Electromagnetic Flowmeter M921
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64
Operation manual
7.5
Flowrate versus diameter
The choice of flowrate for an electromagnetic flowmeter depends on the diameter of the sensor. The higher
pipe diameter, the higher flowrate can be measured. A determining parameter for flowrate is maximum
velocity of the liquid. Maximum velocity is the speed, where the flow of liquid inside pipe is still laminar. In
M921 it is limited to 10m/s (with 125% overload). Speed over 10 m/s is usually too high for industrial
applications. Such diameter of pipe is usually selected, where expected flowrate is between Q
5%
and Q
50%
.
In the table below applicable flowrates for various diameters is displayed in units l/s and m
3
/hr.
Flowrates [ l/s ]
Flowrates [ m3/h ]
DN
Q
0.3%
Q
5%
Q
N
Q
50%
Q
100%
Q
MAX
Q
0.3%
Q
5%
Q
N
Q
50%
Q
100%
Q
MAX
15
0,005
0,09
0,50
0,88
1,77
2,21
0,06
0,32
2,00
3,18
6,36
7,95
20
0,009
0,16
0,90
1,57
3,14
3,93
0,11
0,57
3,20
5,65
11,31 14,14
25
0,015
0,25
1,40
2,45
4,91
6,14
0,18
0,88
5,00
8,84
17,67 22,09
32
0,024
0,40
2,20
4,02
8,04
10,05
0,3
1,5
8,00
14,5
29,0
36,2
40
0,04
0,6
4,0
6,3
12,6
15,7
0,5
2,3
13,0
22,6
45,2
56,6
50
0,06
1,0
6,0
9,8
19,6
24,5
0,7
3,5
20,0
35,3
70,7
88,4
65
0,10
1,7
9,0
16,6
33,2
41,5
1,2
6,0
35,0
59,7
119,5 149,3
80
0,15
2,5
14,0
25,1
50,3
62,8
1,8
9,0
50,0
90,5
181,0 226,2
100
0,24
3,9
20,0
39,3
78,5
98,2
3
14
80
141
283
353
125
0,4
6
30,0
61
123
153
4
22
150
221
442
552
150
0,5
9
50,0
88
177
221
6
32
200
318
636
795
200
0,9
16
100
157
314
393
11
57
300
565
1131
1414
250
1,5
25
150
245
491
614
18
88
500
884
1767
2209
300
2,1
35
200
353
707
884
25
127
800
1272
2545
3181
350
2,9
48
300
481
962
1203
35
173
1000
1732
3464
4330
400
3,8
63
400
628
1257
1571
45
226
1300
2262
4524
5655
500
5,9
98
600
982
1963
2454
71
353
2000
3534
7069
8836
600
8,5
141
800
1414
2827
3534
102
509
3000
5089 10179 12723
700
12
192
1000
1924
3848
4811
139
693
4000
6927 13854 17318
800
15
251
1200
2513
5027
6283
181
905
5000
9048 18096 22620
Table 19 : Applicable flowrates for various diameters
Q
0.3%
- minimum applicable flowrate (minimum flowrate with guaranteed accuracy)
Q
5%
- recommended minimum flowrate (minimum flowrate with best accuracy)
Q
N
- recommended nominal flowrate (expected working flowrate)
Q
50%
- recommended maximum flowrate (maximum flowrate for industrial use)
Q
100%
- maximum applicable flowrate (maximum flowrate with guaranteed accuracy)
Q
MAX
- maximum applicable overload (
Q
125%
) (flowmeter is still measuring)
Table 2: M921 flowrates
A sensor diameter should be chosen to keep real flowrate between Q
5%
and Q
50%
, because in this range the
flowmeter has the best accuracy.
