Charge Conservation - Hint of the Day
in [Design]
|
From: John Larkin on 22 Jul 2010 10:16 On Thu, 22 Jul 2010 07:02:10 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >On Jul 21, 11:12�pm, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Wed, 21 Jul 2010 18:41:50 -0700 (PDT), George Herold >> >> >> >> >> >> <gher...(a)teachspin.com> wrote: >> >On Jul 21, 12:52�pm, John Larkin >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >> On Wed, 21 Jul 2010 07:28:10 -0700 (PDT), George Herold >> >> >> <gher...(a)teachspin.com> wrote: >> >> >On Jul 20, 8:32�pm, Tim Wescott <t...(a)seemywebsite.com> wrote: >> >> >> On 07/20/2010 09:32 AM, Jim Thompson wrote: >> >> >> >> > On Tue, 20 Jul 2010 08:53:22 -0700, Tim Wescott<t...(a)seemywebsite.com> >> >> >> > wrote: >> >> >> >> >> On 07/20/2010 08:24 AM, Jim Thompson wrote: >> >> >> >>> Charge Conservation - Hint of the Day: >> >> >> >> >>> How many Coulombs can a 1mH inductor charged to 1A deliver? >> >> >> >> >> That's insufficient information, and I rather expect that you know it. >> >> >> >> > No. �It's provided to cause young bucks to do some thinking. �Looks >> >> >> > like it didn't work with you :-( >> >> >> >> > (Except that it did annoy Larkin, yet again... so a partial success >> >> >> > :-) >> >> >> >> Since you didn't answer I have to assume that you couldn't. >> >> >> >> Either this is a trick question, and the answer is "however many excess >> >> >> electrons it has sitting on it when I hand it to you", or the answer is >> >> >> "that depends on the coil resistance". >> >> >> >> A 1mH superconducting inductor with 1A will deliver (or flow, if you >> >> >> want to quibble about the common EE definition of "deliver") an infinite >> >> >> charge to a dead short, assuming all conductors are also zero resistance. >> >> >> >> Otherwise a 1mH inductor that sees R ohms of total circuit resistance in >> >> >> the inductor and the load (charge target?) will see it's current decay >> >> >> as (1A)*e^-(R/L)*t; this will integrate to (1A) * (L/R). �So for 1 ohm >> >> >> total resistance that'd be 1mC, for a 10 ohm total resistance that'd be >> >> >> 100uC, for a 0.1 ohm total resistance it'd be 10mC, etc. >> >> >> >> Answers involving loads that aren't purely resistive are more >> >> >> complicated, but still obvious if you can understand the above. >> >> >> >> But to answer how much charge that 1mH inductor _can possibly_ deliver >> >> >> when it has 1A flowing through it depends on the particular inductor's >> >> >> winding resistance and possibly also on whether it's really a 1mH >> >> >> inductor when it has 1A flowing through it. >> >> >> >> You may want to pop over to the closest ASU campus that presents EEE 202 >> >> >> and see if you can audit the course. �This problem is no great mystery >> >> >> for someone who's gotten through sophomore electronics engineering. >> >> >> >> -- >> >> >> >> Tim Wescott >> >> >> Wescott Design Serviceshttp://www.wescottdesign.com >> >> >> >> Do you need to implement control loops in software? >> >> >> "Applied Control Theory for Embedded Systems" was written for you. >> >> >> See details athttp://www.wescottdesign.com/actfes/actfes.html >> >> >> >Hi Tim, �I agree with your calculation. �But not the interpretation. >> >> >Sure you integrate current over time and you get charge. �But this is >> >> >not the charge delivered to a resistor, it is how much charge flowed >> >> >through it. (Oh unless that's what is meant by delivered.) >> >> >> >George H. >> >> >> That's a common way of stating it. When we put parts on boards, their >> >> electrostatic potential is not often of concern. So we say that we put >> >> charge into a capacitor or a battery, literally we say "charge a >> >> battery" or "charge a capacitor" as opposed to "run charge through a >> >> capacitor", and we measure how much in ampere-seconds, namely >> >> coulombs. >> >> >> Since both a cap and a battery save the ampere-seconds and can >> >> return/deliver them later, it's reasonable to think that they stored >> >> charge. >> >> >> The numbers work. Engineering is about what works. >> >> >> John- Hide quoted text - >> >> >> - Show quoted text - >> >> >Yeah sure, I use the same words. �But isn't this the cause of the >> >current .... 