On Wed, 08 May 2013 07:12:45 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>On Wed, 08 May 2013 03:33:16 -0500, John Fields <jfields@austininstruments.com> >wrote: > >>On Tue, 07 May 2013 13:52:45 -0700, John Larkin >><jlarkin@highlandtechnology.com> wrote: >> >>>On Tue, 07 May 2013 15:26:41 -0500, John Fields >>><jfields@austininstruments.com> wrote: >>> >>>>On Mon, 06 May 2013 22:26:54 -0700, John Larkin >>>><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >>>> >>>>>On Mon, 06 May 2013 21:05:15 -0700, josephkk <joseph_barrett@sbcglobal.net> >>>>>wrote: >>>>> >>>>>>On Thu, 02 May 2013 17:54:47 -0700, John Larkin >>>>>><jlarkin@highlandtechnology.com> wrote: >>>>>> >>>>>>>On Thu, 02 May 2013 18:29:42 -0500, John Fields >>>>>>><jfields@austininstruments.com> wrote: >>>>>>> >>>>>>>>On Thu, 02 May 2013 15:05:54 -0700, John Larkin >>>>>>>><jlarkin@highlandtechnology.com> wrote: >>>>>>>> >>>>>>>>>On Thu, 2 May 2013 12:31:43 -0700 (PDT), dagmargoodboat@yahoo.com >>>>>>>>>wrote: >>>>>>>>> >>>>>>>>>>4.7uF 6.3V X5R >>>>>>>>>>dC = -70% @ 6VDC (!!) >>>>>>>>>> http://psearch.murata.com/capacitor/product/GRM188R60J475ME19%23.pdf >>>>>>>>>> >>>>>>>>>>James >>>>>>>>> >>>>>>>>>It's like a tantalum cap rated for X volts, with recommendation to >>>>>>>>>never use it at X volts. >>>>>>>>> >>>>>>>>>(I actually use tantalum caps at rated voltage *if* there's not much >>>>>>>>>charging current available. Otherwise, X/3 is about right.) >>>>>>>> >>>>>>>>--- >>>>>>>>Actually, I think what's being commented on is the unexpected >>>>>>>>tolerance of the capacitance of the cap rather than the cap's >>>>>>>>likelihood of failure as a function of charging current/terminal >>>>>>>>voltage. >>>>>>> >>>>>>>What we're talking about is whether you can, in real life situations, >>>>>>>actually use an X volt rated cap at X volts. >>>>>>> >>>>>>No. JL. You intentionally overgeneralized it from MLCC capacitor voltage >>>>>>coefficient in order to post something, however irrelevant. Raging >>>>>>Narccissist. >>>>> >>>>>It would be a hell of a discussion group if nobody posted anything. >>>> >>>>--- >>>>And that justifies your posting nonsense just to keep yourself in the >>>>limelight? >>> >>>What's nonsense about using a capacitor's nonlinearity to build a >>>parametric frequency divider? >> >>--- >>No one said anything about the _nonlinearity_ of the capacitance >>change, the point was being made that the capacitance change was large >>and unexpected. >>--- >> >>>A few people here seem to have liked it. >> >>--- >>Well, sure. Thread drift happens, but you misunderstood the point >>being presented initially and posted a silly and irrelevant argument. >>--- >> >>>This thread started with capacitor nonlinearity. >> >>--- >>No, this thread started with unexpectedly large change in capacitance >>VS voltage, but no mention was made of non-linearity before your >>initial nonsensical post. >> >>BTW, unlike you, James Arthur posted an excellent and, I believe, >>empirical data set quantifying the change of capacitance with voltage >>for various dielectrics instead of merely mouthing off which is, of >>course, your forte. >>--- >> >>>Where is your promised high-frequency Variac study? >> >>--- >>On the back burner, but what on earth does that have to do with >>capacitance change VS voltage??? >> >>BYW, are you going to spend the rest of your life whining about that >>the same way you whine about Jim's killfiling/not killfiling you? >>--- >> >>>Can you actually do anything but whine? >> >>--- >>Since, according to you, "Crossing Larkin" = "Whine", the answer is a >>resounding "yes". > >Freaking moron.--- Wow, more name-calling? How devastating... --->Non-constant c with change in V *IS* capacitance nonlinearity.--- Actually, no. Constant C with change in V doesn't say anything about the capacitor's linearity, since C isn't changing. Perhaps what you meant to say was that non-constant _change_ in capacitance for a constant _change_ in voltage defines the capacitor's nonlinearity? --->It means that Q <> C * V--- Total nonsense. Q is always equal to C * V. What you should be looking at is y = mx + b --->It causes harmonic distortion in filters and coupling circuits. > >It makes parametric amps and oscillators possible. > >It will make RC timers nonlinear.--- Blah, blah, blah. --->You're not crossing me, you're being stupid about electronics.--- If I weren't crossing you, you wouldn't be replying. --->You won't post the Variac data because you wouldn't know what to measure.--- That's funny! Grasping at straws, are you? -- JF
