Can anybody clarify for me, how to calculate the range of the DP transmitter to be calibrated to measure the flow rate of liquids, steam and gas?

 

Since you are using a DP transmitter, most probably you will be using a orifice plate or pitot tube or V-cone, etc. type flowmeter.

Let us take an example the orifice flowmeter. The maximum DP produced by the orifice plate depends on the bore diameter (d). Normally the orifice plate d/D(pipe dia) should be 0.3 to 0.7. But people tries to take 0.6 (it has some advantages). So if you do orifice plate calculation with some assumed DP and actualflowrate you will get a d/D value. Now by trial and error change the DP so that you come close the o.6 value for d/D.
However, in fact if you subsitute the d/D value and flowrate in standard orifice plate flow calculation formula you will get the approx. DP. This DP you can use as the starting point for flow calculation and fine tuning to get a d/D ratio close to 0.6.

The procedure is same for other types of flowmeters also. Hope this helps.

Cheers,
A.K.Hait