Temperature measurement

Aha! Of course! "Dual slope" :-) ...Jim Thompson

Is it a RC sawtooth relaxation oscillator? If so, what sets the upper threshold? Just the CMOS logic threshold, maybe, and switch between the thermistor and the resistor to cal out its uncertainty.

John

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You may claim to be a physicist, but you don't put your diodes in ice water if you are serious, but in a well-stirred water bath containing lots of crushed ice (made from distlilled or at least de-ionised water). That way you get within 0.001K (not Fahrenheit) of 273.15K (or

And you don't put you diodes in boiling water, but suspend them above a covered glass pot of boiling water, so the diodes are covered by a layer of condensing steam. You also need a barometer to get the exact boiling point - the temperature is only 373.15K at standard atmospheric pressure.

I calibrated a platinum resistance thermomter at the the ice point, the boiling point of water and the boiling point of sulphur for my Ph.D. project

Much easier, but less accurate.

If you program it right. Aspirant physicists don't always dot all the i's and cross all the t's.

-- Bill Sloman, Nijmegen

You probably kill-filed him :)

Actually, I couldn't find it either for some reason. Perhaps another sub-thread?

Oh I see, it is more a way to avoid needing an ADC then, or encoding for digital/isolated tranmission perhaps.

Maybe not. There are CMOS variants that would be OK, but an original NE555 doesn't work at 3V, which is about what the battery power will deliver. 74HC14 is good enough. Or, just use a switch transistor to discharge the capacitor, and program the input pin of your microprocessor as a level comparator to end the cycle and pulse the switch.

If you wanted, you could sample the sawtooth voltage at several points in a fixed-time (monostable PWM output of the microprocessor) gate, and by digitizing and summing get the benefits of dither (your samples would be all over the ADC range, not sensitive to a single dead spot).

If you were not such a filtration retard and a wuss, you would have enough brains to find it in one of the responses.

You are one of those fucktards that claims to be a man, yet will not ask for directions when lost. Yep, yer lost alright.

That junction voltage reading will barely move over a 5 degree range at freezing point. So, no special bath handling is required, needed, nor would it result in any gain in overall accuracy of the span and linearization plot.

In other words, Sloman. You are always either wrong, overkill, or 30 years behind modern technology, and you never fail to meet up with one of those fallacies in your pathetic declarations.

Good job, Billy.

The potential of which varies far more than the junction potential of a diode.

Again, you squall overkill.

He could read junction potential at 5 degrees below freezing, at freezing and at 5 degrees above, and do the same at boiling, and his plots would vary VERY little, if any at all. 150 degrees F is still going to read 150 Degrees F.

And your little optimizations, though proper for a more sensitive device, are absolute overkill for this application.

"Close" on defining those points is "close enough" to make the plotted points as accurate as any other element in the system is.

And your calibration wasn't done to the standard either. The probe probably came with an NIST calibration sheet that was closer than the crap you plotted out.

if you were doing your homework, you MAY have found this. There is a variant for centigrade and fahrenheit. direct read out in millivolts.

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So you couldn't see your errors when you were making them.

It's not. The water is above 100C at the bottom of the pot. Steam condensing from a saturated steam atmosphere doesn't super-heat. You've got to think about thermal gradients when you are setting up a calibration bath.

No, it wasn't lightning proof. And the Ph.D.was never published - I couldn't work out how to write a paper that was shorter than my Ph.D. thesis. It wasn't that I didn't know what I had to compress and skip around, but every time that I started writing, the whole damn story ended up on the paper. I got better at writing papers - for publications about electronics in physics journals - after a few years, but by then there wasn't a lot of point in writing the paper for publication in a chemistry journal.

Sure, but only about the crap electronics they publish in physics journals. And I publish such comments every few years in the Review of Scientific Instruments. The first one there was 1972. The next one that got published was 1996, but then I got lucky, with publications in 1999 and 2004.

Check out John Larkin's comments about physicists as electronic engineers - we don't see eye to eye on everything, but on this point we agree.

Sure, but with your half-baked approach to temperature calibration, you'd got closer to 90% for your $100.

