WO2008037095A1 - Silo scales - Google Patents

Abstract

The apparatus for determining the filling level of silos (1) has at least three tubular supports (5) with a round cross section. At least one of these supports (5) has a sensor which determines the changes in the diameter of this support (5) and uses them to ascertain the axial load. The further supports (5) concomitantly have converters (15) with computers (20). In this case, a tension or pressure element (8) obliquely penetrates the support (5) at an angle a. Since the elastic longitudinal compression is approximately three times as great as the transverse elongation on the basis of the Poisson relationship, additional load on the support (5) results in the tension or pressure element (8) being relieved. If the supports (5) are cooled rapidly, the tension or pressure element (8) initially remains at the original temperature and length. This results in the converters (15) interpreting this as relief of the silo (1). Those sensors which measure the diameters of the supports (5) interpret this in the same manner. Discriminator or differential circuits can be respectively used to distinguish whether these short-term changes in load take place on account of transient changes in temperature or are real changes in load.

Description

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Silo

The present invention relates to a silo balance according to the preamble of claim 1. Silo scales are several known. They are often used as gravimetric dosing scales according to the principle of weight or mass difference determination. For this purpose, the whole silo stands - usually three to four - scales. With their help, the gross weight of the silo is calculated as the sum. The disadvantage of this approach is - among other things - that, for upgrading or retrofitting the silo with the weighing device, this must be lifted from the ground or the support surface and then has to be placed on the force inputs of the measuring cells. This process can only be carried out to a limited extent, especially for silos with many tons of bulk material content. In addition, the differential weighing method is often unnecessarily accurate as the actual dosing method for inventory weighing. An improved weighing device is described in the application WO2006 / 105679 (D1). There, the load borne by the supports of a silo is determined via the elastic elongation of the tubes forming the supports.

The object of the present invention is to provide a force measuring device for silos, with the help of existing silos can be retrofitted quickly and inexpensively, without facing the task of such silos - even in full condition - even stand out from the ground. Furthermore, it is the object of the invention to quickly vary changing temperatures of the silo-bearing frame of changes in the silo weight.

The solution of the problem is reflected in the characterizing part of claim 1 with respect to the basic features, in the further claims with respect to further advantageous embodiments and in claim 10 from the perspective of the measuring method.

Reference to the accompanying drawings, the invention is explained in more detail on the basis of an embodiment. Show it _ _

1 shows a silo according to the prior art,

Fig. 2, four _^ silo supports with schematically shown measuring devices,

3 shows an inventive measuring device in section,

4a, b waveforms of two measuring devices with load change and rapid decrease in temperature of the supports,

Fig. 5 is a logic diagram of signal decisions.

A prior art silo 1 schematically illustrated in FIG. 1 for bulk materials, such as road salt, cement, chemicals, cereals, is generally divided into an upper cylindrical part 2 and a lower part 3 with silo outlet 4 and three or three more supports 5. Such silos 1 are known per se and can be designed as sheet metal structures with a capacity up to about 200 tons. For metering devices according to the so-called loss-in-weight method, it is necessary because of the required accuracy to turn off such a silo 1 with each support 5 on a load cell. Because of the high loads, which are constantly at rest on them, such load measuring cells also have relatively robust primary deformation bodies in connection with high-resolution measuring systems. The disadvantages of such devices are on the one hand in the large aparativen effort, on the other hand in the need to lift such a silo from the ground and turn it off on prepared load cells; Compared with the accuracy of about 1% required for pure stock checks, the accuracies of said metering devices are also generally higher than necessary. It is extremely expensive to install strain gauges (strain gauges) instead of load cells in such designs, which exist in the field and are complex in terms of stressing - such as sill supports designed as truss structures. The relevant weight-proportional compressive stresses must be separated from the bending stresses, which can only be achieved by the Use of numerous DMS succeeds. The correct attachment of strain gages to silos in use is almost hopeless due to the environmental conditions to be observed. Even if these conditions can be created and maintained, the effort to be made is great.

The four supports 5 here are made of tubes with a circular cross-section.

The embodiment of the inventive concept is shown in Figs. 2 to 5. In Fig. 2, the four supports 5 (here with supports 51, 52, 53, 54) - without the silo 1 supported by them - shown. Since the entire silo construction is a substantially statically determined system, the silo is predominantly on two supports opposite one another in the diagonal dl or the diagonal d2, ie on supports 51 and 53 or supports 52 and 54.

