The LT1236 is trimmed to exactly 10.0000VDC. How does this happen? I use our brand new SDM3055 5.5-digit DMM (new production, direct from Siglent) which is "comparison calibrated" to a new DMM6500 that I have access to. Then, the SDM3055 is the basis for "comparison calibrating" my Fluke 87V's.
The DC reference trimming is done with the SDM3055 by powering on both for 24-48 hours before final trimming to 10.0000 which is as good as it gets until we buy a DMM6500 or similar in the near future.
However, after trimming one of the 10V references 2 months ago and keeping it powered on, and after re-checking the SDM3055 vs DMM6500 readings weekly, the 10VDC reference STILL reads exactly 10.0000, spot on, if that's worth anything.
The LT1236 is trimmed to exactly 10.0000VDC. How does this happen? I use our brand new SDM3055 5.5-digit DMM (new production, direct from Siglent) which is "comparison calibrated" to a new DMM6500 that I have access to. Then, the SDM3055 is the basis for "comparison calibrating" my Fluke 87V's.
The LT1236 is trimmed to exactly 10.0000VDC. How does this happen? I use our brand new SDM3055 5.5-digit DMM (new production, direct from Siglent) which is "comparison calibrated" to a new DMM6500 that I have access to. Then, the SDM3055 is the basis for "comparison calibrating" my Fluke 87V's.
I typically think of the errors rather than the accuracy, so I avoid terms like 'spot-on'. To me 'spot-on' just means you don't have enough resolution to see the errors.
-snip-
If that is the way you are doing it, are you saying that your SDM3055 always matches the DMM6500 exactly to the last digit? And then your Fluke 87V matches the SDM3055 to the last digit, each and every time? If so, that is truly exceptional.
What I'm getting at is developing a spec for example, the 10V reference, that says something like, trimmed to four zeroes, plus or minus 2 LSD's over a 6 month period? Maybe?
What I'm getting at is developing a spec for example, the 10V reference, that says something like, trimmed to four zeroes, plus or minus 2 LSD's over a 6 month period? Maybe?My second suggestion is that you change the IC socket and use this:
https://www.mouser.com/ProductDetail/Mill-Max/110-13-308-41-001000?qs=WZeyYeqMOWeYjIS4tXLt7Q%3D%3D
I know your BOM is tight, but I think you may eventually have issues with the style of socket you are using now.
Somewhere, I read about the Nobility of Metals stuff. I like the construction quality of the round gold sockets much better but what do you think about the dissimilarity of the IC pin plating to socket junction effects?
Asking again; does it have distortion specs?
A “relative pure sinewave” is not a spec.
Sorry, I missed your question earlier....
1) Where did you see "relative pure sine wave" ? I don't recall using that term in the AC Reference description.
AC Voltage Reference: Here's a device that generates a relatively pure, NON-FLUCTUATING, adjustable sine wave from 0 to 6VACrms @ 100Hz (fixed frequency) for those who do not have a quality signal generator or alternative.
When designing these references for DMM checking, the frequency, stability and amplitude are much more important than a few percent distortion.
Sorry, I missed your question earlier....
1) Where did you see "relative pure sine wave" ? I don't recall using that term in the AC Reference description.
Your top post, third paragraph.AC Voltage Reference: Here's a device that generates a relatively pure, NON-FLUCTUATING, adjustable sine wave from 0 to 6VACrms @ 100Hz (fixed frequency) for those who do not have a quality signal generator or alternative.
What does "relatively pure" mean to me? Almost, but not quite perfect, in shape.
Asking again; does it have distortion specs?
A “relative pure sinewave” is not a spec.Sorry, I missed your question earlier....
1) Where did you see "relative pure sine wave" ? I don't recall using that term in the AC Reference description.
2) Distortion is less than 10%. Depending on the designs I've used (phase shift, dual integrator, etc. and the type of components and amplitude designed for, it can be less than 1%. The newest designs have about 1-2%.
