Endress+Hauser prowirl 77 - Page 36

Function group: SYSTEM UNITS
The following instructions explain in more detail pages 34 and 37.
Instructions for user-defined corrected volume units:
“Custom flow unit”
or
“Custom total unit”
Examples:
To display the
corrected volume flow of compressed air at 3 bar and 60 °C in “Nm
3
/h”.
The density is 3.14 kg/m
3
for those operating conditions. The density of air at reference conditions
(1.013 bar, 0 °C) is 1.2936 kg/m
3
:
“Custom flow unit” =
To display the
corrected volume total in “Nm
3
” for the same application (compressed air at 3 bar, 60 °C):
“Custom total unit” =
For ideal gases the following simplified formula can be used to calculate corrected volumes only when
reference conditions are at 0 °C and 1.013 bar (abs):
“Custom flow unit”
or
“Custom total unit”
1
.../s → 1
.../min.→ 60
.../h → 3600
.../d → 86400
Fluid density at
operating conditions
for desired time
base (not applicable
for totalizer)
for desired corrected
volume unit
Fluid density at
reference conditions
(e.g. = 0 °C and
1.013 bar)
Ndm
3
/... → 1
Nm
3
/... → 1000
SCF/... → 28.317
Imp.gallon/... → 4.546
ba032y02
1.013 + 273.15
273.15
()
for desired time
base (not appli-
cable for totalizer)
process pressure
in bar (abs)
for desired corrected
volume
Ndm
3
/... → 1
Nm
3
/... → 1000
process temperature °C
ba032y03
3.14
1.2936
3600
1
1000
= 8.738
••
3.14
1.2936
1
1000
= 0.002427
•
6 Device Functions Prowirl 77 PROFIBUS-PA
36 Endress+Hauser