Issues regarding square root calculations and the 4-20 mA range in differential pressure flowmeters

Use Hart to make the changes; Hart provides an option for taking square roots, and after making the changes a square root symbol will appear on the gauge

Hello, in Hart, the square root term is used to determine whether to take the square root from the table header or from the DCS, right?

In general, differential pressure flow meters perform a square root operation on the signal at the transmitter; the flow rate corresponding to 4-20mA is determined through design calculations and cannot be changed arbitrarily.

Check the throttle device calculation sheet; it shows the flow rate range corresponding to the differential pressure range. The differential pressure transmitter can be used for squaring directly, or the squaring can be done on the DCS, depending on your requirements

1. Generally, the square root operation is performed on the differential pressure transmitter; if your transmitter does not support this function, then the square root operation can only be carried out on the DCS. 2. To determine the range, it is necessary to refer to the calculation documents for the throttle device; the value corresponding to 4-20mA can be set using a handheld controller. When taking the square root, it corresponds to flow rate, while when no square root is taken, it corresponds to differential pressure. 3. If possible, it is recommended to display both the differential pressure value and the flow rate value on the gauge, which facilitates observation and zeroing.

Generally, 475 is used to take the square root in the header

Do you know which one to select for taking the square root? Hehe, once you see the linear pattern using the handheld device, just change it to taking the square root

This post was last edited by ウ① How ゞ on 2016-4-8 19:52. All data related to differential pressure flow is calculated based on pipeline and operating condition parameters. For example, the size of the pipeline, the medium being measured, temperature, pressure, density… These parameters are determined through calculations. It is based on these that one decides on the appropriate size for the throttling device, the flow rate that can be achieved under those process conditions, and the range of the corresponding differential pressure transmitter; it is with this information that the instruments are purchased. The differential pressure range and the flow rate range are corresponding to each other; once determined, they cannot be changed arbitrarily, unless there is a discrepancy between the design and the actual conditions, in which case new values for the flow rate and differential pressure ranges need to be calculated. As for taking the square root, it is sufficient to take the square root of one side of the instrument or system; under no circumstances should the square root be taken of both sides. As for which side to use for square rooting, it depends on personal preference. I personally prefer to use square rooting on the instruments; some instruments indicate that square rooting is applied on them in the display module. Since specialized tools such as 475 are required for this, and not all locations have such tools available, I prefer to use system-based square rooting instead

As mentioned above, for differential pressure flowmeters, the calculation is usually done by taking the square root at the meter itself, or it can also be done on the DCS module; however, it’s not possible to take the square root on both sides simultaneously. As for the range and other parameters, these are provided in the detailed calculation documents prepared by the design agency, and they can be set using HART 475. . .

It can be enabled in the table header or via DCS; just avoid enabling it multiple times. The range should be determined based on the data specification sheet of the primary component, rather than assuming it arbitrarily.