10-04-2013 02:03 AM
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?
10-04-2013 02:06 PM
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
10-04-2013 10:49 PM
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?
10-04-2013 10:53 PM
10-04-2013 11:24 PM
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
10-04-2013 11:30 PM
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
10-04-2013 11:30 PM
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
10-05-2013 12:20 AM
Is there any IC which is programmable? For amplification can I use transistor?
10-05-2013 01:32 AM
Programmable i.e. J or K can be changed and for amplification can I use transistor
10-05-2013 12:13 PM
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.