Measuring Temperature

[Rob.Wilson]

Hi Lads a spot of help needed

I need some way of measuring the temperature in a temporary core oven i am going to knock up ,,250C max ,,,,,,,,, I saw some were a set up with a multi meter and two wire wound together   ,,, any idea what type of wire ?  and how do you calibrate it ?  . or dose anyone have a better idea


Thanks Rob

[John Rudd]

There are a number of ways of measuring temp...

Optical pyrometer..( I guess you aint got one to hand....) or there is the simple thermocouple...

A thermocouple is made by twisting together two disimmilar metal wires ( Iron/Constantan) that will generate an emf proportional to temperature...( Its called the Seebeck effect...  I'm a tiffy by trade..)

A standard dvm from Maplins should suffice for measuring the voltage 'though you may need tables to convert from volts to degrees( unlesse the dvm has a t/c input..! )

Have a look here: http://www.tc.co.uk/ I use this company at work, let me know if you have any queries.

[Bluechip]

Rob

I got one of these  .. or similar  .. comes with a (type K ??) thermocouple  

http://www.rapidonline.com/Tools-Fasteners-Production-Equipment/Test-Equipment/Multimeters/328-Digital-LCD-multimeter/31051

Up to circa 900 c IIRC

Will look if interested ..

Quite surprised how accurate it was .. about +/- 6 C at 800 C   Checked by a mate in the test labs @ RR

Dave BC

OOOps EDIT ... spec says type K  .. memory not so shot as I thought  ... Hope yet ..

[Bluechip]

No response from Rob yet !!!

Not gone down another hole has he ....  

[Bluechip]

Could well be ..

Did notice a puff of smoke ....

I, too,  shall retire ...

Dave BC

[raynerd]

...could the voltage not be linked to a PIC microcontroller and converted to the temperature. Would be a nice project there Rob, you said you fancied trying your hand at PICs when I met you earlier in the year!

Chris

[andyf]

Rob, have a look at this:
http://www.johnlewis.com/230335010/Product.aspx
Seems to go up to 320C. At that price, is it worth trying to make your own?

On the KISS principle, rather than building an oven, could you get permission to use the one in the kitchen? The thermometer might still be a good idea though, as oven thermostats can be rather approximate.

Andy

[Rob.Wilson]

Thanks lads 

Lots of top ideas 


John ,, Whats a tiffy ?    ,,,,Seebeck effect 

Dave    i needed my beauty sleep 

Hi Chris ,,,,,,,That one for the future  , i am saving electronics for winter projects ,when the shops too cold

Hi Andy ,, now why did i not think of that     could be the way to go , as this is oven is just a quick knock up job ,, until i can sort out something more permanent for core drying .

The plan was to use the kitchen oven , thats what i normally use ,,,,,,,,,,but the cores for the engine i am working on dont fit   

Thanks Rob 

[Bluechip]

...could the voltage not be linked to a PIC microcontroller and converted to the temperature. Would be a nice project there Rob, you said you fancied trying your hand at PICs when I met you earlier in the year!

Chris

Chris

Not so easy ... output is non-linear ... gruesome ...

Once had a large book about various sensors etc. including thermocouples. Absolutely crawling with narky maths ...here is a quick overview ..



http://en.wikipedia.org/wiki/Thermocouple#Voltage.E2.80.93temperature_relationship

EDIT  'Owd on ... looks like a set of calibration tables here

http://www.temperatures.com/tctables.html

Maybe quite do-able if you need a look-up table in the PIC   

Apologies for my pessimism

Dave BC

[AdeV]

Why beat yourself about the head doing it in a PIC, when it's already been done with an Arduino, and with some nice'n'easy code no less?

In fact, I did one my very self, for measuring exhaust gas temperature, I did a bit of a writeup here: http://www.microcogen.info/index.php?topic=927.0

The code was only a few lines long, its main task was to read the output from the little black chip (that was the hardest bit of the whole task, soldering that little bugger to a DIP socket...) & send it out over the serial port. I can post the code here if anyone's interested.

I bought a fairly expensive thermocouple that's good for 1100 degrees, there are cheaper ones which don't go so high.

[John Rudd]

Thanks lads 

John ,, Whats a tiffy ?    ,,,,Seebeck effect 

Tiffy...An instrument artificer (  I served my time at ICI..)


The Seebeck effect was discovered by a German dude, its the conversion of temperature difference into voltage (millivolts in this case..)

[SKIPRAT]

Hi All

I would cheat and use this it followed me home from a local car boot sale about a couple of years ago it comes in handy now and again i shall have to get a ceramic enclosed thermocouple to use it to its maximum temp though!





Cheers Paul