Hi Stuart,
Hi Charles,
Hi DF96,
Now, what I have said still contains simplifications. But getting right into things Seebeck is a bit OT here. It's just the general point that is important. Dissimilar metals in contact may result in small voltages being generated. These are not capable of large currents at normal wire sizes. I've never made a huge connection to see if I could melt a Loonie (Canadian coin) or anything like that.
-Chris
Well, yes. That was what I was trying to get at. I guess I may not be too clear about my meaning sometimes.
Absolutely! That I won't argue against. My point was that if a nerve did fire in response to a photon strike, it's signal would be lost in among random nerve signals. The brain would very probably ignore one impulse as a means of filtering information.
Hi Charles,
That's really cool stuff. Thanks for posting it!
Hi DF96,
Yes, I didn't want to get into that. Temperature variations in the wire leading to a thermocouple junction can play havoc with a reading. Absolutely true.
The only way to connect the two dissimilar metals would be to spot weld (or similar) them together, or clamp them using an insulating material. Any other metal that becomes part of the junction will drastically alter the behaviour. You certainly cannot use solder unless one wire is ... well ... solder. This wouldn't be useful for high temperature measurements mind you. If welding occurs with another metal (like a normal stick or metallic rod made for welding), it becomes part of the mix and changes the characteristics. Nope, can't do that unless you use an isotherm block connection where you can change the wires to copper. It holds all connections at the same temperature. You also need a compensating junction where either a true 0°C (zero point) is maintained, or the local temperature is accurately measured and a correction is applied to your resulting measured voltage. After all, most everything we measure has a relationship with 0°K. Our zero point compensation simply makes things easier to relate to.
Now, what I have said still contains simplifications. But getting right into things Seebeck is a bit OT here. It's just the general point that is important. Dissimilar metals in contact may result in small voltages being generated. These are not capable of large currents at normal wire sizes. I've never made a huge connection to see if I could melt a Loonie (Canadian coin) or anything like that.
-Chris
Good to hear from you, Joshua. Of course, what you hear is what is, at least in your environment. I hear cable differences, Charles Hansen hears cable differences, both line cord and interconnect, etc, etc. Jack Bybee has made cables, both interconnect and line cord, and I heard differences with a 1/3 million dollar system. My former CTC business partner made line cords and interconnects, with a company called TG Audio, before he died. I heard the differences made with his cables, even before I worked with him, professionally.
There seems to be a group of individuals, citing some scientific training, who just don't BELIEVE what you and I hear, can be possible. AND they would demand some sort of test procedure that would MAKE SURE that these differences could not be heard. Why, you, Joshua, is specifically attacked about this seems to imply that they don't want to confront me directly. However, I can be equally 'criticized' for my opinions, and perhaps they will then confront my 'successes' as merely 'luck', 'bribes', or the foolishness of others. Rather than trusting my listening and experience to make better audio products '-)
There seems to be a group of individuals, citing some scientific training, who just don't BELIEVE what you and I hear, can be possible. AND they would demand some sort of test procedure that would MAKE SURE that these differences could not be heard. Why, you, Joshua, is specifically attacked about this seems to imply that they don't want to confront me directly. However, I can be equally 'criticized' for my opinions, and perhaps they will then confront my 'successes' as merely 'luck', 'bribes', or the foolishness of others. Rather than trusting my listening and experience to make better audio products '-)
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I asked you some specific questions. Evidently, you have no answer to those questions. By avoiding valid technical questions you go on the same way over and over again.
I never said my findings and observations are valid to anyone other than myself.
Yet, it may serve each and every audio enthusiast to use ones' own listening in evaluating sound quality of audio gear.
My listening findings are valid only for me. There is no argue about it.
Those who adhere to measurements only, may do themselves a service should they would try to validate, each for oneself, whether measurements alone give a full picture of the sound quality of audio gear, or not.
That being said, hearing audible differences between different power cords isn't something unique to me only. I know personally many other people who also hear such differences. Of course, different people will prefer different cords to their audio system. This is why my findings as to the preferred power cords are applicable to only. That there are audible difference between different power cords, it's a widely known phenomenon amongst many audio enthusiasts.
