low cost thermocouple DAQ that works with ubuntu linux tia sal22

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Greetings All

I'm looking for a recommendation for a low cost thermocouple DAQ that works with
ubuntu linux.
Can someone recommend one.  I'm trying to record temperture measurements over
time.
tia sal22


Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
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How about this...http://www.mccdaq.com/usb-data-acquisition/usb-2001 -
tc.aspx

Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
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How about this...http://www.mccdaq.com/usb-data-acquisition/usb-2001 -
tc.aspx

Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
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http://www.mccdaq.com/usb-data-acquisition/usb-2001-tc.aspx

Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
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How about this...
http://www.mccdaq.com/usb-data-acquisition/usb-2001-tc.aspx

Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
DA had written this in response to
http://www.electrondepot.com/electronics/low-cost-thermocouple-DAQ-that-works-with-ubuntu-linux-tia-s-103208-.htm
 :

ratullloch_delthis wrote:

If it's low cost you're after, it would be hard to beat TEMPer USB (
(Amazon.com product link shortened) )
which Amazon sells for ~$13 but you can use eBay search skills to find one
for for $7 shipped (from Hong Kong tho - need to wait ~2 weeks to get it
here in US) you'd be limited to -40C to +120C range tho

As far as working with Ubuntu (or other Linux flavors for that matter), it
shows up as a HID (Human Interface Device) and there is a Perl library
(Device::USB::PCSensor::HidTEMPer) you can use to poll it.

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Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22

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http://www.mccdaq.com/daq-software/Linux-Support.aspx

Single channel thermocouple to USB with linux support $99, multiple
channels more $.

Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
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Arduino, USB, minimum 6 analog inputs, Linux support, 37 dollars to
start, then 6 bucks max for additional microcontrollers.



mike

Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
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Thermocouples are really really horrible temperature sensors--almost as
bad as ICs.  Their advantages are small size, relatively low cost, and
(potentially) high speed, but their disadvantage is that it's really
hard to get good measurements.

One reason for this is thermal conduction down the leads (which is a big
problem for most temperature sensors).  There's a worse one, though:
due to their very low sensitivity, thermocouples are extremely
vulnerable to errors caused by offset drift in the circuitry.  See
Figure 20.3 on P. 803 at http://electrooptical.net/www/book/draftthermal.pdf

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
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Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
On Tue, 30 Nov 2010 13:11:18 -0500, Phil Hobbs

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"Thermocouples generate a voltage related to the temperature difference
between two junctions of dissimilar metal wires, and are a pain in the
neck. ... For less specialized applications, avoid thermocouples
like fleas."

Okay, now I'm going to *have* to buy that book!

--
Rich Webb     Norfolk, VA

Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
Op 30-11-2010 20:15, Rich Webb schreef:
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Thermocouples are very linear and can messure upto 2320 degrees celsius.

Nice table in the dutch wiki page.
<https://secure.wikimedia.org/wikipedia/nl/wiki/Thermokoppel

--
pim.

Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
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"Nice and linear" is in the eye of the beholder.  They're a lot better
than thermistors, that's for sure.

And up in the orange-hot region you probably don't care if you're off by
a couple of degrees, but down near room temperature you usually do.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
We've slightly trimmed the long signature. Click to see the full one.
Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22

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Yes, that is a good one, and I can't argue with Phil's assessment of TC
accuracy, but "You can learn all you ever wanted to know about them from
the Omega Engineering catalogue." is true only if you have no interest in
how they actually work (as opposed to how to use them) or how to make a
really good low drift TC measurement system with accurate CJC and high
immunity to EMI, for instance.

There are many trade-offs in sensor selection, and thermocouples excel in
temperature range and durability as well as (sometimes) speed.  A TC can
be smashed flat with a hammer and suffer no loss in accuracy until the
wires break, or welded to metal parts for excellent thermal contact with
the part being measured, for instance.  Try that with a thermistor :-).


Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
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You can solder RTDs down, which is about the same thing.  And the
circuit details aren't really information about the _sensor_--any
sufficiently poor sensor will have those problems.

I've used thermocouples reasonably often, generally running inside an
evaporator or someplace like that, and attached to a Fluke thermocouple
thermometer with built-in cold junction compensation.  That was probably
good to a couple of degrees, which was all I really needed, especially
since I didn't have to replace the TCs, so the measurements correlated
pretty well over time.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
We've slightly trimmed the long signature. Click to see the full one.
Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22

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From the perspective of your book - temperature stabilization of electro-
optical components - I agree completely that thermocouples should
generally be avoided like fleas.  From my perspective, with a background
in power plant control, thermocouples and RTD's are the rule and
thermistors the rare exception.

What really irks me about Omega is that their "Thermocouple Introduction
and Theory" section is actually a "thermocouple introduction and
completely bogus theory".  Correct theory can be found at:
<http://www.electronics-cooling.com/Resources/EC_Articles/JAN97 /
jan97_01.htm>

And better yet is another article which I can no longer find on the web,
which I will post on ABSE with thread title "thermocouple theory article"
in case anyone is interested.

Glen

Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
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I'm not too impressed with the Electronics Cooling article.  The
thermoelectric effect is treated as magic--the two integrals at the
beginning of the article just integrate the magic along the length of
the wire without explaining anything.  There's some useful applications
advice, but there's some pure nonsense, e.g. saying that 20 wire
diameters' worth of lead length is enough to get a good measurement of
gas temperature.  The ratio of the wire's thermal conductance (in W/K)
to its surface area goes as diameter/(length**2), so for a given
accuracy, the required lead length goes as the square root of the wire
diameter.

I agree that Omega isn't the best place to look for the actual physics
of thermocouples, but they do have nice pictures.  Anyway, that physics
is more or less bottomless...you can stick with classical thermodynamics
and use the grand canonical ensemble, but then you get into actual solid
state physics and have to worry about things like the density of states
differences in different crystal orientations, and then you get into the
real quantum mechanics of disordered systems stuff.  As I said,
bottomless, and although I talk a good game, my actual solid state
physics expertise goes about ankle deep.  (I did take graduate solid
state from Walt Harrison, who is the biggest wildman in all of
theoretical sold state physics, but didn't pay enough attention.  Same
with graduate statistical mechanics.)

I'm not the worst offender, though.  A lot of the explanations you hear
about physics have as much merit as the Friday afternoon stock market
guy 'explaining' what happened on Wall Street that week.  The idea that
an electret mic is a variety of capacitance mic is one example, and
almost anything mentioning 'surface states' and 'traps' is another.
It's not that traps and surface states don't exist, but they're very
commonly used as a cloak for ignorance--understandably, since real solid
state measurements are hard, and tend to involve ultrahigh vacuum.

All of that said, for instrument purposes delving into the fine details
of thermocouples is putting lipstick on a pig. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
We've slightly trimmed the long signature. Click to see the full one.
Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
On Fri, 03 Dec 2010 11:01:33 -0500, Phil Hobbs


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  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.

Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
On Fri, 03 Dec 2010 11:01:33 -0500, Phil Hobbs

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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
 
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Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
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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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--
Dr Philip C D Hobbs
Principal
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Re: low cost thermocouple DAQ that works with ubuntu linux tia sal22
On a sunny day (Sat, 04 Dec 2010 09:57:04 -0500) it happened Phil Hobbs

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


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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.




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