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Gas- and Steam Flowcomputer
DigiFlow 515
Operating Manual
11
B:
Volumetric Flowmeters with 4–20mA Output.
(e.g. VORTEX, turbine or PDF with Analog output)
Q
S
p
p
T
T
z
z
A
Vb
V
b
b
b
=
⋅
⋅
⋅
⋅
[
6
]
Q
Q
M
Vb
=
⋅
ρ
0
[
5
]
C:
Differential Pressure Flowmeters With 4–20mA Output And a Square Law Relationship.
(e.g. Orifice Plates, ITABAR-Probes, Pitot Tubes, etc.)
Q
S
p
p
T
T
z
z
A
Vb
Vb
b
b
b
=
⋅
⋅
⋅
⋅
[
7
]
Q
Q
M
b
Vb
=
⋅
ρ
[
5
]
D:
Differential Pressure Flowmeters With 4–20mA Output And a Linear Flow Relationship.
(e.g. D.P. transmitter with integrated square root extractor.)
Q
S
p
p
T
T
z
z
A
Vb
Vb
b
b
b
=
⋅
⋅
⋅
⋅
[
8
]
Q
Q
M
b
Vb
=
⋅
ρ
[
5
]
Pressure and temperature signal are still square rooted, the flow signal are not. This is because the output
from the D.P. transmitter isn’t truly volumetric, but will be affected by a change in density of the gas being
measured.
E:
Dual Differential Pressure Flowmeters With 4–20mA Output.
To increase the range over which flow can measured, two D.P. transmitters with different spans can be con-
nected across a common D.P. device (e.g. Orifice Plate or ITABAR-Probe). Depending on the Output of the
transmitter, equations 5 and 6 or 7 and 8 are used. Separate scaling must be programmed for each transmit-
ter.
Transmitter #2 is selected when signal from Transmitter #1 is higher than 19mA.
Summary of Contents for digiflow 515
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