GB1599199A - Weighing of bulk material - Google Patents

Weighing of bulk material Download PDF

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Publication number
GB1599199A
GB1599199A GB2559978A GB2559978A GB1599199A GB 1599199 A GB1599199 A GB 1599199A GB 2559978 A GB2559978 A GB 2559978A GB 2559978 A GB2559978 A GB 2559978A GB 1599199 A GB1599199 A GB 1599199A
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GB
United Kingdom
Prior art keywords
hopper
weight
charging
time
sample
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB2559978A
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Central Electricity Generating Board
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Central Electricity Generating Board
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Central Electricity Generating Board filed Critical Central Electricity Generating Board
Priority to GB2559978A priority Critical patent/GB1599199A/en
Publication of GB1599199A publication Critical patent/GB1599199A/en
Expired legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01G—WEIGHING
    • G01G13/00—Weighing apparatus with automatic feed or discharge for weighing-out batches of material
    • G01G13/003—Details; specially adapted accessories
    • G01G13/006—Container supply or discharge mechanism
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01G—WEIGHING
    • G01G11/00—Apparatus for weighing a continuous stream of material during flow; Conveyor belt weighers
    • G01G11/04—Apparatus for weighing a continuous stream of material during flow; Conveyor belt weighers having electrical weight-sensitive devices
    • G01G11/043—Apparatus for weighing a continuous stream of material during flow; Conveyor belt weighers having electrical weight-sensitive devices combined with totalising or integrating devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01G—WEIGHING
    • G01G13/00—Weighing apparatus with automatic feed or discharge for weighing-out batches of material
    • G01G13/24—Weighing mechanism control arrangements for automatic feed or discharge
    • G01G13/28—Weighing mechanism control arrangements for automatic feed or discharge involving variation of an electrical variable which is used to control loading or discharge of the receptacle

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Weight Measurement For Supplying Or Discharging Of Specified Amounts Of Material (AREA)
  • Filling Or Emptying Of Bunkers, Hoppers, And Tanks (AREA)

