Hi guys! My under grad study is making a portable ammonia gas sensor. I am now using MQ 137. I already made the codes to produce ppm and rs/ro. Also, i used the data sheet to get the slope of the curve. Now i am confused if how to differ the load resistor. do i need to insert a potentiometer or should i just alter the load resistance defined at the code? thank you so much.

 

by the way, i used an apollo ammonia water strong to test my code, however the bottle did not specify any molarity or concentration so i cannot compare if my result is right or not. but the slope im getting has 55% error than the slope in the data sheet. can anyone pls help me how to calibrate it? Thank you so much