I don't expect anyone and I don't ask anyone to take my word about audible differences between different power cords. Only, it may serve those who wish to know the actual facts of the matter to do some listening tests themselves.
This reminds me of a situation I encountered recently.
The debate between subjectivists and objectivists isn't unique to the forums here. One can finds such debates in most forums dealing with audio and audio gear.
There was such a debate (one of many) in a local audio forum, in my country. As usual, some people claimed vehemently that audible differences between different power cords, none of which is faulty, are impossible, it makes no sense, it contradicts what they learned. So, I invited all the skeptics to my home, to hear for themselves. None of them came, yet they continue to argue that it isn't so, that it cannot be so.
This is but one example of some people who prefer to stick to their belief system, rather than try to find out the facts of the matter.
Again you speculate erroneously about what I'm able and what I'm unable.
It may serve you better should you ask me about it, instead of speculating.
This is so to your view only. The reality is that there are other people with a stand similar to mine.
Yet another erroneous speculation of yours.
You haven’t the faintest idea about my feelings.
So far I you didn't come up with a single fact to support your claims. All you said here, on this topic, apart from some erroneous speculations, are general statements without any reference to any fact. It looks like you are unable to validate your statements.
Hi John,
Those who know the facts of the matter, know the facts.
Some prefer arguing about it, rather than finding out for themselves.
See the true story I narrated in my above post.
Hi John,
Consider yourself, "confronted" then. No fear.
Honestly, are you trying to say that if you had a way to measure an audible imperfection, you wouldn't be right in there listening and measuring in attempts to improve your product? You would of course.
I hear changes and differences. I try to find out why they exist, and once I figure out what differences show up in a measurement, I am pleased that I can then quantify the effect. This is step one in figuring out how to minimize problems. After all, some days I am better at listening than others. Having a number to put on the observation allows me to go back after a period of time to the same issue and know whether I'm moving forward or backward.
After I do commit changes to a design, I have a number of people I can trust who will listen and let me know if I got it right ... or not.
All I'm doing, and several others out there, is making use of all the tools at my disposal. There is nothing wrong with that. However, a person who refuses to use tools that can help them is a fool. Given the equipment you have, and your references to the 7th harmonic (see, I listen / read / pay attention) shows you do the same.
Now, how to justify putting down those people who admit to using measurement equipment while you do the same. Remember, Walt Jung measures performance and so do the other people you hang with. What label to they get?
Now, why do I pay attention to Joshua now and again? Simple, he jumps in with both feet. It's too bad he often hasn't a leg to stand on with the claims he makes. He has requested that people teach him. Not a chance! We can point the way, but until he "mans up" and buys equipment suitable to support his claims, he's just noise.
I do love his point of view though. "Since I can't measure any differences with equipment at my disposal, these differences can not be measured." Well, that's true in his case, but he then goes on to apply that to everyone else. Right there, he has been silly in my book, because that logic is flawed - as you know yourself, John.
Of course, it doesn't help his case when you encourage him with this point of view. The worst part of this is that you yourself take pains to make as careful a measurement as you can. Help the man John. Even if it's off-line, be honest about the things that you have learned to measure as they relate to what you can hear.
Relating what can be heard to what can be measured is called learning, or education. To claim that what you hear can not be measured (by anyone) is the opposite of learning. It is quite okay to admit that you can not measure changes you are hearing, but at least be honest about it. Recognize that some people have the ability to detect performance differences that you can not. Sometimes it is only the difference in the equipment they use, and the environmental situation where noise is minimized. To claim anything else John is, I think, dishonest at some level.
-Chris 🙂
Consider yourself, "confronted" then. No fear.
Honestly, are you trying to say that if you had a way to measure an audible imperfection, you wouldn't be right in there listening and measuring in attempts to improve your product? You would of course.
I hear changes and differences. I try to find out why they exist, and once I figure out what differences show up in a measurement, I am pleased that I can then quantify the effect. This is step one in figuring out how to minimize problems. After all, some days I am better at listening than others. Having a number to put on the observation allows me to go back after a period of time to the same issue and know whether I'm moving forward or backward.
After I do commit changes to a design, I have a number of people I can trust who will listen and let me know if I got it right ... or not.
All I'm doing, and several others out there, is making use of all the tools at my disposal. There is nothing wrong with that. However, a person who refuses to use tools that can help them is a fool. Given the equipment you have, and your references to the 7th harmonic (see, I listen / read / pay attention) shows you do the same.
Now, how to justify putting down those people who admit to using measurement equipment while you do the same. Remember, Walt Jung measures performance and so do the other people you hang with. What label to they get?
Now, why do I pay attention to Joshua now and again? Simple, he jumps in with both feet. It's too bad he often hasn't a leg to stand on with the claims he makes. He has requested that people teach him. Not a chance! We can point the way, but until he "mans up" and buys equipment suitable to support his claims, he's just noise.
I do love his point of view though. "Since I can't measure any differences with equipment at my disposal, these differences can not be measured." Well, that's true in his case, but he then goes on to apply that to everyone else. Right there, he has been silly in my book, because that logic is flawed - as you know yourself, John.
Of course, it doesn't help his case when you encourage him with this point of view. The worst part of this is that you yourself take pains to make as careful a measurement as you can. Help the man John. Even if it's off-line, be honest about the things that you have learned to measure as they relate to what you can hear.
Relating what can be heard to what can be measured is called learning, or education. To claim that what you hear can not be measured (by anyone) is the opposite of learning. It is quite okay to admit that you can not measure changes you are hearing, but at least be honest about it. Recognize that some people have the ability to detect performance differences that you can not. Sometimes it is only the difference in the equipment they use, and the environmental situation where noise is minimized. To claim anything else John is, I think, dishonest at some level.
-Chris 🙂
I never said any such thing.
Once again you put in my mouth things I neither said, nor meant, nor hinted at.
You address me for things you only imagined I said, things I never said actually.
What are trying to achieve by distorting my words?
Oh, I am sure that many audible difference can be measured. Unfortunately, I don't know exactly how to, and neither does anyone else around here, it seems. We are probably measuring the WRONG thing rather than limited in our measurement level.
Some claim to find a direct correlation between their measurements and audible difference.
Only, they refuse to say what they measure and how it correlates to what audible differences.
Hi Joshua,
I'll admit to drawing conclusions about what you are probably observing from years of experience of being able to measure some of these things. You are not the only person who has made claims such as you do. It comes down to whether or not you wish to educate yourself further or not. For that, you will require some test equipment that is obviously better than what you are using. In the event you are surrounded with superior equipment compared to what I'm using, there are only three other conclusions.
1. The equipment doesn't work, or you have no power.
2. You don't know how to properly operate the equipment, or you don't know how to set up an experiment.
3. You are not being truthful.
That's the beauty of a science. For a known experiment, there is a known outcome and known experimental error.
Now, within the limitations I considered earlier, I will accept that you are unable to measure any differences between things you can hear that are different. However, I have also stated that you can not apply the "fact" the you can't measure changes to anyone else. Looking at this situation, this is exactly why you can not make any comment that is relevant to anyone else. So speaking about what you can hear and not hear, measure or not measure, becomes completely irrelevant to anyone else. It's just noise that pops up now and again to support what John says, or to disagree with someone else. When push comes to shove, you always retreat to a comment like "this is what I hear in my system, so it is true for me". In other words, you fully expect to have what you say fully accepted, even against measured performance the agrees with a listening test made by others. Of course, the expectation you have is not reasonable.
With your attitude, I am not going to waste time documenting anything for you. After all, you'll just come back with "I hear something else on my system, so I can't accept what you are saying". You see, I've invested heavily over the course of many years to become educated in the physics of electronics, the operation of test equipment and their limitations. I have also invested heavily in test equipment and time to perform test after test. You have not. Until you do, I don't think it's reasonable for you to disagree with anyone who has. Oh yes, one other thing. Most of us have invested huge amounts of time to listen to sound equipment carefully over many, many years. So you do not hold an advantage there either.