The supports 51, 54 are provided with measuring devices which measure the elastically widened by the load of the silo diameter of these supports 51, 54, for example, according to the document Dl. Housings 6 attached to the supports 51, 54 contain at least parts of such measuring devices. On the supports 52, 53 further measuring devices are mounted, of which in turn at least parts are housed in further housings 7. Such a measuring device is shown in FIG. 3.

A tension or compression element 8, for example in the form of a rod, passes through the support 5 through two holes 9 and forms an angle α with the longitudinal axis 10 of the support 5. On the one hand, the pull or duck element 8 is secured, for example, by a nut 11 which rests on a bolted to the outside of the support 5 first anchor plate 12. On the first anchor plate 12 obliquely opposite side of the support 5, a second anchor plate 13 is eb-outside screwed to the support 5. The tension or pressure element 8 runs there without being touched by a guide element 14 and ends in a transducer 15, which converts the force signal transmitted by the tension or pressure element 8 into a corresponding electrical signal. The tension or pressure element 8 is biased so that the entire force range to be measured by the transducer 15 is detected. Protected against external influences, such as dust, moisture, solar radiation, the transducer 15 through the housing 7. As a transducer 15, all known converters come into question, which forces' can convert into electrical signals with the necessary resolution and reproducibility, such as strain gauge assemblies, optical force transducers and vibrating string transducers. A schematically illustrated cable 16 serves to supply power to the converter and to transmit the electrical signals to further processing units such as computers, transmission devices, if these are not already integrated in the converter. In a preferred embodiment, the angle α is substantially 45 °.

If the silo 1 charged in addition to the existing load, the support 5 is shortened elastic, at the same time the support 5 forming tube elastically expanded. About the Poisson relation μ = (dimensionless) where μ = Poisson number

Δd = expansion of the support 5 d = diameter of the support 5

Δ £ = length change of the support 5 I = length of the support 5,

where μ for steel is about 0.3, it follows that the change in length is about three times as large as the diameter change. In other words, when the silo weight increases or decreases, the length change of the support is three times greater than the corresponding widening or diameter decrease of the support. The tensile or compressive element 8 is thus relieved by the above-mentioned additional load of the silo 1 despite weight-related expansion of the support. This relationship is in an evaluation unit which is integrated in the converter 15 or else contained in an external computer 20 can, stored as a characteristic, together with other apparatus parameters of the converter, as known per se. A tension measuring arrangement which only measures the widening of the tube forming the support 5 (for example the measuring arrangements described above on the supports 51, 54), in contrast, detects an increase in force.

With the described arrangement not only the weight of the silo 1 or its level can be determined, but it is also possible to distinguish transient temperature changes of the supports 5 of real weighing results. This makes it possible, for example by means of discriminator circuits, to distinguish weight changes from transient temperature changes of the supports 51 to 54. It is thus also possible to exclude measurement signals resulting from transient temperature changes from the determination of the silo weight until the temperature equilibrium of support 5 and tension or pressure element 8 has returned to equilibrium. As a rule, such transient temperature changes occur as cooling, in particular when heavy rains in thunderstorms cool the previously sun-irradiated supports.

The behavior of the loads of the transducer 15 and a transducer 17 determining the change in diameter, which is contained in the housings 6 - or may likewise be contained in the computer 20 - is shown in FIG. 4a. The signal changes S _Dia for the transient temperature changes taking into account measuring arrangement and S _D for one, only the changes in the diameter of the support 5 forming pipe, are in opposite direction with load increase. Become the. Supports 5 suddenly cooled, for example, by heavy rain, so on the one hand decreases the diameter S _{D of} the tube due to the temperature drop, on the other hand, also shortens the length of the support 5 quickly, while the tension or pressure element 8 is still substantially at the original temperature located. Therefore, the signal S _D i _a decreases until after some time the temperature compensation of support 5 and tension or pressure element 8 has set, as in Fig. 4b, together with the actual temperature turverlauf, is shown. For a short time, both signals have sign-like simultaneous changes. This change in signatures S _n and S _D i _a , which is concurrent, can now be used to exclude that these signals are interpreted individually as weight or fill level values, as shown in the block diagram according to FIG. 5.