-- Bill Sloman, Nijmegen

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Stringent? By whose standards?

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They come in various flavours. Self-satisfied clown is a known variant.

Very likely. It wasn't designed to met your specification - whatever that was - so it is unlikely that it would have met it. It did meet my specification, and satisfied the guys who examined my Ph.D. thesis.

It is in the University of Melbourne Library, along with every other Ph.D. thesis successfully submitted to the university.

s.trak4.com/

Contentless, but concise.

It gets trickier if you have something to say.

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Why do you think I'm poor?

Accuracy, precision and resolution are three rather different concepts. You've just confused resolution and accuracy, which doesn't suggest that you have much of a clue about what your are talking about.

-- Bill Sloman, Nijmegen

Yeah. that's the moniker you draw, asswipe.

If it doesn't get published, it isn't a thesis. It is nothing more than an idiot and his scratch pad.

It certainly should have been published. My wife's graduate students aim to make their theses out of several published papers. My Ph.D. supervisor didn't make publication a priority - when I tried to publish my M.Sc. work he did go to the trouble of rewriting my draft paper, but I couldn't take his draft seriously and abandoned the project. He never went to the trouble of finding out why I hadn't done anything with his version, and - looking back - this was bad supervision.

Unfortunately, the rules don't say anything about publication - you get the Ph.D. if the thesis is examined and accepted. In Australia there isn't even any kind of public thesis defense, as there is in Europe.

-- Bill Sloman, Nijmegen

You are out of your mind. The junction voltage is an essentially linear function of temperature, and the quality of your calibration can't be better than the quality of your ice point.

I was calibrating a platinum resistance sensor, not a diode.

probably came with an NIST calibration sheet that was closer than the

It certainly didn't come with a - American - National Institute of Standards and Technology calibration, since it originally came from the U.K. and if I could have got hold of such a calibration sheet I would certainly not have spent a could of weeks - off and on - going through what turned out to be an old-fashioned NIST calibration procedure. The published NIST calibration procedure that I could get my hands on at the time dated from the 1920's, and it was only after I'd put in the time setting up the sulfur point and running it for long enough to be tolerably happy with the results I got that I came across reference to a more modern procedure which used the melting point of zinc - at 419.527C - as the high temperature calibration point. I was a bit cross about having spent the extra time on setting up the old-fashioned calibration point, but doing the extra work required to set up the zinc point wasn't going to buy me anything useful.

-- Bill Sloman, Nijmegen

You are letting your imagination run away with you again.

The physical description of temperature involves the distribution of the molecular/atomic population across their various energy levels - as the temperature goes up, more of molecules/atoms are excited to the higher energy levels. This shows up a an increased entropy. It is a long time since I did thermodynamics and statistical mechanics, and I was never that interested - I have worked out the partition function for a couple of simple molecules, but it was a long time ago - so I'd have to dig a bit to pull out the relevant equations and relationships, but I fondly imagine that I could eventually understand anything worth understanding. That wouldn't include your uninformative and pretentious bullshit, which is designed to be difficult to understand.

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I wouldn't know. My Ph.D. was in physical chemistry, measuring the thermal decomposition of nitrosyl bromide, which wouldn't last long in the average navel.

Probably.

Nothing. It was all covered by my research grant.

Martin Brown has said a few words on your way with tensors. Pretentious bullshit doesn't sell well here.

I was paid adequately when I was in work, and I collect pensions from a variety of sources. My wife is still working - full time - so I've delayed collecting from my major pension funds until I turn 70, which means I collect a higher income (since the pension funds don't expect to be paying it for as long). This isn't the kind of choice you can make if you are poor.

Not for the first time you've made an invalid deduction from a piece of information that you failed to interpret correctly. I don't want work because I need the money - I want work because I like doing electronics.

No need. You demonstrated that you don't know what you are talking about, and the best response you can come up with is a reference to used toilet paper?

Not that I know of. He seems to be a professional physicist, and while I've got a number of academic relatives, none of them have the surname Brown, and none of them are in physics.

-- Bill Sloman, Nijmegen