Instructions for Use
– SCHMIDT
®
Flow Sensor SS 20.700
Page 11
Calculation of volume flow
A quasi-parabolic speed profile is formed over the pipe
’s cross-section
under laminar conditions. Whereas the flow velocity at the pipe walls re-
mains almost zero, in the middle of the pipe it reaches the optimum meas-
uring point, its maximum w
N
. This measured variable can be converted
into an average flow velocity
N
w
that is constant over the pipe cross-sec-
tion with the aid of a correction factor the so-called profile factor PF.
The profile factor depends on the inner pipe diameter
7
(see Table 2).
PF
Pipe Ø
Volume flow [m
3
/h]
Inner
Outer
Min. @
@ Sensor measuring range
[mm]
[mm]
0.2 m/s 10 m/s 20 m/s 60 m/s 90 m/s 140 m/s 220 m/s
0.748
39.3
44.5
0.7
32.7
65.3
196.0
294.0
457.3
718.6
0.772
51.2
57.0
1.1
57.2
114.4
343.3
515.0
801.1
1258
0.786
70.3
76.1
2.2
109.8
219.7
659.0
988.5
1537
2416
0.797
82.5
88.9
3.1
153.4
306.8
920.3
1380
2147
3374
0.804 100.8
108.0
4.6
231.0
462.0
1385
2078
3233
5081
0.812 125.0
133.0
7.2
358.7
717.5
2152
3228
5022
7892
0.817 150.0
159.0
10.4
519.8
1039
3118
4677
7276
11434
0.829 206.5
219.1
20.0
999.5
1999
5997
8995
13993
21989
0.835 260.4
273.0
32.0
1700
3201
9605
14408
22412
35219
0.840 309.7
323.9
45.6
2278
4556
13668
20502
31892
50116
0.841 339.6
345.6
54.8
2742
5484
16454
24681
38393
60331
0.845 388.8
406.4
72.2
3611
7223
21669
32504
50562
79455
0.847 437.0
457.0
91.5
4573
9146
27440
41160
64027
100614
0.850 486.0
508.0
113.5
5676
11353
34059
51088
79471
124883
0.852 534.0
559.0
137.4
6869
13738
41216
61824
96170
151125
0.854 585.0
610.0
165.3
8263
16526
49580
74371
115688
181796
0.860 800.0
311.2
15562
31124
93373 140059 217870
342368
0.864 1000
488.6
24429
48858 146574 219861 342006
537438
0.872 1500
1109
55474 110948 332845 499268 776639 1220433
0.877 2000
1983
99186 198372 595118 892677 1388609 2182100
Table 2 Profile factors and volume flows of different pipe diameters
7
Both inner air friction and sensor locking are responsible.
