low cost thermocouple DAQ that works with ubuntu linux tia sal22

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Hmm, that link sends me to "Microthermal imaging in the infrared" Nothing about thermal couples?

George H.

Reply to
George Herold
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Did you fix the wrap ??

Reply to
hamilton

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That didn't help, but I searched the site for "thermocouple" and found it near the end of the list.

George H.

Reply to
George Herold

Take a look at this month's (or maybe last month's) Linux Journal.

It has an article in it about data logging and controlling a fridge from Linux using a Linux embedded device meant for an entirely different purpose.

Reply to
TheQuickBrownFox

OK, I'll bite: What's wrong with explaining electrets as permanently polarized capacitance mics? Are you saying that this is *not* the basic concept, or that it just doesn't go deep enough to do justice?

Like the various "electricity as a flowing liquid" analogies, sometimes a flawed analogy can nevertheless help get a basic concept across... as long as it's clear that it is an analogy and not an equivalence.

Best regards

Bob Masta DAQARTA v5.10 Data AcQuisition And Real-Time Analysis

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Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, FREE Signal Generator Pitch Track, Pitch-to-MIDI DaqMusic - FREE MUSIC, Forever! (Some assembly required) Science (and fun!) with your sound card!

Reply to
Bob Masta

If you have a surface with a nonzero net charge density on its surface (so that it produces an electric field in the air), a small current will flow due to air ions and surface water films. Therefore no object can produce an external field forever without a power source.

Electrets are just poled piezoelectrics.

Cheers

Phil Hobbs

When you

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Phil Hobbs

On a sunny day (Sat, 04 Dec 2010 09:57:04 -0500) it happened Phil Hobbs wrote in :

A current can *only* flow if that object itself is a conductor.

Piezo mikes use the BENDING of a piezo crystal to generate voltage, An electret is in no way related to a piezo mike, if that is what you are implying.

Electret is much more like a capacitor mike, and that also goes for impedance. The old piezo mikes were not very good, maybe speech only, because the forces needed to bend the crystal., non linearity. The electret can give extremely high quality, as hardly any force is needed to move the membrane.

There were piezo pick up elements for vinyl record players, piezo mikes, piezo 'crystal' earphones, most of these later replaced by much more 'HiFi' dynamic stuff.

And 'forever' is something that modern electronics tries to avoid, for sales reasons I suppose. That said I have seem 30 year old electrets working. Considering the 100 years for most FLASH based firmware, I'd say electrets last forever.

It is like your view on LDRs, you probably have never used one.

Reply to
Jan Panteltje

Well, that was masta-fooly stated...

What goes up, must come down...

Spinning wheels, got to go 'round...

Reply to
Sum Ting Wong

with ubuntu linux.

time.

Here is one way...

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Another is to buy a cheap $30 Harbor Freight multimeter that has a serial or USB port on it, and then hack at the output streams from within Ubuntu, if there is no actual Linux app.

Usually, there are only windows applets for that stuff, but you could run that in a window within Ubuntu as well. If DOS applets are available, you could then simply use DOSBox, if it can see the serial or USB ports.

Reply to
TheQuickBrownFox

Resistor bolometer 2 mm sq, 2 mm behind probably a Ge window (in a little to-39 pkg) at whatever needed distance behind a half inch diameter plastic Fresnel lens with some nice read circuitry and LCD display with read and hold mode, etc., and a little laser focal point spotter.

Pretty damned good accuracy from every test I could put it through, from new batteries, all the way down to both cells being dead... the damned thing reads. (obviously the data cell is not completely dead at that point)

$20 at Harbor Freight.

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Reply to
I AM THAT I AM

Air _is_ a conductor, just not a very good one. It contains mobile ions and electrically charged dust. A positively charged surface will attract negative ions and repel positive ones, which means that a small current flows. You don't need much charge to neutralize any plausible surface charge density. Charge 10 pF to 50 volts--neutralizing it takes

14 fA for an hour, or 0.19 fA for a month. We're talking resistances of the order of 200 petaohms (300 million gigohms) to keep it charged for a month. Do the arithmetic.