Crapacitors
Started by ●May 2, 2013
Reply by ●May 8, 20132013-05-08
Reply by ●May 8, 20132013-05-08
On Wed, 08 May 2013 10:45:51 +0100, John Devereux <john@devereux.me.uk> wrote:>John Fields <jfields@austininstruments.com> writes: > > >[...] > >> >> --- >> Since, according to you, "Crossing Larkin" = "Whine", the answer is a >> resounding "yes". > >John. > >FFS. > >Have you really got nothing better to do than obsessively scan every >single word of Larkins posts until you find some creative way to >misinterpret it?--- The devil's in the details, and I think the misinterpretation is yours, since whining is what a dog does when it tries to curry favor from its master after having been punished. -- JF
Reply by ●May 9, 20132013-05-09
On Wed, 08 May 2013 07:13:50 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>On Wed, 8 May 2013 04:49:45 -0700 (PDT), George Herold =<gherold@teachspin.com>>wrote: > >>On May 7, 10:03=A0pm, John Larkin >><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>> On Tue, 07 May 2013 17:39:04 -0700, josephkk =<joseph_barr...@sbcglobal.net>>>> wrote: >>> >>> >>> >>> >>> >>> >On Thu, 2 May 2013 18:42:09 -0700 (PDT), George Herold >>> ><gher...@teachspin.com> wrote: >>> >>> >>On May 2, 6:05 pm, John Larkin <jlar...@highlandtechnology.com> =wrote:>>> >>> On Thu, 2 May 2013 12:31:43 -0700 (PDT), dagmargoodb...@yahoo.com >>> >>> wrote: >>> >>> >>> >4.7uF 6.3V X5R >>> >>> >dC =3D -70% @ 6VDC (!!) >>> >>> = >http://psearch.murata.com/capacitor/product/GRM188R60J475ME19%23.pdf >>> >>> >>> >James >>> >>> >>> It's like a tantalum cap rated for X volts, with recommendation =to>>> >>> never use it at X volts. >>> >>> >>> (I actually use tantalum caps at rated voltage *if* there's not =much>>> >>> charging current available. Otherwise, X/3 is about right.) >>> >>> >>> -- >>> >>> >>> John Larkin Highland Technology, Inc >>> >>> >>> jlarkin at highlandtechnology dot =comhttp://www.highlandtechnology.com>>> >>> >>> Precision electronic instrumentation >>> >>> Picosecond-resolution Digital Delay and Pulse generators >>> >>> Custom laser drivers and controllers >>> >>> Photonics and fiberoptic TTL data links >>> >>> VME thermocouple, LVDT, synchro acquisition and simulation >>> >>> >>I've got this audio amp that runs off 15 volts. >>> >>But I've told people you can stick upto 40V into it. >>> >>(as long as it doesn't over heat.) >>> >>The IC's are good to 60V (I think, LM675?) but I've only got 50V =tants>>> >>as bypass C's. =A0I should do a mod to 100V tants. =A0Someone will =want>>> >>more V. >>> >>> >>George H. >>> >>> >If it were me, i won't use a solid tant at more than 1/2 rated V. >>> >>> >?-) >>> >>> Why are you talking about tantalum caps in a thread about ceramic =caps?>> >>Sorry my fault.... a bit of thread drift. >>(It's all about me after all isn't it? :^) >> > >George did it!And unlike you he stood up and admitted it. ?-)
Reply by ●May 9, 20132013-05-09
On Wed, 08 May 2013 21:27:55 -0700, josephkk <joseph_barrett@sbcglobal.net> wrote:>On Wed, 08 May 2013 07:13:50 -0700, John Larkin ><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > >>On Wed, 8 May 2013 04:49:45 -0700 (PDT), George Herold <gherold@teachspin.com> >>wrote: >> >>>On May 7, 10:03�pm, John Larkin >>><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>>> On Tue, 07 May 2013 17:39:04 -0700, josephkk <joseph_barr...@sbcglobal.net> >>>> wrote: >>>> >>>> >>>> >>>> >>>> >>>> >On Thu, 2 May 2013 18:42:09 -0700 (PDT), George Herold >>>> ><gher...@teachspin.com> wrote: >>>> >>>> >>On May 2, 6:05 pm, John Larkin <jlar...@highlandtechnology.com> wrote: >>>> >>> On Thu, 2 May 2013 12:31:43 -0700 (PDT), dagmargoodb...