorbell transformer blows the budget on a welder? Man, and here I 
thought I was uncle Scrooge.


>> Unless the input diff-amp has a huge common mode range even for fast 
>> stuff such as spikes I am not sure you can do it without another 
>> transformer at the receiving end. Or rather, I've seen cases where it 
>> didn't work.
> 
> I think I have a pretty decent diff-amp. It can handle about 800V p-p
> common mode.
> 

In a welding environment 800V may not be good enough. Plus you'd have to 
check the CMRR for fast pulses, like when the arc starts and stops.


>>> That might be worth something to explore. The burden resistor (1k is
>>> specified) is now on the measurement board itself. I'd like to keep it
>>> there though to keep the installation procedure easy. ...
>>
>> Not good. Increases noise, big time, because the cable is mismatched 
>> because even regular cord won't have a Z of 1000ohms. And if the cable 
>> ever comes off ... tungggg ... phssssss ... *PHUT*
> 
> The cord coming off doesn't seem to be a problem. All similar systems
> I've seen so far have the burden resistor on the measurement board,
> not on the welding transformer. But I'll try it anyways. The old ways
> are not necessarely the best ways :-)
> 

Often they sure aren't. A burden resistor at the other end of a cable is 
usually a bad idea.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Mon, 06 Jul 2009 12:05:37 -0700, Joerg wrote:


 
> In a welding environment 800V may not be good enough.

Which "welding" environments did you have in mind?

-- 

Great advances in Debian Linux; post a bug report and get spam in three 
days.

terryc wrote:
> On Mon, 06 Jul 2009 12:05:37 -0700, Joerg wrote:
> 
> 
>  
>> In a welding environment 800V may not be good enough.
> 
> Which "welding" environments did you have in mind?
> 

The usual. >100 amps, electrodes touching, arcing, getting stuck once in 
a while, thick cables floating around the room, ground potential of 
equipment bouncing, and so on. I once told someone to get his ham radio 
gear out before we start welding a broken gate. "Nah, this stuff is 
tough" ... "Better get it outta here" ... "No, really, it's ok, just get 
cracking on the gate" ... "Ok then" ... bzzt, bzzt, bzzzzzzzzzzt ... 
beep ... *PHUT*

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Mon, 06 Jul 2009 17:38:19 -0700, Joerg wrote:

> terryc wrote:
>> On Mon, 06 Jul 2009 12:05:37 -0700, Joerg wrote:
>> 
>> 
>> 
>>> In a welding environment 800V may not be good enough.
>> 
>> Which "welding" environments did you have in mind?
>> 
>> 
> The usual. >100 amps, electrodes touching, arcing, getting stuck once in
> a while, thick cables floating around the room, ground potential of
> equipment bouncing, and so on. I once told someone to get his ham radio
> gear out before we start welding a broken gate. "Nah, this stuff is
> tough" ... "Better get it outta here" ... "No, really, it's ok, just get
> cracking on the gate" ... "Ok then" ... bzzt, bzzt, bzzzzzzzzzzt ...
> beep ... *PHUT*

Umm, have you ever put a volt meter across the cables?
I was under the impression that that stuff matched the telephone and was 
in the vicinity of 40volts.

I politely suggest that if it was around 800volts, then black and crispy 
would be a welder who made the wrong circuit.

Hint, it is the current that causes the field.





-- 

Great advances in Debian Linux; post a bug report and get spam in three 
days.








-- 

Great advances in Debian Linux; post a bug report and get spam in three 
days.

terryc wrote:
> 
> On Mon, 06 Jul 2009 17:38:19 -0700, Joerg wrote:
> 
> > terryc wrote:
> >> On Mon, 06 Jul 2009 12:05:37 -0700, Joerg wrote:
> >>
> >>
> >>
> >>> In a welding environment 800V may not be good enough.
> >>
> >> Which "welding" environments did you have in mind?
> >>
> >>
> > The usual. >100 amps, electrodes touching, arcing, getting stuck once in
> > a while, thick cables floating around the room, ground potential of
> > equipment bouncing, and so on. I once told someone to get his ham radio
> > gear out before we start welding a broken gate. "Nah, this stuff is
> > tough" ... "Better get it outta here" ... "No, really, it's ok, just get
> > cracking on the gate" ... "Ok then" ... bzzt, bzzt, bzzzzzzzzzzt ...
> > beep ... *PHUT*
> 
> Umm, have you ever put a volt meter across the cables?
> I was under the impression that that stuff matched the telephone and was
> in the vicinity of 40volts.
> 
> I politely suggest that if it was around 800volts, then black and crispy
> would be a welder who made the wrong circuit.
> 
> Hint, it is the current that causes the field.


   Its the collapsing field that generates the HV spikes that can, and
does knock careless welders on their asses.


-- 
You can't have a sense of humor, if you have no sense!

On 25 June, 03:18, "David L. Jones" <altz...@gmail.com> wrote:
> Check out a rather unusual phenomenon you can see on your oscilloscope in my
> latest blog (#14):http://www.alternatezone.com/eevblog/
> See if you can get it to happen on your scope!
> I'll offer a free subscription to my blog for the best screen shot posted
> :->
>
> Oh, and the probe doesn't have to be shorted either.
>
> Have fun.
> Dave.
> --
> ================================================
> Check out my Electronics Engineering Video Blog & Podcast:http://www.alternatezone.com/eevblog/

Do you still get the ringing if the nose of the probe is shorted to
the tip? I thought it was the inductance of the ground lead which
contributed mostly to the ringing.

Joerg <invalid@invalid.invalid> wrote:

>Nico Coesel wrote:
>> Joerg <invalid@invalid.invalid> wrote:
>> 
>>> Nico Coesel wrote:
>>>> Joerg <invalid@invalid.invalid> wrote:
>>>>
>>>>> Nico Coesel wrote:
>>> [...]
>
>>>>> Try differential transfer, shielded twisted pair or Twinax soldered to 
>>>>> the burden resistor, from there to your measurement box, place a 2nd 
>>>>> signal transformer there. Make sure the twisted pair is source- and/or 
>>>> I already went for a differential input. Solves most of the problems,
>>>> but not all but I'm pretty sure the inputs where overdriven as well. I
>>>> fixed that, but didn't field-test it. A 2nd signal transformer won't
>>>> fly because the pulses may be quite long (up to 100ms). 
>>>>
>>> 100msec? Is it a DC welder? Anyhow, 100msec is feasible if you use a 
>>> small doorbell transformer, the kind with two compartments where you can 
>>> scrap one of them out with wire cutters and without having to 
>> 
>> Yup. It's a DC welder. I already tried a small mains transformer but
>> that doesn't work out very well in a test. Besides that would exceed
>> budget and space constraints.
>> 
>
>A doorbell transformer blows the budget on a welder? Man, and here I 
>thought I was uncle Scrooge.

The problem is that there is an existing board. The new board must be
more or less budget neutral. I blew most of the budget on 0.1%
resistors and instrumentation amplifiers.

>>> Unless the input diff-amp has a huge common mode range even for fast 
>>> stuff such as spikes I am not sure you can do it without another 
>>> transformer at the receiving end. Or rather, I've seen cases where it 
>>> didn't work.
>> 
>> I think I have a pretty decent diff-amp. It can handle about 800V p-p
>> common mode.
>> 
>
>In a welding environment 800V may not be good enough. Plus you'd have to 
>check the CMRR for fast pulses, like when the arc starts and stops.

Its for a resistive spot welder. There is no arc. Just tens of
kiloamperes! An arc would be very bad for the particular application.