The only reason permanent magnets don't have the same problem is that there are no magnetic monopoles in nature. If there were a lot of those about, they'd all stick to the ends of a magnet and neutralize the external B field in just the same way that electrons and ions do for the E field in electrets.

implying.

Wrong, sorry--YCLIU. They're made of poled PVDF, which is both piezoelectric and pyroelectric. I've used it a fair amount myself--my Footprints sensors use 9-um PVDF. Piezoelectric response is a tensor quantity--for instance when you put a voltage across a normal AT-cut quartz crystal, it produces a transverse shear (i.e. the cross-section of the plate becomes rhombic in one axis). There's no bending involved. Tuning fork crystals do use bending, but for a general piezoelectric material, any coefficient of strain can produce an E field in any direction. Amorphous or polycrystalline materials like PVDF have simpler behaviour than single crystals.

needed to bend the crystal.,

move the membrane.

Sure, but that has nothing to do with the physics, which isn't at all hard--about eighth grade level, i.e. rubbing balloons on your hair or using a van de Graaf generator.

'crystal' earphones,

The old crystal and ceramic mics used Rochelle salt or PZT or barium titanate or that sort of thing. They have lots of mechanical resonances because they're stiff and heavy compared with a 9-micron PVDF film. Rochelle salt is also fragile and hygroscopic, so it takes some babying if you want decent life.

reasons I suppose.

last forever.

If they don't get hot, their internal polarization lasts many years. My

10-year-old Footprints sensors still work. But I was talking about the external field, i.e. in the air, which decays in a few minutes at most, just like when you stick a balloon to the ceiling after rubbing it on your hair. Capacitance mics work by modulating the plate separation of an air-dielectric capacitor that is held at constant voltage. No bias ==> no change in CV with plate separation ==> no current flow ==> no signal. If you rip an electret mic apart, you'll find that it is metallized on both sides, and the signal is taken between the plates.

It really isn't a capacitance microphone, although its audio characteristics are somewhat similar. The plates don't move together, and there's no net field anyway, even if they did. The physics is the change in the electric polarization due to strain in the material--i.e. a poled piezoelectric.

But you demonstrate my point that the stockmarket-style explanation refuses to die. (It was all due to profit taking/program trading/unwinding short positions/uncertainty about leading economic indicators....)

;)

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

On a sunny day (Sat, 04 Dec 2010 12:32:34 -0500) it happened Phil Hobbs wrote in :

I do not think that is correct.

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Scroll to the bottom, there are 3 types of electret mikes described. The second one described has the electret film fitted to the backplate, where it does *NOT MOVE AT ALL*. The third one has the film on the inside front cover where it does *NOT MOVE EITHER*. That sort of nullifies your argument about strain, except on your mind of course.

Reply to
Jan Panteltje

Some of those things are pretty useful--microbolometers have come a really long way. Consistency is not the same as accuracy, though, and all sensors relying on radiation are (a) vulnerable to emissivity variations, and (2) slow, at least compared to an RTD or thermistor (or thermocouple).

Temperature control lives and dies by loop bandwidth, just like every other control system. Slow sensors ==> poor control. Inaccurate sensors ==>poor control. Fast, accurate sensors plus intelligent sensor placement, insulation to reduce thermal forcing, thermal grounding of leads, .... ==>good control.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

it does *NOT MOVE AT ALL*.

EITHER*.

course.

We're now in violent agreement, I see. I didn't mean "move in the same way", but "move closer together", i.e. the spacing doesn't change, so it can't be a capacitance mic. Clumsily put, admittedly, but the rest of the argument should have removed the ambiguity. Electret mics are not capacitance mics.

Cheers

Phil Hobbs

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Phil Hobbs

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IR sensors are faster, and that includes a bolometer. There is zero settling time, and emissivity will not be a factor, because just like your sensor, this would be "placed" the same every time. Accuracy is dead on, if it was calibrated right in the first place as the circuitry is usually VERY linear and very accurate if any linearization corrections are needed, they are usually hard wired in. I'll bet that it even has ambient compensation built into a single custom MCU/do-it-all chip. Things we had to engineer in with discreet components back when the finished product was $500.

