A special type of flowmeter

Hot-wire air flowmeter, hot-wire air flowmeter refers to a special kind of flowmeter.

The flowmeter adopts the method of isothermal hot wire, as shown in figure 1.In the figure, RH, RK, RA and RB constitute the four arms of the wheaton bridge. The hot-wire RH (usually made of platinum wire) and the temperature compensation resistance RK (cold wire) are placed together in the measured channel to maintain the temperature difference between RH and the airflow at the same level (usually 100ºC or 150 & ordm;C).When the airflow is increased, due to accelerated heat dissipation, RH cooling resistance changes, and the bridge loses balance. At this time, the integrated circuit will raise the bridge pressure to restore the bridge balance, and the pressure drop on RA is usually taken as the measurement signal.

Thebasicprincipleofhot - wireairflowmeteristoarrangea "hot - wire" intheintakepipe. Theessenceof "hot - wire" isathermistor: thetemperaturedecreasesandtheresistancevaluedecreases. ThecontrolcircuitheatsthehotwiretOacertaintemperature Whentheengineisworking, theairintakeaircoolsthehotwire, andthetemperatureofthehotwiredecreases Inordertomaintaintheoriginaltemperatureofthehotwire, thecontrolcircuitincreasestheheatiNgcurrent. Thatis, thelargertheairintake thegreatertheheatingcurrentthatthehotwireneedstoadd, andthecontrolcircuitconvertsthechangeofcurrentintothechangeofvoltageandoutputsitastheairintakesignal.