Flowmeter square root problem
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For integrated differential pressure flowmeters, is it better to perform the square root calculation on-site or in the DCS? Is there any difference? How can one determine whether the data calculated by flow meter manufacturers is accurate?
It doesn’t matter; it’s fine as long as the whole factory uses the same standard. If measurements are taken on-site, it’s easy to check the current and the circuit, as current is linearly related to flow rate.
We usually take square roots within the DCS, as it makes it easier to calibrate the transmitters; otherwise, we would have to distinguish between those that measure differential pressure and those that measure flow rate.
It’s acceptable to take the square root in either place, but it is recommended to standardize this practice by specifying that it should be done in the DCS, rather than on-site
Take the square root on-site; otherwise, the values on-site will not match those in the DCS. To check whether the flow meter is accurate, it’s better to measure its performance after it has been installed and calibrated.
Generally, squaring is performed on the DCS to avoid repeated squaring; to ensure data accuracy, it is necessary to check the set range of the transmitter as well as the DCS range, and to verify that these match those specified in the data sheet
The selection of the square root or linear range shall comply with the following provisions: 1) When a differential pressure flow meter is used to measure gas or steam flow, it is advisable to choose a square root range for the differential pressure flow transmitter; the square root calculation as well as temperature and pressure compensation should be carried out within the control system or flow computer. 2) When a differential pressure flow meter is used to measure liquid flow, it is advisable to choose a linear range for the differential pressure flow transmitter; the square root calculation should be performed within the transmitter, and no temperature or pressure compensation is required； 3) When a differential pressure flow meter is used for special applications, the transmitter of such a flow meter should have a root-mean-square range, so that square root calculations as well as temperature and pressure compensation can be carried out within the control system; refer to SH3005-2016
Taking the square root at a unified location – it’s just that the calculation formula is different