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Topic: High Resolution Thermocouple and Data Log (Read 7 times) previous topic - next topic

WillR

I don't think you understand your problem space well enough to describe it to us.

I think this is an R&D type question...
http://www.micro-epsilon.com/products/temperature-sensors/index.html

Dig around a bit...
http://www.google.ca/#sclient=psy&hl=en&q=infra%20red%20temperature%20sensor%20high%20speed&aq=&aqi=&aql=&oq=&pbx=1&fp=ec885af529af1eb0&pf=p&pdl=300

You can do some more google searches I am sure.
Just another Hacker

Glass

A standard type K thermocouple will work well above the temperature range you are talking about.
At 900F the output will only be around 20 millivolts, so you might want to use an operational amplifier to expand this to about 4 volts.  Alternatively, you could use the ARef input and analogReference() function to scale the Arduino input to 25 or 30 millivolts full scale.  Not sure offhand if one way would be better than the other.  10 bits of A/D would give you +/- about 2 degrees resolution, not counting the limits of error of type K.
A bare-bead thermocouple made of fine wire will give the quickest response time.  Might be hard to seal at high pressures.
Since you are working in a combustion environment (oxidizing? reducing?), this can affect your choice of materials .... type N might be preferable for a reactive environment.  Sheathing can improve resistance greatly but at the expense of response time.
www.omega.com has extensive reference materials on temperature measurement which may be useful.


Another thought:  what is the thermal coefficient of resistance of your ignition coil material ?
If it is high enough, you might be able to measure temperature directly by measuring voltage drop at constant current like a standard 4-wire resistance measurement (or current at constant voltage if that is more convenient).

Glass


Quote
you could use the ARef input and analogReference() function to scale the Arduino input to 25 or 30 millivolts full scale


The minimum recommended reference is around 1 volt. Below that Arduino is too noisy to produce reliable results.

Note also that any attachment to a real thermocouple must use an "ice-point" reference compensation or else you will never know whether you are measuring the temperature at the thermocouple, or the temperature at the junction point.  That is one of the downsides of using real thermocouples.


Thanks, wasn't sure about the noise floor, thats why I inserted a caveat.

Good point about the ice point, too ... most OEM instrumentation fakes this automagically.

B@tto

#8
Mar 16, 2011, 12:42 pm Last Edit: Mar 16, 2011, 12:47 pm by B@tto Reason: 1
You can use an AD595ACD to inferface directly with the thermocouple ==> http://www.datasheetcatalog.com/datasheets_pdf/A/D/5/9/AD595AQ.shtml
and an ADS1213 to improve the speed and the resolution of the measurement ==> http://focus.ti.com/lit/ds/symlink/ads1213.pdf

kf4ixm

Depending on the type of thermocouple you use, you CAN read temperatures up to around 2912 deg. F with type R thermocouples. http://en.wikipedia.org/wiki/Thermocouple You can use a Maxim MAX6675 http://www.maxim-ic.com/datasheet/index.mvp/id/3149 chip to interface with a type K thermocouple that will give you 2012 deg. F. it has built in cold junction compensation also. As far as the 1000 readings a second, i don't know if it can measure and send data that fast, but i do know that it works great for interfacing thermocouples.

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