Where do the flow meter’s on-site display data come from?
Thread Content
The flow meter gauge on site displays both cumulative flow and instantaneous flow. The question now is: what is the source of the cumulative flow data? Is it calculated using 4-20mA signals, or through pulse counting? When settling trades, should people use the cumulative amount on DCS for settlement, or the cumulative amount shown in the table header? I hope the expert can clarify this
The on-site value is consistent with that of the DCS; the DCS value is calculated by the program, while the on-site value is calculated by the flow meter’s module
If no additional compensation calculations (such as for temperature and pressure) are required, the cumulative flow value displayed on the field flowmeter is the most accurate. If it is accumulated in DCS, then the accuracy of communication is higher than that of pulses, which are in the 4-20mA range. Therefore, in some sites, the cumulative values of the meters are communicated to the DCS.
We all rely on the data accumulated from on-site forms
There is only one data source; for example, a Coriolis mass flow meter obtains its values by using sensors that measure the Coriolis force. All forms are illusory
Follow the table header. The cumulative value in the table header is calculated by accumulating the instantaneous values; the calculation cycle is generally shorter than that of DCS, resulting in greater accuracy. If DCS is used for communication, interference protection must be implemented. Current decay must be taken into account, and for higher precision, regular calibration is required.
In accordance with the conventions for measuring and transferring goods, it is still preferred to use the data stored in the flow meter itself as the basis for measurement. However, the amount of data that can be stored in the flow meter is limited. For large-scale trade transactions, it is necessary for the flow meter system to be equipped with secondary instruments (including flow accumulators). Taking ultrasonic natural gas flow meters as an example, if no secondary instruments are available, the flow meter can perform temperature and pressure compensation using the temperature and pressure sensor signals it has, with the resulting values being stored in the flow meter itself； If a secondary meter is installed, then temperature and pressure compensation calculations, historical data retrieval, as well as records of the operator’s actions are all kept – this is the standard approach. There are two scenarios regarding DCS systems: in one case, the flowmeter only sends the volume signal of the flow rate, and the DCS then collects the relevant temperature and pressure signals to carry out temperature and pressure compensation calculations (there are differences here between using custom-compiled compensation formulas and standard software for handling flow data); in the other case, the flowmeter data after temperature and pressure compensation is collected directly. In either case, parties responsible for measurement generally do not use such systems, as there are too many complexities involved – it’s something typical of Chinese practices, you know. .