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1
Weight Measurement Technology
2
Definition of Terms
• Millivolt– 0.001 volts: the unit of measure of output
from sensors• PSI
– Pounds per Square Inch: Unit of measurement of stress used in the application of strain gage sensors
3
Definition of Terms
• Stress– Any action on a body that results in
deformation. Usually measured in pounds per square inch or Pascal's
• Thermal Stress–Two dimensional strain caused
by thermal heating (expansion)or cooling (contraction)
4
Definition of Terms
• Strain– Deformation of a body or structure as a result
of an applied force• Strain Gage
– A device that converts mechanical deflection to an electrical signal
5
Definition of TermsMechanics of a member in compression
• Compression – Stress by forces
pushing together• Tension
– Stress by forces causing extension (pulling)
WL
∆LAt Rest
Add Weight
Mechanics of a member in tension
Add Weight
W
L
∆L
At Rest
6
Definition of Terms
• Poisson’s Ratio– The ratio of transverse strain to
longitudinal strain -- The ratiofor carbon steel is .3
• Shear– The component of a horizontal
beam that is being measuredA D
Shear Area = A x D
7
Definition of Terms
• Live Load– The design capacity of a vessel
• Dead Load– The empty weight of a vessel
8
Definition of Terms
• Wheatstone Bridge– An electrical circuit used to
detect small resistance changes in strain gages
• Signal Lines– In half bridge systems, these
are the lines that return the signal to signal conditioners
+EXC
-EXC
SignalProcessor Transducer
Red
Black
White
OutputSignal
Rd
RcRa
Rb
Note: c dR and R are fixed resistors
9
Definition of Terms
• Sense Lines– In full bridge systems,
these are the lines that bring in the sensed voltage
Signal
+Sense+Excitation
-Sense-Excitation
10
Introduction
• Bolt-On – Transducers attached to existing vessel structural support
• Direct Support – Transducers are built into structural support elements
Both share a common platformSilicon Semiconductor Strain Gages
11
Introduction
• Silicon Semiconductor Strain Gage– Solid state resistors– Manufactured from a single-crystal boule– Acid –etched to require resistance– Glass fused to bending beam
12
Theory
+EXC
-EXC
SignalProcessor Transducer
Red
Black
White
OutputSignal
Rd
RcRa
Rb
Note: c dR and R are fixed resistors
• Wheatstone Bridge– An electrical circuit
used to detect small resistance changes in strain gages
13
Theory
• Compression and expansion.– Poisson’s Ratio.– .3 for carbon steel
14
Theory
• The Bolt-On weight transducer detects and amplifies this change in length and provides a resistance change that is proportional
• Vessel support experiences small strain (length) changes in direct proportion to the change in weight of material in vessel
15
Factors That AffectPerformance
• Rigid Piping Connections• Catwalk• Hidden Load Bearing Members• Vessel goes Through Roof• Tripper Conveyors or Deck Plating
16
Factors That AffectPerformance
• Poor Foundation• Flexible Structure• Uneven Loading
– Structure not level– Off-center loading– Wind– Equipment
Vibration
Side LoadSide load causestension on legs onthis side, whichcould be interpretedas decreased materialweight
Side load causescompression on legson this side, whichcould be interpretedas increased materialweight
Tension and compression equal but opposite; canceleach other if all legs instrumented with L-Cells.
