GB2252420A

GB2252420A - Weighing apparatus

Info

Publication number: GB2252420A
Application number: GB9200517A
Authority: GB
Inventors: James Edward Elsworth; Andrew Patrick Gathercole
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-01-31
Filing date: 1992-01-10
Publication date: 1992-08-05
Anticipated expiration: 2012-01-10
Also published as: GB9102110D0; GB2252420B; GB9200517D0; WO1992014125A1

Abstract

The weighing apparatus (1) comprises a beam (2) which is supported by a knife edge (3) on a frame (4). A receptacle (5) is suspended from the beam (2) on a knife edge (6), and a weight box (7) is suspended from the beam (2) on a knife edge (8). The beam (2) is provided with an anchoring means (9) to which is attached a tension spring (10) carrying a slipper (11) slidably mounted on a support (12) that is part of the apparatus frame (4). In use a mechanical system moves the slipper (11) to a position between the beam (2) and the slipper support (12), and a weight (13) is added to the weight box (7). The turning moment of the weight (13) causes the beam to rotate and this in turn causes the slipper (11) to be nipped between the beam (2) and slipper support (12). The mechanical system used for moving the slipper is then removed. As the spring (10) is now extended, it provides a biassing force that biasses the slipper out of the nipped position. Flowable material is added to the receptacle (5) through an input valve and as the weight of the material in the receptacle increases so the beam-derived load on the slipper (11) - the "nipping" load - progressively decreases until a point is reached at which the biassing force is able to remove the slipper from the nipped position. This removal is detected by sensing means which causes the addition of material to the receptacle to be stopped.

Description

WEIGHING APPARATUS This invention relates to weighing apparatus, and concerns in particular apparatus of the balance beam type useful for weighing bulk flowable material, such as seed.

Apparatus for batching bulk materials hy weight normally involves a receptacle to which is supplied the material to be weighed together with means for controlling the ingress of material - the flow, usually - into the receptacle and means for sensing the combined weight of receptacle and material so that, at a point known as the "final set point", the flow of material into the receptacle may be stopped. In addition, the apparatus commonly includes means for releasing the accumulated material from the receptacle (in the case of net weighers; in the gross weigher case there is means for releasing the material with the receptacle).

As far as their mechanics go, these present-day weighing systems generally fall into two categories.

The first, the mechanical weighers, involves a pivoted balance beam arrangement supporting a material receptacle towards one end and a counterweight carrier towards the opposite end. Material being fed into the receptacle causes the beam to rotate about its fulcrum, and a sensor detects the position corresponding to the final set point, at which the material flow is stopped.

This type of weigher is robust but suffers the disadvantage that the beam must move during the weighing process. Movement requires acceleration, but since the mass to be accelerated consists of both the almost full receptacle and the weight carrier and its weights, and the accelerating force is the difference between the two, and at that stage is necessarily small. and since acceleration is inversely proportional to mass, and directly proportional to force, it follows that the movement is slow, and hence the whole weighing operation is slow.

The second main type of weigher is the load cell weigher, which typically involves mounting the material receptacle directly on one or more load sensing device.

This type is usually electronic, and involves virtually no movement, so that it can weigh more quickly than the mechanical beam variety. However, it is intrinsically delicate, and since the load cells carry the entire deadweight of the receptacle as well as the bulk material they require a high degree of accuracy, and hence are expensive.

The invention suggests a solution to the problem of providing both robustness and effective accuracy without significant expense by proposing what is, in a sense, a combination of the two concepts of mechanical counterweight beam and load sensor device. More specifically, the invention suggests a mechanical device in which by some suitable lever-type arrangement, preferably that of a beam balanced on a fulcrum, the weight - or, rather, the mass - of the receptacle (and the material in or on it) is "balanced" by the equal (or nearly equal) weight (or mass) of a counterweight (of accurately determinable mass), and a load sensor device is employed to detect, and in effect to measure, the difference between the moments of the two, and to cause a signal usable to indicate the desired/correct weight of material in the receptacle, and thus to terminate the weighing process (and so for instance, the feeding of material into the receptacle) at the final set point.

In one aspect, therefore. the invention provides weighing apparatus comprising a mechanical device in which by some suitable lever-type arrangement the weight of the receptacle holding the material being weighed is "balanced" by the equal (or nearly equal) "weight" of a counterforce, and a load sensor device is employed to detect, and in effect to measure, the difference between the moments of the two, and to cause a signal usable to indicate the desired/correct weight of material in the receptacle, and thus to terminate the weighing process.

