A good digital oscilloscope?
in [Design]
|
From: John Larkin on 8 Dec 2009 21:18 On Tue, 08 Dec 2009 17:26:48 -0800, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Tue, 8 Dec 2009 12:32:52 -0600, "Tim Williams" >> <tmoranwms(a)charter.net> wrote: >> >>> "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >>> news:oh6th5903d58sogu3cj8vk3er6r6li9m32(a)4ax.com... >>>> I love our TPS2024. 200 MHz, and all four channels and the trigger >>>> input are fully floating. Wanna clip the probe ground lead onto the >>>> source of a fet that's flailing 400 volts off ground? No problem. >>> Tasty. >>> >>> What's C-to-ground like, is it basically a differential input (2 x 1M || >>> 20pF) with a BNC input? >>> >>> Tim >> >> Something like 35 pF from the BNC outer to ground. I'd prefer less. >> But it's truly floating with pretty much infinite CMRR. I think it's a >> microwave-range FM signal link or something. >> > >Or maybe not. Tektronix went to great lengths WRT isolated channels. >Here is a photo for an older scope from Olaf in the German NG: > >http://www.criseis.ruhr.de/tek222.jpg > >Every data bit seems to have its own personal transformer with trace >"windings". That is some real engineering there. > >Whenever I had to do that (isolated signal transfer in medical) I took >the analog signal and heaved it across just one transformer while >another bigger one supplies the isolated side with power. Results in >very small capacitance which is always a concern for stuff that goes >inside a beating heart. It might be this one... http://www.google.com/patents/about?id=0Nl6AAAAEBAJ&dq=7113750 John
From: Joerg on 8 Dec 2009 21:54 John Larkin wrote: > On Tue, 08 Dec 2009 17:26:48 -0800, Joerg <invalid(a)invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Tue, 8 Dec 2009 12:32:52 -0600, "Tim Williams" >>> <tmoranwms(a)charter.net> wrote: >>> >>>> "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >>>> news:oh6th5903d58sogu3cj8vk3er6r6li9m32(a)4ax.com... >>>>> I love our TPS2024. 200 MHz, and all four channels and the trigger >>>>> input are fully floating. Wanna clip the probe ground lead onto the >>>>> source of a fet that's flailing 400 volts off ground? No problem. >>>> Tasty. >>>> >>>> What's C-to-ground like, is it basically a differential input (2 x 1M || >>>> 20pF) with a BNC input? >>>> >>>> Tim >>> Something like 35 pF from the BNC outer to ground. I'd prefer less. >>> But it's truly floating with pretty much infinite CMRR. I think it's a >>> microwave-range FM signal link or something. >>> >> Or maybe not. Tektronix went to great lengths WRT isolated channels. >> Here is a photo for an older scope from Olaf in the German NG: >> >> http://www.criseis.ruhr.de/tek222.jpg >> >> Every data bit seems to have its own personal transformer with trace >> "windings". That is some real engineering there. >> >> Whenever I had to do that (isolated signal transfer in medical) I took >> the analog signal and heaved it across just one transformer while >> another bigger one supplies the isolated side with power. Results in >> very small capacitance which is always a concern for stuff that goes >> inside a beating heart. > > > It might be this one... > > http://www.google.com/patents/about?id=0Nl6AAAAEBAJ&dq=7113750 > Oh man, some of the patent examiners must really wave stuff through or not pay much attention. Don't they use engineers anymore at the patent office? This is a really old scheme, tons of prior art. Used on ECG units dating almost back to the Romans. So I guess that patent wouldn't have much standing if it ever came to a court challenge. But that's essentially how it's done right. Typically there is a synchronous detector at the other side but the modulation scheme doesn't really matter. On low frequency gear the carrier transformer supplies power to the isolated side at the same time. Of course if the carrier has to be in the GHz range you'd be better off with a third transformer. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 8 Dec 2009 21:59 krw wrote: > On Tue, 08 Dec 2009 14:36:53 -0500, Spehro Pefhany > <speffSNIP(a)interlogDOTyou.knowwhat> wrote: > >> On Tue, 08 Dec 2009 10:28:27 -0800, John Larkin >> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>> On Mon, 7 Dec 2009 22:21:43 -0600, "Tim Williams" >>> <tmoranwms(a)charter.net> wrote: >>> >>>> "Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> wrote in message >>>> news:oFhTm.36236$kY2.31856(a)newsfe01.iad... >>>>> My Tek 485 serves me well. I do have a small assortment of digital scopes >>>>> for portable use to gather basic data and road trip testing how ever, I >>>>> find that my 485 still gives me nice results at the bench as long as I >>>>> don't need live digital storage. >>>>> It's the only scope I have that I can take full advantage of my active >>>>> Fet probes when I need them. >>>> 486 is on my Wish List. And 2465. Yessss, my preciousss.... >>>> >>>> >>>> Tim >>> I love our TPS2024. 