Air Flow Sensor : Circuit, Working, Types, Wiring, Interfacing & Its Applications

There are various types of sensors are used in automobiles to control all the vehicle operations and also to protect from damage like; MAP, engine knock, Throttle position, camshaft position, air flow, engine speed, oxygen, voltage, and many more. Among them, an airflow sensor is one type of automotive sensor. The first plug-in mass air flow sensor was invented in 1996 by DENSO. So their continuous developments within automotive technologies are leading the method for high-range auto parts. This sensor detects the quantity of air drawn into the vehicle engine & relays a signal to the ECU (engine control unit). This article discusses an overview of an airflow sensor or MAF sensor, its working, and its applications.

What is an Air Flow Sensor?

An airflow sensor is a type of automobile sensor used to measure the speed of airflow throughout a system like HVAC, combustion engines & also industrial processes. So the ECU (engine control unit) simply estimates the amount of fuel mass required to maintain air as well as fuel in balance depending on the real-time inputs. An alternate name for an airflow sensor is the MAF (Mass Air Flow) sensor, MAF, or air meter which changes the amount of air entering the engine of the vehicle into a voltage signal for measuring its load. In addition, air density can be changed by various factors like pressure, temperature, humidity, and many more.

Airflow Sensor Working Principle

An airflow sensor works by simply measuring the variation within the resistance of a hot wire & changing it into electrical signals and passing it to the ECU (engine control unit). This signal is used to determine the fuel amount to infuse into the engine.

The airflow sensor includes two wires like electrically heated & the other wire is not. Whenever a thin wire of this sensor is heated at a stable temperature & located in the airflow path then it cools it down in a way that is proportional simply to the speed of airflow.

Whenever the difference in temperature between the sensor wires varies, the sensor automatically increases or decreases the flow of current throughout the wire. After that, the current is transmitted into the ECU & changed into voltage (or) frequency to translate it into airflow.

Air Flow Sensor Circuit Diagram

Generally, air flow detection is very useful in various circuits. So a simple air flow sensor circuit is shown below which is used to detect the air flow available. This airflow circuit doesn’t need any RTD (or) Zener diode but this circuit uses a simple AC bulb filament including some components for detecting the air. The required components to make this air sensor circuit mainly include; LM358 IC, LM7805, Resistors like; 680ohm, 100ohm, 10K & 330ohm, 100uF capacitor, 50k variable resistor, LED, 12V power supply, incandescent bulb, jumper wire, push button and DC fan. Connect this circuit as per the below circuit shown.

Working

This airflow sensor circuit is shown below which is used to detect the air flow. This circuit works with a 12V DC supply. The significant component used in this circuit is the bulb filament because it is accountable for making a difference in voltage whenever there is air presence. The bulb filament in this circuit has the NTC (negative temperature coefficient), so its filament resistance will change inversely toward the temperature. Once the temperature is higher, then filament resistance is low.

Whenever there is no air by default, the bulb filament’s resistance value will be low due to some heat within it. When air flow supplies from it the temperature of the bulb filament decreases and the filament resistance will be increased.

So due to this change within the resistance, a voltage variation is produced across the bulb filament which is caught by LM358 IC & produces a low signal. This IC is connected in comparator mode so it compares input voltage through the reference voltage & provides the output correspondingly.
A Potentiometer in this circuit is used to calibrate the circuit, an LED is useful in indicating airflow, and both the push button & a DC fan are used to flow the air supply throughout the filament.

Types of Air Flow Sensor

There are different types of airflow sensors which are discussed below.

Volume Air Flow Sensor

Volume air flow sensor is used to measure volume flow, filter monitoring, differential pressure & liquid levels detection. These types of airflow sensors are applicable in a medical, clean room, & filter technology within air conditioning ducts, ventilation, spray booths & industrial kitchens mainly for monitoring filters & measurement of level or to control frequency converters.

MAF Sensor

MAF sensor is also known as a mass air flow sensor which is used in automobiles for detecting the mass flow rate of air that goes through the engine of a vehicle as well as the amount of fuel injection.
For the engine control unit of the vehicle, the air mass data is required for balancing & also delivering the accurate fuel mass toward the engine. Air will change its density through pressure as well as temperature. Air density will change within automotive applications, with the altitude, the ambient temperature & the utilization of forced induction, so these sensors are more suitable as compared to volumetric flow sensors to decide the amount of intake air in every cylinder.

Vane Type Mass Air Flow Sensor

The sensor that has a metered vane that is located along the flowing air direction is known as a type of mass air flow sensor. This type of airflow sensor is used to measure the amount of air passing through them.

The vane in this sensor is connected simply to a spring & arranged in its rest position. But whenever the air begins to flow, then the vane will get relocated under the spring pressure. So this deflection can be changed into the voltage signal using a potentiometer. After that, it is used to decide the speed of airflow.

Hot-Wire Air Flow Sensor

This type of airflow sensor is used in several modern vehicles for measuring the air mass entering the engine. This sensor plays a key role in engine management & optimization by simply providing information to the ECU (engine control unit) to adjust the mixture of air-fuel for very efficient combustion.

The main function of this sensor is to measure the incoming air volume as well as density. So this data is significant mainly for the engine control unit to decide how much fuel to infuse into the combustion chambers to maintain the right air-fuel ratio

Air density mainly depends on altitude, temperature & forced induction application. These sensors are more helpful & suitable for deciding air intake quantity in each of the cylinders as compared to volumetric flow-type sensors.

Air Flow Sensor Wiring Diagram

The wiring diagram of the airflow sensor (mass air flow sensor) is shown below which is designed based on the construction, year, type, demand & model. These wiring diagrams are available in four forms 3-wire, 4-wire, and 5-wire. So, here we are wiring a 4-wire air flow sensor which is explained in the below section.

The 4-wire air flow sensor wiring diagram has a 12V positive power supply (hot-wire), IAT (Intake Air temperature signal) signal, MAF signal & MAF GND.

A 12V positive power supply (hot-wire) is connected to a fuse & a relay within the fuse box. Next, the mass air flow signal wire can be connected to the ECU of the vehicle. This signal wire simply transmits the sensor signal to the ECU. The ground wire of the MAF sensor can be used as a common GND connection for both the ECU & sensor of the vehicle.

The signal circuit of the airflow sensor can be designed into the MAF sensor to measure the amount of flowing current throughout the sensor and change this current supply into voltage. After that, it transmits it into the ECU of the vehicle through the MAF signal cable. So this signal circuit is grounded separately. Additionally, the sensor includes an integrated IAT sensor, that provides the IAT signal to notice the intake air temperature signal.

Air Flow Sensor Interfacing with Arduino

The air flow sensor (Anemometer sensor) is a low-cost sensor with Arduino friendly. This sensor is also called wind sensor Rev. p which has hardware compensation mainly for ambient temperature & stands for PTC thermistors. This airflow sensor is used to detect hurricane-force storms exclusive of saturating which ranges from 0 – 150Mph storms. It provides upto 3.3V output sense voltage which is most appropriate for all ranges of Arduino development boards & microcontrollers.

This sensor works simply by thermal anemometer-based method or hot wire method which provides sense out through heating an element as well as the power variation necessary to maintain the heat on heat element throughout wind flow. Whenever the airflow increases, then suddenly the heating element loses heat & needs more power to maintain warm. When there is no wind the heating element stays stable. Thus it measures & also draws the variation between the current &power flowing throughout the heating element.

The technical specifications of this sensor mainly include;

• Its voltage supply ranges from 4 to 5 volts.
• Its current supply ranges from 20 to 40mA.
• Its wind velocity ranges from 0 to 60mph.

Pin Description:

The pin configuration of the airflow sensor (or) wind sensor in the Rev. P version is available in a 5-pin configuration which is shown below.

• The GND pin is used for the common GND connection of the circuit.
• V+ pin is the input voltage pin of the sensor and is connected to the Arduino.
• OUT or Ao pin is the analog o/p signal of the air sensor which is used for determining the sum of flowing current supply throughout the air sensor.
• TMP pin provides the temperature output which is a simple voltage divider through a thermistor as well as a resistor. The output of this pin is high at lower temperatures & decreases at high temperatures.
• The RV pin is the reference voltage used for the calibrated output. This pin does not drop voltage under 1.8V even at room temperature. This voltage cannot be affected by the calibration potentiometer.

The connections of this interfacing follow as;

• Connect this sensor’s GND pin to the Arduino’s GND pin.
• The V+ pin of the sensor is connected to the Vin pin of Arduino.
• The OUT pins of the sensor are connected to the Ao pin of the Arduino.
• The TMP pin of the sensor is connected to the A2 pin of the Arduino.
• The sensor’s RV pin is not connected.