When designing these references for DMM checking, the frequency, stability and amplitude are much more important than a few percent distortion. These are fixed, low frequency sine wave generators and they aren't aimed for audio use. I have a line of low distortion 1KHz-20Khz sine gens for that.
How about you guys with much more sophisticated measuring setups buy a few of these AC & DC references and actually put them to the test? I would make a special price of 50% of my cost to you and after you evaluate and report, I'll give you a free sample from the first production run. Partners anyone?
When designing these references for DMM checking, the frequency, stability and amplitude are much more important than a few percent distortion.
I'm afraid you're wrong there; you do need low distortion. If you look at mains voltage, it has flat tops (caused by capacitor input supplies) and a true-RMS meter gives a very different answer to a mean reading meter calibrated RMS of sine wave. Total harmonic distortion on mains with those flat tops is typically 3%.
2) Distortion specifications for all such outputs are: Less Than 1%.
With a source of a precise, 50% duty cycle square wave, 12.000VDC @ 100Hz, crest factor of 1, in theory, that should equate to a precise 6VACrms display on a properly calibrated true-RMS meter, right.
Interestingly, the display on our new Siglent SDM3055 shows "6.0004" but on all of our less-than-1-year-old Fluke 87's the display is "6.011 to 6.013" on their 6V range (They have about 10% overrange capability).
It is my understanding that they both use similar TRMS conversion protocols. Comments?
With a source of a precise, 50% duty cycle square wave, 12.000VDC @ 100Hz, crest factor of 1, in theory, that should equate to a precise 6VACrms display on a properly calibrated true-RMS meter, right.
Interestingly, the display on our new Siglent SDM3055 shows "6.0004" but on all of our less-than-1-year-old Fluke 87's the display is "6.011 to 6.013" on their 6V range (They have about 10% overrange capability).
It is my understanding that they both use similar TRMS conversion protocols. Comments?
I believe they both use AD chips, but different versions. What is the "precise" source of your sqware wave and how precise is it specfied to be?
A TRMS meter should do a reasonable--but not perfect--job in this instance. Again, I concentrate on the source of errors and there are some additional sources of error when using a non-sinusoid as your test stimulus. The specifications for the Fluke 87V allow for up to 64 counts of error (1% + 4 counts) for signals within 1kHz BW and then 2% for signals above 1kHz BW. To begin any analysis of the errors involved with non-sinusoid signals, calculate the contribution of the harmonics beyond the 1kHz point, in this case the 11th harmonic and up. Or just Google it.
I saw that this explosively growing market had a gap of available, affordable (very low cost) but still useful "ballpark" references to do some function testing of their low cost devices.
I saw that this explosively growing market had a gap of available, affordable (very low cost) but still useful "ballpark" references to do some function testing of their low cost devices.
Frankly, I don't see that market need. I already have a "ballpark reference", namely the digital multimeter I bought. If I were to spend time and money to obtain another reference on top of that, I would want something a bit more definitive.
"I have always wondered whether I can trust my meter. Nevermore! Now I wonder whether I can trust my cheap homebrew voltage reference."
My point was that oscilloscopes are very poor for revealing distortion and that by the time you can see distortion on an oscilloscope (such as flat topped mains), it can be pretty bad, and that some distortions (flat topped mains) cause significantly different measurements between different methods of measurement. <snip>
By the way, your oscilloscope trace doubled the errors achievable because you only exercised half of its ADC's range, throwing away a bit of resolution. And even as shown, it's not a smooth sine wave - it has visible steps.
There are no excuses in test and measurement. If you want to calibrate even a 3 1/2 digit DMM, then you need something ten times better, so you can't verify your tester with an oscilloscope. You either need your tester to be better by design or verified by something better. A recording quality soundcard is a very good start.
Here's some better resolution for you. See any flat tops or bottoms or weirdly shaped curves other than what looks like perfectly shaped sine waves?
