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Mass airflow sensor basics | MAF sensor working

This page describes basic function of Mass airflow sensor (i.e. MAF sensor). It mentions Mass airflow sensor(MAF sensor) construction and working of Mass airflow sensor(MAF sensor). It mentions advantages and disadvantages of MAF sensor over Vane meter.

Definition: The sensor used to determine mass flow rate of the air is known as mass airflow sensor. The air mass details are required in order to balance correct amount of fuel mass to the vehicle engine.

As air density depends on temperature, altitude as well as application of forced induction, MAF sensors are more useful and more appropriate to determine quantity of air intake in each of the cylinder compare to volumetric flow sensors.

Mass Airflow sensor and Oxygen Sensor are used together to control air/fuel ratio accurately in the engine.

Mass Airflow Sensor-MAF sensor construction

MAF sensor position

The figure-1 depicts position of Air Flow Sensor. As shown it is placed between air cleaner and throttle body directly in intake air stream. The Mass Airflow Sensor (MAF sensor) converts amount of air available in the engine into voltage signal. Air volume information is essential to calculate load in the ECM (Engine Control Module). The information will help for the following.
• How much fuel to inject
• When to iginite cylinder
• When to shift transmission

Following are the types of Mass Airflow sensors:
• Vane Airflow Meter
• Karmen Vortex
• Hot Wire MAF Sensor

Mass Airflow Sensor(MAF sensor) working

Mass Airflow Sensor

The Hot Wire type of MAF sensor is most common and most popular. It consists of thermistor, platinum hot wire and electronic control circuit. The same has been depicted in the figure-2.

Let us understand working of hot wire mass airflow sensor.
• Thermistor measures incoming air temperature.
• Hot wire is kept at constant temperature with respect to thermistor using electronic control circuit.
• When air flow increases, hot wire loses heat and control circuit compensates this by increasing more current through the wire.
• At the same time Control circuit measures current flow and proportionately puts out voltage signal.

MAF sensor curve

The MAF sensor curve for air flow versus output voltage is shown in the figure-3 above.

Advantages of Hot Wire MAF Sensor

Following are the advantages of Hot Wire MAF Sensor:
• It responds faster to changes in air flow rate.
• It is less sensitive to location as well as orientation.
• It is durable as there are no moving parts.
• It is less expensive.
• Avoids use of separate pressure sensor and temperature sensor to determine air mass.
• Smaller size.

Disadvantages of Hot Wire MAF Sensor

Following are the disadvantages of Hot Wire MAF Sensor:
• Oil and dirt contaminates hot wire and hence deteriorates accuracy of sensor.
• Thin platinum wire can get damage if not handled properly.

Sensor RELATED LINKS

Also refer IoT compliant sensors which includes ambient light sensor, optical sensor, gesture sensor, proximity sensor, touch sensor, fingerprint sensor etc.

Refer Sensors and transducers article which covers types, basic functions and provide links to sensors and transducers. It include temperature sensor, humidity sensor, strain sensor, proximity or occupancy sensor, force or load sensor, voltage and current sensor, pressure sensor, speed sensor, resistance sensor, power sensor, level sensor, event or state sensor etc.

Sensors and Transducers Related Links

Proximity Sensor
Occupancy Sensor vs Motion Sensor
LVDT and RVDT sensor
Position, displacement and level sensor
force sensor and strain sensor
temperature sensor
pressure sensor
Humidity sensor
MEMS sensor
Touch sensor
Haptic sensor
Wireless sensor

RF and Wireless Terminologies


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