The weighing apparatus of the invention may be used not only to weigh batches of material - the material is fed in some convenient incremental manner to the receptacle until sufficient has been supplied thereto but also, as a check weigher, for weighing predetermined quantities of previously batched material. For the most part the apparatus is the same for each of these uses.

The inventive weighing apparatus is a mechanical device using levers. Most preferably it is in effect a balance, employing a beam balanced on a fulcrum, so that the receptacle is supported on or from the beam and at or near one end thereof, with the counterforce applied at or near the opposite end.

The intended weight of the receptacle and its contents is roughly balanced by the counterforce, conveniently an actual counterweight - that is to say, the lever moment of the receptacle plus contents roughly corresponds to the lever moment of the counterforce. It will be clear that the counterforce may in effect be slightly greater than the receptacle/contents force, slightly smaller, or exactly the same, the load sensor device being arranged to act appropriately.

Although, as noted above, the counterforce conveniently takes the form of an actual counterweight indeed, it is preferably a box containing one or more individual weight, a weight that is attachable to the beam (like the slider on a conventional Doctor's weighing machine), or a weight that is an integral part of the beam - it can if preferred by provided in a number of other ways - for example. as the force exerted by a spring, or as a compressed air/piston arrangement.

Moreover, it can be provided as a combination of several smaller forces, and in this latter respect there may be employed a system of graduated forces - in the simplest form one large force and one small one - the application of which can be varied (as a result of the signal output following load sensor operation) to allow first a coarse and then one or more finer indication of the (approach of the) final set point. A system like this utilising two counterweights is described hereinafter with reference to the accompanying Drawings.

In one embodiment, best suited for batch weighing, the counterforce effectively has a greater magnitude than the combined force of receptacle and required quantity of material, so that the required direction of the load sensor (force sensing) device is constant, whether the receptacle be empty or contain material up to the required quantity. Furthermore, in operation the force contribution from the sensing device decreases while the receptacle is filling with material. At the final set point, the force contribution of the force sensing device is smaller than it is with an empty receptacle. The difference in magnitude between, on the one hand, the combined receptacle and required quantity of material, and on the other hand, the fixed force, may be small.Thus, the actual force contribution of the force sensing device at the final set point is small, the majority of the counterforce being provided by the fixed counterforce.

The receptacle may take any convenient form, and may be either separate (as a sack or basket) or an integral part (like a hopper) of the apparatus. The feed means may likewise be any appropriate (a belt feeder, for example), and the filled receptacle may be removed or emptied in any suitable way.

The apparatus of the invention employs a load sensor rather than a position sensor, so that virtually no movement of the lever system is necessary, and so the apparatus is simple, robust, and fast. The arrangement is such that the load sensor measures the difference between the moments of the almost full receptacle and of the counterforce (counterweight), so that any inaccuracy on the part of the load sensor is reflected in a much lower inaccuracy in the weight of the bulk material at the instant the final set point is reached.

Accordingly, for any given accuracy of the complete system, the accuracy of the load sensor can be substantially Sower, which allows a low cost system.

The load sensor may take any convenient form, such as a resistive or piezoelectric load cell, but one very simple form consists of a slidable member, or slipper, which is biased to move in one direction (to cause an indicator signal to be generated) but is restrained from so doing by the lever part of the apparatus, which part blocks the movement when in the unbalanced state but permits it when in the balanced state. This can operate rather like the sear of a trigger (where fractional movement of the trigger system permits gross movement of the cocked firing pin/bolt combination), but most preferably it iiivolves instead the frictional forces set up when the slipper is actually nipped, pinched or squeezed between the lever part and some other section of the apparatus.The primary forces acting on the lever are the weight of the receptacle/contents and the counterforce, and the degree of nip is a function of the difference between these two. If the lever part is that supporting the counterforce (on the counterweight side of a balance beam, for instance), thenr as the receptacle fills with material, the degree of nip decreases until, at the final set point, the bias is able to make the slipper slip relative to the parts nipping it. This change in the position of the slipper will be rapid; it can be detected, and used to cause (a signal to be generated that can itself be employed to cause) the flow of material into the receptacle to be stopped.

At this point it will be observed that the preferred slipper-using balance beam/counterweight form of the weighing apparatus of the invention, suitable for batch weighing flowable material, may be defined as comprising: a beam pivoted about a fulcrum, the beam being provided with counterforce weighing means on one side of the fulcrum and a receptacle for receiving material to be weighed on the other side of the fulcrum; a slipper; and a slipper support, in close proximity to the beam and fixed in space; such that in use, when the turning moment of the receptacle and its contents is less than that of the weighing means the slipper is in a nipped position between the beam and the slipper support and is biassed away from the nipped position by a biassing force, and the slipper is moved (to cause signal output) by that biassing force when the apparatus approaches equilibrium.

The details of the slipper, its bias, and the way its movement (under that bias) away from its nipped position causes signal output, may be of almost any kind. In essence, though, the slipper is little more than a block of material (a metal, say), the bias is such as might be provided by a compression or tension spring, or by a hanging weight, or especially by a standard spring biassed single acting air cylinder, and the signal generation is conveniently effected by the slipper's or the biassing means' movement operating a switch in some suitable electrical circuit (conveniently the piston of the air cylinder is magnetic, and triggers an associated magnetic reed switch). Some details of an air cylinder system are described further hereinafter with reference to the accompanying Drawings.

Although in its simplest form the weighing apparatus of the invention uses a single load sensor device, it can employ two or more, arranged (possibly in parallel, possibly in series) in a sort of sequence to indicate weighed material amounts progressively closer and closer to the desired final set point weight. In this way, for example, a bulk material may to start with be fed to the receptacle at a high rate until it is within 5% of the desired amount, and then more slowly until it is within 1%, and then more slowly still, to improve overall accuracy, until it actually reaches the desired amount.This embodiment of the invention, in its more preferred balance beam/slipper guise, may be defined as a weighing apparatus of the beam type for batch weighing flowable material, comprising a beam pivoted about a fulcrum, the beam being provided with counterforce weighing means on one side of the fulcrum, a receptacle for receiving material to be weighed on the other side of the fulcrum, and a resting edge; a plurality of slippers; a slipper support, in close proximity to the beam and fixed in space; and a load sharing beam which lies between the resting edge of the beam and the slipper support; such that in use, when the turning moment of the receptacle and its contents is less than that of the weighing means the resting edge of the beam lies on the load sharing beam, the slippers are in a nipped position between the load sharing beam and the slipper support and are biassed away from the nipped position by one or more biassing force, and the slippers are moved sequentially (to cause sequential signal output) by the biassing force as the apparatus approaches equilibrium.

The apparatus of the invention is particularly useful for weighing batches of a bulk flowable material in granular form (for example, seeds) or powdered form, but it can also be applied to the weighing of liquids.

Moreover, as noted above it can be employed as a check weigher. In an embodiment of the invention wherein the counterforce is equal in magnitude to the combined force of receptacle and the required quantity of material, which embodiment is suited to the check weighing of previously batched material, two load sensor devices preferably biassed slippers - are positioned adjacent and between members of the apparatus such that they may be pressed between the members if the difference between, on the one hand, the combined receptacle and required quantity of material, and on the other hand, the fixed force, is sufficient to overcome the bias.

Using slippers, in operation first they are urged into their biassed positions, then the material is loaded into the receptacle, and then the urging cause is removed. The subsequent positions of the slippers then determine the degree of accuracy of the batch of material; if either slipper remains nipped then the batch differs from the required quantity, the sense of the difference being determined by which slipper remains nipped, while, conversely, if both slippers slip then the quantity of material is correct. The tolerance is determined by the geometry of the apparatus (includiny the position of the slippers), by the degree of friction, and hy the extent of the bias. In a balance beam embodiment, the beam has a very small amount of free movement, before abutting a slipper on either side, nipping it up against a fixed member of the apparatus' frame.

Various embodiments of the invention are now described, though by way of illustration only, with reference to the accompanying Drawings in which: Fiaure 1 shows a side view of a weighing apparatus of the invention; Figures 2A, B & C show sections (corresponding to one on the line II-II in Figure 1) of various versions of the same weighing apparatus but with different load sensor arrangements; Figures 3 & 4 show side views (!ike that of Figure 1) of two variations of the weighing apparatus; and Figures 5A, B & C show respectively a schematic of an air cylinder biassing system and the switching and timing arrangements therefor.

The weighing apparatus shown in Figure 1 (generally 1) comprises a beam (2) which is supported by a knife edge (3) on a frame (4). A receptacle (5) is suspended from the beam 2 on a knife edge (6), and a weight box (7) is suspended from the beam 2 o a knife edge (8).

The beam 2 is provided with an anchoring means (9) to which is attached a tension spring (10) carrying a slipper (11) slidably mounted on a support (12) that is part of the apparatus frame 4.

In use a mechanical system (not shown in Figure 1) moves the slipper 11 (to the left, as viewed) to a position between the beam 2 ad the slipper support 12, and a weight (13) is added to the weight box 7. The turning moment of the weight 13 causes the beam to rotate, and this in turn causes the slipper 11 to be nipped between the beam 2 and slipper support 12 (i.e.

the slipper is in a nipped position). The mechanical system used for moving the slipper is then removed. As the spring 10 is now extended, it provides a biassing force that biasses the slipper out of the nipped position (to the right, as viewed).

Flowable material is added to the receptacle 5 through an input valve (not shown in Figure 1), and as the weight of the material in the receptacle increases so the beam-derived load on the slipper 11 - the "nipping" load - progressively decreases until a point is reached at which the biassing force is able to remove the slipper from the nipped position. This removal is detected by sensing means (not shown in Figure 1) which causes the addition of material to the receptacle to be stopped.

The weighing apparatus can be tared by adding weights to the weight box 7 when the receptacle 5 is empty. These weights can be adjusted so that the slipper 11 just moves when subjected to its biassing force, or the beam 2 is on the point of equilibrium (i.e. the beam is in balance), or the slipper just does not move. The material "in fly" at the moment of closure of the input valve can be compensated for on a trial and error basis.

In alternative embodiments the flowable material can be added to the receptacle 5 using a multi-stage input valve which has one or more coarse stages as well as a final, fine stage. In order to control the change between the stages the following systems can be employed: a) In one system a secondary weight is added to the receptacle 5. This results in the slipper being pulled out of the nipped position when the weight of material reaches the weight of the weight 13 minus the secondary weight value. The slipper movement causes the input valve to change to a less coarse or a fine stage, the slipper then to be urged (by means not shown) back into the nipped position, and the secondary weight then to be lifted clear of the receptacle. This cycle can be repeated with other secondary weights of diminishing size.

b) In a further system the biassing force on one slipper - the "coarse" one - is greatly increased, thus causing that slipper to come out of the nipped position well before equilibrium is achieved.

c) In other systems two or more slippers are held in position by a load sharing lever system. Examples of this are shown in Figure 2.

In Figure 2A, a load sharing beam (14) lies asymmetrically under a knife edge (17) of the beam 2 and above the slipper support 12 and nips two slippers (15 and 16). When the turning moment of the weight means is greater than that of the receptacle and its contents the knife edge 17 of the beam 2 lies on the load sharing beam 14, and the two slippers 15 and 16 are held in a nipped position between the load sha-ring beam 14 and the slipper support 12. Slipper 15 is a coarse slipper, while 16 is a fine slipper. Both slippers carry an equal biassing force, and as the receptacle 5 is filled a point is reached at which the biassing force acting on the coarse slipper 15 is sufficient to move the coarse slipper. This movement is detected, and the stage of the input valve is changed.The apparatus is arranged such that the coarse slipper 15 does not corne out from under the load sharing beam 14.

A slightly different version is shown in Figure 2B.

The load sharing beam 14 lies symmetrically under the knife edge of the beam 2 and above the slipper support 12. When the turning movement of the weighing means is greater than that of the receptacle and its contents the knife edge 17 lies on the load sharing beam 14, and the two slippers 15 and 16 are held in the nipped position between the load sharing bean and the slipper support.

Slipper 15 is a coarse slipper while slipper 16 is a fine slipper. The coarse slipper carries a greater biassing force than the fine slipper, and as the receptacle 5 is filled a point is reached at which the biassing force acting on the coarse slipper is sufficient to move that slipper. This movement is detected, and the stage of the input valve is changed.

The apparatus is arranged such that the coarse slipper 15 does not come out from under the load sharing beam 14.

Figure 2C shows yet another way of achieving a similar effect. In this embodiment the two slippers 15 and 16 rest one on the other, and the operation of one (as the load in the receptacle increases) causes a change in the feed rate, material then being fed in at the new rate until the load changes sufficiently for the other to operate. It works as follows. When the arrangement is set up a higher biassing force is applied to one slipper (the coarse one) than to the other (the fine one; this one is continuously urged into its nipped position until the coarser slipper has moved). Material is then fed to the weighing receptacle at a high (coarse) rate, until the coarser slipper moves, whereupon the output signal switches the feed rate to the low (fine) rate, and then removes the fine slipper urge.