'confusion'? >> >> >NPI >> >> >It's kinda like the water in a hose analogy of current in circuits. >> >It mostly works... but you can't spray charge out the end of a >> >circuit, you've gotta have a conductor attached. �(let's assume no >> >high voltages.) >> >> >We really only measure voltages and currents, we all know there are >> >charges moving around, but as soon as you try and get them to hold >> >still they disappear. �(Well you can use a Faraday bucket.) >> >> >I've been looking at flux leakage with our Keithley 601B >> >electrometer. �At the 10^11 ohms scale (with the multiplier set at X10 >> >or X30) I can't walk near the circuit with out upsetting things. >> >> >George H. >> >> I have a 610C >> >> ftp://jjlarkin.lmi.net/Keithley_1gig.JPG >> >> On the 1e-14 amp range, with just an open Pomona plug as an antenna, I >> can shuffle my feet on the carpet 10 feet away and pin the meter. >> >> Beautiful gadget. >> >> John- Hide quoted text - >> >> - Show quoted text - > >Opps, the number is 610B. (I'm always getting the numbers confused.) >I've only got a 1 Gohm resistor to check the 'calibration' with. But >it seems to work great. I'll post a flux report over on SEB. (bottom >line, all rosin based fluxes seem to work fine for high impedance >circuits. ) > >George H. The Keithley manual says to replace the high-value resistors every *six months*. I got mine off ebay and I bet it's been a while. It looks to me like my high-end ohms measurements are a bit high; a 1T resistor, which is probably OK, reads about 1.4T. Some day I may replace a few resistors with more modern parts which, I hope, will drift less. Roger rosin flux. On some of our impedance-sensitive boards, we specify rosin flux paste solder and organic solvent wash. We do that in-house, but if we send stuff for assembly out it's hard to find anybody who hasn't gone all water-based. John
From: George Herold on 22 Jul 2010 16:13 On Jul 22, 10:16 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Thu, 22 Jul 2010 07:02:10 -0700 (PDT), George Herold > > > > > > <gher...(a)teachspin.com> wrote: > >On Jul 21, 11:12 pm, John Larkin > ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> On Wed, 21 Jul 2010 18:41:50 -0700 (PDT), George Herold > > >> <gher...(a)teachspin.com> wrote: > >> >On Jul 21, 12:52 pm, John Larkin > >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> >> On Wed, 21 Jul 2010 07:28:10 -0700 (PDT), George Herold > > >> >> <gher...(a)teachspin.com> wrote: > >> >> >On Jul 20, 8:32 pm, Tim Wescott <t...(a)seemywebsite.com> wrote: > >> >> >> On 07/20/2010 09:32 AM, Jim Thompson wrote: > > >> >> >> > On Tue, 20 Jul 2010 08:53:22 -0700, Tim Wescott<t...