We had this here, yesterday (photo is from last year though), top view from a friend's deck:
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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
he
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.
Podcast:
Scope vertical amps don't ring.
John
Legs.
in my
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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/
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
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
Same in this here lab :-)
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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
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 :-)
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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. OTOH that provides a good business opportunity 8-D
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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
Because that's what it said to do in the instructions that came with the kit.
Cheers! Rich
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!"
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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.
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...
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!"
--------------------------------------------------------------
[...]
Recipe against headache in cases like this: Proper matching of literally everything, shielding, a glass or two of Beerenburger.
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.
If it's fed 1kHz then 1kHz should come out.
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*
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.
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