1. Classification of Air Flow Sensors According to different methods of detecting intake air volume, air flow meters can be divided into two types: volumetric and mass. Among them, the volumetric type is divided into blade type, Kalman vortex type, and core type; Quality based air flow meters are divided into hot wire type and hot film type. Many cars such as Mercedes Benz, BMW, Volkswagen, etc. use hot film air flow meters. Early engine fuel injection systems were divided into two types: D-type (pressure type) and L-type (air flow type). The D-type fuel injection system does not have an air flow sensor. Figure 2-2 shows the basic control architecture of the D-type fuel injection system. Figure 2-4L Basic Control Architecture of Fuel Injection System for L-type Engine The fuel injection system for L-type engine (Figure 2-5) adopts a direct measurement method, which uses an air flow sensor to directly measure the air flow into the intake pipe. L-type sensors are divided into two types: volumetric flow sensors and mass flow sensors. Figure 2-5L fuel injection system million car purchase subsidy

2. How to calibrate thermal mass flow meters

The core methods for calibrating thermal mass flow meters are divided into three categories, which are suitable for different scenarios: real flow calibration method is accurate but costly, dry calibration method is convenient but slightly less accurate, and comparative calibration method requires serial standard equipment. 1. Real flow calibration method (accuracy priority scenario) uses actual fluid (such as gas) in conjunction with a standard calibration device to compare the measured flow meter data with known flow values, and the error value directly reflects the calibration result. This method requires a laboratory level flow standard device, which is commonly used in measurement certification, high-precision industrial production, and other scenarios. However, the equipment investment and site requirements are high. Dry calibration method (rapid on-site detection) is based on the mathematical model of the sensor provided by the manufacturer, inputting parameters such as fluid type, temperature, pressure, etc., and simulating flow output through theoretical calculations. Suitable for daily maintenance or on-site testing without actual flow conditions, it is easy to operate and cost-effective, but relies on the accuracy of equipment factory parameters. Drift errors may occur after long-term use.

3. Comparative calibration method (series comparison verification) installs the flow meter to be calibrated in series with a certified standard flow meter, synchronously measures the flow data of the same pipeline, and compares the differences. This method is suitable for online calibration or environments with mature flow systems, but standard flow meters must be regularly calibrated, and the installation positions of the two meters must meet the requirements of flow stability. After understanding the logic of selecting calibration methods, it is necessary to confirm whether the fluid properties parameters (such as gas composition, viscosity), temperature and pressure range are consistent with the calibration conditions before operation, in order to avoid calibration failure due to differences in operating conditions.

3. How much does a thermal mass flowmeter cost?

4. Working principle of thermal gas mass flowmeter

Thermal gas mass flowmeter works based on the

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