>>>> That might be worth something to explore. The burden resistor (1k is
>>>> specified) is now on the measurement board itself. I'd like to keep it
>>>> there though to keep the installation procedure easy. ...
>>>
>>> Not good. Increases noise, big time, because the cable is mismatched 
>>> because even regular cord won't have a Z of 1000ohms. And if the cable 
>>> ever comes off ... tungggg ... phssssss ... *PHUT*
>> 
>> The cord coming off doesn't seem to be a problem. All similar systems
>> I've seen so far have the burden resistor on the measurement board,
>> not on the welding transformer. But I'll try it anyways. The old ways
>> are not necessarely the best ways :-)
>> 
>
>Often they sure aren't. A burden resistor at the other end of a cable is 
>usually a bad idea.

I hope I can get some testing on a real rig this week.

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------

Michael A. Terrell wrote:
> terryc wrote:
>> On Mon, 06 Jul 2009 17:38:19 -0700, Joerg wrote:
>>
>>> terryc wrote:
>>>> On Mon, 06 Jul 2009 12:05:37 -0700, Joerg wrote:
>>>>
>>>>
>>>>
>>>>> In a welding environment 800V may not be good enough.
>>>> Which "welding" environments did you have in mind?
>>>>
>>>>
>>> The usual. >100 amps, electrodes touching, arcing, getting stuck once in
>>> a while, thick cables floating around the room, ground potential of
>>> equipment bouncing, and so on. I once told someone to get his ham radio
>>> gear out before we start welding a broken gate. "Nah, this stuff is
>>> tough" ... "Better get it outta here" ... "No, really, it's ok, just get
>>> cracking on the gate" ... "Ok then" ... bzzt, bzzt, bzzzzzzzzzzt ...
>>> beep ... *PHUT*
>> Umm, have you ever put a volt meter across the cables?
>> I was under the impression that that stuff matched the telephone and was
>> in the vicinity of 40volts.
>>
>> I politely suggest that if it was around 800volts, then black and crispy
>> would be a welder who made the wrong circuit.
>>
>> Hint, it is the current that causes the field.
> 

Hint: There's lots of inductances involved, wanted ones as well as 
undesired ones. Inductance -> current -> current suddenly stops -> 
inductance says "I don't think so!" -> tsssk ... *PHUT*

> 
>    Its the collapsing field that generates the HV spikes that can, and
> does knock careless welders on their asses.
> 

And mains connected power supplies. That's what croaked in the radio. 
The spikes on a mains circuit of sufficient length (and thus impedance) 
look rather terrifying.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Nico Coesel wrote:
> Joerg <invalid@invalid.invalid> wrote:
> 
>> Nico Coesel wrote:
>>> Joerg <invalid@invalid.invalid> wrote:
>>>
>>>> Nico Coesel wrote:
>>>>> Joerg <invalid@invalid.invalid> wrote:
>>>>>
>>>>>> Nico Coesel wrote:
>>>> [...]
>>>>>> Try differential transfer, shielded twisted pair or Twinax soldered to 
>>>>>> the burden resistor, from there to your measurement box, place a 2nd 
>>>>>> signal transformer there. Make sure the twisted pair is source- and/or 
>>>>> I already went for a differential input. Solves most of the problems,
>>>>> but not all but I'm pretty sure the inputs where overdriven as well. I
>>>>> fixed that, but didn't field-test it. A 2nd signal transformer won't
>>>>> fly because the pulses may be quite long (up to 100ms). 
>>>>>
>>>> 100msec? Is it a DC welder? Anyhow, 100msec is feasible if you use a 
>>>> small doorbell transformer, the kind with two compartments where you can 
>>>> scrap one of them out with wire cutters and without having to 
>>> Yup. It's a DC welder. I already tried a small mains transformer but
>>> that doesn't work out very well in a test. Besides that would exceed
>>> budget and space constraints.
>>>
>> A doorbell transformer blows the budget on a welder? Man, and here I 
>> thought I was uncle Scrooge.
> 
> The problem is that there is an existing board. The new board must be
> more or less budget neutral. I blew most of the budget on 0.1%
> resistors and instrumentation amplifiers.
> 

Then there's cost reduction potential :-)

No way to clamp anything so you don't need all these precision parts?