Now, given that you are bringing up the power cable thing as of late, allow me to report on what I have seen. In any case where a changed power cord makes any difference in audible performance, I have been able to see changes in the signal. To make this easier for you, all that needs to be done is to run a low distortion test signal (a sine wave, but you can use a cosine wave if you feel like being different) into the equipment, then notch out the signal using a THD meter or similar and feeding the monitor output from the THD meter into a good spectrum analyzer. The current popular USB connected 'Scope type instruments, or the inexpensive 'scopes or spectrum analyzers are probably not sensitive enough to show these changes. You really must confirm your test equipment is up to the job you're asking of it. If anyone is lucky enough to have a recent or current Audio Precision system, that should be enough. I'm not sure about a System One, but it's probably good enough as well.
If you want, I can give you a list of equipment I am using. It involves a lot of Hewlett Packard stuff.
-Chris
I'll admit to drawing conclusions about what you are probably observing from years of experience of being able to measure some of these things. You are not the only person who has made claims such as you do. It comes down to whether or not you wish to educate yourself further or not. For that, you will require some test equipment that is obviously better than what you are using. In the event you are surrounded with superior equipment compared to what I'm using, there are only three other conclusions.
1. The equipment doesn't work, or you have no power.
2. You don't know how to properly operate the equipment, or you don't know how to set up an experiment.
3. You are not being truthful.
That's the beauty of a science. For a known experiment, there is a known outcome and known experimental error.
Now, within the limitations I considered earlier, I will accept that you are unable to measure any differences between things you can hear that are different. However, I have also stated that you can not apply the "fact" the you can't measure changes to anyone else. Looking at this situation, this is exactly why you can not make any comment that is relevant to anyone else. So speaking about what you can hear and not hear, measure or not measure, becomes completely irrelevant to anyone else. It's just noise that pops up now and again to support what John says, or to disagree with someone else. When push comes to shove, you always retreat to a comment like "this is what I hear in my system, so it is true for me". In other words, you fully expect to have what you say fully accepted, even against measured performance the agrees with a listening test made by others. Of course, the expectation you have is not reasonable.
With your attitude, I am not going to waste time documenting anything for you. After all, you'll just come back with "I hear something else on my system, so I can't accept what you are saying". You see, I've invested heavily over the course of many years to become educated in the physics of electronics, the operation of test equipment and their limitations. I have also invested heavily in test equipment and time to perform test after test. You have not. Until you do, I don't think it's reasonable for you to disagree with anyone who has. Oh yes, one other thing. Most of us have invested huge amounts of time to listen to sound equipment carefully over many, many years. So you do not hold an advantage there either.
Now, given that you are bringing up the power cable thing as of late, allow me to report on what I have seen. In any case where a changed power cord makes any difference in audible performance, I have been able to see changes in the signal. To make this easier for you, all that needs to be done is to run a low distortion test signal (a sine wave, but you can use a cosine wave if you feel like being different) into the equipment, then notch out the signal using a THD meter or similar and feeding the monitor output from the THD meter into a good spectrum analyzer. The current popular USB connected 'Scope type instruments, or the inexpensive 'scopes or spectrum analyzers are probably not sensitive enough to show these changes. You really must confirm your test equipment is up to the job you're asking of it. If anyone is lucky enough to have a recent or current Audio Precision system, that should be enough. I'm not sure about a System One, but it's probably good enough as well.
If you want, I can give you a list of equipment I am using. It involves a lot of Hewlett Packard stuff.
-Chris
Give it a break.
John, I do not think you are being entirely honest about your last post. If so, you wasted good money on the test gear you have bought.
I know I am getting value with mine, and I am in no way an exceptional technician.
Okay, care to make a clear statement that explains how you see things?
