Sensor’s measuring potentiometer is made on a ceramic substrate. Its output voltage depends on the position of the barrier position and the barrier position itself depends on the volume of the airflow. Supply voltage is fed to the potentiometer. The barrier is mechanically connected to the potentiometer wiper (3). The sensor is also equipped with an additional barrier (2), which serves not only for balance but as damper against fluctuations. This barrier is placed into the airflow consumed by the engine and is moved proportionately with increasing or decreasing the airflow. Sensors for volume consumption of air (fig.5) have an air barrier (4) equipped with a return spring. MAF sensor for volume consumption of air – VAF sensor Hot film sensors tend to be more robust and less susceptible to contamination than hot-wire types. One side of the film encounters cooling airflow, while the shielded backside maintains a consistent temperature, and the current differential between the two is measured and relayed as a square-wave digital frequency output, between around 30Hz at idle and 150Hz at wide-open throttle. Hot-film MAF sensors function much like a hot wire sensor, and used a centrally-heated film or metallic grid-type element. MAF sensor which measures the mass of air flow – Hot Film sensor (HFM) This process is controlled by the onboard controller. Thus all the dirt stick to the wire is burned. To prevent the pollution after turning off the engine, the wire is heated to a temperature of 1000 º C for 1 sec. The temperature changes simultaneously influence both the heated resistance conductor (2) and the temperature compensation resistor (4), and thus the Wheatstone resistor bridge remains balanced.ĭuring operation the platinum wire inevitably pollutes. Changes of temperature are compensated by the resistor (4), which is a platinum ring, suspended into the air stream. This current also flows through a calibration resistor and forms a voltage drop which enters the onboard controller for calculation of the quantity of the injected fuel. This process continues until the temperature and resistance of the conductor does not lead to system balance. The Wheatstone resistor bridge is asymmetrical and a voltage appears which is submitted to an amplifier and directed to raise the wire temperature. Constant temperature of approximately 100 ºС is maintained by increasing or decreasing the electrical current flowing through the circuit while the incoming airflow cools the wire.īy increasing the airflow, platinum wire gets cool and its resistance decreases. Heated platinum wire, suspended in the engine’s air stream (3), is one of the legs of a Wheatstone bridge. Operation of MAF is based on the principle of constant temperature. Hot wire (2) with diameter of 70μm is mounted in a measuring tube located before the throttle valve. MAF sensor which measures the mass of air flow – Hot Wire sensor This type of sensor is not sensitive to the pulsations associated with opening and closing of intake valves and the output reading does not depend on the density of incoming air. Nowadays the most common are MAF, because they don’t have mechanical moving parts and have great performance and accuracy. A sensor which measures the mass (kg/h) of the air flow – Hot Film MAF (HFM).A sensor which measures the mass (kg/h) of the air flow – Hot Wire MAF sensor (also known as HLM). A sensor which measures the volume (l / h) of the air flow – Vane Meter Sensor (VAF and also known as LMM).Sensor’s output signal frequency or duty cycle depends on the air consumption – HFM sensors. Sensor’s output signal voltage depends on the air consumption – VAF and Hot Wire sensors. 2 shows the MAF made by GM.Īccording to the principle of operation are: 1 shows the MAF sensor made by BOSCH, and fig. MAF usually is placed after the air filter and before the throttle valve in the air flow sucked into the engine.įig. Air consumption is one of the basic parameters for calculating the necessary amount of fuel. The sensor for volume consumption of air is used in many systems for management of engines for measuring value of the transitory cost of air. It is intended to be insensitive to the density of the air. A mass air flow (MAF) sensor responds to the amount of air flowing through a chamber containing the sensor.
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