Metrology - my second hobby

A.N.T.

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#1
Looks like this section was quiet for a while, let's wake it up a bit with some pictures of naked ... things.

I have two hobbies, both in the electronics domain, but on two opposing sides of it. One is in audio, where the subjective listening is a king and measurements are only a necessary evil. The second one is in metrology, aiming at the most precise measurements physically possible (obviously, for a given hobby budget, that is). As much as I enjoy a new cassette deck in my collection or a new phono stage design, I may drool all over the place getting a piece of equipment which has no practical purpose whatsoever except for extremely accurate measurements *. Metrology in electronics is an area where "ppm" ("parts per million") is a common denomination. In some areas, inhabited by timenuts (I don't venture there, it is too scary) even "parts per billion" measurement accuracy might be considered mediocre. In my home lab I have a resistance reference and a voltage reference accurate to better than 10ppm. Today I have received a new device for my home lab, after waiting a considerable time for it to arrive from the US. The unit was made almost exactly 50 years ago, in Nov 1971. When I've checked it on arrival it was faulty. I had to open and fix it. Fortunately, the fault was a simple one, two bits were touching each other and it was probably one of the simplest repairs I've done in my practice. After the fix it performs according to the specification. This device can output a very accurate fraction of the input voltage, with 1ppm steps and accuracy of 10ppm full scale. So, here it is in all its dressed and undressed glory.

Cheers

Alex

P.S. - * one can use this thing as a volume control, I suppose. Mono. Unless you get a second one.

P.P.S. - don't even ask how much a modern equivalent of it might cost.







 

vince666

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#2
wow! and so those are like rotary selectors with extremely precise wire resistors attached on? (that's the best I can guess, from my ignorant point of view, sorry).

Indeed, I sort of remember that you were also involved in measurement instruments (don't remember exactly where I had read this info) but I sort of thought that was your actual "main" work.

Anyways, I think it's quite correct if i say that, regarding people as accurate and knowledgeable as you, the difference of calling something a hobby or a work is just related about the time you can spend on it without any external pressures and not just about the "quality" of what you're doing there, because I bet it's first class as always.

That said, now I do understand a bit better the true meaning of certain debates about measurements and specs related to the audio matters, you happened to be involved at "that other place" during the past years.
In the same way, the actual meaning of your own avatar is a lot clearer now. :D

Hey, Alex... and how many times your metrology hobby (and related way of thinking) , did actually blend/overlap with your audio hobby in a very useful and constructive way?
Sure, I doubt most if not all audio measurements need 1 ppm-alike precision (which is like 0.0001% precision range, if i am correct) but, hey, at least you can know very well which actual degree of precision is needed for a given task/measurement and why, which isn't bad at all.

PS: The only time I had actually heard about the "ppm" thing, it was while studying some chemistry matters at university, a few decades ago. (or also by reading the label on the bottles of mineral drinking water, where some use to give the amount of the various salts/ions into the water just as parts per million)... so, it's nice to learn about new things! :)

thanks for sharing,

Vince.
 

A.N.T.

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#3
Hey, Alex... and how many times your metrology hobby (and related way of thinking) , did actually blend/overlap with your audio hobby in a very useful and constructive way?
Hmm, a rather interesting question. And the answer is - all the time. Metrology teaches you that there are no total certainty, that you need to pay attention to small things, not normally measurable in a standard "audio" way. That something we usually assume as a linear device in audio, say, a simple resistor, is actually all over the place if you look at it closer. Effects are not normally considered important in audio domain could be quite huge in metrological domain. This knowledge helps. I would never say "there is no measurable difference between these two amplifiers", simply because there is always a measurable difference, even between two amplifiers of the same model and consecutive serial numbers! What to do with that measured difference, how to interpret it, is a completely different matter. At least in metrology you can satisfy a measuring device, in a way it is simpler than to satisfy a pair of ears.

Cheers

Alex
 

vince666

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#4
So, even if (to tell it in a "bold" way) audio allows greater "tolerances" than metrology in general, the audio is still a very picky matter and, not being easy (or even possible) to directly interpret certain measurements in audio terms, they will/can still have their own importance, so we must rely on ears too.

Then, metrology is a matter which is possible to know and investigate in a better and more detailed way while audio partially falls into the "black magic" stuff, if i've understood correctly what you really mean.

Well, I will tell you a "secret" now... I had started studying Mechanical Engineering in early 90s but, at some point, I had stopped before actually completing it... but, recently, I am restarting to study (even if not full time as back then) while hoping to finally get my ME degree (better late than never).
Amongst the matters which I hadn't studied back then and which I still need to start studying from scratch, there is a matter which might have something in common with metrology... its "classic" italian name (because the names of the matters changed a bit here, over the years) was "misure e strumentazioni industriali" (which is literally: "measurements and industrial instrumentations")... of course, it's mostly aimed at the mechanical side of things in my case, but I believe some basic principles/ideas in this matter might be shared with the metrology you are talking about in electronics.
Maybe this is also a reason why I found your post quite interesting.

Actually, I am about to start reading/studying the book I have here which, by my own teacher's choice, it's written in english (not a real problem for me at now, luckily).
Its title is "Measurement Systems - application and design" by Ernst O. Doebelin.
I hope my poor brain won't burn on this book... not that easy to restart studying such matters at almost 50 yrs old and after a couple decades (if not more) I had lost this habit! :oops::D


Cheers,

Vince.
 
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borchee

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#8
Hi Alex,

I wonder what sort of a force-gauge you're using to set VTF with turntables and which unit the results are represented in... newtons, ponds?

Cheers
Borut
 

nakdoc

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#9
I have been preaching for years that audio tests do not correlate to good sound, but no one seems to agree.
Years ago I grabbed a vacuum tube precision voltage source box from a university dumpster. The thing was loaded with OA2 and OA3 tubes. I tossed it, because I was looking for audio tubes. I did save a sexy photomultiplier tube though.
 

nakdoc

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#11
Agree that tubes are sexy?

Anyone who has listened to different power amps knows that watts, for one, are not equal. Power measurements have got to be the best example of how tests can lead one astray.
 

J!m

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#14
Those dynode plates are all over Star Wars.

Otherwise, my heaviest use of tubes is within my bicycle tires. My Counterpoint amps use them for voltage gain I think. MOSFET outputs.
 
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