200 MHz, and all four channels and the trigger >>> input are fully floating. Wanna clip the probe ground lead onto the >>> source of a fet that's flailing 400 volts off ground? No problem. >>> >>> John >> Shame about that antediluvian CF card slot that can't write to even a >> 2G card. 8-( > > Beats waiting 3 minutes to write to floppy. > But wouldn't you think a scope of this day and age would come with a USB stick slot? I mean, it's been years now ... Mine did :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 8 Dec 2009 22:49 On Tue, 08 Dec 2009 18:54:33 -0800, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Tue, 08 Dec 2009 17:26:48 -0800, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> John Larkin wrote: >>>> On Tue, 8 Dec 2009 12:32:52 -0600, "Tim Williams" >>>> <tmoranwms(a)charter.net> wrote: >>>> >>>>> "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >>>>> news:oh6th5903d58sogu3cj8vk3er6r6li9m32(a)4ax.com... >>>>>> I love our TPS2024. 200 MHz, and all four channels and the trigger >>>>>> input are fully floating. Wanna clip the probe ground lead onto the >>>>>> source of a fet that's flailing 400 volts off ground? No problem. >>>>> Tasty. >>>>> >>>>> What's C-to-ground like, is it basically a differential input (2 x 1M || >>>>> 20pF) with a BNC input? >>>>> >>>>> Tim >>>> Something like 35 pF from the BNC outer to ground. I'd prefer less. >>>> But it's truly floating with pretty much infinite CMRR. I think it's a >>>> microwave-range FM signal link or something. >>>> >>> Or maybe not. Tektronix went to great lengths WRT isolated channels. >>> Here is a photo for an older scope from Olaf in the German NG: >>> >>> http://www.criseis.ruhr.de/tek222.jpg >>> >>> Every data bit seems to have its own personal transformer with trace >>> "windings". That is some real engineering there. >>> >>> Whenever I had to do that (isolated signal transfer in medical) I took >>> the analog signal and heaved it across just one transformer while >>> another bigger one supplies the isolated side with power. Results in >>> very small capacitance which is always a concern for stuff that goes >>> inside a beating heart. >> >> >> It might be this one... >> >> http://www.google.com/patents/about?id=0Nl6AAAAEBAJ&dq=7113750 >> > >Oh man, some of the patent examiners must really wave stuff through or >not pay much attention. Don't they use engineers anymore at the patent >office? This is a really old scheme, tons of prior art. Used on ECG >units dating almost back to the Romans. So I guess that patent wouldn't >have much standing if it ever came to a court challenge. Unless it's "as applied to oscilloscopes" or something. I recall isolated-input opamps that did this many decades ago. John
From: krw on 8 Dec 2009 23:09
On Tue, 08 Dec 2009 18:59:11 -0800, Joerg <invalid(a)invalid.invalid> wrote: >krw wrote: >> On Tue, 08 Dec 2009 14:36:53 -0500, Spehro Pefhany >> <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >> >>> On Tue, 08 Dec 2009 10:28:27 -0800, John Larkin >>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>> On Mon, 7 Dec 2009 22:21:43 -0600, "Tim Williams" >>>> <tmoranwms(a)charter.net> wrote: >>>> >>>>> "Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> wrote in message >>>>> news:oFhTm.36236$kY2.31856(a)newsfe01.iad... >>>>>> My Tek 485 serves me well. I do have a small assortment of digital scopes >>>>>> for portable use to gather basic data and road trip testing how ever, I >>>>>> find that my 485 still gives me nice results at the bench as long as I >>>>>> don't need live digital storage. >>>>>> It's the only scope I have that I can take full advantage of my active >>>>>> Fet probes when I need them. >>>>> 486 is on my Wish List. And 2465. Yessss, my preciousss.... >>>>> >>>>> >>>>> Tim >>>> I love our TPS2024. 200 MHz, and all four channels and the trigger >>>> input are fully floating. Wanna clip the probe ground lead onto the >>>> source of a fet that's flailing 400 volts off ground? No problem. >>>> >>>> John >>> Shame about that antediluvian CF card slot that can't write to even a >>> 2G card. 8-( >> >> Beats waiting 3 minutes to write to floppy. >> > >But wouldn't you think a scope of this day and age would come with a USB > stick slot? I mean, it's been years now ... > >Mine did :-) You'd think. AIUI, USB sticks are a PITA to write but the work only has to be done once. |