Look at it this way Joshua, the very fact that anyone can hear (for real of course) a performance difference resulting from some change in equipment means that the signal to the loudspeaker is different in some way. That means that, by using appropriate equipment, a difference can be measured. This is an inescapable fact. Speakers only react to the signal they are sent. To put it in another way, if a difference in sound can be heard, that difference in sound can be measured.
-Chris
John, I do not think you are being entirely honest about your last post. If so, you wasted good money on the test gear you have bought.
I know I am getting value with mine, and I am in no way an exceptional technician.
Joshua, I paraphrased you.
These are some of a few similar statements you have made very recently.
Okay, care to make a clear statement that explains how you see things?
Yeah, and I've repeatedly stated that good designers use both listening tests and measurements. What's your point?
Actually, your last quote should have read " That there are audible difference between different power cords, it's a widely known belief amongst many audio enthusiasts." Maybe add "without any technical training in electronics" as well. You see, here you are insinuating that the beliefs of an untrained group (in audio electronics) of people have a belief that is more valid than what another group of trained (in audio electronics) of people know, have observed are saying.
Look at it this way Joshua, the very fact that anyone can hear (for real of course) a performance difference resulting from some change in equipment means that the signal to the loudspeaker is different in some way. That means that, by using appropriate equipment, a difference can be measured. This is an inescapable fact. Speakers only react to the signal they are sent. To put it in another way, if a difference in sound can be heard, that difference in sound can be measured.
-Chris
What claims are you referring to, claims I actually made, or those you only put in my mouth?
Do you know what test equipment I'm using? Or is it another speculation of yours?
You continue to put in my moth things I never said.
I never said that I'm unable to measure differences between things I can hear differences.
This is yet another thing I never said.
Reasonable to who?
What attitude are you referring to?
Attitude based on what I actually said, or based on what you only put in my mouth?
I never said such a thing. The quotation marks on your above sentence do not refer to anything I actually said.
Yet another speculation of yours. What actual information do you have on my investment in test equipment and time to perform tests?
Reasonable to who?
So do I.
Only, I choose power cords to my system according to how they sound, not only according to how they are tested, or how the signal is tested.
This is so because of I found no direct correlation between the measurements results and the sound quality. That is, as long as something isn't faulty, which is being expressed with too much noise level, or too high distortion level.
Saying that you see changes to the signal without stating what seen changes have what effect on the sound quality is meaningless.
I did run those tests many times, alongside many other tests.
So far I didn't find a direct correlation between those tests and sound quality.
First I'd like you to reply the technical questions I asked you.
As long as you refuse to state what correlation you found between what measurements to what audible sound qualities, a list of test equipment will do no one no good.
BTW, I have HP 400MHz scope and HP distortion analyzer, alongside other measuring equipment.
You distorted both my words and my meaning.
Why do you insist on distorting my words?
Since you stated here that you can measure differences in different power cords, or see changes in the signal with different power cords, your above statement is meaningless. What you say here contradicts what you wrote elsewhere about your own findings.
It is you who insinuate here that audible differences between different power cords is only a belief. Again, this insinuation of yours contradicts what you wrote elsewhere about your own findings.
Agreed.
Unless you state what measurements results correlate to what audible effects, your above statement have no practical value.
If you read their spec the input impedance starts lowish and rises to 30M IIRC. Probably a storage element in there charging, maybe a very good flying capacitor sampler. BTW it's not possible to build a DC amplifier with any technology I know of with these input specs. What we can't figure out is how the thermocouple potentials are dealt with. Even two slightly different copper alloys have a few micro-volts/degree. We're talking micro-degrees of iso-thermalness. They show experiments at 4 Kelvin and the meter at room temperature, the mind boggles.
Maybe the answer is in a Mayan Codex, so this only has a year or so to go.
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Anatech, I really don't understand what you are talking about. However, I do think that I understand Joshua and his audio experiences.
I have always believed in measuring IF POSSIBLE. It makes it easier to convince others, if I can also offer a good solid measurement. However, when it comes to cables and power cords, I have found little that really correlates to precisely what we hear when comparing different components.
