Transcript Accuracy of Continuous Level Measurement Systems in Dry

Accuracy of Continuous Level
Measurement Systems in Dry
Bulk Applications and
Performance Expectations
By
Greg DeRudder,
Technical Sales Support Manager
Monitor Technologies LLC
Copyright © 2004, Monitor Technologies LLC. All rights reserved
CM Console Picture
Multi-Station and
Single Station
CM3A and CM4
Control Console
2
Weight, the Final Frontier!
3
Factors Contributing to
Errors in Calculated Values
•
•
•
•
•
•
•
Error in Height & Width
Cone Height
Inside Diameter
Corrugated Walls
Bulk Density
Packing Factors
Bridges & Rat Holes
4
Factors Contributing to
Errors in Calculated Values
• Inside Diameter vs: Outside Diameter
The dimensions shown at left represent
a difference of 1 inch of silo diameter
error. Using the OD of 15 feet (a radius
of 7.5’) calculates a volume per linear
foot of 176.714ft3.
R 7.50'
To Outside
R 7.46'
To Inside
Using the radius of 7.46, the volume is
174.834ft3. The difference is 1.88ft3
per linear foot. If your Bulk Density is
40lbs/ft3, the weight error is 75.2 lbs/ft.
A 30ft straight wall would represent an
error of 2,256lbs. 40 feet would
represent 3,008 lbs.
5
Terms and Other
Considerations
•
•
•
•
•
•
•
Direct Distance Measurement
Calculated Level Measurement
Calculated Volume Measurement
Bulk Density
Calculated Weight Representation
Angle of Repose
Packing Factor
6
• Distance to material is actually measured
• Material Level is calculated
• Level = Vessel Height - Distance Measured
Distance
11.54'
Vol repose
23.00'
Vol cylinder
Level
11.46'
Vol cone
7
• Calculated Volume Measurement
Vcyl = π
r2 H
Distance
11.54'
10.00'
=3.14 x 56.25 x 4.85 3.85' 1.00'
=856.63ft3
Vol repose
2.00' 4.85'
Vol cylinder
Vcone = .2618(D2 + Dd + d2) H
Vol cone
6.60'
= .2618(225 +15 + 1) 6.6
= 416.42ft3
8
Definitions
• Bulk Density is weight as a function of volume
=
___________
3
9
Definitions
• Calculated Weight Representation
– Weight Approximations can be easily
calculated when the volume of material and
the Bulk Density of the Material are known
Material Weight = Material Volume x Bulk Density
10
Assumptions
• The Vessel is center filled from a single point on center
• The sensor (if smart weight & cable) is mounted at 1/6th
Diameter from the outer wall
• The vessel is discharged from the bottom on center
15.00'
2.50'
10.00'
1.00'
2.00'
When a SiloPatrol unit is
mounted at 1/6D, the volume of
air represented in Green equals
the volume of material
represented in Red
11
Vred = π r2 h/3 = (3.14 x 25 x 2) / 3
=52.33ft3
Vgreen = Volume of 1 ft of straight
wall = VCyl minus VOrange
15.00'
2.50'
VCyl
10.00'
1.00'
= π r2 h = 3.14 x 56.25 x 1
= 176.625ft3
2.00'
VOrange = .2618 (D2 + Dd + d2) h
=.2618(225 + 150 + 100) x 1
= 124.35ft3
3
Vgreen =176.625 - 124.35 = 52.275ft
12
Proving 1/6D Volume Analysis
VGreen = Volume of 1 ft of straight
wall (VCyl) minus Vorange
VCyl
15.00'
= 176.625ft3
VOrange = 124.35ft3
2.50'
VGreen = 176.625ft3 - 124.35ft3 = 52.275ft3
10.00'
1.00'
2.00'
Vred = 52.33ft3  VGreen = 52.275ft3
 = .055ft3
or about 2.2 lbs. @40 lbs/ft3
13
Considerations for Equipment that
does not use Gravity
• When using Ultrasonic measurement equipment
there will almost always be an angle in the
measurement to consider that, because of gravity,
does not exist with plumb bob type measurement
14
Distance
11.54'
11.01'
(@ 1/6 D)
23.43'
Level
23.00'
11.46'
15
20.64'
21.22'
23.61'
23.00'
16
Ultrasound Flight Characteristics
A Sensor that is aimed straight
down in an empty silo
condition is prone to false
material Distance
measurements. In this example,
with 23 feet being programmed
as the maximum measuring
distance, we can expect the
display to reflect the time of
flight of Echo 1 to be
interpreted as the Valid Echo
for the following pulse. The net
result would be a displayed
distance of around 8 feet.