My point was that oscilloscopes are very poor for revealing distortion and that by the time you can see distortion on an oscilloscope (such as flat topped mains), it can be pretty bad, and that some distortions (flat topped mains) cause significantly different measurements between different methods of measurement. <snip>
By the way, your oscilloscope trace doubled the errors achievable because you only exercised half of its ADC's range, throwing away a bit of resolution. And even as shown, it's not a smooth sine wave - it has visible steps.
There are no excuses in test and measurement. If you want to calibrate even a 3 1/2 digit DMM, then you need something ten times better, so you can't verify your tester with an oscilloscope. You either need your tester to be better by design or verified by something better. A recording quality soundcard is a very good start.
Here's some better resolution for you. See any flat tops or bottoms or weirdly shaped curves other than what looks like perfectly shaped sine waves?
I agree, that scopes don't agree nicely with DMM measurements. I just view them as guidelines/approximations.
My point was that oscilloscopes are very poor for revealing distortion and that by the time you can see distortion on an oscilloscope (such as flat topped mains), it can be pretty bad, and that some distortions (flat topped mains) cause significantly different measurements between different methods of measurement. <snip>
By the way, your oscilloscope trace doubled the errors achievable because you only exercised half of its ADC's range, throwing away a bit of resolution. And even as shown, it's not a smooth sine wave - it has visible steps.
There are no excuses in test and measurement. If you want to calibrate even a 3 1/2 digit DMM, then you need something ten times better, so you can't verify your tester with an oscilloscope. You either need your tester to be better by design or verified by something better. A recording quality soundcard is a very good start.
Here's some better resolution for you. See any flat tops or bottoms or weirdly shaped curves other than what looks like perfectly shaped sine waves?
That's as convincing as putting a voltmeter on a battery and asking whether the displayed voltage is wierd.QuoteI agree, that scopes don't agree nicely with DMM measurements. I just view them as guidelines/approximations.
If the instruments are in cal, they should "agree". That's "agree" within the limits of their specification, of course.
Anybody selling calibration tools realluy ought to know that instinctively. It shouldn't need to be said.
My point was that oscilloscopes are very poor for revealing distortion and that by the time you can see distortion on an oscilloscope (such as flat topped mains), it can be pretty bad, and that some distortions (flat topped mains) cause significantly different measurements between different methods of measurement.
If I listened to that kind of unhelpful crap, I'd never produce a product.
Here's my preliminary spec for the AC Reference Module:
Adjustable Sine Wave Output 0-6VACrms @ 100Hz, into 10MegOhm Non-capacitive Load, Less Than 1% THD, 6 Month Accuracy 0.5%, 76 Degrees F, 60% Humidity, Free Periodic Re-Cals.
My point was that oscilloscopes are very poor for revealing distortion and that by the time you can see distortion on an oscilloscope (such as flat topped mains), it can be pretty bad, and that some distortions (flat topped mains) cause significantly different measurements between different methods of measurement.
In practical terms, discussing actual devices that might reasonably be used with the sort of reference mentioned here, I think that distortions not visible on an oscilloscope trace are unlikely to cause significant errors when comparing meters that use a TRMS conversion system. This is assuming a fundamental of 100Hz as shown. Things would change if one of the meters was a reasonably accurate average-responding system. Unfortunately I don't have time or bench space to spare at the moment, but a simple experiment with an AWG could show this quite easily.
If I listened to that kind of unhelpful crap, I'd never produce a product.
Here's my preliminary spec for the AC Reference Module:
Adjustable Sine Wave Output 0-6VACrms @ 100Hz, into 10MegOhm Non-capacitive Load, Less Than 1% THD, 6 Month Accuracy 0.5%, 76 Degrees F, 60% Humidity, Free Periodic Re-Cals.
