Siemens SITRANS P DS III Operating Instructions Manual page 113

Note
When using the "Flow rate" block, other square root extracting characteristic curves must be
deactivated if required. (The "characteristic curve" parameter must be "linear", as root
extraction is already implemented in "flow rate" measuring mode).
DV [x] Device variable x
MA Start of scale value
ME Full scale value
Figure 7-5 Functions of the "Flow rate" block
In the calculation example, the two pairs of values 0%;0% and 100%;100% are configured
for the customized "characteristic curve". This setting corresponds to a bisection of the input
value for all output values.
Configure the output scaling "volumetric flow" with a unit from the volume flow range and the
measuring limits for the device variable "Volumetric flow". In the calculation example, 0 l/s
and 1000 l/s are defined as lower and upper measuring limits. The volumetric flow rate is
500 l/s at a prevailing process pressure of 0.5 bar.
The "Mass flow rate" device variable is automatically activated when the "Flow rate" block is
configured. If you have not yet configured a value for the density, the initial value of 1 kg/l is
preset.
In the calculation example, a mass of 2000 kg/s is derived for the "mass flow rate" device
variable at a value of 1 kg/l. The density value entered is only used to calculate the mass
flow rate. The entered value of density has no effect on the diaphragm calculation that is to
be carried out by the user.
In SIMATIC PDM or the HART communicator, the "Flow rate" block is configured in an online
dialog box in an extremely compact manner. In this online dialog box, you can compile all
values in a menu and transfer them to the device collectively.
SITRANS P DS III with HART
Operating Instructions, 06/2013, A5E00047092-09
MF Mass flow rate
p Pressure
VF Volumetric flow
Operating functions through HART
7.3 Selecting the measuring modes
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