Thermal gas mass flow meters are recognized and used by more and more users because of their unique and excellent performance, and are now used in many gas flow measurement applications. However, there are many problems and misunderstandings in these applications. Many users have misunderstood the hot gas mass flowmeter. Some people blindly think that the thermal flowmeter can measure gas under all working conditions, while others reject the thermal flowmeter and reject it. Problems in many applications have encountered a lot of accumulation in actual production. Share some feelings here.
Help thermal operators in various industries to select hot gas quality meters correctly. We will address three aspects:
1. Correctly understand the principle of the thermal gas quality meter
The origin of the hot gas mass meter is the hot wire anemometer. The temperature of the platinum wire is proportional to the change in flow rate: the higher the flow rate, the greater the heat dissipation. The following is a brief explanation of why the gas mass flow rate can be obtained by detecting heat changes.
Formula: H = m × Cp × ΔT
The measured heat quantity H is also set as the temperature difference ΔT. For a gas with a specified specific heat capacity Cp, the mass flow rate m of the gas can be directly obtained.
Use microscopic methods to explain why it is a direct gas mass flow measurement.
2. Correctly understand the performance of the thermal gas quality meter
A high-quality thermal flowmeter must have two main characteristics: a good probe manufacturing process and a complete real-flow calibration device. We analyze these two features separately:
Probe manufacturing process: The principles and principles of the thermal flowmeter we talked about in the past are the core of the hot gas mass flowmeter from the probe. It may be the credit performance of the flowmeter's measurement accuracy, repeatedly determining saturation and durability , Low flow rate. The probe is made of platinum wire and sheathed stainless steel. Platinum heating wires are conductive, and jacketed stainless steel is also conductive, which means that the gap between them has very good thermal conductivity, but it is not conductive. This leads to the core of all thermal flowmeters-gap filling materials and heating probe packaging process:
The thicker the intermediate layer, the worse the thermal conductivity, the worse the temperature sensitivity, and the worse the response delay. When the gap is organic, it easily ages, causing cracks in the packing, and the flowmeter shows zero drift. If there is a small amount of air in the gap, the tiny air will expand because the probe is always heated and will not cause any fluctuations.
3. Correct selection of hot gas quality meter
There are data to prove the possibility of faulty flow measurement. The wrong choice of the flow meter accounts for 70% of the quality of the flow meter product or 30% for other reasons. There are many types of flow measurement options. Users of hot gas mass flowmeters should pay special attention not to select specific types of flowmeters. You only need to specify as much operational status data and some technical requirements as possible. In such a flow range (standard recommended flow unit, use side), the medium will be measured in diameter pipes, pipes, operating pressure, operating temperature, if explosion-proof requirements, signal power accuracy required level, flowmeter at ambient temperature , Where measures are applied on the dryness and cleanliness of the process (process control or trade measurement) media. In order to measure the flow rate of the mixed gas, a percentage value must be given for each medium. Finally, let me remind you that if there are conditions on site, a flow meter should be integrated. When it is split, because the signal transmission cable is measured as part of the bridge, there is also a resistance itself, no matter how good it is, because the resistance of the probe with a very small resistance value is combined with the resistance of the cable affects the operation and processing of the electronic circuit combined with the on-site environment The effect of the lead to resistance drift. If you need to choose splitting, it is recommended that the splitting distance be as short as possible. Choosing the right hot gas mass flowmeter is important to learn to master the principle and performance measurement of the product. Product manufacturers and business people should do more in-depth communication to distinguish brand characteristics. You can choose a hot gas mass flow product that meets your needs.