A flow sensor circuit for a fluid flowpath comprising: a processing unit , a self-heated thermistor , and a constant voltage or constant current source ; wherein said self-heated thermistor is situated in the fluid flowpath ; said flow sensor circuit is configured to: apply a high current to said self-heated thermistor during a first time period (T1); obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a second time period (T2); calculate the average (T2av) and standard deviation (T2sd) of said measurements obtained during T2 using said processing unit ; apply a low current to said self-heated thermistor during a third time period (T3); obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a fourth time period (T4); calculate the average (T4av) and standard deviation (T4sd) of said measurements obtained during T4 with said processing unit ; and ascertain the state of said flowpath using said T2sd and said T4sd with said processing unit , wherein the state of said flowpath indicates whether the fluid in the fluid flowpath is flowing normally, contains bubbles or is clogged, or contains air or is stopped. a processing unit , a self-heated thermistor , and a constant voltage or constant current source ; wherein said self-heated thermistor is situated in the fluid flowpath ; said flow sensor circuit is configured to: apply a high current to said self-heated thermistor during a first time period (T1); obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a second time period (T2); calculate the average (T2av) and standard deviation (T2sd) of said measurements obtained during T2 using said processing unit ; apply a low current to said self-heated thermistor during a third time period (T3); obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a fourth time period (T4); calculate the average (T4av) and standard deviation (T4sd) of said measurements obtained during T4 with said processing unit ; and ascertain the state of said flowpath using said T2sd and said T4sd with said processing unit , wherein the state of said flowpath indicates whether the fluid in the fluid flowpath is flowing normally, contains bubbles or is clogged, or contains air or is stopped. apply a high current to said self-heated thermistor during a first time period (T1); obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a second time period (T2); calculate the average (T2av) and standard deviation (T2sd) of said measurements obtained during T2 using said processing unit ; apply a low current to said self-heated thermistor during a third time period (T3); obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a fourth time period (T4); calculate the average (T4av) and standard deviation (T4sd) of said measurements obtained during T4 with said processing unit ; and ascertain the state of said flowpath using said T2sd and said T4sd with said processing unit , wherein the state of said flowpath indicates whether the fluid in the fluid flowpath is flowing normally, contains bubbles or is clogged, or contains air or is stopped. <EOS>