Floating the 'scope
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From: Jamie on 6 Mar 2010 12:26 John Larkin wrote: > On Fri, 5 Mar 2010 19:05:54 -0800 (PST), George Herold > <ggherold(a)gmail.com> wrote: > > >>Why do they make 'scope inputs ground referenced to the third wire of >>the AC plug? Today I smoked the 10 ohm resistor that was separating >>The AC ground from the 'ground' of my circuit. I'd forgotten to float >>the 'scope and connected -15V to the ground clip of the scope probe. >> >>George H. > > > That's a safety thing. > > Our TPS2024 has four truly floating channels and floating trigger > input. You can hook a scope ground clip anywhere. > > John > So does my cheap crappie OWEN 20 mhz hand held. That also includes isolation between the DMM inputs.
From: krw on 6 Mar 2010 13:27 On Sat, 06 Mar 2010 22:51:11 +1100, John Tserkezis <jt(a)techniciansyndrome.org.invalid> wrote: >On 6/03/2010 8:09 PM, The Phantom wrote: > >> Tektronix has probes designed to solve these problems: >> http://www2.tek.com/cmswpt/psdetails.lotr?ct=PS&cs=psu&ci=13471&lc=EN > >> They are specifically intended for floating use with the TPS2000 series scopes, >> which, as John mentioned, have true isolated inputs. > >> Or, you can use these probes with an ordinary scope: >> http://www2.tek.com/cmswpt/psdetails.lotr?ct=PS&cs=psu&ci=13415&lc=EN > > Ah, I stand corrected. > > Though it still needs to be said, if someone is of the mentality that >they can freely dismantle a piece of equipment that says "do not >dismantle" to intentionally remove a safety mechanism (against the law >the last time I checked), I'd like to see a citation for the above. Sure, such modifications would leave one exposed to litigation and it may not be legal to SELL a modified widget in some jurisdictions, but I'd like to see a cite that says it's illegal for one to modify one's own property. > what is the likelyhood they're going to use >the right probes for the job? A competent engineer certainly would. These things *are* designed for engineers to use. > After all, if they obviously don't care about the now live metal bits >of the casing, what makes you think they're going to worry about a probe >in the first place? Who, exactly, is "they"? > What if they have to make an adjustment? > Make sure they just touch the plastic bits and avoid the metal bits? When working with dangerous voltages, that's my plan. > Make sure they unclip the probe first? Huh? > More importantly, if they live through all those don't cares, what >makes you think they're going to care enough to warn other users? Other users should know something. Obviously not a good assumption in some cases. > Yeah right, I see that happening. Can I watch you?
From: John Tserkezis on 6 Mar 2010 14:46 On 7/03/2010 5:27 AM, krw(a)att.bizzzzzzzzzzzz wrote: > I'd like to see a citation for the above. Sure, such modifications would > leave one exposed to litigation and it may not be legal to SELL a modified > widget in some jurisdictions, but I'd like to see a cite that says it's > illegal for one to modify one's own property. So your legal advice is that it's ok to disable a safety device? More so, and to not replace it with something else after you've disabled it? >> what is the likelyhood they're going to use >> the right probes for the job? > A competent engineer certainly would. These things *are* designed for > engineers to use. Use yes, butcher no. >> After all, if they obviously don't care about the now live metal bits >> of the casing, what makes you think they're going to worry about a probe >> in the first place? > Who, exactly, is "they"? Hacks, keep up with it, the questions are only going to get harder. >> What if they have to make an adjustment? >> Make sure they just touch the plastic bits and avoid the metal bits? > When working with dangerous voltages, that's my plan. Good luck, it's been nice knowing you. >> Make sure they unclip the probe first? > Huh? Yeah, thought as much. >> More importantly, if they live through all those don't cares, what >> makes you think they're going to care enough to warn other users? > Other users should know something. So you're saying that it's MY fault that YOU'VE disabled a safety device? >> Yeah right, I see that happening. > Can I watch you? Guessing I'll be living longer, that will be *me* watching *you*.
From: krw on 6 Mar 2010 15:03 On Sun, 07 Mar 2010 06:46:19 +1100, John Tserkezis <jt(a)techniciansyndrome.org.invalid> wrote: >On 7/03/2010 5:27 AM, krw(a)att.bizzzzzzzzzzzz wrote: > >> I'd like to see a citation for the above. Sure, such modifications would >> leave one exposed to litigation and it may not be legal to SELL a modified >> widget in some jurisdictions, but I'd like to see a cite that says it's >> illegal for one to modify one's own property. > > So your legal advice is that it's ok to disable a safety device? You have a real reading comprehension problem, don't you? > More so, and to not replace it with something else after you've >disabled it? See above. >>> what is the likelyhood they're going to use >>> the right probes for the job? > >> A competent engineer certainly would. These things *are* designed for >> engineers to use. > > Use yes, butcher no. Your uninformed opinion. >>> After all, if they obviously don't care about the now live metal bits >>> of the casing, what makes you think they're going to worry about a probe >>> in the first place? > >> Who, exactly, is "they"? > > Hacks, keep up with it, the questions are only going to get harder. Obviously they are, since you can't answer. Although, since you can't read it does make it hard to answer. >>> What if they have to make an adjustment? >>> Make sure they just touch the plastic bits and avoid the metal bits? > >> When working with dangerous voltages, that's my plan. > > Good luck, Luck has nothing to do with it. I've been around long enough so I'm not afraid of my shadow, unlike some here. > it's been nice knowing you. I can't say the same. >>> Make sure they unclip the probe first? > >> Huh? > > Yeah, thought as much. If you're not touching anything "hot", who cares if you unclip the probe? >>> More importantly, if they live through all those don't cares, what >>> makes you think they're going to care enough to warn other users? > >> Other users should know something. > > So you're saying that it's MY fault that YOU'VE disabled a safety device? Apparently you're too stupid to live - not my problem. >>> Yeah right, I see that happening. > >> Can I watch you? > > Guessing I'll be living longer, that will be *me* watching *you*. You must be DimBulb's brother.
From: The Phantom on 6 Mar 2010 15:19
On Sat, 06 Mar 2010 12:26:16 -0500, Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> wrote: >John Larkin wrote: > >> On Fri, 5 Mar 2010 19:05:54 -0800 (PST), George Herold >> <ggherold(a)gmail.com> wrote: >> >> >>>Why do they make 'scope inputs ground referenced to the third wire of >>>the AC plug? Today I smoked the 10 ohm resistor that was separating >>>The AC ground from the 'ground' of my circuit. I'd forgotten to float >>>the 'scope and connected -15V to the ground clip of the scope probe. >>> >>>George H. >> >> >> That's a safety thing. >> >> Our TPS2024 has four truly floating channels and floating trigger >> input. You can hook a scope ground clip anywhere. >> >> John >> >So does my cheap crappie OWEN 20 mhz hand held. That also includes >isolation between the DMM inputs. Is this a two channel scope? If so, what does an ohmmeter measure between the shells of the two BNC inputs of the two channels? Aren't the two BNC input grounds connected to the same internal ground reference? > > |