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
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
ks with ubuntu linux.
s over time.
How about this...
ks with ubuntu linux.
s over time.
How about this...
ks with ubuntu linux.
s over time.
ks with ubuntu linux.
s over time.
How about this...
On a sunny day (Mon, 29 Nov 2010 16:36:56 GMT) it happened ratullloch_delthis wrote in :
with ubuntu linux.
time.
I cannot recommend anything, but I designed and build this:
Panteltje Atomics Brightens up your day
If it's low cost you're after, it would be hard to beat TEMPer USB (
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.
------------------------------------- /_/ ((@v@)) ():::() VV-VV
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Well, thermocouple wire is pricey, so you want short thermocouple wires. A thermocouple doesn't work without a reference junction, so there has to be a thermal block somewhere (and the inside of a hot computer case is the wrong place), So, you're talking about a computer=3D>cable=3D>
block, with multiple analog channels (the computer has to read, at minimum, the thermocouple and a temperature-of-block sensor). The thermal block can be as simple as a potmetal enclosure with a terminal strip and sense diode, or you can get fancy with batteries and preamps.
Branch #1: DAQ card in computer, cable/preamp box you build or buy Branch #2: DAQ system on powered tether/cable (probably USB) and some custom work to connect the thermocouples properly Branch #3: Data logger with battery power, occasionally hook to the computer to download. This gives a few advantages (no ground requirements).
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
with ubuntu linux.
time.
other
How very iranic of you.
-- John
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
"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
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