@yahoo.com >>>> >>> wrote: >>>> >>>> >>> >4.7uF 6.3V X5R >>>> >>> >dC = -70% @ 6VDC (!!) >>>> >>> >http://psearch.murata.com/capacitor/product/GRM188R60J475ME19%23.pdf >>>> >>>> >>> >James >>>> >>>> >>> It's like a tantalum cap rated for X volts, with recommendation to >>>> >>> never use it at X volts. >>>> >>>> >>> (I actually use tantalum caps at rated voltage *if* there's not much >>>> >>> charging current available. Otherwise, X/3 is about right.) >>>> >>>> >>> -- >>>> >>>> >>> John Larkin Highland Technology, Inc >>>> >>>> >>> jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com >>>> >>>> >>> Precision electronic instrumentation >>>> >>> Picosecond-resolution Digital Delay and Pulse generators >>>> >>> Custom laser drivers and controllers >>>> >>> Photonics and fiberoptic TTL data links >>>> >>> VME thermocouple, LVDT, synchro acquisition and simulation >>>> >>>> >>I've got this audio amp that runs off 15 volts. >>>> >>But I've told people you can stick upto 40V into it. >>>> >>(as long as it doesn't over heat.) >>>> >>The IC's are good to 60V (I think, LM675?) but I've only got 50V tants >>>> >>as bypass C's. �I should do a mod to 100V tants. �Someone will want >>>> >>more V. >>>> >>>> >>George H. >>>> >>>> >If it were me, i won't use a solid tant at more than 1/2 rated V. >>>> >>>> >?-) >>>> >>>> Why are you talking about tantalum caps in a thread about ceramic caps? >>> >>>Sorry my fault.... a bit of thread drift. >>>(It's all about me after all isn't it? :^) >>> >> >>George did it! > >And unlike you he stood up and admitted it. > >?-)Got anything interesting to say about capacitors? -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●May 9, 20132013-05-09
On 9 touko, 00:36, John Fields <jfie...@austininstruments.com> wrote:> On Wed, 08 May 2013 07:12:45 -0700, John Larkin > >Non-constant c with change in V *IS* capacitance nonlinearity. > > Actually, no. > Constant C with change in V doesn't say anything about the capacitor's > linearity, since C isn't changing. > Perhaps what you meant to say was that non-constant _change_ in > capacitance for a constant _change_ in voltage defines the capacitor's > nonlinearity?I think the definition JL uses, is standard - i.e. that a capacitor as a default has a linear charge-voltage relationship, and the constant of proportionality is C, the capacitance. This relates to the large subset of more general electric circuits, namely *linear* circuits, which are much simpler to treat mathematically than general circuits. For instance, the superposition principle applies, which is one consequence of the fact that network equations can be Laplace transformed into s-domain without invoking convolutions and other mathematical nastieties. In order a network to be linear one, its circuit elements must be linear elements, i.e. resistors with the linear I-V relation, capacitors with the linear Q-V relation, inductors with the linear phi-I relation, and so on [*]. It is unfortunate that the constant of proportionality, C, is called "capacitance" because it sounds so similar to "capacitor" that one might indeed think that it is the linear C-to-something (maybe voltage) relation which defines the the linear capacitor. However, it is the linear Q-V relationship which ties the capacitor to the family of linear circuit elements, which we know and love, not the linear C-V relationship. What JF wants to call the linear capacitor, might in general usage be called a linear *varactor*, obeying the linear relation C = C0 + k_C * V, which would imply Q = C0*V + 1/2*k_C*V^2 . But then there is a risk someone begins to call the constant of proportionality k_C the varactance, which sounds a lot like "varactor"...> >It means that Q <> C * V > > Total nonsense. > Q is always equal to C * V.There are two possible definitions one might use, when moving outside the realm where the C was originally defined (the linear circuit theory): Fields uses the definition C = Q / V, whereas Larkin seems to use C = dQ / dV . In the linear case the two coincide. If someone continues to use the linear theory concept of "capacitance" in the nonlinear case, this suggests that he/she may want to linearize the nonlinear circuit for small signals at some dc setpoint. If so, Larkin's definition is the correct one to use. Regards, Mikko [*] Recall that Q and Phi are actually just shorthand for integrals of the system variables Q=Int(I dt) and phi=Int(V dt), so the confusion is about which are the dynamic variables and which are the coefficients in the governing (linear) differential equations. And, what is the most fruitful nomenclature to use, when expanding into the nonlinear diff. eq. realm.