(a)seemywebsite.com> > >> >> >> > wrote: > > >> >> >> >> On 07/20/2010 08:24 AM, Jim Thompson wrote: > >> >> >> >>> Charge Conservation - Hint of the Day: > > >> >> >> >>> How many Coulombs can a 1mH inductor charged to 1A deliver? > > >> >> >> >> That's insufficient information, and I rather expect that you know it. > > >> >> >> > No. It's provided to cause young bucks to do some thinking. Looks > >> >> >> > like it didn't work with you :-( > > >> >> >> > (Except that it did annoy Larkin, yet again... so a partial success > >> >> >> > :-) > > >> >> >> Since you didn't answer I have to assume that you couldn't. > > >> >> >> Either this is a trick question, and the answer is "however many excess > >> >> >> electrons it has sitting on it when I hand it to you", or the answer is > >> >> >> "that depends on the coil resistance". > > >> >> >> A 1mH superconducting inductor with 1A will deliver (or flow, if you > >> >> >> want to quibble about the common EE definition of "deliver") an infinite > >> >> >> charge to a dead short, assuming all conductors are also zero resistance. > > >> >> >> Otherwise a 1mH inductor that sees R ohms of total circuit resistance in > >> >> >> the inductor and the load (charge target?) will see it's current decay > >> >> >> as (1A)*e^-(R/L)*t; this will integrate to (1A) * (L/R). So for 1 ohm > >> >> >> total resistance that'd be 1mC, for a 10 ohm total resistance that'd be > >> >> >> 100uC, for a 0.1 ohm total resistance it'd be 10mC, etc. > > >> >> >> Answers involving loads that aren't purely resistive are more > >> >> >> complicated, but still obvious if you can understand the above. > > >> >> >> But to answer how much charge that 1mH inductor _can possibly_ deliver > >> >> >> when it has 1A flowing through it depends on the particular inductor's > >> >> >> winding resistance and possibly also on whether it's really a 1mH > >> >> >> inductor when it has 1A flowing through it. > > >> >> >> You may want to pop over to the closest ASU campus that presents EEE 202 > >> >> >> and see if you can audit the course. This problem is no great mystery > >> >> >> for someone who's gotten through sophomore electronics engineering. > > >> >> >> -- > > >> >> >> Tim Wescott > >> >> >> Wescott Design Serviceshttp://www.wescottdesign.com > > >> >> >> Do you need to implement control loops in software? > >> >> >> "Applied Control Theory for Embedded Systems" was written for you. > >> >> >> See details athttp://www.wescottdesign.com/actfes/actfes.html > > >> >> >Hi Tim, I agree with your calculation. But not the interpretation. > >> >> >Sure you integrate current over time and you get charge. But this is > >> >> >not the charge delivered to a resistor, it is how much charge flowed > >> >> >through it. (Oh unless that's what is meant by delivered.) > > >> >> >George H. > > >> >> That's a common way of stating it. When we put parts on boards, their > >> >> electrostatic potential is not often of concern. So we say that we put > >> >> charge into a capacitor or a battery, literally we say "charge a > >> >> battery" or "charge a capacitor" as opposed to "run charge through a > >> >> capacitor", and we measure how much in ampere-seconds, namely > >> >> coulombs. > > >> >> Since both a cap and a battery save the ampere-seconds and can > >> >> return/deliver them later, it's reasonable to think that they stored > >> >> charge. > > >> >> The numbers work. Engineering is about what works. > > >> >> John- Hide quoted text - > > >> >> - Show quoted text - > > >> >Yeah sure, I use the same words. But isn't this the cause of the > >> >current .... 'confusion'? > > >> >NPI > > >> >It's kinda like the water in a hose analogy of current in circuits. > >> >It mostly works... but you can't spray charge out the end of a > >> >circuit, you've gotta have a conductor attached. (let's assume no > >> >high voltages.) > > >> >We really only measure voltages and currents, we all know there are > >> >charges moving around, but as soon as you try and get them to hold > >> >still they disappear. (Well you can use a Faraday bucket.) > > >> >I've been looking at flux leakage with our Keithley 601B > >> >electrometer. At the 10^11 ohms scale (with the multiplier set at X10 > >> >or X30) I can't walk near the circuit with out