low cost thermocouple DAQ that works with ubuntu linux tia sal22

ks with ubuntu linux.

s over time.

How about this...

tc.aspx

ks with ubuntu linux.

s over time.

How about this...

tc.aspx

ks with ubuntu linux.

s over time.

ks with ubuntu linux.

s over time.

How about this...

If it's low cost you're after, it would be hard to beat TEMPer USB (

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

Arduino, USB, minimum 6 analog inputs, Linux support, 37 dollars to start, then 6 bucks max for additional microcontrollers.

mike

with ubuntu linux.

time.

I can't help with the Linux part, but maybe you can use some circuits I developed for my Windows-based Daqarta system. There is a simple temperature to frequency converter at . It uses an LM335 temperature sensor plus an LM331 V-F, powered from a 9V battery.

Besides the schematic and design formulas, there is a link there to a printable board layout if you want to roll your own. There is also a link to an ExpressPCB board layout that you can modify and/or submit to ExpressPCB to have them make the boards. (I have no connection to ExpressPCB, but their software seems to have an easy learning curve, and is free for non-commercial use.)

Note that all this assumes you have Linux software that can measure frequencies. (Daqarta does that in Windows, plus provides calibration for direct temperature readout in C or F, including negative readings.)

Best regards,

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

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!

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

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

"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

Thermocouples are very linear and can messure upto 2320 degrees celsius.

Nice table in the dutch wiki page.

--
pim.

with ubuntu linux.

time.

Do you really have to use thermocouples? They are the hardest way to measure temperature. I prever the Analog Devices AD590 series, I think there is also a plastic-package version, the AD592. They are a

2-terminal sensor, where current is proportional to absolute temperature. So, room temperature is 20 C or 293 K, so it conducts a current of 29.3 uA.

Jon

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 :-).

Not to mention that they involve a reference junction for which you must know the temperature. Unless you have an ice bath handy, this involves an independent non-thermocouple sensor like a thermistor, diode, or IC. So just use that instead! (Unless you need really high temperatures.)

One good thing about TCs is that they don't need typically calibration... they are supposed to conform to a standard for the TC type (J, K, R, S etc). You just measure the output voltage, correct for the reference junction temperature, and look up the temperature for that voltage. Accuracy is typically +/-2 degrees C. But the voltages are really small: 1 mv or less at room temperature (0.10 mV for R or S types).

I'd say, save the thermocouples for the really hot stuff. For "normal" temperatures (say, freezing to boiling water ranges), you can get much better precision and accuracy, not to mention convenience, from an IC.

Best regards,

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

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!

"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
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

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
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

If all you need is a degree or two's accuracy near room temperature, almost any method will work. IC temperature sensors are generally fairly putrid--slow, inaccurate, and noisy.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

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:

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

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
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net