Description

(54) IMPROVEMENTS IN OR RELATING TO THE WEIGHING OF BULK MATERIAL (71) We, CENTRAL ELECTRICITY GEN ERATING BOARD, a British Body Corporate, of Sudbury House, 15 Newgate Street, London, EC 1 A 7AU, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment:- This invention relates to the weighing of bulk material.
According to one aspect of the present invention, a method of weighing bulk material comprises the steps of feeding the material into holding means, intermittently discharging said holding means into a hopper supported on or by one or more load cells, removing the material from the bottom of the hopper at a substantially uniform rate, determining the weight of the hopper and its contents immediately before and immediately after each time it is charged from said holding means to determine thereby either the amount of material fed into the hopper by subtracting the measured weight immediately before charging from the subsequently measured weight after charging or the amount of material removed from the hopper by subtracting the weight before charging from the previously measured weight after charging, measuring the rate of change of the weight of the hopper and its contents when the material is being removed therefrom and correcting the difference in the weights after and before charging the hopper, in accordance with the measured rate of removal of material, for the amount of material removed from the hopper in the time period between the determination before charging and the subsequent determination after charging, i.e. the time period within which the hopper is being charged.
It will be seen that, by this method, the change of weight of the hopper and its contents is measured each time a load of material is put into the hopper. Although material is continuously discharged from the hopper, this discharge rate is measured to corrent for any discharge occurring between the two weight determinations before and after loading the hopper.
The material is fed into the holding means and intermittently discharged into the hopper. The material may be transported to the holding means intermittently or in a steady flow, e.g. on a conveyor.
The operation is cyclic and it is immaterial whether the measured weight before charging is compared with the previously determined or with the subsequently determined weight after charging the hopper. If the weight of the hopper and contents before a load is fed into it is compared and the weight determined immediately after loading, then the difference is the amount of material fed into the hopper; the difference is corrected for the amount leaving the hopper between these two measurements. The weight before loading however may be compared with the previously determined weight after the hopper had previously been located to obtain the amount of material discharged from the hopper, this being corrected as described.
It will be appreciated and normally the discharging of the holding means into the hopper is effected in a time period short compared with the duration of discharge of the hopper. Provided the rate of discharge from the hopper is predictable, the material can be weighed accurately despite the fact that it is leaving the hopper at the same time as further material is being put in the hopper.
Viewing the invention from another aspect, apparatus for weighing bulk material comprises a hopper supported on or by a load cell or cells, holding means for batching material and then rapidly charging it into said hopper at intervals, means for removing material from the hopper at a substantially uniform rate, data processing means respon sive to the output of the load cell or cells for determining the difference in weight of the hopper and contents before and after it is charged to determine thereby either the amount of material fed into the hopper by subtracting the measured weight immediately before charging from the subsequently measured weight after charging or the amount of material removed from the hopper by subtracting the weight before charging from the previously measured weight after charging, said data processing means furthermore being arranged to determine the rate of removal of material from the hopper by sampling the output of the load cell or cells and to correct, in accordance with the determined rate of removal, each determined difference for the amount of material removed from the hopper in the time period between the determination before charging and the subsequent determination after charging, i.e. the time period within which the hopper is being charged.
In the following description, reference will be made to the accompanying drawings in which: Figure 1 is a diagram illustrating one embodiment of apparatus for the weighing of bulk material; Figure 2 illustrates a modification of part of the apparatus of Figure 1; and Figure 3 is a graphical diagram for explaining the operation of the apparatus of Figures 1 and 2.
Referring to Figure 1, there is shown diagrammatically apparatus for the weighing of bulk material arriving on a conveyor 10.
The material falls off the end of the conveyor onto a collecting tray 11 which is pivotally mounted at 12 and normally biased by a counterweight 13 so that the tray is held up with the counterweight abutting a stop 14.
When sufficient material accumulates in the tray, its weight overcomes the bias and this accumulated material is discharged into a hopper 15 supported on or by load cells 16.
A conveyor 17 is disposed below the outlet of hopper 15 and the hopper discharges at a constant rate determined by the discharge mechanism. A vibratory feeder (not shown) is provided on the bottom frame of the hopper 15 to help produce a steady flow of material from the hopper and to prevent the formation of bridges of material within the hopper. Such bridges are undesirable since the sudden collapse of such a bridge produces impulse loading of the load cells. It may be preferred to inhibit operation of the vibratory feeder during the time that the hopper is being charged.