Here, four computers 20 are shown, which each determine the weight information from the elastic deformation of the supports 51, 52, 53, 54, wherein in the exemplary embodiment according to FIG. 2 on the supports 51, 54 the pure diameter changes and in the supports 53, 55 are measured by the inclined by the angle α tensile or compressive elements 8, the superimposed longitudinal compression and the diameter changes. The changes in the measurement results, ie .DELTA.S _{D a of} the inclined tensile or compressive elements and the changes in the diameter .DELTA.S _D those measuring devices which determine the diameter of the supports 51, 54, are from the computers 20 to four discriminators 21, 22, 23, 24 transmitted. Each of the discriminators 21 to 24 respectively forms the difference of the measurement results (S (t) -S (t + Δt) where Δt is a predetermined time difference.) Also schematically included in this check circuit are six AND gates 25 to 30, the link The supports 51, 53 face each other diagonally with respect to the arrangement of the four supports 51 to 54. The same applies to the supports 52 and 54. With reference to FIGS Now, for a material outflow from the silo, 1 S _D (t) - S _D (t + Δt)> 0, analogously, S _Dia (t) - S _Dia (t + Δt) <0 The discriminators 21 and 22 have Outputs 31 (for> 0) and 32 (for <0) and corresponding to 33 (for ≥O) and for 34 (for <0) For the described case of discharge of the silo so the outputs 31 of discriminator 21 and 34 of Discriminator 22 active These signals are forwarded to an AND gate 26 and open this: it is made and processed and forwarded as known per se a weighing. The same happens when loading the silo, the outputs 32nd of discriminator 21 and 33 of discriminator 22 are active, thereby opening another AND gate 27: Weighing is performed. If, however, the frame of the silo 1 consisting of the supports 51 to 54 is suddenly cooled, for example by a rainstorm, at high ambient temperature, the tensile or pressure element 8 in the supports 52, 53 initially remains at the high ambient temperature, as already stated while the temperatures of the supports 51 to 54 decrease rapidly. This results in the outputs 32, 34 of the discriminators becoming active. These signals are fed to another AND gate, which is opened with it and prevents further processing of the weighing until the results of the discriminators 21, 22 allow this again. In complete analogy to the discriminators 21, 22 further discriminators 23, 24 are connected, which in turn, in complete analogy AND gates 28, 29, 30 control. These procedural measures have the effect that only real processes, such as loading and unloading of the silo 1, are accepted and processed as relevant weighing processes. In particular, it is prevented that sudden cooling of the supports 51-54 are interpreted as draining, for example due to thunderstorms. With such an interpretation, as known, a refilling or delivery of the ensiled bulk material would be initiated via telecommunications equipment,. this because of a now recognized as artifact false signal.

Another method of eliminating such jumps in temperature from interpretation as weight jumps is to form the difference between the signals: the sensors detecting the change in diameter S _D and the tension or pressure elements 8 penetrating the supports 5 at angle α connected transducers 15 deliver substantially the same signals at the output of the transducers. The difference of these signals will therefore be essentially = 0. This eliminates a discrimination procedure. Such a difference formation can be done with a - known per se - differential circuit. In silos with only three supports 5 usually one of the three supports 5 is used both with a transducer 15 at an angle α inclined tensile or Druckelement- 8, in addition to the diameter of the support 5 detecting sensor. The difference of the signals then takes place between the signals on the same support, while the two other supports are each used with a measured at the angle α and the diameter S ₀ detecting signal for subtraction. In a further embodiment, all supports 5 are equipped both with measuring arrangements, which measure according to the prior art, the change of the diameter S _D (t), as well as with those which enforce the supports 5 at an angle α and thus S _D i _a measure up. Preferably, the associated transducers 15 are accommodated in said housings 7.

