Is the flow rate measured by a differential pressure flow meter the same as that measured by an ultrasonic flow meter?
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With an ultrasonic flow meter, an accurate flow rate can be obtained in the DCS without taking a square root, whereas with a differential pressure flow meter, an accurate flow rate requires taking a square root in the DCS. When an ultrasonic flow meter and differential pressure flow meters are both installed on the same pipeline to measure flow rate (in this case, two differential pressure flow meters are installed on that pipeline, yielding different flow rate values; one of them feeds the value to the DCS after taking the square root, while the other feeds the value to the DCS without taking the square root), then which differential pressure flow meter’s measured value will be the same as that measured by the ultrasonic flow meter?
This post was last edited by piaopingke on 2015-12-22 at 11:48. For differential pressure flow meters, the flow rate is in a linear relationship with the square root of the differential pressure; if the design and installation of the flow meter are correct, its measurement results should be similar to those of a flow meter based on the square root of the differential pressure.
If all the flow meters are accurate and installed in accordance with requirements, one of them will match the value after taking the square root.
One with square root function and one without. Are you using a differential pressure flow transmitter that outputs the flow signal directly? Only in such cases is it not necessary to apply the square root function on either the instrument side or the DCS side. If the design is fine and installation goes smoothly, the traffic should be more or less the same
For measuring flow rate with a differential pressure transmitter, there are two methods: with an indicator on site and with a control room interface.
Check how the output setting is configured for your differential pressure transmitter; if it’s a linear output, the DCS must apply a square root operation； If the differential pressure transmitter is set to output the square root value, the DCS only needs to set the K coefficient properly for linearity
Check how the output setting is configured for your differential pressure transmitter; if it’s a linear output, the DCS must apply a square root operation； If the differential pressure transmitter is set to output the square root value, the DCS only needs to set the K coefficient properly for linearity
The upstairs option is the correct one. Where the square root is taken does not affect the accuracy of the measurement. With the accuracy of the differential pressure sensor remaining unchanged, it is merely a calculation that does not affect the result.
Theoretically, the test results obtained using any testing method should be consistent, with no deviations
A differential pressure flow meter calculates the flow rate based on the measured differential pressure; the flow rate is proportional to the square root of the differential pressure. As can be seen from the theoretical formula, the differential pressure needs to be taken to the power of one half, so a flow rate that does not take this square root into account is incorrect, resulting in an underestimation of the actual flow rate. Therefore, all differential pressure flow meters require the use of the square root operation. An ultrasonic flow meter measures flow velocity to calculate flow rate; the principles of these two types of flow meters are different. Theoretically, the flow rate obtained by taking the square root of the differential pressure is consistent with that measured by ultrasonic methods. The balanced flow meter is the flow meter with the best overall performance among differential pressure type flow meters. The accuracy of an A+Qmc balanced flow meter can reach 0.5 grade, and the flow rate calculated by taking the square root of the measured differential pressure is more accurate than that determined by ultrasonic methods.