14.83'
18.64'
16.43'
17
Effects of Angle of Repose and Sensor
Mounting location @ 200 of Material Slope
2.50'
2.50'
18
19.16' 18.26'
17.34'
16.50'
23.00'
6.50'
RED
Magenta
Blue
Black
Distance Calculated Calculated Calculated Difference
Measured Cone Level Volume
Weight From Actual
16.5
6.5
410.11
16,404
2,120
17.34
5.66
357.11
14,284
Actual
18.26
4.74
299.06
11,963
-2,322
19.16
3.84
242.28
9,691
-4,593
Accumulation of Error
Silo Height
Silo Diameter
Cone Height
Discharge Diameter
Bulk Density (lbs./cubic foot)
Total Volume (Cubic Feet)
Total Weight (Pounds)
Volume Error
Weight Error
Actual
Adjust H
55.00
54.50
15.00
15.00
8.00
8.00
1.00
1.00
40.00
40.00
8,806.13
8,718.06
352,245.02 348,722.50
0
88.06
0
3,522.52
Adjust D Adjust Cone H
54.50
54.5
14.92
14.92
8.00
7.5
1.00
1.00
40.00
40.00
8,471.77
8225.52
338,870.63
329,020.81
334.36
492.54
9,851.87
9,849.81
15.00'
Adjust BD
54.5
14.92
7.5
1.00
39.00
7757.17
302,529.78
714.59
26,491.04
In the chart above, 4 of 5 variables are slightly altered one
at a time. See the error figures in each column and how
the accumulate. Please note that Bulk Density has the
most severe impact on the accuracy of volume and weight
calculations.
47.00'
8.00'
1.00'
19
Consider a Silo That can Hold 133,036 lbs of Material
Published Accuracy of SiloPatrol
equipment is:
3326 ft3
<.5% of the Distance Measurement
Published Accuracy of Ultrasonic
Equipment is:
133,305 lbs.
23.00'
.2% of the distance/.05% of the range
Published accuracy of Load Cell
System is:
.2% Full Scale
6.50'
20
A Distance measurement of 16 feet is taken ...
2.50'
Published Accuracy of SiloPatrol equipment is:
<.5% of the Distance Measurement = .08feet
so, worst volume error = 14.13ft3 = 565lbs
16.00'
Published Accuracy of Ultrasonic Equipment is:
.2% of the distance/.05% of the range = .032 feet
23.00'
so, worst volume error = 5.6 ft3 = 226.08 lbs.
Published accuracy of Load Cell System is:
.2% Full Scale = 233.26 lbs worst case
6.50'
21
List Price Comparison
for four Silos
• 16 Load Cells & Mounting Plates
• Display, Analog Card, Scanner
– List less installation costs
• SMU for 4 Silos
• 8 Channel HMI
– List for SiloPatrol less installation
• Ultrasonic and Accessories
$17,680
2,885
$20,565
$4,480
745
$5,225
$6,020
– Does not include Display Device
22
Summary
•
•
•
•
Obtain Accurate Dimensional Data
Obtain Accurate Bulk Density Information
Follow Factory Installation Guidelines
You should get acceptable - repeatable
calculated measurement data
• If you still need better accuracy numbers,
employ the use of a Linearization Table or
Curve-Fit-Weight Table
23
Coming Soon to a Silo Near You!
The Greg DeRudder Action
Figure can be yours for as
little as $400.00/Travel day
plus expenses on new startups! Call for details or a fixed
fee quotation.
24