The load cells 16 produce electrical outputs which are summed in a stable analogue summing amplifier 20 having zero error and range controls 21 for calibration purposes.
The output of this amplifer is then regularly repetitively sampled and digitised in an analogue-to-digital converter 22 and the digital output is fed to a data processor 23 for processing.
Referring now to Figure 3, this graphical diagram shows a typical cycle of variation of totalised signal from the amplifier 20 plotted as ordinates with time as the abscissa.1 At the point A, material begins to be loaded into the hopper 15. The impulse from the sudden loading causes the signal to overshoot to B.
Charging of the hopper is completed with possibly small further oscillations in signal amplitude. At point C, the material is being discharged and the signal represents the instantaneous total weight of the hopper and its contents. The analogue-to-digital converter 22 feeds repetitively sampled signals in digital form into the data processor 23. The data processor detects the sudden increase in weight of the hopper at the point A to initiate the required computation. The sampling rate typically is so fast that sample point is, for practical purposes, the actual start of loading. For processing, the lowest sample in the cycle before the datum time and the first sample after non-oscillating conditions are reached in the cycle after the datum time are selected.During this time period D to E, that is to say between the time at point A when loading commences and the time when steady discharge is measured, it is assumed that either material is being discharged from the hopper at the same rate as before time D or no material is being discharged because the vibratory feeder is shut down. The data processor 23 monitors the state of the vibratory feed so that the existence of one or other of these conditions is recognised.
The difference in vertical displacement between points A and C represents the net transfer of material into the hopper from the batching means. During the time period D to E, material will have been discharged from the hopper if the feeder was operating and hence, to calculate the gross amount of material charged into the hopper, the data processor 23 uses the monitored discharge rate prior to the time D, this rate being multiplied by the time period D to E to give the correction to be added to the vertical component A to C to form the gross weight of material delivered to the hopper. If the vibratory feeder is stopped during the hopper filling, this correction is inhibited automatically by the data processor monitoring the vibrator state.
The hopper 15 and conveyor 17 are arranged so that there is a substantially constant rate of discharge from the hopper and thus, unless the hopper has become empty, the slopes of the graph of Figure 3 during the time periods before D and after E will be substantially the same.
It will be seen therefore that the data processing requires essentially means for temporarily storing the total hopper weight at each sample time and the rate of change of hopper weight. When a rise in weight is sensed, the previous sample on the straight line part of the graph before loading of the hopper begins is the weight to be subtracted from the hopper weight determined after the hopper loading is completed and any significant mechanical oscillations of the load cell output has ceased. both weights being corrected to bring them to the estimated values at a suitable datum time, conveniently the time E, using the measured rates of change.
As an alternative to determining the amount put into the hopper in each load cycle, one could determine, from the same data, the amount discharged from the hopper; in this case one would, for example, subtract the weight at a time F towards the end of the discharge part of the cycle, when the hopper is next loaded, and subtract this weight from the weight at C extrapolated back to the time D. It will be appreciated that this is a different mathematic processing of the same data and, considered over a long period, will give the same total.
Figure 2 illustrates an alternative method of batching material and feeding it into a hopper. The material which typically arrives as a steady stream on a conveyor 30, is discharged on a rotatable paddle member 31 having, in this particular example, three blades 32 which extend generally radially from a central drum 33, the axis of which is horizontal. The'outer ends of the blades are inclined, as shown at 34, to the radial direction of the inner parts of the blades.
Material builds up between the blades until, due to the shaping, it spreads outwardly in one direction, causing the drum to rotate in the direction of the arrow 35. The material falls down into the hopper 15, of which only the upper part is shown in Figure 2. The conveyor 30 delivers material into the next compartment between the blades and is positioned so that the impulse of the falling material prevents the paddle member 31 from rotating too far.
Although the weighing device has been described more particularly in combination with a batching device for periodically charging the hopper 15, in some case no batching device is required. For example, material such as coal or ore might be loaded into the hopper by use of a grab which is employed for taking the material, for example, from the hold of a ship or other bulk transporter.
