Flow transmitter
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This post was last edited by Luo Jinpeng on 2012-5-23 at 10:21. How can one determine the flow rate on site based on the percentage shown on the flow transmitter?
Actual flow rate = Percentage % X (flow rate range), and that is the actual flow rate! The range can be obtained from the control room panel or via the communicator!
Using this method gives different results, which differ significantly from what is displayed on the DCS; we use the %X upper limit
Is the transmitter on site a differential pressure type? Then you might need to take a square root.
If the transmitter is of the differential pressure type, then calculations are done in this way; the operating pressure indicated on the transmitter is 0~25 kp
1. Since flow rate is proportional to the square root of differential pressure, please refer to the flow equation in articles on differential pressure flow meters (available on this forum) for details. The square root of the flow rate can either be calculated within the system or within the meter; only one of these options can be used. 2. When performing individual unit verification, first use HART to switch back to the non-square-root mode (the absence of a square root symbol on the LCD indicates the non-square-root mode). The zero point and range are calibrated using a 4–20 milliampere linear scale; after calibration, use HART to switch back to the square-root mode. 3. The square-rooted output current value needs to be calculated; the square-rooted value corresponding to 7 mA should be around 11 milliamps. 【Corresponding values between differential voltage output current and square-root output current】 Differential voltage output current Square-rooted output current 4mA 4mA 8mA 12mA 12mA 15.3mA 16mA 17.9mA 20mA 20mA Example of calculation method: For instance, if the differential voltage output current is 12mA, which corresponds to 1/2 of the full scale, the square root of this value is √2/2; multiplying this by the full scale gives 16mA×√2/2 + 4mA = 15.3mA. This information was already available on the forum earlier; I’m just reusing it here
The flow transmitter value should be the square root of the percentage, multiplied by the range
Not all flowmeters require taking a square root; it specifically refers to the differential pressure here! ! ! ! !