Title; Measurement of the Weight of Bulk Materials

Field of invention

This invention concerns the measurement of the weight of bulk materials particularly when stored in silos and the like.

Background to the invention

It is often necessary to know the weight of powdered or granulated materials when contained in storage silos and the like. Where the silo is free standing and separate from other structures, the silo can be mounted on a weighing platform and the empty weight of the silo deducted from any measured weight of the silo when filled or partly filled to thereby give the weight of the contents .

Difficulties arise when the silo actually forms part of another structure and cannot be readily isolated from the structure for weighing purposes.

One alternative to weighing the silo is to provide level sensing means within the silo to measure the upper level of the material in the silo. Provided the bulk density of the stored material is known and the internal dimensions of the silo are also available, the weight of the material in the silo may be calculated from height of the material measured by the level sensing means -

This alternative method suffers from the disadvantage that

an accurate figure for bulk density must be known and this is not always available. In addition voids can arise within the silo during filling so that a totally false figure for the weight of the contents may be obtained since the height as measured by the level sensing means may be grossly overestimated.

It is an object of the present invention to provide an improved method and apparatus for weighing the contents of the silo by direct measurement and which does not require an assessment of the bulk density of the stored material.

Summary of the invention

According to one aspect of the present invention in a method of estimating the weight of the powdered or granulated contents of a silo the powdered or granulated material is first vibrated so as to remove voids and the like and thereafter the pressure of the contents of the silo acting on the floor of the silo is measured by direct ^' measurement using a strain gauge or the like and the weight of the silo contents calculated using the known cross-sectional geometry of the interior of the silo.

According to another aspect of the present invention apparatus for performing the invention comprises means for vibrating particulate material contained within a silo and pressure transducer means for converting downward pressure into an electrical signal proportional to the force acting on the pressure transducer and calibrated read-out means for displaying as a numerical value the weight of the particulate material in the silo.

In the method and apparatus the vibrating means may be

operated mechanically or electrically or. electomagnetically or electrostatically. In a preferred embodiment an airstream is caused to flow through the particulate material so as to produce separation of the individual particles to enable the particulate material to settle uniformly within the silo and remove voids and non- homogeneous packing.

Thus in accordance with the method, the preparation step may involve activating a vibrator associated with the silo or introducing one or more jets of air into the interior of the silo so as to disturb and agitate and otherwise vibrate the particulate material therewithin.

In accordance with the apparatus, vibrator means may be fitted within the silo or adapted to communicate with the interior of the silo so as to agitate the particulate material or a fan or air pump may be provided in association with suitable ducting to introduce one or more jets of air into the interior of the silo so as to agitate and thereby vibrate the particulate material therewithin.

It may be sufficient to agitate or otherwise vibrate the particulate material as it enters the silo so that a direct reading of the pressure and therefore weight of particulate material can be obtained as the silo is filled.

The invention is not limited to any particular method or apparatus for measuring pressure but a particularly preferred method is the use of a strain gauge and the mounting of a strain gauge is important.

It is of course essential that the' strain gauge is mounted

on a member which is rigidly held at its ends but"-can deflect under the particulate material loading and a preferred mounting point is a cross-member associated with a bin discharge unit such as that manufactured and sold as the Hogan Bin Discharger.

The function of the Hogan Bin Discharger is to impart vibration so as to fluidise particulate material thereabove. Once fluidised, the true pressure exerted by the material above the bin discharger can be measured by direct reading using the strain gauge.

Preferably the latter forms part of an electrical bridge circuit in known manner and electrical signal amplifying circuits are provided for converting the very small error signal introduced as the bridge moves out of balance with increased loading. The signal may be converted from an analogue signal to a digital signal and thereafter digitally processed so as to obtain a total weight signal by simply multiplying the pressure value by the known area of the silo. This gives the weight of the material directly particularly where the silo is parallel sided.

A digital read-out device is preferably provided so as to display the actual weight of the material within the silo at any instant in time.

The invention prevents overloading of a silo due for example to the use of particulate material which contains a larger amount of moisture than normal and which therefore adds weight to the overall material.

By utilising a level sensing device within the silo, it is also possible to check to ensure that voids and

cavitations have not occurred within the contents as it is loaded into the silo by comparing the expected weight for any given height with the actual weight.

The invention thus enables silos to be mounted in structures with every confidence that overloading will not occur and that wherever possible the silo will be properly and completely filled at least to a given maximum weight and will not include voids and cavities.

The invention will now be described by way of example, with reference to the accompanying drawings, in which:

Figure 1 diagrammatically illustrates a parallel sided silo with a bin discharger at its lower end which includes vibratory fluidisation means and a strain gauge;

Figure 2 is a similar schematic illustration of a parallel sided silo with a strain gauge at its lower end and air fluidisation means mounted above the lower end of the silo;

Figure 3 illustrates as a perspective underside view a so- called Hogan Bin Discharger; and

Figure 4 gives details of the intermediate structural beam within the bin discharger of Figure 3, and Figure 4A shows how the strain gauge is mounted thereon.

Detailed description of the drawings

In Figure 1 a parallel sided silo 10 contains particulate material such as powdered material 12 and the base of the silo is closed by a Hogan Bin Discharger frame 14. A

strain gauge 16 is mounted on a beam cross-member of the bin discharger frame (not shown in detail) and serves to register the deflection of the beam under the downward loading of the particulate material 12.

The actual deflection will be determined by the actual weight acting on the bin discharger frame and in particular on the cross-member to which the strain gauge is mounted, it is possible to compute the weight of the material within the silo by multiplying the pressure by a mean value for the area of the silo interior. The computed value for the weight of the particulate material is therefore not dependent on the bulk density of the material nor on the measurement of the height of the material within the silo.

As previously mentioned a height measuring device such as 20 may be provided with a sensor which for example hangs down within the silo at 22. This enables the height of the material to be measured and checked against the computed weight value using the strain gauge output. By using a look-up table it is possible to determine whether or not the computed weight value is lower than would be expected which would indicate an excessively dry material or voids or cavities within the contents.

It is important that the bin discharger includes vibratory fluidisation means for vibrating the powdered material since only when the material is in a truly fluidised condition is the weight of the contents of the silo directly proportional to the measured force of deflection.

Figure 2 shows an alternative arrangement in which similar

reference numerals have been used to denote parts and contents previously described with reference to Figure 1. However, in place of the Hogan Bin Discharger frame 14, an air inlet pipe 24 is provided with a nozzle such as 26 for deflecting air into the lower end of the silo 10 to thereby agitate and fluidise the material therewithin. In this event it is merely necessary to mount the strain gauge 16 on a structural member which closes off the bottom of the silo and is approximately centrally located relative to the silo cross-sectional area.

A Hogan Bin Discharger frame is shown in Figure 3. Across the frame extends a blade support beam 28 and centrally of the beam are mounted two brackets 30 and 32 respectively. The strain gauge 16 is mounted vertically below the support beam 28 and is carried at its upper end by bracket 32 and its lower end by the bracket 30.

Figure 4 is a side view of the blade support means 28 and illustrates the two mounting brackets 30 and 32 in more detail. The strain gauge 16 is also visible as is also a signal cable 34 which extends along the underside of the beam 28 to electrical signal processing apparatus. The latter is shown in Figure 4A. The input signal from the strain gauge is first amplified by an amplifier 36 and the signal is then converted to a digital signal by an analogue to digital converter 38. The digital value is scaled by multiplying or dividing stage 40, whose constant by which the incoming signal is multiplied or divided is adjustable by means of a control 42. The latter is preset during initial installation to take account of the geometry of the particular silo. The scale output signal is supplied along signal path 44 to a digital read-out device 46.