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

2 CM Console Picture Multi-Station and Single Station CM3A and CM4 Control Console

3 Weight, the Final Frontier!

4 Factors Contributing to Errors in Calculated Values Error in Height & Width Cone Height Inside Diameter Corrugated Walls Bulk Density Packing Factors Bridges & Rat Holes

5 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 ft 3. Using the radius of 7.46, the volume is ft 3. The difference is 1.88ft 3 per linear foot. If your Bulk Density is 40lbs/ft 3, 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. To Outside To Inside

6 Terms and Other Considerations Direct Distance Measurement Calculated Level Measurement Calculated Volume Measurement Bulk Density Calculated Weight Representation Angle of Repose Packing Factor

7 Distance to material is actually measured Material Level is calculated Level = Vessel Height - Distance Measured

8 Calculated Volume Measurement V cyl = π r 2 H =3.14 x x 4.85 =856.63ft 3 V cone =.2618(D 2 + Dd + d 2 ) H =.2618( ) 6.6 = ft 3

9 Definitions Bulk Density is weight as a function of volume = ___________ 3

10 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

11 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 When a SiloPatrol unit is mounted at 1/6D, the volume of air represented in Green equals the volume of material represented in Red

12 V red = π r 2 h/3 = (3.14 x 25 x 2) / 3 =52.33ft 3 V green = Volume of 1 ft of straight wall = V Cyl minus V Orange V Cyl = π r 2 h = 3.14 x x 1 = ft 3 V Orange =.2618 (D 2 + Dd + d 2 ) h =.2618( ) x 1 = ft 3 V green = = ft 3

13 V Green = Volume of 1 ft of straight wall (V Cyl ) minus V orange V Cyl = ft 3 V Orange = ft 3 V Green = ft ft 3 = ft 3 V red = 52.33ft 3  V Green = ft 3  =.055ft 3 or about 2.2 lbs/ft 3 Proving 1/6D Volume Analysis

14 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

15 1/6 D)

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17 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.

Effects of Angle of Repose and Sensor Mounting 20 0 of Material Slope 18

19 Accumulation of Error 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.

20 Published Accuracy of SiloPatrol equipment is: <.5% of the Distance Measurement Published Accuracy of Ultrasonic Equipment is:. 2% of the distance/.05% of the range Published accuracy of Load Cell System is:.2% Full Scale Consider a Silo That can Hold 133,036 lbs of Material 3326 ft 3 133,305 lbs.

21 Published Accuracy of SiloPatrol equipment is: <.5% of the Distance Measurement =.08feet so, worst volume error = 14.13ft 3 = 565lbs Published Accuracy of Ultrasonic Equipment is:. 2% of the distance/.05% of the range =.032 feet so, worst volume error = 5.6 ft 3 = lbs. Published accuracy of Load Cell System is:.2% Full Scale = lbs worst case A Distance measurement of 16 feet is taken...

22 List Price Comparison for four Silos 16 Load Cells & Mounting Plates $17,680 Display, Analog Card, Scanner 2,885 –List less installation costs $20,565 SMU for 4 Silos $4,480 8 Channel HMI 745 –List for SiloPatrol less installation $5,225 Ultrasonic and Accessories $6,020 –Does not include Display Device

23 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

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