AnsweredAssumed Answered

EVAL-AD7792, Thermocouple Configuration and Calibration

Question asked by 1ConfusedEngineer on Jul 29, 2016
Latest reply on Aug 19, 2016 by jcolao

Dear Tech Support,


I currently am developing a project using your AD7792 ADC on the EVAL-AD7792 Evaluation Board with the Evaluation Software in a temperature sensing, thermistor/thermocouple configuration (as seen on page 28 of the ADC's datasheet) and am having some confusion. So you understand my current system, I am using a typical type K thermocouple along with a thermistor and a Reference resistor.


My first question is: are there ideal values for resistors coming off the thermocouple into the AIN1 terminals? I imagine I would want them pretty small due to the small signal from the thermocouple. Or are they only required for noise filtering purposes along with the capacitors? (currently only have resistors in line).


My second and most important question is regarding your calibration process. According to page 26 of the ADC's datasheet the calibration process for higher gains takes 4 cycles to complete. This is where I'm confused, for when I select one of the calibration options from the drop down menu in the mode registry on the EVAL Software it almost immediately goes into "idle" mode. I know this is the correct process of the ADC from the datasheet but my sample time takes 4-5 seconds and I was expecting roughly 20 seconds(4x a single sample) of calibration time. Is selecting the calibration option all that I need to do? Please send me your procedure for calibration and any recommendations you may have for me at this time.