17
Factors That AffectPerformance
• Shock Loads• Excessive electrical noise or heat
18
Bolt on Weight Measurement
19
Introduction
• Bolt-on provides continuous bulk material inventory
• Immune to material characteristics• Provides weight not level• Non-intrusive• Ideal for renovations or retrofits• Install without interrupting production
20
Microcell
• A half bridge strain gage device used to transform a mechanical motion into an electrical signal
21
L-Cell
• Dual axis strain gage device used to transform a mechanical motion into an electrical signal; minimizes environmental effects
22
Type of Legs
Channel Unequal Angle
Pipe Legs
Square Tubing
RectangularTubing
H or I Beam
EqualAngle
23
Type of Legs
• Pipe Legs
24
Leg Bending
25
Lateral Stain
26
Compression/Expansion
27
psi CalculationLegged Vessel
live load (working capacity)live load per leg =number of legs
live load per legload factor (psi) =
steel area calculation
B
A
C
D
B
C
A
C
T
B
AA
B
A
B
T
Area = 3.13 x D x TPipe Legs
Area = (2A + 2B) x TTubular Legs
Area = (A + B) x CAngle Legs
Area = 2 x B x C + {A - (2C)} x DH or I Beam Legs
28
Horizontal Location onVertical Legs
• Square tubing• Rectangular tubing• H & I beam• Channels• Angle with equal or unequal legs • Vertical pipe legs
29
Vessel Free Leg
30
Support Legs
N=2N=2N=0
N=0
With X-BracesWithout X-Braces
31
Leg Accuracy Chart
0123456789
0 1000
2000
3000
4000
5000
6000
7000
8000
9000
{Stress in PSI}
{± E
rror
%}
Outside N=0Outside N=1Outside N =2Inside N=0Inside N=1Inside N=2
32
psi Calculation HorizontalBeam Supported Vessels
live load (working capacity)live load per support point =
two times the number of support beams
live load per support pointload factor (psi) =
shear area calculation
A D
Shear Area = A x D
33
Horizontal BeamsLeft & Right Same Side of Web
supportpoint
loadpoint
supportpoint
34
Horizontal BeamsLeft & Right Opposite Side of Web
supportpoint
loadpoint
supportpoint
35
Horizontal BeamsLeft or Right Back-To Back
supportpoint
loadpoint
supportpoint
36
Horizontal BeamsLeft or Right Single L-Cell
supportpoint
loadpoint
supportpoint
37
Horizontal BeamsLeft & Right Back-to-Back
loadpoint
supportpoint
supportpoint
38
Horizontal BeamsExcitation Wiring
• L-Cell orientation is the determining factor for reversing the excitation wiring.– If the the L-Cell is
located to the right of the Load Point then the excitation is reversed.
• i.e. red to black and black to red
loadpoint
RevRed t
ersedo B
Ec
xcik &
aBtat
laionc
Wirino Re
gd
NorRed t
malR
Ee
xd
ciat&
atla
ioc
nk
Wo
iringBlao B t ck la k t
39
Horizontal Accuracy Chart
0
1
2
3
4
5
6
7
8
9
0 1000
2000
3000
4000
5000
6000
7000
8000
9000
{Stress in PSI}
± E
rror
%
4 Cells/Beam
2 Cells/Beam
1 Cell/Beam
40
Skirted SiloSilo Layouts
Legend:= L-Cell Set= Junction Box= Door
1516
14
13
12
11
1098
7
6
5
4
32
1
24' (7.3m) Diameter9'5" (2.9m)
L-Cell Spacing
21
3
4
5
6
7
89 10
11
12
13
14
15
1617
26' (7.9m) Diameter9'5" (2.9m)
L-Cell Spacing
12
3
4
5
6
7
8
910 11 12
13
14
15
16
17
1819
20
28' (8.5m) Diameter8'10" (2.7m)
L-Cell Spacing
123
4
5
67
8 910
11
12
13
14
21' (6.4m) Diameter9'5" (2.9m)
L-Cell Spacing
9' (2.7m) Diameter9'5" (2.9m)
L-Cell Spacing
1
4
62
53
12
3
4 56
7
8
12' (3.7m) Diameter9'5" (2.9m)
L-Cell Spacing
12
3
4
56
7
8
9
10
15' (4.6m) Diameter9'5" (2.9m)
L-Cell Spacing
12
3
4
5
6 7 8
9
10
11
12
18' (5.5m) Diameter9'5" (2.9m)
L-Cell Spacing
41
psi CalculationSkirted Silo
D
T
live load (working capacity)load factor (psi) =
3.14 x D x T
42
Skirted SiloL-Cell Sets
Cable routing through3/16" hole
43
Skirt Accuracy Chart
02468
1012141618
0 1000
2000
3000
4000
5000
6000
7000
8000
9000
{Skirt Stress in PSI}
{± E
rror
%}
Best CaseWorst Case
44
Bolt-On Weight Technology
• Evaluate customer data requirements• Level-by-weight and weight-by-level systems are at best
a 10% system• Bolt-on not affected by
– Angle of repose– Rat-holing– Bridging– Moisture content– Compaction– Vapors– Dust