Reply by ●May 9, 20132013-05-09
On May 9, 5:58=A0am, Mr Stonebeach <r...@wmail.fi> wrote:> On 9 touko, 00:36, John Fields <jfie...@austininstruments.com> wrote: > > > On Wed, 08 May 2013 07:12:45 -0700, John Larkin > > >Non-constant c with change in V *IS* capacitance nonlinearity. > > > Actually, no. > > Constant C with change in V doesn't say anything about the capacitor's > > linearity, since C isn't changing. > > Perhaps what you meant to say was that non-constant _change_ in > > capacitance for a constant _change_ in voltage defines the capacitor's > > nonlinearity? > > =A0 I think the definition JL uses, is standard - i.e. that a capacitor > as > a default has a linear charge-voltage relationship, and the constant > of proportionality is C, the capacitance. > > =A0 This relates to the large subset of more general electric circuits, > namely *linear* circuits, which are much simpler to treat > mathematically than general circuits. For instance, the superposition > principle applies, which is one consequence of the fact that network > equations can be Laplace transformed > into s-domain without invoking convolutions and other mathematical > nastieties. > > =A0 In order a network to be linear one, its circuit elements must be > linear elements, i.e. resistors with the linear I-V relation, > capacitors > with the linear Q-V relation, inductors with the linear phi-I > relation, > and so on [*]. > > =A0 It is unfortunate that the constant of proportionality, C, is called > "capacitance" because it sounds so similar to "capacitor" that > one might indeed think that it is the linear C-to-something (maybe > voltage) relation which defines the the linear capacitor. However, it > is the linear Q-V relationship which ties the capacitor to the family > of linear circuit elements, which we know and love, not the linear > C-V relationship. > > What JF wants to call the linear capacitor, might in general usage > be called a linear *varactor*, obeying the linear relation > C =3D C0 + k_C * V, which would imply Q =3D C0*V + 1/2*k_C*V^2 . > But then there is a risk someone begins to call the constant of > proportionality k_C the varactance, which sounds a lot like > "varactor"...Nice, I might have written that with a minus sign, C =3D C0 - k_C * V,> > > >It means that Q <> C * V > > > Total nonsense. > > Q is always equal to C * V. > > =A0 There are two possible definitions one might use, when moving > outside the realm where the C was originally defined (the linear > circuit theory): Fields uses the definition C =3D Q / V, whereas Larkin > seems to use C =3D dQ / dV . In the linear case the two coincide. > If someone continues to use the linear theory concept of > "capacitance" > in the nonlinear case, this suggests that he/she may want to > linearize > the nonlinear circuit for small signals at some dc setpoint. If so, > Larkin's definition is the correct one to use.Interesting.. so I wonder which definition the manufacturers use? Differential or do they measure how much charge it takes to get to some voltage? If I had some of these crapacitors I could try a measurement. George H.> > Regards, > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Mikko > > [*] Recall that Q and Phi are actually just shorthand for integrals > of > the system variables Q=3DInt(I dt) and phi=3DInt(V dt), so > the confusion is about which are the dynamic variables and which > are the coefficients in the governing (linear) differential equations. > And, what is the most fruitful nomenclature to use, when > expanding into the nonlinear diff. eq. realm.
