Seeking advice on flow meter issues; thank you very much

I don’t know what type of flow meter you have either They operate on different principles. There is a procedure called low-flow resection; you might want to learn about it.

All flowmeters have a suitable flow range; when the flow rate exceeds this range, the error becomes very large, to the point where it is impossible to take a measurement or to estimate the error.

This post was last edited by qugd on 2018-1-28 at 20:33. If it’s a differential pressure flow meter, this accuracy is quite acceptable. Based on the data, the fluctuation range is only 2.5 to 3%, and this level of precision is already quite good for gas metering. In gas metering, factors such as the measurement conditions and methods of the flowmeter, its selection, manufacturing precision, installation location, and environmental changes have a significant impact on the measurement results. The compressibility of the gas itself, along with the lag in the propagation of pressure fluctuations during transmission and the pressure buffering that occurs in between, all affect the accuracy of the flowmeter’s measurements. The software calculation accuracy of a flow meter is one thing, while the actual usage accuracy is another. The situation you mentioned later is precisely caused by pressure buffering during gas conduction. You can try installing the flow meter a little upstream on the pipeline. If you are measuring steam and the pipeline is very long, there may be a period during which accurate measurement is not possible, as there is water pressure ahead of the steam. It is recommended to improve operational stability by adding temperature and pressure compensation to the flow meter, which might yield better results.

The most likely cause of errors in gas flow meters is the issue of temperature and pressure compensation. Generally, flow meters installed in gas supply pipelines do not have this compensation feature; instead, a temperature and pressure value must be entered manually, allowing the instrument to convert the flow rate under actual conditions to the flow rate under standard conditions. As a result, errors occur when the pressure conditions are abnormal (for example, at low flow rates). Additionally, something that needs to be taken into account when selecting a flow meter is that all flow meters have a minimum flow rate requirement; in other words, below a certain flow rate, the flow meter cannot guarantee accuracy. The most common value is 0.5 m/s for measuring liquids using electromagnetic methods. In many desulfurization and denitrification projects, electromagnetic sensors are required, yet the flow rate is extremely low; in such cases it’s not possible to use this method, as the principles behind it don’t allow it.

For standard gas flow meters (i.e., those with comprehensive temperature and pressure compensation functions as well as dedicated flow integrators), there is a \"minimum flow rate requirement\" – that is, a lower limit on flow rate. This requirement ensures that measurement is possible, but it does not guarantee that the measurement will be within the accuracy range (i.e., within a 2-fold accuracy margin). The range within which accuracy is guaranteed is usually from 5% to 10% of the upper flow limit (referred to as the flow transition point) up to the upper flow limit itself； In reality, within this range, only the accuracy guaranteed by the calibration of the flow meter under standard conditions is achieved; however, due to the fact that it is used under non-standard conditions in actual field situations, additional errors occur. Therefore, there is an optimal operating range for the flow meter, which is usually between 30–40% and 80–90% of the flow rate limit. This range is determined by taking into account factors such as measurement accuracy and the reliability of the meter’s operation. Additionally, regarding the \"flow turning point\" of gas flow meters, this concept was originally developed in Western countries; it is not included in our standards. Accuracy is evaluated across the entire range of flow rates, which poses difficulties for manufacturers. In practice, many products are deemed unqualified, and it was only later that this concept was adopted, following the practices of those Western countries, in light of these practical challenges.

This post was last edited by Sikong Zhaixing on 2018-2-2 20:14. First, you need to check whether there are any issues with the instruments on site as well as the side pipes. Are there any impurities such as water droplets accumulated in the pressure guide tube? According to Yi Ou’s understanding, it’s because the pressure guiding tube is dirty, which results in additional errors; the smaller the flow rate, the greater the relative error. Or there may be leaks in the pressure tap piping and instruments, with air leakage causing distortion of the differential pressure and resulting in errors.