Detecting the peak value
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From: Jim Thompson on 3 Aug 2010 10:42 On Mon, 02 Aug 2010 21:04:49 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Sun, 01 Aug 2010 10:19:51 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >>On Sun, 01 Aug 2010 10:06:49 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Sun, 1 Aug 2010 16:00:54 GMT, hal(a)nospam.com wrote: >>> >>>> >>>>On 1-Aug-2010, Jim Thompson >>>><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >>>> >>>>> On Sun, 1 Aug 2010 15:29:19 GMT, hal(a)nospam.com wrote: >>>>> >>>>> >Hello all, >>>>> > >>>>> >I've been following this thread and it has brought up some issues I'm >>>>> >currently working on. First of all, I'm a hobbyist that likes to learn >>>>> >by >>>>> >doing; as such, I'm interested in making a circuit do what I want without >>>>> >regards to a BOM - especially in regards to performance. In other words, >>>>> >I >>>>> >like "best" rather than "cheapest" or "easiest." >>>>> > >>>>> >Currently I'm working on a LCR meter for personal use with better than >>>>> >.1% >>>>> >accuracy (closer to .02% if possible) for all functions. Also, all >>>>> >calibration will be internal and automatic; I have quite a few of >>>>> >Vishay's >>>>> >S102C series resistors (.01%, 2ppm) so I have a ready internal reference >>>>> >to >>>>> >use, keeping all measurements ratiometric if possible, and use resistance >>>>> >as >>>>> >the "known" in all equations. >>>>> > >>>>> >I'm measuring capacitance using constant-current charge time, so I >>>>> >already >>>>> >will know the capacitance >>>>> >>>>> Are you not deluding yourself that you know "constant-current" to 0.1% >>>>> accuracy? >>>> >>>>Probably so - hence my request for suggestions. I suppose that I should >>>>have emphasized that this is not only something that I do for enjoyment, but >>>>to _learn_. As such, I would welcome feedback on not only that I *am* going >>>>wrong, but *how* as well. >>>> >>>> >>> >>>You don't really need an accurate current source, just a fairly stable >>>one. Dump the current into a reference resistor (you need one of those >>>anyhow) and measure it, then use the same current on your cap. >>> >>[snip] >> >>Larkin misses the Early-effect/channel-length-modulation errors as the >>voltage changes. >> >> ...Jim Thompson > >That is a real issue with better and best grade caps, i would be more >worried about the measurement problems created by dielectrics with >serious voltage non-linearities like Z5U. Why ?:-) Can a Z5U stay within even 1% for a few seconds when left alone? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Spice is like a sports car... Performance only as good as the person behind the wheel.
From: Grant on 3 Aug 2010 17:46 On Tue, 03 Aug 2010 07:42:46 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Mon, 02 Aug 2010 21:04:49 -0700, >"JosephKK"<quiettechblue(a)yahoo.com> wrote: > .... >>That is a real issue with better and best grade caps, i would be more >>worried about the measurement problems created by dielectrics with >>serious voltage non-linearities like Z5U. > >Why ?:-) > >Can a Z5U stay within even 1% for a few seconds when left alone? That's the crazy cap that traps charge so 'well' you got to heat them up to release it? Grant.
From: JosephKK on 4 Aug 2010 03:02 On Mon, 02 Aug 2010 17:17:13 +1000, Grant <omg(a)grrr.id.au> wrote: >On Sun, 01 Aug 2010 23:35:21 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: > >>On Fri, 30 Jul 2010 07:28:22 -0700 (PDT), john1987 >><conphiloso(a)hotmail.com> wrote: >> >>>Hi, >>> >>>The accuracy requirements are as follows >>> >>>1. The frequency of the sine wave is 100 kHz. +/- 3us >>>2 The amplitude is 2 volts peak to peak, it should be accurately >>>measured at +/- 1.9 volts. >>>Its not a home work. :) >>> >>> >>>Thanks >>> >>>John >>> >>+/- 3 uS out of 5 uS (for a half cycle) is pretty sloppy. A constant >>delay filter of 100 nS and a comparator will yeild much better >>results. >> >> |\ >> signal --------+------------------|+\ >> | | \ >> | | \ >> | | >--------- out >> | | / >> + (| 100 nS)------|- / >> | / >> |/ >> >>Bias etc., ommited. >> >>Somewhat subject to high frequency noise and amplitude wobble. >>Typically withing a few degrees. > >Forgive me being pedantic, but do you want little 's' for seconds above, >rather than big 'S' for Siemens(sp?) (which I never did quite figure out, >umho or something warpedly related to ohms?) > >Grant. Cause i thought it would be clearer to OP in this case (without buggering up things with pros too much).