You should be able to put the "unhelpful crap" into perspective with mathematical arguments or experimental demonstrations. For example, how much difference between TRMS meters might you see with a signal that has 1% THD? (probably not much) Also, which harmonics are present in your signal? (It matters, possibly a lot)
As for your AC specs, I would observe that 10M "non-capacitive" is probably a grossly insufficent spec for an AC source since many meters have much lower impedances, like 1M + 150pF. You'd need to know your output source impedance (it's probably much, much lower than 1M) and figure out what errors you might have with various loads. You might also want to explain how you're substantiating the 1% THD spec and the 6-month accuracy spec. If the answer is "it's just my best guess, but hey they're cheap", well I suppose that'll have to do.
I have a hunch that it might be much lower than 1%. But for what these references are designed to do, 1% is plenty adequate. I'll let someone with a $10,000 Spectrum Analyzer prove me wrong.
Your last comment about the harmonics has me confused. With substantial output low-pass filtering built in to my modules, I didn't think harmonic content would matter much based upon the suppression provided by the LP filtering. Comments?
I don't see the distortion that critical.
<SNIPPED>
Driving the output directly from an OP-amp can be an issue. The current is sufficient, but op-amps don't like driving capacitive loads. E.g. 150 pF (1.5 m of cable or a DMM input) can be enough to make an TL07x wired as a buffer oscillate. Even those OP-amps that are specified to drive quite some capacitance are not not really happy about capacitive loading.
As much as I like to do things in a purely old fashioned analogue way, an accurate, reasonably stable and inexpensive AC source is best to be made by digital synthesis with a microcontroller and a DAC. There are microcontroller chips made with internal DACs, band-gap references and even look-up tables for sinewave generation. All you need to add is an output buffer/filter and you'll get a reference AC source with better than 0.1% accuracy and stabiltiy.
Cheers
Alex
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I'm mainly a marketing guy. I realize that engineers and dedicated electronic theoreticians may not appreciate that but here's my philosophy regarding my original intent in this thread:
What I mean by that is, if the goddamned thing works well enough to satisfy the target market that it's aimed at, build it and sell it!
not to mention professional appearance (especially if you pay a little extra for black solder mask lol), which may improve sales.
I *despise* black solder mask. I want to see where the traces go, even if I'm not repairing it, or have the plots available. I'd regard it as 'wannabe-cool' which is most definitely not the same as 'professional'.
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I'm mainly a marketing guy. I realize that engineers and dedicated electronic theoreticians may not appreciate that but here's my philosophy regarding my original intent in this thread:
Several people have, belatedly, begun to smell that. It would have helped everybody if you had made that clear earlier.Quote
What I mean by that is, if the goddamned thing works well enough to satisfy the target market that it's aimed at, build it and sell it!
A key part of marketing is to give sufficient information to determine what a product won't do.
It would have helped if you did that explicitly, rather than leaving it to people to ask questions and make inferences.
We've all seen claims/patents for better mouse traps and apple corer/peelers. Almost all aren't any such thing.
What I mean by that is, if the goddamned thing works well enough to satisfy the target market that it's aimed at, build it and sell it! Continued attempts at perfecting it will lead to fewer and fewer sales!
If anyone has more suggestions or input, please continue to weigh in with an eye towards what I reiterated above.
an island off the coast of a real continent, which island is known to be populated by many of corrupt morals, conversational hyperbole, achievemental dysfunction and an affinity for inbred and, in several cases, immoral so-called "royalty" admiration syndrome.wtf have I just read.
does it really belong here?
What I mean by that is, if the goddamned thing works well enough to satisfy the target market that it's aimed at, build it and sell it! Continued attempts at perfecting it will lead to fewer and fewer sales!
If anyone has more suggestions or input, please continue to weigh in with an eye towards what I reiterated above.
First, R&D can and should result in better performance and lower costs. Both are reasonable goals for improvement.
Second, your concept of 'well enough to satisfy the target market' is a pretty modest goal simply because your target market seems to explicitly be users without the means to critically evaluate the product in any meaningful way. They're relying on you!
Here's quick drawn schematic of a simple Wein-Bridge 100Hz (Wien or Wein) Oscillator using a simple gain limiting for amplitude stability, followed by 2nd Order Active LPF to reduce harmonic content. Bridge Oscillator should produce a respectable sine-wave output if not forced into excessive limiting, so LPF may not be required.
