RMS 621 11 Appendix
Endress+Hauser 67
Example:
Flow measurement in a steam pipe line using a Deltatop Pitot tube
• Tube internal diameter: 350 mm
• k-factor (correction factor for the resistance factor of the tube): 0.634
• Working range DP: 0 - 51. 0 mbar (Q: 0-15000 m
3
/h)
Hints for set up:
• Flow Æ Flow 1; Differential pressure Æ Pitot pressure; Signal type Æ 4...20 mA; Correction Æ
Yes; Tube data ÆInternal diameter 350 mm; Correction table Æ Point 1: Flow 0 m
3
; Factor
0.634; Correction table Æ Point 2: Flow 15000 m
3
/h; Factor 0.634.
Hint to differential pressure measurement
If all differntial pressure measurement point data is available (tube internal diameter, ß or k-factor)
it is recomended that the improved method be used (fully compensated flow calculation).
If the required data are not available the differential pressure transmitter output signal is scaled and
transmitted as volume or mass (see the following table). Please note however, that a signal scaled
to mass can no longer be compensated therefore it is always recommended that the DP transmitter
should be scaled to operating volume (mass : density in rated condition = operating volume). The
mass flow can then be calculated in the device using the operating density dependent on the
temperature and pressure. Here it is a partially compensated flow rate calculation because the rated
squared density is contained within the operating volume (see above).
How should the device and sensor be set up?
Example:
Accuracy of a steam flow measurement using an oriface plate dependent on measurement method
• Corner tap orifice plate DP0 50: Internal pipe diameter 200 mm; ß = 0.7
• Flow operating range: 10 to 6785 m
3
/h (0 to1635 mbar)
• Ratings: 10 bar; 180 °C; 5,15 kg/m
3
; 4000 m
3
/h
• Process temperature: 190 °C
• Process pressure (real value): 9.5 bar
• Differential pressure: 526 mbar
• Result using the traditional differential pressure method:
Operating volume: 4000 m
3
/h Mass flow: 20.58 t/h (density: 5.15 kg/m)
Sensor Device
1. traditional
method
No data available re: tube diameter and diameter ratio ß (K factor on Pitot tubes).
a) (Default)
Squared curve e.g. 0...1000 m
3
(t)
Flow rate input (operating volume or
mass)
Linear curve, e.g. 0...1000 m
3
(t)
b) Linear curve, e.g. 0...2500 mbar Flow rate input (operating volume or mass)
Squared curve, e.g. 0...1000 m
3
(t)
2. improved
method
Tube diameter and diameter ratio ß (k factor on Pitot tubes) available.
a) (Default) Linear curve e.g. 0...2500 mbar Special flow rate (DP) e.g. Orifice
Linear curve, e.g. 0...2500 mbar
b) Squared curve, e.g. 0...1000 m
3
(t) Special flow rate (DP) e.g. Orifice
Squared curve 0...2500 mbar
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