In a further embodiment, shown in Figure 3, the biassing force is provided by a small weight (18) which is carried by a bell crank lever (19). The bell crank lever is attached to the slipper support 12 by an extension (20) which allows the bell crank lever to pivot about a point (21), and is connected to the slipper 11 by a tie (22).

Yet another embodiment is shown in Figure 4, where the slipper 11 is nipped not between the beam 2 and an extension of the frame (as 12) but between the main frame support (30) and an extension of the balance arm (31). The effect, however, is just the same.

Figure 5 shows details of one particular slipper arrangement. The slipper itself is a cuboid of metal (51) attached to a standard single acting air cylinder (52). As is commonly the case, the cylinder incorporates an internal compression coil spring (53) between the piston (54) and the cylinder end (55) to bias the piston in one direction. Air pressure (at 56) may then be applied to the other end to overcome the spring force and actuate the piston. The piston incorporates a magnet (not shown separately) which can actuate a reed switch (57) mounted on the outside of the cylinder, when piston and reed switch are in line.

Figure 5A shows how such a cylinder 52 can be used to guide and push the slipper 51. The cylinder is mounted pivotally (at 58) at its non-piston end, and the slipper is screwed directly onto the threaded end (59) of the piston rod (60). The slipper 51 is free to slide between the beam 2 and the slipper support 12 under the influence of the spring 53, unless either t is nipped by the downward Eorce or the beam bm or the cylinder i is extended by air pressure on the back of the piston 54.

The reed switch 57 is closed when the cylinder is extended.

The reed switch is connected to a relay, to sensors on the discharge door of the receptacle, and to air valves which control the weigher input and the slipper cylinder. None of these devices is shown per se, but the connections thereto are shown schematically in the form of a ladder diagram in Figure 5B. The operation of the system is as follows.

At Switch-On the discharge door is closed. Thus, the Door Open sensor is open, the Door Closed sensor is closed, the relay is not energised, the Weigher Input is closed, and the slipper cylinder is actuated by air pressure from its valve (this combination of states is shown diagrammatically in Figure 5C). Subsequent events are shown in the diagram. Thus, the discharge door is opened, so the Door Closed sensor becomes open and the Door Open sensor becomes closed. This results in the relay being energised, which in turn results in air pressure being removed from the slipper cylinder.

However, the cylinder remains extended because of the nip on the slipper (because the contents of the receptacle have started to discharge.). When the discharge door closes, the Dor Open sensor opens, and then the Door Closed sensor closes. The latter event opens the input valve. At the set point, the slipper slips, and the reed switch opens, de-energising the relay. This closes the input valve, and also returns the slipper cylinder to its extended position. With the relay now de-energised, the input valve does not re-open.

Claims

1. Weighing apparatus comprising a mechanical device in which by some suitable lever-type arrangement the weight of the receptacle holding the material being weighed is "balanced" by the equal (or nearly equal) "weight" of a counterforce, and a load sensor device is employed to detect, and in effect to measure, the difference between the moments of the two, and to cause a signal usable to indicate the desired/correct weight of material in the receptacle, and thus to terminate the weighing process.

2. Weighing apparatus as claimed in Claim 1 in the form of a balance, employing a beam balanced on a fulcrum, so that the receptacle is supported on or from the beam and at or near one end thereof, with the counterforce applied at or near the opposite end.

3. Weighing apparatus as claimed in either of the preceding Claims, wherein the counterforce takes the form of an actual counterweight or the force exerted by a spring-biassed compressed air/piston arrangement.

4. Weighing apparatus as claimed in any of the preceding Claims, wherein the counterforce is provided as a combination of several smaller forces.

5. Weighing apparatus as claimed in Claim 4, wherein there is employed a system of graduated forces the application of which can be varied (as a result of the signal output following load sensor operation) to allow first a coarse and then one or more finer indication of the (approach of the) final set point.

6. Weighing apparatus as claimed in any of the preceding Claims, wherein the load sensor takes the form of a slidable member, or slipper, which is biased to move in one direction (to cause an indicator signal to be generated) but is restrained from so doing by the lever part of the apparatus, which part blocks the movement when in the unbalanced state but permits it when in the balanced state.