Code

The required Arduino code for this interfacing includes the following.

const int OutPin = A0; // wind sensor analog pin hooked up to Wind P sensor “OUT” pin
const int TempPin = A2; // temp sensor analog pin hooked up to Wind P sensor “TMP” pin
void setup() {
Serial.begin(9600);
}
void loop() {
// read wind
int windADunits = analogRead(OutPin);
// Serial.print(“RW “); // print raw A/D for debug
// Serial.print(windADunits);
// Serial.print(“\t”);
// wind formula derived from wind tunnel data, anemometer and some fancy Excel regressions
//This scaling doesn’t have any temperature correction in it yet
float windMPH = pow((((float)windADunits – 264.0) / 85.6814), 3.36814);
Serial.print(windMPH);
Serial.print(” MPH\t”);
// temp routine and print raw and temp C
int tempRawAD = analogRead(TempPin);
// Serial.print(“RT “); // print raw A/D for debug
// Serial.print(tempRawAD);
// Serial.print(“\t”);
// convert to volts then use the formula from the datasheet
// Vout = ( TempC * .0195 ) + .400
// tempC = (Vout – V0c) / TC see the MCP9701 datasheet for V0c and TC
float tempC = ((((float)tempRawAD * 5.0) / 1024.0) – 0.400) / .0195;
Serial.print(tempC);
Serial.println(” C”);
delay(750);
}

The Arduino board is powered with 9V with an external power board & the sensor is powered from the Arduino board’s Vin pin. Upload the above code into the Arduino & monitor the analog o/p voltage & changes in temperature on the OUT pin & TMP pin of the airflow sensor for detecting the wind speed.
The output of the analog sensor is logarithmic so the sensor picks up & monitors extremely little airflow at low ranges although it won’t saturate at complete power until the air flow attains about 60mph.

The voltage signal attained from the analog pin (Ao pin) of the sensor is proportional directly to the wind speed. The fundamental principle of the air sensor is similar to conventional hot wire technology. So this technique is outstanding for low wind to moderate wind speeds & this method is appropriate to measure the direction of indoor airflow.

Advantages & Disadvantages

The advantages of airflow sensors include the following.

• The airflow sensor is very simple to install.
• These are not expensive.
• This sensor measures the whole pressure and the static air flow pressure & the average air velocity.
• More design options are obtainable.
• These sensors are simpler to maintain due to the lack of moving parts.
• This is the most common type of sensor to use in measuring airflow.

The disadvantages of airflow sensors include the following.

• This sensor can be affected by gas inclusions and vibration sensitivity whenever they are installed improperly.
• These are expensive as compared to other sensors.
• It has reduced air intake & also performance.
• These sensors need calibration.
• Air flow sensors are easily contaminated, leading to failure and malfunction.
• This sensor causes various problems like loss of power, mild to severe hesitation, not restricted to rough idle, poor fuel economy, etc.
• A bad air flow sensor causes your vehicle to face poor drivability problems like engine stalling, hesitation, or jerking in acceleration.

Applications/Uses

The applications of airflow sensors include the following.

• Airflow sensor is used for measuring & also controlling the flow speed of air within ventilation & air conditioners.
• This sensor helps in analyzing the flow speed of air within fuel-injected combustion engines.
• It is used in automotive, industrial, and commercial applications.
• These sensors are found frequently within analytical chemistry equipment.
• Airflow sensor is used in gas chromatography to identify compounds that are not identified.
• These sensors are used in medical devices, chemical factories, testing, and analytical applications.
• This sensor is used to trace flow speed data of both the injection procedure of the sample into the machine & the flow speeds throughout the separation columns.
• The application of an airflow sensor is the mass flow speed analysis for air in fuel-injected combustion engines.
• It applies to gas analysis devices, ventilators, oxygen concentrators, density testing devices, and air quality sampler measuring devices.
• An MAF sensor is utilized within automobile engines to help in controlling combustion efficiency.
• The sensor tells the engine computer if the car is at the bottom of the atmosphere or high on a mountaintop (or in between) where there is less oxygen.
• This sensor allows efficient and precise control of HVAC systems.
• This sensor is utilized in ventilation systems for monitoring the breathing cycle of patients.

Thus, this is an overview of the airflow sensor, working, circuit, types, wiring, interfacing, and its applications. Air flow sensors are appropriate for the measurement & control of air supplies within ventilation & ACs. These sensors are very easy to install & measure the whole pressure, the stationary air flow pressure & the average air velocity. Here is a question for you, what is a flow sensor?