Vacuum flowmeter | Gauge pressure, absolute pressure and atmospheric pressure: analysis of pressure relationship in flowmeter measurement

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What are the symptoms of a broken air flow meter? The signal from the air flow meter is the core data of the engines electronic control system. Once the sensor malfunctions, it will have a significant impact on the normal operation of the engine. The fault indicator light of the car will light up, and the engine will experience idle shaking, poor acceleration, stall after starting, and other situations. Due to the development of industry in China, there have been many changes in the types of air flow meters for various working conditions. According to the development of the times, air flow meters can be divided into four types: L-type, D-type, hot wire type, and hot film type. The first generation L-type air flow meter has the simplest structure. Of course, there are no models currently in use. The second type is the D-type air flow meter, which is an upgraded version of the first generation air flow meter and can improve the performance of the air flow meter. The third type is the widely used hot wire air flow meter. The biggest feature is the use of the characteristics of thermistors to maintain a constant temperature of the hot wire, thereby ensuring stable accuracy in measuring intake air. The structure and working principle of the hot film air flow meter are similar to those of a hot wire flowmeter, mainly to improve the disadvantage of the hot wire becoming dirty after long-term use (which can cause inaccurate measurement values). It is currently the most widely used flowmeter. The structure of the air flow meter is shown in the following figure. The gas flowmeter is composed of a Wheatstone bridge consisting of a thermistor, a platinum hot wire, and two precision resistors inside. The engine ECU mentions providing current to the power transistor to heat the platinum wire to a certain temperature. When air flows through the temperature sensor and platinum wire, it will take away the heat of the platinum wire. At this point, the electronic control unit will increase the voltage flowing through the Wheatstone bridge, which is proportional to the amount of intake air passing through the intake pipe. The electronic control unit will calculate the fuel injection quantity based on this value, thereby changing the empty fuel ratio. The reason for the malfunction of the air flow meter is that various faults may occur during the use of the air flow meter, which affects its normal use. The main reasons for air mass flow meters are as follows: 1. Malfunction in the air mass flow meter circuit. During normal operation of the engine control system, all sensors must provide accurate and reliable data. When the liquid level of the sensor circuit malfunctions, causing the output signal to exceed the normal value of the specified range, the engine electronic control unit cannot recognize the signal normally. For example, if the maximum voltage output by the sensor is 5V, the ECU cannot correctly know what information the sensor is transmitting. The ECU will store the fault information in the memory and output the fault code at the same time. The output voltage of the air flow meter is between 0.2-4.9V. When the ECU receives voltage signals that exceed this range multiple times, it will report relevant fault codes. However, the engine ECU occasionally does not notice abnormal voltage, which may be caused by accidental contact between lines or vehicle bumps during driving. If the fault code P0100 is output, it indicates that the sensor circuit i

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