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Hi, I’m your assistant for industrial control systems. Last time we discussed the principle of mass flow meters; this time we’ll talk about their general selection criteria. Hurry up and get your notebooks ready to take notes. 1. Pay attention to choosing the right brand: Generally, it is necessary to comprehensively consider factors such as the product quality of the manufacturer, sales price, after-sales service, technical level, product features, production scale, and corporate reputation. 2. Pay attention to selecting the correct range: ① Convert the flow rate you need into a flow rate under standard conditions (mass flow rate). ②Using the mass flow rate conversion coefficient table provided by the manufacturer, convert the mass flow rate value of the gas you are using into an equivalent mass flow rate value for nitrogen (the calibration gas). If you wish to calibrate according to the gas you actually use, please inform the manufacturer. Further answers regarding the mass flow conversion coefficient are provided below. ③Determine the required standard range. Manufacturers usually have their own standard ranges for various specifications, and the maximum flow rate you actually use should be below a certain standard range value. The selection of the standard range should avoid being too large or too small. The error indicator for mass flow rate is specified as a percentage of the full-scale value; if the actual flow rate is low while a large full-scale value is chosen, the relative error of the measurement will be high. 3. Pay attention to choosing the correct working pressure indicator: The working pressure indicators may vary for different products, so make sure to select a product that is suitable for you. In addition to the maximum operating pressure, a mass flow controller (MFC) has another pressure-related parameter: the operating pressure difference, which is the pressure difference between the inlet and outlet sides of the MFC. This factor should be taken into consideration when selecting an MFC, as well as during its use. 4. Pay attention to the type of splitter inside the product: The type of splitter is not a technical specification, but it is mentioned here as something users should keep in mind because we have encountered some usage issues caused by splitters in actual use. The common types of splitters are tubular, conical, and powder metallurgy; each has its own characteristics. Generally speaking, the first type is less likely to get clogged, thus having a longer service life, while the last type tends to get clogged more easily. We have encountered several cases where users used a well-known imported MFC (powder metallurgy flow divider), and blockages occurred quite quickly even though the air supply was strictly filtered ； After switching to our product, it has been working properly ever since. The problem is obviously with the shunt. According to analysis, it is likely that the gas being used has strong adhesion, which causes blockages in the powder metallurgy diverter. Of course, the powder metallurgy diverter also has its advantages, while other dividers have their shortcomings; users should consider their own operating conditions when making a decision. 5. Pay attention to choosing appropriate accuracy metrics: Accuracy, linearity, and repeatability are several important indicators, among which repeatability is particularly crucial in many applications. It isn’t necessary to aim for the highest values; one should consider their actual needs. If users are not confident in the metrics provided by the manufacturer, those who have the means can conduct their own calibrations. For the calibration method, please refer to the relevant information below. 6. Pay attention to choosing the appropriate response time metric: Some application systems have high requirements regarding the response time of MFC, and users should consider their own circumstances accordingly. While considering the response time metric, attention should also be paid to its response process and dynamic characteristics. 7. Pay attention to any requirements regarding the installation location: Some manufacturers’ products require to be installed horizontally. 8. Pay attention to the product’s dynamic response characteristics: Some systems have high requirements regarding the dynamic response to traffic; in such cases, users should understand in detail the response characteristics of the specific product. 9. Pay attention to the stability of the zero point: For measuring products, the stability of the zero point is extremely important, yet it is also difficult to ensure. The zero-point stability of different products may vary. 10. Note the scope of application: There is a specific range of applicability regarding the operating environment, medium temperature, gas supply pressure, and the nature of the medium (especially in cases involving corrosive gases). Please make sure to read the instructions or consult the manufacturer. 11. The order should specify: product name, model, flow rate specifications, calibration gas, operating gas (especially corrosive gases), and the type and quantity of connectors. That’s it for now. Feel free to leave comments, engage in discussions, and follow us.