Claims

- Patent claims An apparatus for determining the level of silos (1) for bulk materials, wherein each silo (1) rests on at least three substantially vertically extending tubular supports (5), or these supports (5) have vertical sections and substantially circular cross-sections and at least one of these at least three supports (5) force measuring arrangements are mounted, which are the load-dependent elastic expansion of the diameters of the supports, characterized in that at least one of these three supports (5) each carry a measuring arrangement, which in addition to the load-dependent elastic change the diameter of the support (5) determines the load-dependent elastic change in length of the support, and this measuring arrangement passes through the support (5) with an element. 2. A device according to claim 1, characterized in that the at least one of the supports (5) with a Längsachfee (10) mounted measuring arrangement consists of a transducer (15) for converting mechanical loads into electrical signals, - this converter ( 15) mechanically acting tensile or compressive element (8) is present, a first on the outer wall of the support (5) fixed anchor plate (12) is present, on which the tension or pressure element (8) with a nut (11) GE is secured, a second anchor plate (13) is present, which is attached to the first anchor plate opposite the outer wall of the support (5) and carries the transducer (15) with the tension or pressure element (8), and each transducer (15) is connected to a computer (20), the tensile or compressive element (8) with the longitudinal axis (10) forms an angle α. IU 3. A device according to claim 2, characterized in that the material of the tensile or compressive element (8) is the same as that of the support (5) 4. Device according to claim 2, characterized in that the angle α is substantially 45 °. 5. Device according to claim 2, characterized marked, that the tension or pressure element (8) is biased. 6. The device according to claim 2, characterized in that all the supports (5) are each provided with a Messan- order, the tensile or compressive element (9) with the longitudinal axis (10) forms an angle α, as well as with one each Measuring arrangement which determines the change in the diameter of the support (5). 7. Device according to claim 2-5, characterized in that the silo (1) comprises a discriminator circuit with four discriminators (21,22, 23, 24) and AND gates (25, 26, 27, 28, 29, 30) and each of the discriminators (21 to 24) has two outputs (31 and 32, 33 and 34, 35 and 36, 37 and 38), the first of said outputs (31, 33, 35, 37) being active, if the respective signal to be discriminated is ≥O and the second mentioned outputs (23, 34, 36, 38) are active, if the respective signal to be discriminated is <0, each computer (20) connects one of the discriminators (21, 22, 23, 24), which respectively compares a measurement result S (t) with that which is measured a predetermined time interval Δt later, and if the measurement arrangements which determine the elastic change of the diameter of the support (5) S _D - - and those which have a tensile or compressive element (8) inclined by the angle α, S _Ω ± _a leads to signaturally equidirectional results of the temporal changes of the measurement results, the AND gates (25 and 28) are opened, which thereby further process prevent the electrical measurement results in weight specifications of all supports (5). 8. The device according to claim 7, characterized marked, that in the measuring arrangements, which determine the elastic change of the diameter of the support (5) S _D , and those which have an inclined by the angle α tensile or compressive element (8) , S _Ω ± _a leads to unsubstantiate sign- ary results of the temporal changes of the measurement results, the AND gates (26 and 29) or the AND gates (27 and 30) are opened, which thereby further processing the electrical measurement results in weight specifications of all Allow supports (5). 9. Device according to claim 8, characterized in that the determined weights of all supports (5) in the computer (20) are added up to a total weight. 10. A method for determining the level of silos (1) according to one of the claims 1 to 9, characterized in that the at least three supports (5) of the silo (1) are equipped with different force measuring arrangements, wherein at least one support (5) a force measuring arrangement is equipped, which measures the load-dependent elastic expansion of the diameter S _{D of} the support (5) and at least one of the supports (5) with a support (5) at an angle a. passing tensile or compressive element (8) is provided, which the superimposed load-dependent compression and the lastab- pending expansion of the diameter of the support (5) S _D i _a measures. 11. The method according to claim 10, marked thereby, that the difference of the signals of a respective transducer (15) at an angle α inclined tensile or compressive element (8) and one each the elastic widening of the diameter of the support (5 ) detecting sensor is formed. 12. The method according to claim 10, characterized in that the values S _D (t) and S _D i _a (t) are measured and compared with the respectively a predetermined time interval .DELTA.t later measured values S _D (t + .DELTA.t) and Soi _a (t + Δt) are negative, these measurements are interpreted as a transient decrease in temperature of the supports (5) and the weight values determined from the signals S _D (t + Δt) and S _D i _a (t + Δt) are discarded. 13. The method according to claim 12, characterized in that in the case that said differences S _D (t) -s _D (t + .DELTA.t) and S _Dia (t) -S _Dia (t + .DELTA.t) unequally sign bear , these measurements are allowed and processed to a cumulative value of the loads of all supports (5).