Well, it was precision lab instrumentation outputs. All the Harbor Freight item has is a readout.

I'll bet that it can be relied on to plus or minus 0.3 degrees though.

They range from about 1.5 us to about half a second in response time.

It probably takes a typical TC junction a tenth of a second to settle through with a 'bead' size of about .75 to 1 mm.

Reply to
I AM THAT I AM

with ubuntu linux.

time.

They can have long soak times, lengthening response time. If that is a factor.

IR is much faster and just as accurate and repeatable, and especially so if the usage is meant to look at the same target constantly.

Why folks shy away from IR thermometry is beyond me.

Reply to
I AM THAT I AM

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0.3 degrees is nowhere near close enough for instruments. For industrial control, that would often be just fine. However, you massively underestimate the contribution of emissivity error.

Radiation coupling is very poor at room temperature--a vacuum gap between two surfaces of unit emissivity is equivalent to the thermal conductivity of about 5 mm of air. (I once had occasion to calculate that for a sensor design.) That means that the same sensor in intimate contact with the given surface would be at least an order of magnitude faster, and probably two orders.

Optical pyrometry also doesn't work too well through insulation. ;)

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

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I never said that it was. I am talking about the device I posted a link to. The devices I used to make, twenty years ago were far more accurate than that, so they have gotten even better since. That has nothing to do with this cheap cen-tech device for consumer use.

Usually not.

Not at all. All the operator need to do is make the needed compensations for his readings. Again it comes down to operator understanding.

So IF you had said it is very easy to forget about emissivity, you might be closer to being right. Instead you make a blanket claim that I do not know about emissivity, which is untrue.

That is silly. IR is instant. it travels at light speed. The thermocouple has to soak up the temperature it is sensing, and it has to settle in at that temperature. That takes time because metal does not conduct heat through itself instantaneously. The IR device gives an accurate reading within milliseconds of viewing the target.

IR and the air gap between it and what it reads has no such restriction because the air AND the bolometer do NOT need to be brought up to the test temperature.

Another KNOWN factor. However, my cheap device still tells me the wall temp of my room from 12 feet away just as well as it does from an inch away. It works fine.

Reply to
I AM THAT I AM

On a sunny day (Sat, 04 Dec 2010 14:09:56 -0500) it happened Phil Hobbs wrote in :

it does *NOT MOVE AT ALL*.

EITHER*.

course.

Oh no.

It all depends, apart from the issues of ego and losing face, for a man it is better to admit he is wrong, simply, at times, a pussy will blow smoke and go side-paths. You show how much you know about piezo, but this was about electrostatics. Apples and oranges.

Let's look a bit closer.

If you take 'capacitor mike' literally, as one MIGHT do, then neither the capacitor mike, nor the electret mike, really uses the CAPACITANCE. One could make a 'capacitor mike' by making a tuned circuit (LC) oscillator, and have one fixed and one moving membrane form a capacitor, and the frequency would change under influence of the capacitance, so under the influence of the membrane moving, so under the influence of air pressure changes, say audible sound if it is in the air pressure changes occur in the right frequency range. There is a square in there somewhere, so it would not be all that linear over a large movement. Once could use a FM radio to detect this if the circuit was made to oscillate in the FM band. Maybe the correct word here is 'parametric'.

Then there is the real 'capacitor mike' as we call it, and that is actually an 'electrostatic mike',

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where something moves RELATIVE TO (old Einstein ;-) something else, where one of the objects carries a charge. This is the SAME in the 'capacitor mike' and the 'electret mike'.

The difference is that the capacitor mike needs an external supply for the voltage, and the electret uses a polarised film, so needs no external supply, simpler, cheaper, better, no hum, no filtering problems.

So for all practical purposes, and all theoretical purposes, we can compare a 'capacitor mike' with an 'electret mike', as both use exactly the same mechanism. Thank you for your attention and have a nice day.

PS There are also electrostatic speakers, Quad comes to mind as a manufacturer. Very much HiFi. I have even listened to electrostatic headphones. El Pante

Reply to
Jan Panteltje

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