Reply by ●May 9, 20132013-05-09
On May 9, 9:04=A0am, George Herold <gher...@teachspin.com> wrote:> On May 9, 5:58=A0am, Mr Stonebeach <r...@wmail.fi> wrote: > > > > > > > On 9 touko, 00:36, John Fields <jfie...@austininstruments.com> wrote: > > > > On Wed, 08 May 2013 07:12:45 -0700, John Larkin > > > >Non-constant c with change in V *IS* capacitance nonlinearity. > > > > Actually, no. > > > Constant C with change in V doesn't say anything about the capacitor'=s> > > linearity, since C isn't changing. > > > Perhaps what you meant to say was that non-constant _change_ in > > > capacitance for a constant _change_ in voltage defines the capacitor'=s> > > nonlinearity? > > > =A0 I think the definition JL uses, is standard - i.e. that a capacitor > > as > > a default has a linear charge-voltage relationship, and the constant > > of proportionality is C, the capacitance. > > > =A0 This relates to the large subset of more general electric circuits, > > namely *linear* circuits, which are much simpler to treat > > mathematically than general circuits. For instance, the superposition > > principle applies, which is one consequence of the fact that network > > equations can be Laplace transformed > > into s-domain without invoking convolutions and other mathematical > > nastieties. > > > =A0 In order a network to be linear one, its circuit elements must be > > linear elements, i.e. resistors with the linear I-V relation, > > capacitors > > with the linear Q-V relation, inductors with the linear phi-I > > relation, > > and so on [*]. > > > =A0 It is unfortunate that the constant of proportionality, C, is calle=d> > "capacitance" because it sounds so similar to "capacitor" that > > one might indeed think that it is the linear C-to-something (maybe > > voltage) relation which defines the the linear capacitor. However, it > > is the linear Q-V relationship which ties the capacitor to the family > > of linear circuit elements, which we know and love, not the linear > > C-V relationship. > > > What JF wants to call the linear capacitor, might in general usage > > be called a linear *varactor*, obeying the linear relation > > C =3D C0 + k_C * V, which would imply Q =3D C0*V + 1/2*k_C*V^2 . > > But then there is a risk someone begins to call the constant of > > proportionality k_C the varactance, which sounds a lot like > > "varactor"... > > Nice, I might have written that with a minus sign, > =A0C =3D C0 - k_C * V, > > > > > > > > > > >It means that Q <> C * V > > > > Total nonsense. > > > Q is always equal to C * V. > > > =A0 There are two possible definitions one might use, when moving > > outside the realm where the C was originally defined (the linear > > circuit theory): Fields uses the definition C =3D Q / V, whereas Larkin > > seems to use C =3D dQ / dV . In the linear case the two coincide. > > If someone continues to use the linear theory concept of > > "capacitance" > > in the nonlinear case, this suggests that he/she may want to > > linearize > > the nonlinear circuit for small signals at some dc setpoint. If so, > > Larkin's definition is the correct one to use. > > Interesting.. so I wonder which definition the manufacturers use? > Differential or do they measure how much charge it takes to get to > some voltage? > > If I had some of these crapacitors I could try a measurement. > > George H.Just plotting numbers from some of the previously posted data sheets. It looks like it has to be the differential definition. (otherwise I get C*V products that are constant or even decreasing as the voltage is increased.) George H.> > > > > > > Regards, > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Mikko > > > [*] Recall that Q and Phi are actually just shorthand for integrals > > of > > the system variables Q=3DInt(I dt) and phi=3DInt(V dt), so > > the confusion is about which are the dynamic variables and which > > are the coefficients in the governing (linear) differential equations. > > And, what is the most fruitful nomenclature to use, when > > expanding into the nonlinear diff. eq. realm.- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -
Reply by ●May 9, 20132013-05-09
On May 9, 10:03=A0am, George Herold <gher...@teachspin.com> wrote:> On May 9, 9:04=A0am, George Herold <gher...@teachspin.com> wrote: > > > > > > > > > > > On May 9, 5:58=A0am, Mr Stonebeach <r...@wmail.fi> wrote: > > > > On 9 touko, 00:36, John Fields <jfie...@austininstruments.com> wrote: > > > > > On Wed, 08 May 2013 07:12:45 -0700, John Larkin > > > > >Non-constant c with change in V *IS* capacitance nonlinearity. > > > > > Actually, no. > > > > Constant C with change in V doesn't say anything about the capacito=r's> > > > linearity, since C isn't changing. > > > > Perhaps what you meant to say was that non-constant _change_ in > > > > capacitance for a constant _change_ in voltage defines the capacito=r's> > > > nonlinearity? > > > > =A0 I think the definition JL uses, is standard - i.e. that a capacit=or> > > as > > > a default has a linear charge-voltage relationship, and the constant > > > of proportionality is C, the capacitance. > > > > =A0 This relates to the large subset of more general electric circuit=s,> > > namely *linear* circuits, which are much simpler to treat > > > mathematically than general circuits. For instance, the superposition > > > principle applies, which is one consequence of the fact that network > > > equations can be Laplace transformed > > > into s-domain without invoking convolutions and other mathematical > > > nastieties. > > > > =A0 In order a network to be linear one, its circuit elements must be > > > linear elements, i.e. resistors with the linear I-V relation, > > > capacitors > > > with the linear Q-V relation, inductors with the linear phi-I > > > relation, > > > and so on [*]. > > > > =A0 It is unfortunate that the constant of proportionality, C, is cal=led> > > "capacitance" because it sounds so similar to "capacitor" that > > > one might indeed think that it is the linear C-to-something (maybe > > > voltage) relation which defines the the linear capacitor. However, it > > > is the linear Q-V relationship which ties the capacitor to the family > > > of linear circuit elements, which we know and love, not the linear > > > C-V relationship. > > > > What JF wants to call the linear capacitor, might in general usage > > > be called a linear *varactor*, obeying the linear relation > > > C =3D C0 + k_C * V, which would imply Q =3D C0*V + 1/2*k_C*V^2 . > > > But then there is a risk someone begins to call the constant of > > > proportionality k_C the varactance, which sounds a lot like > > > "varactor"... > > > Nice, I might have written that with a minus sign, > > =A0C =3D C0 - k_C * V, > > > > > >It means that Q <> C * V > > > > > Total nonsense. > > > > Q is always equal to C * V. > > > > =A0 There are two possible definitions one might use, when moving > > > outside the realm where the C was originally defined (the linear > > > circuit theory): Fields uses the definition C =3D Q / V, whereas Lark=in> > > seems to use C =3D dQ / dV . In the linear case the two coincide. > > > If someone continues to use the linear theory concept of > > > "capacitance" > > > in the nonlinear case, this suggests that he/she may want to > > > linearize > > > the nonlinear circuit for small signals at some dc setpoint. If so, > > > Larkin's definition is the correct one to use. > > > Interesting.. so I wonder which definition the manufacturers use? > > Differential or do they measure how much charge it takes to get to > > some voltage? > > > If I had some of these crapacitors I could try a measurement.I've got a few reels, but I can't remember where!> Just plotting numbers from some of the previously posted data > sheets. > It looks like it has to be the differential definition. =A0(otherwise I > get C*V products that are constant or even decreasing as the voltage > is increased.)The mfrs.clearly use C=3DdQ/dV. Capacitance meters do too. -- Cheers, James Arthur
Reply by ●May 9, 20132013-05-09