upsetting things. > > >> >George H. > > >> I have a 610C > > >>ftp://jjlarkin.lmi.net/Keithley_1gig.JPG > > >> On the 1e-14 amp range, with just an open Pomona plug as an antenna, I > >> can shuffle my feet on the carpet 10 feet away and pin the meter. > > >> Beautiful gadget. > > >> John- Hide quoted text - > > >> - Show quoted text - > > >Opps, the number is 610B. (I'm always getting the numbers confused.) > >I've only got a 1 Gohm resistor to check the 'calibration' with. But > >it seems to work great. I'll post a flux report over on SEB. (bottom > >line, all rosin based fluxes seem to work fine for high impedance > >circuits. ) > > >George H. > > The Keithley manual says to replace the high-value resistors every > *six months*. I got mine off ebay and I bet it's been a while. It > looks to me like my high-end ohms measurements are a bit high; a 1T > resistor, which is probably OK, reads about 1.4T. Some day I may > replace a few resistors with more modern parts which, I hope, will > drift less. > > Roger rosin flux. On some of our impedance-sensitive boards, we > specify rosin flux paste solder and organic solvent wash. We do that > in-house, but if we send stuff for assembly out it's hard to find > anybody who hasn't gone all water-based. > > John- Hide quoted text - > > - Show quoted text - Ahh, the resistors in this thing are as old as the hills. It's been sitting on a shelf collecting dust for at least eight years. Back in 2002 the boss was trying to do some field emmision measurments, but we couldn't get a good enough vacuum. The 10^9 ohm scale looks good, but 10^10 is high by ~10% and 10^11 is high by maybe 30%. This is with the meter multiplier in the x0.1 position, with 1 G ohm across the input. The end of the meter needle is oscillating like crazy.. maybe +/- 5%. I must be seeing electric fields in the room... 60Hz AC maybe? George H.
From: Grant on 22 Jul 2010 18:19 On Thu, 22 Jul 2010 07:02:10 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >On Jul 21, 11:12 pm, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Wed, 21 Jul 2010 18:41:50 -0700 (PDT), George Herold >> >> >> >> >> >> <gher...(a)teachspin.com> wrote: >> >On Jul 21, 12:52 pm, John Larkin >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >> On Wed, 21 Jul 2010 07:28:10 -0700 (PDT), George Herold >> >> >> <gher...(a)teachspin.com> wrote: >> >> >On Jul 20, 8:32 pm, Tim Wescott <t...(a)seemywebsite.com> wrote: >> >> >> On 07/20/2010 09:32 AM, Jim Thompson wrote: >> >> >> >> > On Tue, 20 Jul 2010 08:53:22 -0700, Tim Wescott<t...(a)seemywebsite.com> >> >> >> > wrote: >> >> >> >> >> On 07/20/2010 08:24 AM, Jim Thompson wrote: >> >> >> >>> Charge Conservation - Hint of the Day: >> >> >> >> >>> How many Coulombs can a 1mH inductor charged to 1A deliver? >> >> >> >> >> That's insufficient information, and I rather expect that you know it. >> >> >> >> > No. It's provided to cause young bucks to do some thinking. Looks >> >> >> > like it didn't work with you :-( >> >> >> >> > (Except that it did annoy Larkin, yet again... so a partial success >> >> >> > :-) >> >> >> >> Since you didn't answer I have to assume that you couldn't. >> >> >> >> Either this is a trick question, and the answer is "however many excess >> >> >> electrons it has sitting on it when I hand it to you", or the answer is >> >> >> "that depends on the coil resistance". >> >> >> >> A 1mH superconducting inductor with 1A will deliver (or flow, if you >> >> >> want to quibble about the common EE definition of "deliver") an infinite >> >> >> charge to a dead short, assuming all conductors are also zero resistance. >> >> >> >> Otherwise a 1mH inductor that sees R ohms of total circuit resistance in >> >> >> the inductor and the load (charge target?) will see it's current decay >> >> >> as (1A)*e^-(R/L)*t; this will integrate to (1A) * (L/R). So for 1 ohm >> >> >> total resistance that'd be 1mC, for a 10 ohm total resistance that'd be >> >> >> 100uC, for a 0.1 ohm total resistance it'd be 10mC, etc. >> >> >> >> Answers involving loads that aren't purely resistive are more >> >> >> complicated, but still obvious if you can understand the above. >> >> >> >> But to answer how much charge that 1mH inductor _can possibly_ deliver >> >> >> when it has 1A flowing through it depends on the particular inductor's >> >> >> winding resistance and possibly also on whether it's really a 1mH >> >> >> inductor when it has 1A flowing through it. >> >> >> >> You may want to pop over to the closest ASU campus that presents EEE 202 >> >> >> and see if you can audit the course. This problem is no great mystery >> >> >> for someone who's gotten through sophomore electronics engineering. >> >> >> >> -- >> >> >> >> Tim Wescott >> >> >> Wescott Design Serviceshttp://www.wescottdesign.com >> >> >> >> Do you need to implement control loops in software? >> >> >> "Applied Control Theory for Embedded Systems" was written for you. >> >> >> See details athttp://www.wescottdesign.com/actfes/actfes.html >> >> >> >Hi Tim, I agree with your calculation. But not the interpretation. >> >> >Sure you integrate current over time and you get charge. But this is >> >> >not the charge delivered to a resistor, it is how much charge flowed >> >> >through it. (Oh unless that's what is meant by delivered.) >> >> >> >George H. >> >> >> That's a common way of stating it. When we put parts on boards, their >> >> electrostatic potential is not often of concern. So we say that we put >> >> charge into a capacitor or a battery, literally we say "charge a >> >> battery" or "charge a capacitor" as opposed to "run charge through a >> >> capacitor", and we measure how much in ampere-seconds, namely >> >> coulombs. >> >> >> Since both a cap and a battery save the ampere-seconds and can >> >> return/deliver them later, it's reasonable to think that they stored >> >> charge. >> >> >> The numbers work. Engineering is about what works. >> >> >> John- Hide quoted text - >> >> >> - Show quoted text - >> >> >Yeah sure, I use the same words. But isn't this the cause of the >> >current .... 'confusion'? >> >> >NPI >> >> >It's kinda like the water in a hose analogy of current in circuits. >> >It mostly works... but you can't spray charge out the end of a >> >circuit, you've gotta have a conductor attached. (let's assume no >> >high voltages.) >> >> >We really only measure voltages and currents, we all know there are >> >charges moving around, but as soon as you try and get them to hold >> >still they disappear. (Well you can use a Faraday bucket.) >> >> >I've been looking at flux leakage with our Keithley 601B >> >electrometer. At the 10^11 ohms scale (with the multiplier set at X10 >> >or X30) I can't walk near the circuit with out upsetting things. >> >> >George H. >> >> I have a 610C >> >> ftp://jjlarkin.lmi.net/Keithley_1gig.JPG >> >> On the 1e-14 amp range, with just an open Pomona plug as an antenna, I >> can shuffle my feet on the carpet 10 feet away and pin the meter. >> >> Beautiful gadget. >> >> John- Hide quoted text - >> >> - Show quoted text - > >Opps, the number is 610B. (I'm always getting the numbers confused.) >I've only got a 1 Gohm resistor to check the 'calibration' with. But >it seems to work great. I'll post a flux report over on SEB. (bottom >line, all rosin based fluxes seem to work fine for high impedance >circuits. ) > >George H. Is there a proviso: uncooked rosin? Dark overheated rosin looks leaky to me, imagining a high carbon content. Grant.
