Shohadawy

I want to ask about thermocouple calibration in order to let the pic16f877 microcontroller to calculate the temperature value corresponding to the thermocouple reading and display the result on an LCD

dknguyen

You don't need to calibrate a thermocouple. THey are made very accurately already. What you need to do is amplify the voltage, linearize it, and provide a reference.

You first need a very quiet differential amplifier. A thermocouple puts out about 40uV/C and you need to amplify this to something where the PIC can actually read it. YOu can either make the amplifier gain all funny so the temperature reading is linear with the output voltage, or you can just make a linear amplifier and linearize it in software. You the need an absolute temperature sensor that is at the same temperature at the "close" end of the TC so the PIC can reference the relative temperature reading of the TC (between it's two ends) to give you the absolute temperature at the far end.

Consider using something like the AD597/AD595 or MAX6675 that does all this work for you. If you still insist then you have to go out and Google for the thermocouple output voltage vs temperature curves/equations - they won't be pretty.