BOM for just electronic components should be between $0.34 and $1.56, so should suffice as a Cheap Sine-Wave AC source.
Anyway, we haven't built this, someone give it a try and would expect this to outperform the schematic shown earlier. If anyone builds this, please report back results.
Best,
Here's quick drawn schematic of a simple Wein-Bridge 100Hz (Wien or Wein) Oscillator using a simple gain limiting for amplitude stability, followed by 2nd Order Active LPF to reduce harmonic content. Bridge Oscillator should produce a respectable sine-wave output if not forced into excessive limiting, so LPF may not be required.
BOM for just electronic components should be between $0.34 and $1.56, so should suffice as a Cheap Sine-Wave AC source.
Anyway, we haven't built this, someone give it a try and would expect this to outperform the schematic shown earlier. If anyone builds this, please report back results.
Best,
Which opamp part numbers would you suggest to employ? LM358, TL072? Other?
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However, after trimming one of the 10V references 2 months ago and keeping it powered on, and after re-checking the SDM3055 vs DMM6500 readings weekly, the 10VDC reference STILL reads exactly 10.0000, spot on, if that's worth anything.
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The wien bridge oscillator can get a good sine quite well, but the amplitude stability is usually not that great. In the version with just the simple rectifier and zener to reduce the gain the amplitude will not be very stable amplitude. E.g. there are 2 diodes in series to the zener and the capacitor ratio will also effect the needed gain. So I would expect something on the order of -8 mV_pp/K or close to -0.1%/K for the amplitude stabilty.
There are better ways to stabilize to amplitude, e.g. with an active rectifier or measureing the peak voltage and than actively regulate the oscillator gain. The LPF after the oscillator is only a thing to improve on the harmonics and this is no longer needed with a regulated (e.g. with a JFET) amplitude.
I'm mainly a marketing guy. I realize that engineers and dedicated electronic theoreticians may not appreciate that [...]
...
I'm mainly a marketing guy. I realize that engineers and dedicated electronic theoreticians may not appreciate that but here's my philosophy regarding my original intent in this thread:
Several people have, belatedly, begun to smell that. It would have helped everybody if you had made that clear earlier.Quote
What I mean by that is, if the goddamned thing works well enough to satisfy the target market that it's aimed at, build it and sell it!
A key part of marketing is to give sufficient information to determine what a product won't do.
It would have helped if you did that explicitly, rather than leaving it to people to ask questions and make inferences.
We've all seen claims/patents for better mouse traps and apple corer/peelers. Almost all aren't any such thing.
Ya know, I've never been a fan of your arrogant, self-serving, hyper-critical posts in my own, and several other threads. Guys like you NEVER have anything good to say unless you're touting your own imagined success so, your remarks and criticisms and admitted paranoid suspicions as to where I'm coming from are all wasted hot air on me.
I've noted previously how your baselessly superior attitude tends to embarrass and chase away those participants who you deem to be less learned than you and, therefore, not worthy of your respect to at least be courteous toward their requests for help in some of your replies.
Do me a favor and put me on your ignore list and I'll do the same for you. That way, other participants won't have to witness your desperate attempts to throw a wet blanket on any more of my posts.
EDIT: deleted an asinine reference I made to his homeland. Sorry. Temper got the best of me for a moment.
I'm mainly a marketing guy. I realize that engineers and dedicated electronic theoreticians may not appreciate that [...]
Belatedly commenting, although I've been lurking from the start, so not exactly one of those late-coming naysayers
As a marketing chap I am surprised you don't see the benefit of having this on a pukka PCB. The first time I saw it in the buy/sell area I just passed straight over on the basis it was an amateur lash-up, and I suspect there will be a number of potential users who have similarly done so. IMO, making it look the part would be a better improvement than improving the specs so far as sales go.
