FREQUENCY AIR FLOW METER

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In the automotive environment a frequency is used in the airflow meter. The frequency, not the amplitude nor the PWM (Pulse Width Modulation), contains the information of the amount of airflow.

The engine manufacturer chooses a frequency as information carrier because it can be counted (over time) and has a much higher resolution compared to analogue signals in a noisy engine compartment. Sometimes the PWM of the frequency signal is a measure of the temperature, thus transmitting TWO signals over one wire.

 

A frequency signal can be modified by routing it through a unit as follows:

  • Count the frequency and convert its engineering units (Hz)
  • Add the mapping information, e.g. 1%
  • Output the new frequency.

 

With this simple arrangement the ECU sees a 1% higher airflow as the one measured by the airflow meter.

The actual conversion is done one every frequency period, thus giving instantaneous control.

The mapping information depends on the engine operating point such as idling, light load, cruising or full throttle.

If the airflow is used to determine the operating point, then the unmodified frequency signal must be used.



FREQUENCY MODIFICATION CAN BE DONE BY THE FOLLOWING UNITS:

 

VISIT THE FOLLOWING LINKS FOR MORE INFORMATION ON THE FREQUENCY AIR FLOW METER: