Notes On The Mechanical Load Of The; Probe - Endress+Hauser Levelflex FMP56 Operating Instructions Manual

Levelflex FMP56, FMP57 FOUNDATION Fieldbus
Endress+Hauser
6.1.3 Notes on the mechanical load of the probe
Tensile load
Bulk solids exert tensile forces on rope probes which increase with:
• The probe length, i.e. the maximum cover
• The bulk density of the product
• The silo diameter and
• The diameter of the probe rope
As the tensile forces also depend greatly on the flowability of the product, a higher safety
factor is necessary for highly viscous products and if there is a risk of cornice buildup. In
critical cases it is better to use a 6 mm (0.24 in) rope instead of a 4 mm (0.16 in) one.
The same forces also act on the silo ceiling. The tensile forces on a fixed rope are always
greater, but cannot be calculated. Observe the tensile loading capacity of the probes.
Ways to reduce the tensile forces:
• Shorten the probe.
• If the maximum tensile load is exceeded, check whether it would be possible to use a
non-contact ultrasonic or level radar device.
The following diagrams show typical loads for common bulk solids as reference values. The
calculation was performed for the following conditions:
• Calculation according to DIN 1055, Part 6 for the cylindrical part of the silo
• Suspended probe (probe end not fixed at the bottom)
• Free-flowing bulk solid, i.e. mass flow. A calculation for core flow is not possible. In the
event of collapsing cornices, considerably higher loads can occur.
• The specification for tensile forces contains safety factor 2 (in addition to the safety
factors already contained in DIN 1055), which compensates for the normal fluctuation
range in pourable bulk solids.
60
50
40
30
20
10
0
0
 5 Silica sand in metal silo with smooth walls; tensile load as a function of level L for rope diameters
6 mm (0.24 in) and 4 mm (0.16 in)
A Silo diameter 12 m (40 ft)
B Silo diameter 9 m (30 ft)
C Silo diameter 6 m (20 ft)
D Silo diameter 3 m (10 ft)
5 10 15 20 25
L [m]
Mounting
40
36
32
28
A
B
24
20
C
16
12
D
8
4
0
30 35
A0017170
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