From: JosephKK on 4 Aug 2010 03:29 On Tue, 03 Aug 2010 18:38:49 +1000, Grant <omg(a)grrr.id.au> wrote: >On Mon, 02 Aug 2010 20:59:47 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: > >>On Mon, 02 Aug 2010 11:10:41 +1000, Grant <omg(a)grrr.id.au> wrote: >> >>>On Sun, 01 Aug 2010 09:17:59 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >>> >>>>On Sun, 1 Aug 2010 16:00:54 GMT, hal(a)nospam.com wrote: >>>> >>>>> >>>>>On 1-Aug-2010, Jim Thompson >>>>><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >>>... >>>>>> Are you not deluding yourself that you know "constant-current" to 0.1% >>>>>> accuracy? >>>>> >>>>>Probably so - hence my request for suggestions. I suppose that I should >>>>>have emphasized that this is not only something that I do for enjoyment, but >>>>>to _learn_. As such, I would welcome feedback on not only that I *am* going >>>>>wrong, but *how* as well. >>>> >>>>Yep. A welcome change in SED direction. >>>> >>>>Pondering that, it's going to be tricky to make a loop-stabilized >>>>current source that tracks a slewing capacitor's change in voltage >>>>(Early-effect or channel-length modulation). >>> >>>Wish my memory or filing system was better, there's a circuit I saw >>>that used an opamp to supply fixed voltage offset to an RC to get >>>linear cap charging. It's related to capacitor multiplier circuits >>>and ramp generators. >>> >>>Constant voltage across resistor == constant current into cap over >>>the working range of the opamps. >>> >>>But I can't find the thing, does it ring a bell? >>> >>>Grant. >> >>Actually it sounds kind of like a varaition of a Phantastron. > >And that don't ring a bell, you having a lend of me? :) Too many, too easy to find with a search. And too many could be clearer than mine. IIRC is agressively used some imperfections in pentodes to fight / semi-cancel other imperfections. > >One day I'll put these .pdfs into some mind-mapping thingy so I can find >the stuff again. Sometimes I'll spend hours going through circuits for >ideas, concepts. App notes, data sheets, and so on. But the recall is >a bit scrambled these days, too much information. > >Grant.
From: JosephKK on 4 Aug 2010 03:40
On Tue, 03 Aug 2010 07:42:46 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Mon, 02 Aug 2010 21:04:49 -0700, >"JosephKK"<quiettechblue(a)yahoo.com> wrote: > >>On Sun, 01 Aug 2010 10:19:51 -0700, Jim Thompson >><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >> >>>On Sun, 01 Aug 2010 10:06:49 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>On Sun, 1 Aug 2010 16:00:54 GMT, hal(a)nospam.com wrote: >>>> >>>>> >>>>>On 1-Aug-2010, Jim Thompson >>>>><To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >>>>> >>>>>> On Sun, 1 Aug 2010 15:29:19 GMT, hal(a)nospam.com wrote: >>>>>> >>>>>> >Hello all, >>>>>> > >>>>>> >I've been following this thread and it has brought up some issues I'm >>>>>> >currently working on. First of all, I'm a hobbyist that likes to learn >>>>>> >by >>>>>> >doing; as such, I'm interested in making a circuit do what I want without >>>>>> >regards to a BOM - especially in regards to performance. In other words, >>>>>> >I >>>>>> >like "best" rather than "cheapest" or "easiest." >>>>>> > >>>>>> >Currently I'm working on a LCR meter for personal use with better than >>>>>> >.1% >>>>>> >accuracy (closer to .02% if possible) for all functions. Also, all >>>>>> >calibration will be internal and automatic; I have quite a few of >>>>>> >Vishay's >>>>>> >S102C series resistors (.01%, 2ppm) so I have a ready internal reference >>>>>> >to >>>>>> >use, keeping all measurements ratiometric if possible, and use resistance >>>>>> >as >>>>>> >the "known" in all equations. >>>>>> > >>>>>> >I'm measuring capacitance using constant-current charge time, so I >>>>>> >already >>>>>> >will know the capacitance >>>>>> >>>>>> Are you not deluding yourself that you know "constant-current" to 0.1% >>>>>> accuracy? >>>>> >>>>>Probably so - hence my request for suggestions. I suppose that I should >>>>>have emphasized that this is not only something that I do for enjoyment, but >>>>>to _learn_. As such, I would welcome feedback on not only that I *am* going >>>>>wrong, but *how* as well. >>>>> >>>>> >>>> >>>>You don't really need an accurate current source, just a fairly stable >>>>one. Dump the current into a reference resistor (you need one of those >>>>anyhow) and measure it, then use the same current on your cap. >>>> >>>[snip] >>> >>>Larkin misses the Early-effect/channel-length-modulation errors as the >>>voltage changes. >>> >>> ...Jim Thompson >> >>That is a real issue with better and best grade caps, i would be more >>worried about the measurement problems created by dielectrics with >>serious voltage non-linearities like Z5U. > >Why ?:-) > >Can a Z5U stay within even 1% for a few seconds when left alone? > > ...Jim Thompson Not when you put a voltage ramp to it. OPs measurement method. It goes very squirrely by 20% of rated voltage. Time required to get outside 1% is sub-microsecond. I would not trust them to stay within 1% on any paramater for one millisecond in real use. Doesn't mean they can't be useful. |