I have invested in a fair amount of added test equipment over the last 15 years, just to attempt to measure differences in wires, to little or no avail. It is NOT that I can't measure differences, but presenting my evidence, that I can generate at any time, is scoffed at here and ridiculed by people who have little or no test equipment. Therefore, without advocating any particular wire or line cord, I can only comment that I have heard differences between them, and that we (that is my audio associates) take them very seriously, especially in listening room set-ups at CES, etc. I suspect that measurements will be available someday, that will give a better understanding as to what the differences are, but I don't need to wait to use what works with my ears and those of my associates. However, I don't think that a one or two tone static test is going to be the answer, these tests are already fairly sophisticated, and found wanting.
I suspect asymmetrical waveforms, and perhaps varying dynamic range test signals like live music might be the ultimate answer. We are not there yet.
I have always believed in measuring IF POSSIBLE. It makes it easier to convince others, if I can also offer a good solid measurement. However, when it comes to cables and power cords, I have found little that really correlates to precisely what we hear when comparing different components.
I have invested in a fair amount of added test equipment over the last 15 years, just to attempt to measure differences in wires, to little or no avail. It is NOT that I can't measure differences, but presenting my evidence, that I can generate at any time, is scoffed at here and ridiculed by people who have little or no test equipment. Therefore, without advocating any particular wire or line cord, I can only comment that I have heard differences between them, and that we (that is my audio associates) take them very seriously, especially in listening room set-ups at CES, etc. I suspect that measurements will be available someday, that will give a better understanding as to what the differences are, but I don't need to wait to use what works with my ears and those of my associates. However, I don't think that a one or two tone static test is going to be the answer, these tests are already fairly sophisticated, and found wanting.
I suspect asymmetrical waveforms, and perhaps varying dynamic range test signals like live music might be the ultimate answer. We are not there yet.
Hi Ed,
I am with Scott on this one. I dont see how low level voltage depandant resistance would be missed by the instrumentation companies, they would be all over it for sensors etc.
I think you have a combination of measurement artefacts and low level flicker noise from your several/many milliohms of dirty contact resistance.
I can see that a dirty contact would have excess flicker noise like the old style compressed carbon black resistors of long ago. As scott says the carbon resistors are now often pyrolytic carbon film that doesnt have this mechanism. But the excess noise only occurs on the contact resistance, not the whole circuit resistance (but I am sure you are well aware of that).
If you look at this page: EM Electronics range of miniature amplifier modules for high resolution temperature measurement and calorimetry. Resolve micro degrees with Thermocouples. his first ever customer was the National Physical Laboratory, National Physical Laboratory that is Britains version of NIST. his P12 instrument was also developed for them. If it was suffering from these steps and dead zones then the NPL is one of the few organisations that would certainly call him out for it not achieving what was promised. He is certainly measuring well below the level you are currently measuring at. the unintended thermocouples are certainly problematic even at the nanovolt level. but the huge size of the copper lugs helps reduce any rapid temperature changes there.
I suspect that internally there are only 4 or 5 junctions to control. My guess on the resistance budget is 10 milliohms for the feedback resistor (perhaps 10K above that to the amplifier output) and 10 milliohms for the relay contacts, then 10 milliohms for the transformer primary, so that means it is going to be 6 awg or above?
Wrinkle
I am with Scott on this one. I dont see how low level voltage depandant resistance would be missed by the instrumentation companies, they would be all over it for sensors etc.
I think you have a combination of measurement artefacts and low level flicker noise from your several/many milliohms of dirty contact resistance.
I can see that a dirty contact would have excess flicker noise like the old style compressed carbon black resistors of long ago. As scott says the carbon resistors are now often pyrolytic carbon film that doesnt have this mechanism. But the excess noise only occurs on the contact resistance, not the whole circuit resistance (but I am sure you are well aware of that).