On May 9, 10:15=A0am, dagmargoodb...@yahoo.com wrote:> On May 9, 10:03=A0am, George Herold <gher...@teachspin.com> wrote: > > > > > > > On May 9, 9:04=A0am, George Herold <gher...@teachspin.com> wrote: > > > > On May 9, 5:58=A0am, Mr Stonebeach <r...@wmail.fi> wrote: > > > > > On 9 touko, 00:36, John Fields <jfie...@austininstruments.com> wrot=e:> > > > > > On Wed, 08 May 2013 07:12:45 -0700, John Larkin > > > > > >Non-constant c with change in V *IS* capacitance nonlinearity. > > > > > > Actually, no. > > > > > Constant C with change in V doesn't say anything about the capaci=tor's> > > > > linearity, since C isn't changing. > > > > > Perhaps what you meant to say was that non-constant _change_ in > > > > > capacitance for a constant _change_ in voltage defines the capaci=tor's> > > > > nonlinearity? > > > > > =A0 I think the definition JL uses, is standard - i.e. that a capac=itor> > > > as > > > > a default has a linear charge-voltage relationship, and the constan=t> > > > of proportionality is C, the capacitance. > > > > > =A0 This relates to the large subset of more general electric circu=its,> > > > namely *linear* circuits, which are much simpler to treat > > > > mathematically than general circuits. For instance, the superpositi=on> > > > principle applies, which is one consequence of the fact that networ=k> > > > equations can be Laplace transformed > > > > into s-domain without invoking convolutions and other mathematical > > > > nastieties. > > > > > =A0 In order a network to be linear one, its circuit elements must =be> > > > linear elements, i.e. resistors with the linear I-V relation, > > > > capacitors > > > > with the linear Q-V relation, inductors with the linear phi-I > > > > relation, > > > > and so on [*]. > > > > > =A0 It is unfortunate that the constant of proportionality, C, is c=alled> > > > "capacitance" because it sounds so similar to "capacitor" that > > > > one might indeed think that it is the linear C-to-something (maybe > > > > voltage) relation which defines the the linear capacitor. However, =it> > > > is the linear Q-V relationship which ties the capacitor to the fami=ly> > > > of linear circuit elements, which we know and love, not the linear > > > > C-V relationship. > > > > > What JF wants to call the linear capacitor, might in general usage > > > > be called a linear *varactor*, obeying the linear relation > > > > C =3D C0 + k_C * V, which would imply Q =3D C0*V + 1/2*k_C*V^2 . > > > > But then there is a risk someone begins to call the constant of > > > > proportionality k_C the varactance, which sounds a lot like > > > > "varactor"... > > > > Nice, I might have written that with a minus sign, > > > =A0C =3D C0 - k_C * V, > > > > > > >It means that Q <> C * V > > > > > > Total nonsense. > > > > > Q is always equal to C * V. > > > > > =A0 There are two possible definitions one might use, when moving > > > > outside the realm where the C was originally defined (the linear > > > > circuit theory): Fields uses the definition C =3D Q / V, whereas La=rkin> > > > seems to use C =3D dQ / dV . In the linear case the two coincide. > > > > If someone continues to use the linear theory concept of > > > > "capacitance" > > > > in the nonlinear case, this suggests that he/she may want to > > > > linearize > > > > the nonlinear circuit for small signals at some dc setpoint. If so, > > > > Larkin's definition is the correct one to use. > > > > Interesting.. so I wonder which definition the manufacturers use? > > > Differential or do they measure how much charge it takes to get to > > > some voltage? > > > > If I had some of these crapacitors I could try a measurement. > > I've got a few reels, but I can't remember where! > > > Just plotting numbers from some of the previously posted data > > sheets. > > It looks like it has to be the differential definition. =A0(otherwise I > > get C*V products that are constant or even decreasing as the voltage > > is increased.) > > The mfrs.clearly use C=3DdQ/dV. =A0Capacitance meters do too. > > -- > Cheers, > James Arthur- Hide quoted text - > > - Show quoted text -Yeah don't bother with any measurment. The link from JL (other thread) to clifton labs also shows that it's dQ/dV. George H.