WHAT WE CLAIM IS:- 1. A method of weighing bulk material comprising the steps of feeding the material into holding means, intermittently discharging said holding means rapidly into a hopper supported on or by one or more load cells, removing the material from the bottom of the hopper at a substantially uniform rate, determining the weight of the hopper and its contents immediately before and immediately after each time it is charged from said holding means to determine thereby either the amount of material fed into the hopper by subtracting the measured weight immediately before charging from the subsequently measured weight after charging or the amount of material removed from the hopper by subtracting the weight before charging from the previously measured weight after charging, measuring the rate of change of the weight of the hopper and its contents when the material is being removed therefrom and correcting each difference between the determinations before and after charging the hopper in accordance with the measured rate of removal of material, for the amount of material removed from the hopper in the time period between the determination before charging and the subsequent determination after charging, i.e. the time period within which the hopper is being charged.
2. A method as claimed in claim 1 wherein the discharging of the holding means into the hopper is effected in a time period short compared with the duration of discharge of the hopper.
3. A method as claimed in either claim 1 or claim 2 wherein the correction for the amount of material removed during the time between the determination before charging and the subsequent determination after charging is effected before the subtraction.
4. A method as claimed in either claim 1 or claim 2 wherein the correction for the amount of material removed during the time between the determination before charging and the subsequent determination after charging is effected after subtraction.
5. Apparatus for weighing bulk material comprising a hopper supported on or by a load cell or cells, holding means for batching material and then rapidly charging it into the hopper at intervals, means for removing material from the hopper at a substantially uniform rate, data processing means responsive to the output of the load cell or cells for determining the difference in weight of the hopper and contents before and after it is charged to determine thereby either the amount of material fed into the hopper by subtracting the measured weight immediately before charging from the subsequently measured weight after charging or the amount of material removed from the hopper by subtracting the weight before charging from the previously measured weight after charging, said data processing means furthermore being arranged to determine the rate or removal of material from the hopper by sampling the output of the load cell or cells and to correct, in accordance with the
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. processing requires essentially means for temporarily storing the total hopper weight at each sample time and the rate of change of hopper weight. When a rise in weight is sensed, the previous sample on the straight line part of the graph before loading of the hopper begins is the weight to be subtracted from the hopper weight determined after the hopper loading is completed and any significant mechanical oscillations of the load cell output has ceased. both weights being corrected to bring them to the estimated values at a suitable datum time, conveniently the time E, using the measured rates of change. As an alternative to determining the amount put into the hopper in each load cycle, one could determine, from the same data, the amount discharged from the hopper; in this case one would, for example, subtract the weight at a time F towards the end of the discharge part of the cycle, when the hopper is next loaded, and subtract this weight from the weight at C extrapolated back to the time D. It will be appreciated that this is a different mathematic processing of the same data and, considered over a long period, will give the same total. Figure 2 illustrates an alternative method of batching material and feeding it into a hopper. The material which typically arrives as a steady stream on a conveyor 30, is discharged on a rotatable paddle member 31 having, in this particular example, three blades 32 which extend generally radially from a central drum 33, the axis of which is horizontal. The'outer ends of the blades are inclined, as shown at 34, to the radial direction of the inner parts of the blades. Material builds up between the blades until, due to the shaping, it spreads outwardly in one direction, causing the drum to rotate in the direction of the arrow 35. The material falls down into the hopper 15, of which only the upper part is shown in Figure 2. The conveyor 30 delivers material into the next compartment between the blades and is positioned so that the impulse of the falling material prevents the paddle member 31 from rotating too far. Although the weighing device has been described more particularly in combination with a batching device for periodically charging the hopper 15, in some case no batching device is required. For example, material such as coal or ore might be loaded into the hopper by use of a grab which is employed for taking the material, for example, from the hold of a ship or other bulk transporter. WHAT WE CLAIM IS:-
1. A method of weighing bulk material comprising the steps of feeding the material into holding means, intermittently discharging said holding means rapidly into a hopper supported on or by one or more load cells, removing the material from the bottom of the hopper at a substantially uniform rate, determining the weight of the hopper and its contents immediately before and immediately after each time it is charged from said holding means to determine thereby either the amount of material fed into the hopper by subtracting the measured weight immediately before charging from the subsequently measured weight after charging or the amount of material removed from the hopper by subtracting the weight before charging from the previously measured weight after charging, measuring the rate of change of the weight of the hopper and its contents when the material is being removed therefrom and correcting each difference between the determinations before and after charging the hopper in accordance with the measured rate of removal of material, for the amount of material removed from the hopper in the time period between the determination before charging and the subsequent determination after charging, i.e. the time period within which the hopper is being charged.