If you look at this page: EM Electronics range of miniature amplifier modules for high resolution temperature measurement and calorimetry. Resolve micro degrees with Thermocouples. his first ever customer was the National Physical Laboratory, National Physical Laboratory that is Britains version of NIST. his P12 instrument was also developed for them. If it was suffering from these steps and dead zones then the NPL is one of the few organisations that would certainly call him out for it not achieving what was promised. He is certainly measuring well below the level you are currently measuring at. the unintended thermocouples are certainly problematic even at the nanovolt level. but the huge size of the copper lugs helps reduce any rapid temperature changes there.
I suspect that internally there are only 4 or 5 junctions to control. My guess on the resistance budget is 10 milliohms for the feedback resistor (perhaps 10K above that to the amplifier output) and 10 milliohms for the relay contacts, then 10 milliohms for the transformer primary, so that means it is going to be 6 awg or above?
Wrinkle
No, because the junction is not important provided that the junction is all at the same temperature. The thermal voltage is generated in the wires leading to the junction: thermal gradient causes voltage gradient. As the voltage gradient depends on the metal two different metals will generate two different voltages - we measure the difference. The voltage at the junction (which we don't measure because we can't measure it easily) is something different. Introducing an extra metal at the junction has no effect because emf's will cancel. The need for cold junction compensation is a separate issue. Everybody 'knows' that the thermal voltage is generated at the junction - everybody is wrong! See this discussion. Anyway, going OT so I won't pursue this any further.anatech said:
It's pretty clear that Ed and JC are wed to their results. Probably time to lighten up since no amount of contrary evidence seems to matter.
I think this all started over why IC's and power cords matter. I consider dirty or bad contacts pathological and all cables are subject to them. I'm a long way from thinking any previously unknown physics is involved.
I think this all started over why IC's and power cords matter. I consider dirty or bad contacts pathological and all cables are subject to them. I'm a long way from thinking any previously unknown physics is involved.
Scott,
You make an assumption that is at such a low level I think you miss something important.
I think you could build such a meter by switching a capacitor (Flying cap as mentioned) between the input and an internal reference. The other end of the capacitor is amplified (AC signal of course) and passed through a very narrow band filter. The frequency should be of course the switching rate. (Now you might want to parallel switches to reduce contact noise.) (Average the signal etc. nothing magic at this point.)
If the control circuit starts the reference at 1/2 scale and then increases it by a bit it can then decided if the error got smaller or larger and make the correction in the right direction. It can repeat this until there is no error voltage. Then the input impedance will be quite high because the capacitor is being charged by the reference.
Now the interesting effect is that the voltage source under test is at some point required to sink current!
As to the input connections four wire would be nice, but even with 2 wire any oxide or other high resistance film would be cleared by the reverse voltage.
OT. TC's 101
Another way to look at a TC. Two ends of a length wire, each at a different temperature, will generate an EMF. But, you need very long meter leads to be able to measure that EMF.
If you want to measure that EMF moe conveniently, run a second wire from one end to the other end where you van measure the EMF. However, if you use the SAME kind of wire to bring the EMF back to the meter, the EMF's will cancel. To circumvent this, use a different type of wire, e.g. if the first wire you used was copper, the return wire must be iron, or some other dissimilar material.
If you do this, you now have a thermocouple. The output in uV/K varies depending upon the type of wires used. The EMF vs K is not linear.
So, its not at the JUNCTION that the EMF is produced, but between the ends of the wire (so the junction end and the 'other' end). CJC is simply there so you have a reference point against which to compare your EMF.
Another way to look at a TC. Two ends of a length wire, each at a different temperature, will generate an EMF. But, you need very long meter leads to be able to measure that EMF.
If you want to measure that EMF moe conveniently, run a second wire from one end to the other end where you van measure the EMF. However, if you use the SAME kind of wire to bring the EMF back to the meter, the EMF's will cancel. To circumvent this, use a different type of wire, e.g. if the first wire you used was copper, the return wire must be iron, or some other dissimilar material.
If you do this, you now have a thermocouple. The output in uV/K varies depending upon the type of wires used. The EMF vs K is not linear.
So, its not at the JUNCTION that the EMF is produced, but between the ends of the wire (so the junction end and the 'other' end). CJC is simply there so you have a reference point against which to compare your EMF.
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