>>>> Unless the input diff-amp has a huge common mode range even for fast 
>>>> stuff such as spikes I am not sure you can do it without another 
>>>> transformer at the receiving end. Or rather, I've seen cases where it 
>>>> didn't work.
>>> I think I have a pretty decent diff-amp. It can handle about 800V p-p
>>> common mode.
>>>
>> In a welding environment 800V may not be good enough. Plus you'd have to 
>> check the CMRR for fast pulses, like when the arc starts and stops.
> 
> Its for a resistive spot welder. There is no arc. Just tens of
> kiloamperes! An arc would be very bad for the particular application.
> 

Until the spot contact lets go at a not so good moment, or one of the 
panels to be welded had a bad spot there, or a cable breaks, and so on. 
Never assume things to remain as perfect as they are on paper or in the 
engineering lab.


>>>>> That might be worth something to explore. The burden resistor (1k is
>>>>> specified) is now on the measurement board itself. I'd like to keep it
>>>>> there though to keep the installation procedure easy. ...
>>>> Not good. Increases noise, big time, because the cable is mismatched 
>>>> because even regular cord won't have a Z of 1000ohms. And if the cable 
>>>> ever comes off ... tungggg ... phssssss ... *PHUT*
>>> The cord coming off doesn't seem to be a problem. All similar systems
>>> I've seen so far have the burden resistor on the measurement board,
>>> not on the welding transformer. But I'll try it anyways. The old ways
>>> are not necessarely the best ways :-)
>>>
>> Often they sure aren't. A burden resistor at the other end of a cable is 
>> usually a bad idea.
> 
> I hope I can get some testing on a real rig this week.
> 

Good! I'd test for faulty conditions as well, like the ones above.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Tue, 07 Jul 2009 14:03:41 -0700, Joerg wrote:


> And mains connected power supplies. That's what croaked in the radio.
> The spikes on a mains circuit of sufficient length (and thus impedance)
> look rather terrifying.

If you live anywhere near high voltage power lines, be very afraid if 
they ever collapse. The induced voltages in length of cable are 
interesting.


-- 

Great advances in Debian Linux; post a bug report and get spam in three 
days.

terryc wrote:
> On Tue, 07 Jul 2009 14:03:41 -0700, Joerg wrote:
> 
> 
>> And mains connected power supplies. That's what croaked in the radio.
>> The spikes on a mains circuit of sufficient length (and thus impedance)
>> look rather terrifying.
> 
> If you live anywhere near high voltage power lines, be very afraid if 
> they ever collapse. The induced voltages in length of cable are 
> interesting.
> 

I remember a report and a photo where some guy installed a cable TV 
hookup at a house near power lines. It cinged the whole side of the house.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

blackhead wrote:
> On 25 June, 03:18, "David L. Jones" <altz...@gmail.com> wrote:
>> Check out a rather unusual phenomenon you can see on your
>> oscilloscope in my
>> latest blog (#14):http://www.alternatezone.com/eevblog/
>> See if you can get it to happen on your scope!
>> I'll offer a free subscription to my blog for the best screen shot
>> posted :->
>>
>> Oh, and the probe doesn't have to be shorted either.
>>
>> Have fun.
>> Dave.
>> --
>> ================================================
>> Check out my Electronics Engineering Video Blog &
>> Podcast:http://www.alternatezone.com/eevblog/
>
> Do you still get the ringing if the nose of the probe is shorted to
> the tip?

Yes.

>I thought it was the inductance of the ground lead which
> contributed mostly to the ringing.

Nope. As I've said, it works without the groud lead even attched, or even on 
a bit of coax.

Dave.
-- 
================================================
Check out my Electronics Engineering Video Blog & Podcast:
http://www.alternatezone.com/eevblog/