2025-11
07Everything you want to know about the accuracy comparison of gas mass flow meters is here
In communication with customers, YIDU often receives feedback that when testing different brands of flow meters in series, it is found that there are differences in their readings. Does this mean that the accuracy of a certain device is not up to standard? The answer is not so simple. As a precision measuring device, the reading differences of flow meters are often caused by multiple factors. This article will analyze common reasons to help you scientifically understand comparative test results.
Common reasons for differences in readings of different flow meters
1. Error superposition of flowmeter itself
Two flow meters with an accuracy of 1% F.S. are compared in series, and in the worst case, the difference may be close to 2% F.S., which may lead people to mistakenly believe that one of them has exceeded the accuracy limit.
2. Inconsistent gas types
If air is introduced for testing, but the gas type of the two flow meters is not both air, the readings will be different.
3. Inconsistent definition of standard conditions
Two flow meters are compared to the mass flow , provided that the standard condition definition is the same, the standard condition pressure is usually 101.325kPaA, and the standard condition temperature is 0 ℃, 15 ℃, 20 ℃, 25 ℃, etc. Before testing, it is necessary to ensure that the standard condition temperature is the same (note that the standard condition temperature is the same, not the actual temperature). The YIDU flowmeter can switch between the above four standard temperature conditions.
4. The range difference is too large
It is meaningless to compare the accuracy of a flow meter with a 100SLPM range and a flow meter with a 1SLPM range, as flow meters often have poor accuracy in the small range. A flow meter with a range of 100SLPM (assuming an accuracy of 1% F.S.) may have an error of up to 1SLPM when measuring a flow rate of 1SLPM.
5. Different temperatures and pressures
If a flow meter is under high pressure and another flow meter is under normal pressure, pressure induced drift will be introduced, and temperature drift will also be introduced due to different temperatures.
6. Pipeline connection issues
Leakage or loose connections in pipelines can result in different actual flow rates between the two flow meters; When the flow measurement range is small and the intermediate pipeline is long and thick, the volumetric effect is more obvious, and the readings of the two flow meters will also be inconsistent. If the outlet end of a flow controller is closely connected to another flow meter, it will also affect the accuracy of the other flow meter.
7. Misunderstandings caused by different measurement principles
There are significant differences in response speed (measurement sensitivity), gas switching principle, and other aspects between laminar differential pressure flow meters and thermal flow meters, which can easily induce testers to use incorrect methods for testing. For example, when the pressure of the gas source fluctuates, due to the fast response speed of the laminar differential pressure principle, the measured value will also fluctuate, while the measured value of the thermal flowmeter will appear relatively stable. In addition, it is often misunderstood that if two nitrogen flow meters with different principles are both filled with air for comparison and converted using their respective conversion methods, the results obtained are likely to be inconsistent.
8. Different traceability
Flow meters need to transmit standards through traceability, and the traceability of flow meters from different manufacturers is also different. YIDU flow meters can be traced back to the National Institute of Metrology in China, while imported brand flow meters may be traced back to other institutions. Even if both flow meters are within the nominal accuracy range, there may still be some differences in readings.
In addition to the above reasons, the zero drift of the flowmeter, the accuracy and stability of the sensor will also affect the measured value.
How to conduct traffic comparison correctly?
The two flow meters to be tested mainly need to meet the following requirements
1. The range is close;
2. The standard temperature is consistent;
3. The gas type is consistent and consistent with the actual introduced gas;
4. The test conditions (i.e. temperature and pressure) are similar, and it is best to measure at room temperature and pressure;
5. Choose appropriate pipe diameter and ensure smooth pipeline flow. If the measuring range of the flowmeter to be tested is small, the middle pipeline should be as short as possible to reduce the impact of volumetric effect; If the range is large, the two flow meters need to be separated by a distance to avoid the upstream flow meter affecting the inlet flow state of the downstream flow meter. Ensure that the pipeline is not leaking or blocked, and select the appropriate pipe diameter.
In summary, if the readings of two flow meters are inconsistent, it is not advisable to hastily judge that one of them does not meet the accuracy standards. It is also necessary to check the testing process and compare it with the device of authoritative institutions. A more convenient approach is to use the YIDU P series handheld flowmeter to obtain a certificate from an authoritative institution. As a flow standard device, it can compare the flow rate of your flowmeter and flow controller in various scenarios