2. A method as claimed in claim 1 wherein the discharging of the holding means into the hopper is effected in a time period short compared with the duration of discharge of the hopper.
3. A method as claimed in either claim 1 or claim 2 wherein the correction for the amount of material removed during the time between the determination before charging and the subsequent determination after charging is effected before the subtraction.
4. A method as claimed in either claim 1 or claim 2 wherein the correction for the amount of material removed during the time between the determination before charging and the subsequent determination after charging is effected after subtraction.
5. Apparatus for weighing bulk material comprising a hopper supported on or by a load cell or cells, holding means for batching material and then rapidly charging it into the hopper at intervals, means for removing material from the hopper at a substantially uniform rate, data processing means responsive to the output of the load cell or cells for determining the difference in weight of the hopper and contents before and after it is charged to determine thereby either the amount of material fed into the hopper by subtracting the measured weight immediately before charging from the subsequently measured weight after charging or the amount of material removed from the hopper by subtracting the weight before charging from the previously measured weight after charging, said data processing means furthermore being arranged to determine the rate or removal of material from the hopper by sampling the output of the load cell or cells and to correct, in accordance with the
determined rate of removal, each determined difference for the amount of material removed from the hopper in the time period between the determination before charging and the subsequent determination after charging, i.e. the time period within the hopper is being charged.
6. Apparatus as claimed in claim 5 wherein said data processing means comprise means for periodically sampling the weight of the hopper and its contents, means responsive to the rise in weight of the hopper and contents between successive samples to determine a datum time for each charge/discharge cycle and means for selecting the lowest sample in the cylce before the datum time and the first sample after non-oscillating conditions are reached in the cycle after the datum time, and wherein the data processing means further includes means responsive to the measured rates of change for deriving, from the selected lowest sample, the weight at the datum time in the cycle immediately after said lowest sample if no material has been added to the hopper between the sample time and the datum time and for deriving, from the first sample after nonoscillating conditions are reached, the weight at the preceding datum time in the cycle if no material had been removed from the hopper after it had been fully charged.
7. Apparatus as claimed in claim 5 wherein the data processing means includes means for periodically sampling the weight of the hopper and its contents, means responsive to the rise in weight of the hopper and its contents between successivse samples to determing a datum time for each charge/discharge cycle and means for selecting the lowest sample in the cycle before the datum time and the first sample after non-oscillating conditions are reached in the cycle after the datum time and wherein the data processing means further includes subtracting means for subtracting the selected sample weight before loading the hopper from the selected sample weight after loading the hopper, to determine thereby the amount of material put into the hopper, the means responsive to the measured rate of change in said data processing means further being arranged to effect the correction of the selected sample weights either before or after the subtraction is effected.
8. Apparatus as claimed in claim 5 wherein the data processing means includes means for periodically sampling the weight of the hopper and its contents, means responsive to the rise in weight of the hopper and its contents between successive samples to determine a datum line for each charge/discharge cycle and means for selecting the lowest sample in the cycle before the datum time and the first sample after non-oscillating conditions are reached in the cycle after the datum time and wherein the data processing means further includes subtracting means for subtracting the selected sample weight at the end of the discharge period from the selected sample weight after the hopper is loaded, to determine thereby the amount of material leaving the hopper, the means responsive to the measured rates of change in said data processing means further being arranged to effect the correction of the selected sample weights either before or after the subtraction is effected.
9. A method of weighing bulk material substantially as hereinbefore described with reference to the accompanying drawings.
10. An apparatus for weighing bulk material substantially as hereinbefore described with reference to the accompanying drawings.
GB2559978A 1978-05-31 1978-05-31 Weighing of bulk material Expired GB1599199A (en)

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GB2559978A GB1599199A (en) 1978-05-31 1978-05-31 Weighing of bulk material

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GB2559978A GB1599199A (en) 1978-05-31 1978-05-31 Weighing of bulk material

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2520108A1 (en) * 1982-01-20 1983-07-22 Teccon Utvecklings Ab METHOD AND INSTALLATION FOR DETERMINING VALUES DEPENDING ON THE MASS FLOW OF A DOSING MATERIAL

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2520108A1 (en) * 1982-01-20 1983-07-22 Teccon Utvecklings Ab METHOD AND INSTALLATION FOR DETERMINING VALUES DEPENDING ON THE MASS FLOW OF A DOSING MATERIAL

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