From: JosephKK on 22 Jul 2010 22:30 On Tue, 20 Jul 2010 18:42:29 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Tue, 20 Jul 2010 17:32:12 -0700, Tim Wescott <tim(a)seemywebsite.com> >wrote: > >>On 07/20/2010 09:32 AM, Jim Thompson wrote: >>> On Tue, 20 Jul 2010 08:53:22 -0700, Tim Wescott<tim(a)seemywebsite.com> >>> wrote: >>> >>>> On 07/20/2010 08:24 AM, Jim Thompson wrote: >>>>> Charge Conservation - Hint of the Day: >>>>> >>>>> How many Coulombs can a 1mH inductor charged to 1A deliver? >>>> >>>> That's insufficient information, and I rather expect that you know it. >>> >>> No. It's provided to cause young bucks to do some thinking. Looks >>> like it didn't work with you :-( >>> >>> (Except that it did annoy Larkin, yet again... so a partial success >>> :-) >> >>Since you didn't answer I have to assume that you couldn't. >> >>Either this is a trick question, and the answer is "however many excess >>electrons it has sitting on it when I hand it to you", or the answer is >>"that depends on the coil resistance". >> >>A 1mH superconducting inductor with 1A will deliver (or flow, if you >>want to quibble about the common EE definition of "deliver") an infinite >>charge to a dead short, assuming all conductors are also zero resistance. >> >>Otherwise a 1mH inductor that sees R ohms of total circuit resistance in >>the inductor and the load (charge target?) will see it's current decay >>as (1A)*e^-(R/L)*t; this will integrate to (1A) * (L/R). So for 1 ohm >>total resistance that'd be 1mC, for a 10 ohm total resistance that'd be >>100uC, for a 0.1 ohm total resistance it'd be 10mC, etc. > >Dumping that inductor into 1 ohm makes the exact same waveform across >the resistor as if you discharged a 1 millifarad cap charged to 1 >volt. Ditto 0.001 coulombs. Nice crosscheck. > >John > How about that, a sensible answer for one case. Let us see what you can do if you try to generalize it.
From: George Herold on 23 Jul 2010 09:29
On Jul 22, 6:19 pm, Grant <o...(a)grrr.id.au> wrote: > On Thu, 22 Jul 2010 07:02:10 -0700 (PDT), George Herold <gher...(a)teachspin.com> wrote: > >On Jul 21, 11:12 pm, John Larkin > ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> On Wed, 21 Jul 2010 18:41:50 -0700 (PDT), George Herold > > >> <gher...(a)teachspin.com> wrote: > >> >On Jul 21, 12:52 pm, John Larkin > >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> >> On Wed, 21 Jul 2010 07:28:10 -0700 (PDT), George Herold > > >> >> <gher...(a)teachspin.com> wrote: > >> >> >On Jul 20, 8:32 pm, Tim Wescott <t...(a)seemywebsite.com> wrote: > >> >> >> On 07/20/2010 09:32 AM, Jim Thompson wrote: > > >> >> >> > On Tue, 20 Jul 2010 08:53:22 -0700, Tim Wescott<t...(a)seemywebsite.com> > >> >> >> > wrote: > > >> >> >> >> On 07/20/2010 08:24 AM, Jim Thompson wrote: > >> >> >> >>> Charge Conservation - Hint of the Day: > > >> >> >> >>> How many Coulombs can a 1mH inductor charged to 1A deliver? > > >> >> >> >> That's insufficient information, and I rather expect that you know it. > > >> >> >> > No. It's provided to cause young bucks to do some thinking. Looks > >> >> >> > like it didn't work with you :-( > > >> >> >> > (Except that it did annoy Larkin, yet again... so a partial success > >> >> >> > :-) > > >> >> >> Since you didn't answer I have to assume that you couldn't. > > >> >> >> Either this is a trick question, and the answer is "however many excess > >> >> >> electrons it has sitting on it when I hand it to you", or the answer is > >> >> >> "that depends on the coil resistance". > > >> >> >> A 1mH superconducting inductor with 1A will deliver (or flow, if you > >> >> >> want to quibble about the common EE definition of "deliver") an infinite > >> >> >> charge to a dead short, assuming all conductors are also zero resistance. > > >> >> >> Otherwise a 1mH inductor that sees R ohms of total circuit resistance in > >> >> >> the inductor and the load (charge target?) will see it's current decay > >> >> >> as (1A)*e^-(R/L)*t; this will integrate to (1A) * (L/R). So for 1 ohm > >> >> >> total resistance that'd be 1mC, for a 10 ohm total resistance that'd be > >> >> >> 100uC, for a 0.1 ohm total resistance it'd be 10mC, etc. > > >> >> >> Answers involving loads that aren't purely resistive are more > >> >> >> complicated, but still obvious if you can understand the above. > > >> >> >> But to answer how much charge that 1mH inductor _can possibly_ deliver > >> >> >> when it has 1A flowing through it depends on the particular inductor's > >> >> >> winding resistance and possibly also on whether it's really a 1mH > >> >> >> inductor when it has 1A flowing through it. > > >> >> >> You may want to pop over to the closest ASU campus that presents EEE 202 > >> >> >> and see if you can audit the course. This problem is no great mystery > >> >> >> for someone who's gotten through sophomore electronics engineering. > > >> >> >> -- > > >> >> >> Tim Wescott > >> >> >> Wescott Design Serviceshttp://www.wescottdesign.com > > >> >> >> Do you need to implement control loops in software? > >> >> >> "Applied Control Theory for Embedded Systems" was written for you. > >> >> >> See details athttp://www.wescottdesign.com/actfes/actfes.html > > >> >> >Hi Tim, I agree with your calculation. But not the interpretation. > >> >> >Sure you integrate current over time and you get charge. But this is > >> >> >not the charge delivered to a resistor, it is how much charge flowed > >> >> >through it. (Oh unless that's what is meant by delivered.) > > >> >> >George H. > > >> >> That's a common way of stating it. When we put parts on boards, their > >> >> electrostatic potential is not often of concern. So we say that we put > >> >> charge into a capacitor or a battery, literally we say "charge a > >> >> battery" or "charge a capacitor" as opposed to "run charge through a > >> >> capacitor", and we measure how much in ampere-seconds, namely > >> >> coulombs. > > >> >> Since both a cap and a battery save the ampere-seconds and can > >> >> return/deliver them later, it's reasonable to think that they stored > >> >> charge. > > >> >> The numbers work. Engineering is about what works. > > >> >> John- Hide quoted text - > > >> >> - Show quoted text - > > >> >Yeah sure, I use the same words. But isn't this the cause of the > >> >current .... 'confusion'? > > >> >NPI > > >> >It's kinda like the water in a hose analogy of current in circuits. > >> >It mostly works... but you can't spray charge out the end of a > >> >circuit, you've gotta have a conductor attached. (let's assume no > >> >high voltages.) > > >> >We really only measure voltages and currents, we all know there are > >> >charges moving around, but as soon as you try and get them to hold > >> >still they disappear. (Well you can use a Faraday bucket.) > > >> >I've been looking at flux leakage with our Keithley 601B > >> >electrometer. At the 10^11 ohms scale (with the multiplier set at X10 > >> >or X30) I can't walk near the circuit with out upsetting things. > > >> >George H. > > >> I have a 610C > > >>ftp://jjlarkin.lmi.net/Keithley_1gig.JPG > > >> On the 1e-14 amp range, with just an open Pomona plug as an antenna, I > >> can shuffle my feet on the carpet 10 feet away and pin the meter. > > >> Beautiful gadget. > > >> John- Hide quoted text - > > >> - Show quoted text - > > >Opps, the number is 610B. (I'm always getting the numbers confused.) > >I've only got a 1 Gohm resistor to check the 'calibration' with. But > >it seems to work great. I'll post a flux report over on SEB. (bottom > >line, all rosin based fluxes seem to work fine for high impedance > >circuits. ) > > >George H. > > Is there a proviso: uncooked rosin? Dark overheated rosin looks > leaky to me, imagining a high carbon content. > > Grant.- Hide quoted text - > > - Show quoted text - I heard that before... about burnt rosin. Maybe I'll get out the big soldering gun and burn some.... George |