Perhaps the problem is that you're really a marketing guy and don't have the apps, or experience, to create PCBs. If that's the case, the solution may be to ask someone to do them for you. They are not very complex and should be pretty simple to do. If you then order just five, you'll get a professional-looking PCB at less than a dollar, possibly half that if you happen upon a coupon or something. As others have noted, that would improve the reliability in both building and ongoing use, and make it quicker and simpler to assemble. And at similar, or lower, hard cost than the boards you're using.
So yeah, tggzzz's comments can be not always the most adequated ones, but at least I have seen him stating he had been made aware he was wrong. That's something I have still not see coming from you. I'm sure you are able to simply state your goals, letting aside any aggresivity, probably originated from any perceived attack to the quality of your product. I for one would greatly appreciate that. Otherwise I'll stick with the people that isn't selling anything. just saying.
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[3] possibly due to the Dunning-Krueger syndrome
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[3] possibly due to the Dunning-Krueger syndrome
Please stop spouting that bloody stupid term, it encourages copycat use on the forum that takes a while to die down (or at least has in the past). BTW, you spelt Kruger wrong.
So yeah, tggzzz's comments can be not always the most adequated ones, but at least I have seen him stating he had been made aware he was wrong. That's something I have still not see coming from you. I'm sure you are able to simply state your goals, letting aside any aggresivity, probably originated from any perceived attack to the quality of your product. I for one would greatly appreciate that. Otherwise I'll stick with the people that isn't selling anything. just saying.
Where I'm not reasonably sure of something, I'll either not comment or I'll add caveats. When I realise I've made a mistake, I don't try to revise history, and I do try to apologise. IMHO constructive conversations cannot occur without that.
I'm very tolerant of beginners asking information, provided they listen to the answers, and think. Watching someone's capabilities improve is a profound pleasure.
We all make mistakes; that's part of learning. However, as I taught my daughter, "let's make new mistakes".
I'm less tolerant of people who don't listen[3], or don't learn, or choose not to improve, or do who misrepresent other people's position[1], or who continue to misrepresent their product[2] (typically to ignorant managers).
I've spent a lifetime being plagued by salesman/companies who make impossible claims for their products. I know others feel the same!
[1] often in the form of chosing to omitting relevant context, or with strawman arguments
[2] e.g. if their product does what they claim, then they've solved the Byzantine General's problem or the split brain problem, or broken the laws of thermodynamics etc.
[3] possibly due to the Dunning-Krueger syndrome
So yeah, tggzzz's comments can be not always the most adequated ones, but at least I have seen him stating he had been made aware he was wrong. That's something I have still not see coming from you. I'm sure you are able to simply state your goals, letting aside any aggresivity, probably originated from any perceived attack to the quality of your product. I for one would greatly appreciate that. Otherwise I'll stick with the people that isn't selling anything. just saying.
Where I'm not reasonably sure of something, I'll either not comment or I'll add caveats. When I realise I've made a mistake, I don't try to revise history, and I do try to apologise. IMHO constructive conversations cannot occur without that.
I'm very tolerant of beginners asking information, provided they listen to the answers, and think. Watching someone's capabilities improve is a profound pleasure.
We all make mistakes; that's part of learning. However, as I taught my daughter, "let's make new mistakes".
I'm less tolerant of people who don't listen[3], or don't learn, or choose not to improve, or do who misrepresent other people's position[1], or who continue to misrepresent their product[2] (typically to ignorant managers).
I've spent a lifetime being plagued by salesman/companies who make impossible claims for their products. I know others feel the same!
[1] often in the form of chosing to omitting relevant context, or with strawman arguments
[2] e.g. if their product does what they claim, then they've solved the Byzantine General's problem or the split brain problem, or broken the laws of thermodynamics etc.
[3] possibly due to the Dunning-Krueger syndromeTO TGGZZZ: Please either contribute something sane, meaningful, helpful and relevant to this thread discussion or else take your thread-clogging demented crap to some other thread. Thank you.
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EDIT: deleted an asinine reference I made to his homeland. Sorry. Temper got the best of me for a moment.