Reply by ●May 9, 20132013-05-09
On Thu, 9 May 2013 07:19:28 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On May 9, 10:15�am, dagmargoodb...@yahoo.com wrote: >> On May 9, 10:03�am, George Herold <gher...@teachspin.com> wrote: >> >> >> >> >> >> > On May 9, 9:04�am, George Herold <gher...@teachspin.com> wrote: >> >> > > On May 9, 5:58�am, Mr Stonebeach <r...@wmail.fi> wrote: >> >> > > > On 9 touko, 00:36, John Fields <jfie...@austininstruments.com> wrote: >> >> > > > > On Wed, 08 May 2013 07:12:45 -0700, John Larkin >> > > > > >Non-constant c with change in V *IS* capacitance nonlinearity. >> >> > > > > Actually, no. >> > > > > Constant C with change in V doesn't say anything about the capacitor's >> > > > > linearity, since C isn't changing. >> > > > > Perhaps what you meant to say was that non-constant _change_ in >> > > > > capacitance for a constant _change_ in voltage defines the capacitor's >> > > > > nonlinearity? >> >> > > > � I think the definition JL uses, is standard - i.e. that a capacitor >> > > > as >> > > > a default has a linear charge-voltage relationship, and the constant >> > > > of proportionality is C, the capacitance. >> >> > > > � This relates to the large subset of more general electric circuits, >> > > > namely *linear* circuits, which are much simpler to treat >> > > > mathematically than general circuits. For instance, the superposition >> > > > principle applies, which is one consequence of the fact that network >> > > > equations can be Laplace transformed >> > > > into s-domain without invoking convolutions and other mathematical >> > > > nastieties. >> >> > > > � In order a network to be linear one, its circuit elements must be >> > > > linear elements, i.e. resistors with the linear I-V relation, >> > > > capacitors >> > > > with the linear Q-V relation, inductors with the linear phi-I >> > > > relation, >> > > > and so on [*]. >> >> > > > � It is unfortunate that the constant of proportionality, C, is called >> > > > "capacitance" because it sounds so similar to "capacitor" that >> > > > one might indeed think that it is the linear C-to-something (maybe >> > > > voltage) relation which defines the the linear capacitor. However, it >> > > > is the linear Q-V relationship which ties the capacitor to the family >> > > > of linear circuit elements, which we know and love, not the linear >> > > > C-V relationship. >> >> > > > What JF wants to call the linear capacitor, might in general usage >> > > > be called a linear *varactor*, obeying the linear relation >> > > > C = C0 + k_C * V, which would imply Q = C0*V + 1/2*k_C*V^2 . >> > > > But then there is a risk someone begins to call the constant of >> > > > proportionality k_C the varactance, which sounds a lot like >> > > > "varactor"... >> >> > > Nice, I might have written that with a minus sign, >> > > �C = C0 - k_C * V, >> >> > > > > >It means that Q <> C * V >> >> > > > > Total nonsense. >> > > > > Q is always equal to C * V. >> >> > > > � There are two possible definitions one might use, when moving >> > > > outside the realm where the C was originally defined (the linear >> > > > circuit theory): Fields uses the definition C = Q / V, whereas Larkin >> > > > seems to use C = dQ / dV . In the linear case the two coincide. >> > > > If someone continues to use the linear theory concept of >> > > > "capacitance" >> > > > in the nonlinear case, this suggests that he/she may want to >> > > > linearize >> > > > the nonlinear circuit for small signals at some dc setpoint. If so, >> > > > Larkin's definition is the correct one to use. >> >> > > Interesting.. so I wonder which definition the manufacturers use? >> > > Differential or do they measure how much charge it takes to get to >> > > some voltage? >> >> > > If I had some of these crapacitors I could try a measurement. >> >> I've got a few reels, but I can't remember where! >> >> > Just plotting numbers from some of the previously posted data >> > sheets. >> > It looks like it has to be the differential definition. �(otherwise I >> > get C*V products that are constant or even decreasing as the voltage >> > is increased.) >> >> The mfrs.clearly use C=dQ/dV. �Capacitance meters do too. >> >> -- >> Cheers, >> James Arthur- Hide quoted text - >> >> - Show quoted text - > >Yeah don't bother with any measurment. The link from JL (other >thread) to clifton labs also shows that it's dQ/dV. > >George H.Good c-meters apply a small ac voltage, millivolts, and measure the small resulting ac current. They put DC bias on top of that. Of course, people can choose to define C = Q/V like they choose to define R = E/I and always be right. I did use c and C somewhere above, as the incremental and gross capacitances. The Boonton 72 series are great c-meters, available used fairly cheap. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
