Equation for Flow conversion in DCS


Thread Starter



Can any one help how to calculate this DP flow in m3/hr.

In field we use DP flow meter in range of 0-500 mbar (the equivalent flow rate is 20,000 Kg/hr). The transmitter is calibrated for 0-500 mbar with linear characteristics.

In DCS system, we need show in m3/hr. The range in DCS is 0-39m3/hr.
I used the formula: Qv = 3.14*d(sq)*(sq.root(2*Delta P)/ rho (1-(d/D)power4)))

My question is for Delta P, Shall I use 500 mbar or 20,000 kg/hr?

When you say that 0-500 mbar = 0-20,000 Kg/hr, was that calculation done using the same medium (properties) that is flowing through the pipe and the primary flow element?

If so, on the DCS side, you just need to square root the 0-100.0% 4-20mA signal and scale it by the density ratio.

How many Kg of the flow medium are in 1 m^3?

On the transmitter side:
4-20mA = 0-100.0% flow rate which represents 0-500mbar (linear) which represents 0-20,000Kg/hr (when square rooted).

How many Kg of the flow medium are in 1 m^3?
If the flow medium were water, it would be 1000 Kg = 1m^3

Then 0-500mbar = 0-20,000Kg/hr = 0-20.00 m^3/hr (water)

So your DCS calculation would then be
sq rt of the 4-20mA signal (0-100.0%) would represent 0-20.0 m3/hr, for water.

If the density were 0.80, then 0-20,000Kg/hr(whatever medium) = 0-25.0 m^3/hr

If the density were 1.20, then 0-20,000Kg/hr(whatever medium) = 0-16.6 m^3/hr
Thank you very much David!

The flow rate is 20,000 Kg/hr which is equivalent to 500 mbar (max).
Liquid density is 515 Kg/m3
In DCS System we use this formula:
Q = x * √∆P
x = (39/√√∆Pmax): √∆Pmax = 500 mbar
If the flow rate is 500 bar i.e 39 m3/hr.
Then Qv = (39/√∆Pmax)* √∆P.
√∆P = Current value which is with in the range of (0-500mbar).