What is the application of Wheatstone bridge in automobile air flow sensor?

1. Hot Wire/Thermal Mode Air Flow Sensor Appearance

There are many types of air flow sensors. The most commonly used ones are hot wire and thermal mode, which are mass flow detection sensors. (Tip: The hot wire type cancels the self-cleaning signal line and is a five-pin sensor)

2. Practical Application of Hot Wire/Hot Mold Air Flow Sensor

In the past, Nissan's hot-wire air flow sensor not only had a self-cleaning function, but also had a variable resistor, which was manually adjusted to change the concentration of the mixture at idle speed. Nowadays, closed-loop control has been widely used in automobile engine mixtures, and the concentration of the mixture no longer needs to be manually adjusted, so the variable resistor has been cancelled.

Nissan hot wire air flow sensor

1.6L Corolla Hot Wire Air Flow Sensor

Jetta/Santana hot mode air flow sensor

3. Working Principle of Hot Wire/Thermal Mode Air Flow Sensor

An air flow sensor that uses a hot wire or a hot film as a heating element, the heating element (hot wire or hot film) resistor RH and the temperature compensation resistor (intake air temperature sensor) RT are respectively connected to the two arms of the Wheatstone bridge circuit.

When the temperature of the heating element is higher than the intake air temperature, the bridge voltage can reach a balance, and the heating current is controlled by the control circuit A with current amplification function to keep the difference between RH and RT constant.

Wheatstone bridge structure diagram

4. Internal structure and working data of hot wire/thermal mode air flow sensor

Three-wire air flow sensor

Four-wire air flow sensor

Five-wire air flow sensor