7. Weighing apparatus as claimed in Claim 6, wherein restraint of the slipper involves the frictional forces set up when the slipper is actually nipped, pinched or squeezed between the lever part and some other section of the apparatus.

8. Weighing apparatus as claimed in either of the preceding Claims and suitable for batch weighing flowable material, comprising: a beam pivoted about a fulcrum, the beam being provided with counterforce weighing means on one side of the fulcrum and a receptacle for receiving material to be weighed on the other side of the fulcrum; a slipper; and a slipper support, in close proximity to the beam and fixed in space; such that in use, when the turning moment of the receptacle and its contents is less than that of the weighing means the slipper is in a nipped position between the beam and the slipper support and is biassed away from the nipped position by a biassing force, and the slipper is moved (to cause signal output) by that biassing force when the apparatus approaches equilibrium.

9. Weighing apparatus as claimed in any of the preceding Claims, wherein there are two or more load sensor devices in a sequence to indicate weighed material amounts progressively closer and closer to the desired final set point weight.

10. Weighing apparatus as claimed in any of the preceding Claims and substantially as hereinbefore described.

10. Weighing apparatus as claimed in Claim 9, comprising a beam pivoted about a fulcrum, the beam being provided with counterforce weighing means on one side of the fulcrum, a receptacle for receiving material to be weighed on the other side of the fulcrum, and a resting edge; a plurality of slippers; a slipper support, in close proximity to the beam and fixed in space; and a load sharing beam which lies between the resting edge of the beam and the slipper support; such that in use, when the turning moment of the receptacle and its contents is less than that of the weighing means the resting edge of the beam lies on the load sharing beam, the slippers are in a nipped position between the load sharing beam and the slipper support and are biassed away from the nipped position by one or more biassing force, and the slippers are moved sequentially (to cause sequential signal output) by the biassing force as the apparatus approaches equilibrium.

11. Weighing apparatus as claimed in any of the preceding Claims and substantially as hereinbefore described.

Amendments to the claims have been filed as follows 1. Weighing apparatus comprising a mechanical device in which by some suitable lever-type arrangement the weight of the receptacle holding the material being weighed is "balanced" by the equal (or nearly equal) "weight" of a counterforce, and a load sensor device is employed to detect, and in effect to measure, the difference between the moments of the two, and to cause a signal usable to indicate the desired/correct weight of material in the receptacle, and thus to terminate the weighing process, and wherein the load sensor takes the form of a slidable member, or slipper, which is biased to move in one direction (to cause an indicator signal to be generated) but is restrained from so doing by the lever part of the apparatus, which part blocks the movement when in the unbalanced state but permits it when in the balanced state.

6. Weighing apparatus as claimed in any of the preceding Claims, wherein restraint of the slipper involves the frictional forces set up when the slipper is actually nipped, pinched or squeezed between the lever part and some other section of the apparatus.

7. Weighing apparatus as claimed in any of the preceding Claims and suitable for batch weighing flowable material, comprising: a beam pivoted about a fulcrum, the beam being provided with counterforce weighing means on one side of the fulcrum and a receptacle for receiving material to be weighed on the other side of the fulcrum; a slipper; and a slipper support, in close proximity to the beam and fixed in space; such that in use, when the turning moment of the receptacle and its contents is less than that of the weighing means the slipper is in a nipped position between the beam and the slipper support and is biassed away from the nipped position by a biassing force, and the slipper is moved (to cause signal output) by that biassing force when the apparatus approaches equilibrium.

8. Weighing apparatus as claimed in any of the preceding Claims, wherein there are two or more load sensor devices in a sequence to indicate weighed material amounts progressively closer and closer to the desired final set point weight.

9. Weighing apparatus as claimed in Claim 8, comprising a beam pivoted about a fulcrum, the beam being provided with counterforce weighing means on one side of the fulcrum, a receptacle for receiving material to be weighed on the other side of the fulcrum, and a resting edge; a plurality of slippers; a slipper support, in close proximity to the beam and fixed in space; and a load sharing beam which lies between the resting edge of the beam and the slipper support; such that in use, when the turning moment of the receptacle and its contents is less than that of the weighing means the resting edge of the beam lies on the load sharing beam, the slippers are in a nipped position between the load sharing beam and the slipper support and are biassed away from the nipped position by one or more biassing force, and the slippers are moved sequentially (to cause sequential signal output) by the biassing force as the apparatus approaches equilibrium.