Dp to Flow formula
As we know in DP flow measurement the mA we obtained from the transmitter has to be converted in the square root extractor to obtain the volumetric flow rate. In this article, we will see how to easily find the flow rate and DP value and vice versa by the means of a Dp to flow formula.
As an instrumentation professional if you are working in the field if the flow transmitter is not scaled to the flow rate. Then the DP flow transmitter will normally show that differential pressure value(an ex:1500mmh2o).In order to obtain the flow we can use this simple formula to find the flow rate.
FLOW ACTUAL= SQRT(DP actual / DP span) * FLOW Span
![\[FLOW actual = \left ( \sqrt\frac{ DP actual}{DP span} \right )*FLOW span\]\](https://instrumentationbasic.com/wp-content/ql-cache/quicklatex.com-954bffaa722f4dd0a5181dc092aaaa3f_l3.png "Rendered by QuickLaTeX.com")
Let us consider the DP range of the flow transmitter is 0 to 1000 and the corresponding flow ranges from 0 to 200. Technicians observe a DP value of 500 Kpa in the field. He wants to find the actual flow by using DP to flow formula
![\[FLOW actual = \left ( \sqrt\frac{ 500}{1000} \right )*200\]\[= \left ( \sqrt0.5 \right )*200\]\[= 0.707*200\]\[FLOW actual= 141.42\]\](https://instrumentationbasic.com/wp-content/ql-cache/quicklatex.com-329d762f3bd1fe43c0ed6420ad9c9992_l3.png "Rendered by QuickLaTeX.com")
If you want to check the regular method and how this conversion takes place check here.
Similarly from the DCS side if the square root is configured in the transmitter itself in SCADA you will get only the flow rate, in order to find the measured DP value use this formula.
ACTUAL DP=( (ACTUAL FLOW / FLOWspan) ^2 )* DPspan
![\[DP actual = \left ( \frac{ FLOW actual}{FLOW span} \right )^2 *DP span\]\](https://instrumentationbasic.com/wp-content/ql-cache/quicklatex.com-f456329e832612cce615aface1e9ad87_l3.png "Rendered by QuickLaTeX.com")
The same transmitter technician observed the display is configured only to flow reading 150 m^3/hr, he wants to find the actual DP value.
![\[DP actual = \left ( \frac{ 150}{200} \right )^2 *1000\]\[DP actual = 562.5\]\](https://instrumentationbasic.com/wp-content/ql-cache/quicklatex.com-97de4fa3ad9638ab8c64abc71961de17_l3.png "Rendered by QuickLaTeX.com")
