Measuring Mode "Flow Rate - Siemens SITRANS P DS III Operating Instructions Manual

Operating functions through HART
7.3 Selecting the measuring modes
7.3.7

Measuring mode "Flow rate"

Description
When you activate the "Flow rate" measuring mode, only two other device variables are
active: volumetric flow and mass flow rate. If another block was active earlier, the
corresponding device variables remain inactive and have the "CONSTANT" status. The
"Flow rate" block here represents a series of permanently interconnected functions which
you need to configure with appropriate parameters.
DV Device variable
MA Start of scale value
ME Full scale value
Figure 7-4 Measuring mode "Flow rate"
Functions of the "Flow rate" block
The "Input scaling, pressure" function defines the pressure range of 0 to 2 bar that is
interpreted as 0 and 100% by the following square root extracting function. A process
pressure of 0.5 bar has been assumed in the following figure.
In the "Flow rate" measuring mode, a square root extracting characteristic curve "srlin2" is
plotted with a fixed root application point of 10%.
In the calculation example, the input value for the "root extraction function" is approx. 25 %
for a prevailing process pressure of 0.5 bar. The output value is approximately 50%.
112
SITRANS P DS III with HART
Operating Instructions, 06/2013, A5E00047092-09