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Interfacing TC directly with arduino without any extra circuitary involved.

I want to interface thermocouple to arduino board directly. I have an anlog pin which will read the analog input directly. Then why I need to extra circuitary to read the voltage sent from TC.


I will be using either J or K and termperature range from 0-500 Deg C. For corresponding voltages will be from minimum 0 to something.


What are the difficulties?

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Kudos are always welcome if you got solution to some extent.

I need my difficulties because they are necessary to enjoy my success.
--Ranjeet
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Message 1 of 13
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Sure you can connect a TC signal directly to an Analog input if you only need plus or minus 50 degree Centigrade resolution and you don't care if room temperature variations affect the accuracy of your readings.  The output of a Type J thermocouple is approximately 5mV per 100 degrees Centigrade and the output of a Type K thermocouple is approximately 4mv per 100 degrees Centigrade. An Arduino ADC is a 10 bit ADC,  This a resolution of 1 part in 1024.  With a full scale range of 5 volts an Arduino ADC has a resolution of approximately  5 mV.  Which is approximately equal to the change in output voltage you get from either a Type J or K thermocouple with a 100 degree Centigrade change in temperature. 

Other people who need better resolution and accuracy than what you will get when you connect a TC directly to an Analog input use:

<https://www.sparkfun.com/products/306>

Or <http://www.adafruit.com/products/269>

For a TC table see:

<http://www.ni.com/white-paper/4231/en/#toc1>

hrh1818

hrh1818

Message was edited by: hrh1818

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Message 2 of 13
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Thanks for the reply,

Now arduino resolution is 5mv and take an example of J and in that for 150 --> 8.010 and for 155 --> 8.286 and you see that 0.2V difference. and I am sure this can be detected by arduino.. Correct me if it is wrong.

Then why I should use that IC?

--------------------------------------------------------------------------------------------------------
Kudos are always welcome if you got solution to some extent.

I need my difficulties because they are necessary to enjoy my success.
--Ranjeet
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Message 3 of 13
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AD595-AQ and MAX31855 is only for K? I am not sure which one I will gonna use?

--------------------------------------------------------------------------------------------------------
Kudos are always welcome if you got solution to some extent.

I need my difficulties because they are necessary to enjoy my success.
--Ranjeet
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Message 4 of 13
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Because the table I supplied a link to is in millivolts.   Go bJack and read read the Overview at the top of the table.

herh1818

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Message 5 of 13
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Got the points..Thanks but it didnt clicked me. So can I use transistor for amplification of mV signal. I saw the pricing at its 1K approx. All the link you gave is for K only. But I need is J or K

--------------------------------------------------------------------------------------------------------
Kudos are always welcome if you got solution to some extent.

I need my difficulties because they are necessary to enjoy my success.
--Ranjeet
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Message 6 of 13
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Yes both of the devices I listed are for type K thermocouples.  But if you prefer to use type J Thermocouples similar devices are available.

hrh1818

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Message 7 of 13
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Is there any IC which is programmable? For amplification can I use transistor?

--------------------------------------------------------------------------------------------------------
Kudos are always welcome if you got solution to some extent.

I need my difficulties because they are necessary to enjoy my success.
--Ranjeet
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Message 8 of 13
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Programmable i.e. J or K can be changed and for amplification can I use transistor

--------------------------------------------------------------------------------------------------------
Kudos are always welcome if you got solution to some extent.

I need my difficulties because they are necessary to enjoy my success.
--Ranjeet
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Message 9 of 13
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The MAX31855 says that it can do K, J, N, S, T, E, and R type thermocouples.  Using a "transistor" doesn't make any sense because it is a very basic electrical component that is used to build other circuits.

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Message 10 of 13
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