A single thermistor operated like this is only useful if the temperature of the incoming air is constant. A thermal airflow sensor will typically use two sensor elements. One sensor measures the airflow temperature and the control scheme holds the other sensor at a constant temperature above the aiflow temperature by varying the drive current through the sensor. The drive current is then proportional to mass air flow and is compensated for airflow temperature (for linear sensors). This is the scheme used in the Mass Airflow (MAF) sensors used on many car engines. You could use a single sensor and alternate between measuring airflow temperature and volume I suppose, but this will greatly limit the response time. Using thermistors is a pain because the very high degree of non-linearity makes the above scheme more difficult (i.e. a constant temperature difference is not a constant resistance difference). Using more linear sensors can give a much simpler design e.g. the link blow uses NPN transistors as the temperature sensors: http://electronicdesign.com/test-amp-measurement/series-connected-transisto= rs-use-differential-heating-sense-airflow -- Mike On 29 August 2016 at 03:29, Dwayne Reid wrote: > The most reliable air-flow sensor that I am aware of is a simple > thermistor. You pass enough current through the thermistor that it > self-heats to some temperature well above ambient. The resistance > changes in a reliable and repeatable fashion as the amount of air > passing over the thermistor changes. More airflow results in a lower > temperature. > > Easy to implement and very inexpensive. > > dwayne > > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .