GB2132761A

GB2132761A - Measuring mass flow rate of particulate material

Info

Publication number: GB2132761A
Application number: GB08325972A
Authority: GB
Inventors: Takefumi Horiuchi; Takeo Kawate; Tadashi Tado; Akira Morikawa; Yasuji Yoneda
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 1982-09-28
Filing date: 1983-09-28
Publication date: 1984-07-11
Also published as: GB8325972D0

Abstract

A method for measuring the mass flow rate of particulate material during transfer through a conduit pipe by detection of vibrations caused by collisional energy of said particulate material, said method comprising: detecting vibrations occurring at the surface of said conduit pipe 1; extracting from detected vibrations a particular frequency range of vibrational acceleration in the form of a voltage signal 7; calculating the average value of said frequency range to produce a corresponding voltage signal 8; feeding the calculated signal to an arithmetic conversation circuit 10 to produce a voltage signal indicative of the mass flow rate of said particulate material corresponding to said effective value on the basis of predetermined correlation between said mass flow rate and the effective value. A correction, based on the flow rate 12 may also be provided. <IMAGE>

Description

SPECIFICATION Method and apparatus for measuring flow rate of particulate material This invention relates to a method and apparatus for measuring the flow rate of various particulate materials which are for example dispersed in a gas flow, namely, in a solid-gas dual phase flow (hereinafter referred to simply as "dual phase flow" for brevity). Preferably the invention concerns a method for measuring the mass flow rate of particulate material in a dual phase flow accurately in a simple manner without hindering the dual phase flow in any substantial degree.

In order to realise automation of a process using a dual phase flow (e.g. a process of blowing fine pulverised coal into a blast furnace) smoothly, there invariably arises a necessity for accurately metering the flow rate of the particulate material. On the other hand, the flow rate of particulate material is usually required in units of weight in a dual phase flow transfer process, so that it is the general practice to resort to a mass flow meter for the measurement of the dual phase flow rate. The mass flow meters which have thus far been developed in the art are largely classified into the following three types.

(I) A direct type mass flow meter which is adapted to detect directly the quantity proportional to the mass flow rate (eg utilising the Coriolis force which is proportional to the mass flow rate); (II) An indirect type mass flow meter which is adapted to measure the mass flow rate by the combined use of a velocimeter and densimeter (eg a correlation method which measures the velocity of particulate material by way of fluctuations in electrostatic capacity between two points and detects the density on the basis of the absolute value of the electrostatic capacity); and (III) An indirect type mass flow meter using a differential pressure flow meter (eg measuring the solid-gas ratio and the gas flow rate from a pressure differential between a straight pipe portion and an enlarged pipe portion provided in the course of a pipe).

However, the above mentioned mass flow meters have inherent drawbacks and problems. Namely, the direct type mass flow meter (I) has the drawback that it is not very accurate due to the difficulty of determining the mass flow rates of the solid and gas phases separately, coupled with the problem of complex maintenance and service of its vibrating and detecting portions. With regard to the indirect type mass flow meter (II), there are problems that the measured values are likeiy to contain errors as the dielectric constant varies depending upon the moisture content in the particulate material, and the zero point of the particulate densimeter drifts because of the deposition of particulate materal on the pipe wall, requiring complex maintenance and service.

Problems with the differential pressure type mass flow meter (III) are that the dual law of similarity is established only for lean dual phase flows and is not applicable to thick dual phase flows, and the measuring portion and the differential pressure port are often clogged with the particulate material. Thus, in the absence of a satisfactory method for the measurement of the flow rate of dual phase flows, there has been an urgent demand for a measuring method which permits smooth automatic operation of equipment using a dual phase flow transfer process.

The present invention provides a method for measuring the mass flow rate of particulate material through a pipe by detection of vibrations caused by the collision of said particulate material, said method comprising: detecting said vibrations at a predetermined metering section of said pipe; forming a voltage signal related to the detected vibrations in a predetermined frequency range of the vibrations; calculating an effective value of said voltage signal to produce a voltage signal of the calculated effected value; feeding the calculated effective voltage signal to an arithmetic conversion circuit to produce a voltage signal indicative of the mass flow rate of said particulate material corresponding to said calculated effective voltage value on the basis of predetermined correlation between said mass flow rate and said calculated effective voltage signal.

The invention also provides apparatus for measuring the mass flow rate of particulate material through a pipe by detection of vibrations caused by the collision of said particulate material, said apparatus comprising means for detecting vibrations at a predetermined metering section of said pipe, means for forming a voltage signal relating to the detected vibrations in a predetermined frequency range of the vibrations, means for calculating an effective value of said voltage signal to produce a voltage signal of the calculated effective value, an arithmetic conversion circuit for receiving said calculated effective voltage signal to produce a voltage signal indicative of the mass flow rate of said particulate material corresponding to said calculated effective voltage signal on the basis of predetermined correlation between said mass flow rate and said calculated effective voltage signal.

The above mentioned method and apparatus which determines the mass flow rate from the vibrations measured by a vibrometer installed on the pipe, has an advantage that the installation and maintenance of the vibrometer are possible without hindering the dual phase flow in any substantial degree. However, if the vibrations at the pipe surface (the vibrations in a direction perpendicular to the dual phase flow) are relied on as an element of measurement, there is a possibility of the accuracy of measurement being impaired by the adverse effect of external disturbances such as other vibrations in the transverse direction of the pipe.

Therefore, in a preferred form of the present invention, at least one rod-like or tubular vibratory member is inserted across the flow passage of the particulate material at a suitable position of the pipe in a direction perpendicular to the length of the pipe, and the vibration of the vibratory member caused by collision thereagainst of the particulate material is detected.

Most preferably, a tubular resilient member is inserted on the upstream and downstream sides of the vibratory member thereby to shield the distrubing vibrations of the conduit pipe itself from a metering section including the vibratory member.

Preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a partially cutaway side view of a conduit pipe with a vibratory member according to the present invention; Figure 2 is a frequency spectrum diagram of voltage signals produced from detected vibrations; Figure 3 is a correlation diagram between the mass flow rate of the particulate material and the effective value; Figures 4 and 5 are block diagrams explanatory of signal processing operations for the determination of the mass flow rate; Figures 6(A) and 6(B), Figures 7(A) and 7(B), and Figures 8 to 10 are schematic illustrations showing modifications of the vibratory member; Figure 11 is a schematic fragmentary illustration showing a manner of mounting the vibratory member;; Figure 12 is a schematic longitudinal sectional view of a metering section employing resilient members according to the invention; Figure 13 is a schematic sectional view taken on line ll-ll of Fig. 12; Figure 14 is a partially cutaway schematic illustration showing another example of connecting the tubular resilient member to the conduit pipe and metering section; Figure 15 is a schematic longitudinal sectional view showing another embodiment of the vibrationally insulated metering section according to the invention, and, Figures 16 and 17 are frequency spectrum diagrams obtained in hammering tests.

According to the present invention, the vibration at the surface of a transfer pipe or the vibration of a vibratory member inserted in a transfer pipe is detected as mentioned hereinbefore. In any case, the signals obtained from the detected vibrations are processed in the same manner as will be described in detail hereinlater.

For example, Fig. 1 shows a method using a rod-like or tubular vibratory member 2 which is inserted radially across a conduit pipe 1 at a suitable position thereof. One end of the vibratory member 2 is embedded in a vibration detecting block 3 which is mounted on the outer side of the pipe wall and provided with a vibration receiver 4 either on the front side (the upstream side) or on the rear side (the downstream side) to detect the vibration of the vibratory member 2 in the transverse direction thereof (in the axial direction of the pipe, in the flow direction of the particulate material).

The effective value of the vibrational acceleration is extracted from the output of the vibration receiver, and the mass flow rate of the particulate material corresponding to the extracted effective value is determined by reference to a predetermined relation between the effective value and the mass flow rate by the method as will be described in detail hereinafter.

For instance, when the particulate material is transferred pneumatically under the conditions in which the nzass flow rate of the particulate material is 9.1 kg/min, the gas velocity is 1 5 m/sec and the solid-gas ratio is 3.1, the vibrational acceleration has the frequency spectrum as shown in Fig. 2 in a particular frequency range (0. to 20 kHz). On the other hand, with the gas velocity of 1 5 m/sec the mass flow rate of the particulate material is in direction relation to the effective value of the vibrational acceleration in a particular frequency range (0 to 20 kHz) as shown in Fig. 3.Therefore, the correlation of the mass flow rate with the effective value of the vibrational acceleration is determined beforehand for particular conditions, and it possible to determine the mass flow rate of the particulate material accurately by simply applying the measured effective value of the vibrational acceleration to the predetermined correlation diagram.

The following are practical signal processing methods useful for the detection of vibrations.

(1) A method of extracting a vibration signal of the entire frequency range; (2) A method of extracting a vibration signal of only a particular frequency range which has a high degree of correlation with the mass flow rate of the particulate material; and (3) A method of taking the ratio of a vibration signal of a particular frequency range with a high degree of correlation with the mass flow rate of the particulate material to a vibration signal of a frequency range with little variation in the output.

In a case where the velocity of the particulate material flowing throuqh the pipe changes, adversely affecting the correlation between the effective value of the vibrational acceleration and the mass flow rate of the particulate material, there may also be provided a velocimeter on the pipe in the above mentioned methods (1) to (3) thereby to correct the errors which would otherwise creep into the output value under such conditions.

Preferred examples of the above mentioned three methods are given in the following description, starting with the method (2) for convenience of explanation.

Fig. 4 illustrates in block diagram form the arrangement of a signal processing circuit suitable for the method (2). In this instance, the vibrations which are caused by collision of transferred particulate material are transmitted to the vibration receiver 4 through the vibration detecting block 3 (see Fig. 1) are constantly detected and the resulting detection signals are fed to a vibrometer amplifier 6 in a signal processor 5. The vibrometer amplifier 6 sends the detected signals to a band pass filter 7 after conversion into the vibrations have been converted into voltage vibration signals (hereinafter referred to simply as "voltage signal" for brevity). The band pass filter 7 extracts only the voltage signals of a predetermined frequency range from the input voltage signals which include components of the entire frequency range.This predetermined frequency range is preselected in consideration of the diameter of the pipe 1 as well as the diameter and properties of the vibratory member 2 to secure a desired suitable sensitivity to vibration, and may be preset to cover an arbitrary range. In order to utilise the frequency spectrum in the predetermined frequency range, it has to be transformed into an effective spectrum value (hereinafter referred to simply as "effective value" for brevity) in the predetermined frequency range. For this purpose, the vibration waveform in the predetermined frequency range is subjected to square averaging at an effective value circuit 8, squaring all of the vibrational accelerations followed by averaging ( x X 2).Thus the average vibrational acceleration which serves as an effective value is given in the form of a signal of a certain voltage.

The above mentioned predetermined frequency includes a noise region in which the vibrational acceleration does not change.

Therefore, the signal is processed in a bias adjusting circuit 9 to remove the bias component in that region, and a corrected effective value is sent to an arithmetic circuit 10.

The arithmetic circuit 10 comprises a permutation circuit operating on the basis of a correlation line prepared.from the previous experimentally measured correlation between the mass flow rate of the particulate material and said effective value such as is shown in Fig. 3, for example. Thus, the actual value which is fed from the bias adjusting circuit 9 is subjected to the above described signal processing by the arithmetic circuit 10 to produce a voltage signal related to the mass flow rate (Kg/min) of the particulate material.

The mass flow rate of the particulate material which flows through the pipe can be confirmed by consulting a display/recorder 11 which constantly indicates the exact value of the mass flow rate.

Where the signal processing method (1) is adopted, the band pass filter 7 of Fig. 4 is omitted, and the voltage signal of the entire frequency range which is produced by the vibrometer amplifier 6 from the output signals of the vibration receiver 4 is fed to the effective value circuit 8 and the succeeding stages to process the signal in the same manner as in the above described method (2).In a case where it is required to add the velocity of the particulate material to the signal processing for the purpose of correction as mentioned hereinbefore, a velocimeter 1 2 is mounted in a suitable position on the pipe 1 as indicated in phantom in Fig. 4, and a voltage signal corresponding to the output value of the velocimeter 1 2 is applied to the arithmetic circuit 10 to allow for correction and to permit more accurate measurement of the mass flow rate of the particulate material.

Fig. 5 illustrates in block diagram one particular example of the signal processing circuit according to the above mentioned method (3), which is basically the same as the arrangement employed in Fig. 4 except for the following aspects. From the voltage signal of the vibrometer amplifier 6, the band pass filter 7 extracts a voltage signal of a predetermined frequency range which undergoes large variations in amplitude during transfer of the particulate material, and the vibration waveform is converted into a DC signal at the effective value circuit 8 by the square averaging as described hereinbefore. In the arrangement of Fig. 5, the DC signal is sent to a divider 1 3 after removing a non-varying bias component of a particular frequency range at the bias adjusting circuit 9 as before.Simultaneously with the foregoing signal processing operation, the voltage signal from the vibrometer amplifier 6, which is in a predetermined frequency range with only small changes in amplitude, is extracted by a band pass filter 7' and converted into a DC signal by square averaging the vibration waveform at an effective value circuit 8' before sending same to a lower limit adjusting circuit 9'. Circuit (2) (ie components 7', 8', 9') is provided to prevent saturation of the output of the divider 1 3 when the value of denominator is extremely small as compared with the value of numerator, and serves to set the lower limit value of the denominator.The DC signals produced by the adjusting circuits 9 and 9' are fed to the divider 1 8 for division, and then to the arith metic circuit 10 and mass flow rate indica tor/recorder 11 to record the mass flow rate in a manner similar to Fig. 4. In this case, the accuracy of measurement can also be enhanced by correcting the output value of the arithmetic circuit 10 with a signal from a velocimeter 1 2 mounted in a suitable position on the pipe 1.

Although the foregoing description deals with a simple construction of the present invention, it is to be noted that the shape and the position of the vibratory member 2 can be changed in various ways as exemplified in the following modifications. Firstly, Figs. 6(A) and 6(B) show a modification employing two vibratory members 2a and 2b which are inserted in two spaced positions in the flow direction of the particulate material and disposed at right angles with each other, picking up the vibrations of the vibratory members by vibrometers 4a, 4b respectively.Where a single vibratory member 2 is used as shown in Fig. 1, the vibrometer produces a particular output level irrespective of the direction of insertion of the vibrometer as long as the flow of the particulate material is uniform across the flow passage, but the output of the vibrometer becomes uneven and inaccurate if the distribution of the particulate material is nonuniform. The errors of measurement due to such localised flows of the particulate material can be reduced significantly by inserting two vibratory members 2a and 2b at different angles as shown in Figs. 6(A) and 6(B) and processing the average values of vibrations detected by the vibratory members 2a and 2b in the above described manner.This sort of error can be reduced further by employing three vibratory members 2a to 2c which are inserted at 60 shifted positions as shown in Figs. 7(A) and 7(B), and averaging the values of vibrations detected by the three vibratory members.

Although a plurality of vibratory members are used in the foregoing modifications, Figs.

8 and 9 illustrate further modifications where there is provided a vibratory member 2 with a number of radially extending ribs so that the particulate material collides with the vibratory member at a number of different radial positions across the cross sectional area of the pipe 1 to reduce the errors of measurement which would otherwise by caused by the localised distribution of the particulate material as mentioned herein before. Thus, the rod-like or tubular vibratory member 2 to be used in the present invention may consist of a straight unitary body or an assembly of straight structural members (including curved structural members in some cases). Funda mentally, the vibration detecting block 3 and vibration receiver 4 are attached separately to the respective vibratory members 2a to 2c.

However, it is also possible to provide a single vibration detecting block 3 and a vibration receiver 4 on the pipe wall at an intermediate position between two vibratory members 2a and 2b as shown particularly in Fig. 10, picking up the integrated value of longitudinal vibrations transmitted from the vibratory members 2a and 2b through the pipe wall or differentiating it to observe the changing con ditions.

Although there is no restriction in particular with regard to the manner of mounting the vibratory member 2 on the pipe, a general method to secure the vibratory member in position is shown in Fig. 11. More particu larly, in the example of Fig. 11, a pair of holes 14 are provided in the pipe wall at radially opposing positions, and the vibratory member 2 is connected to the vibration de tecting block 3 at one end remote from the end with a male screw 1 5 which is passed through a hole 14 remote from the vibration detecting block 3 and fixed in position by a nut 16. Indicated at 16 in Fig. 11 is a sealing washer.

Although not particularly pointed out in the foregoing description, it should be noted that the flow meter is arranged to detect only the vibrations in the axial direction of the pipe and to eliminate substantially most of the transverse vibrations which would otherwise affect the measurement of flow rate.

In detecting the vibrations caused by colli sion of the particulate material, the present method adopts as a measuring element only the vibration in the flow direction which accu rately correlates with the mass flow rate of the particulate material, so that by reducing the influence of disturbances in the transverse direction of the pipe, we ensure a high signal to noise ratio. Consequently, the measurement is extremely accurate and reliable and can contribute to the automation of various dual phase flow transfer processes including the feeding of pulverised fuel in a furnace oper ation.

The embodiments and experimental data shown in Figs. 1 to 11 are based on the above mentioned method of detection (detec tion of vibrations in the axial direction of the pipe).

Shown in Fig. 1 2 and onwards are further embodiments of the invention which can at tain an even higher accuracy of measurement and in which a metering section is inserted at a suitable position along the length of a conduit pipe through a pair of short, tubular resilient members thereby to insulate the met ering section from any vibrational disturbance in the conduit pipe itself.

Referring to Figs. 1 2 and 13, a metering section 101 is inserted between conduit pipe portions 102 by tubular resilient members 1 03. The particulate material which is trans ferred in the direction indicated by blank arrows hits against and vibrates a rod-like or tubular vibratory member 104 which is radi I ally mounted substantially across the centre of the metering section 1. The vibration detecting block 107 in the same manner as in the foregoing embodiments, and the detected vibration is converted into voltage signals at a signal processor 107. The voltage signals are processed in the same manner as in the foregoing embodiments and thus the description in this regard is omitted to avoid repetition.

The embodiment of Figs. 1 2 and 1 3 shows a particular construction of an insulated metering section which is free from disturbing vibrations of the conduit pipe portions 102.

As is clear from these Figures, the metering section 101 is connected to the conduit pipe portions 202 through the tubular resilient members 103, so that any vibrations of the pipe portions 102 are mostly absorbed by the resilient members 103 without being transmitted to the metering section 101 in any substantial degree. Therefore, the vibration receiver 106 detects substantially only the vibrations which are caused by collision of the particulate material flowing through the metering section 101, thereby exclusively detecting the vibrations which are related to the mass flow rate of the particulate material, free of the above mentioned disturbances.As shown in the drawings, the vibration detecting means may include the vibratory member which extends across the flow passage to detect the vibrations caused by collision of the particulate material thereagainst (eg (1) to detect all of the longitudinal and transverse vibrations of the metering section and extract a particular vibrational frequency range which has the highest correlation with the mass flow rate, or (2) to detect only the vibrations in the direction transverse of the vibratory member or in the flow direction, eliminating the vibrations in a direction perpendicular to the flow direction which only poorly correlate with the mass flow rate of the particulate material), or may have the vibration receiver directly mounted on the pipe wall of the metering section in the manner as described hereinbefore to detect the vibrations caused by collision of the particulate material against the metering section.

There may be employed any other means as long as it can detect the vibrations resulting from the collision energy of the particulate material. In any case, the vibrations of the metering section are insulated from the disturbing vibrations of the upstream and downstream pipe portions 102 to ensure an extremely high accuracy of measurement. Although a tubular rubber pipe is used as a resilient member 103 in the embodiment of Fig. 12, it may be replaced by a bellows tube or other resilient structure. Further, the resilient members 103 which are shown as connected to the metering section 101 and the conduit pipe portions 102 through a push-in joint with stopper projections (and a hose clip indicated at 108) in Fig. 12, may be replaced by other connecting methods, for example, by the method as shown in Fig. 4.More particu larly, in the example of Fig. 14, the conduit pipe 102 and metering section 101 are provided with flanges 102a and 101a at the opposing connecting ends, respectively, secured to each other through a resilient mem ber 103 by means of a number of nuts and bolts 109.

Referring now to Fig. 15, there is shown a further embodiment of the invention which is basically the same as the one shown in Fig.

1 2 in construction, and therefore like compo nent parts are designated by the same refer ence numerals. In the embodiment of Fig. 15, the conduit pipe portions 102 are joined with the resilient members 103 by connecting adaptors 110 each with a flange of a large diameter, and the metering section 101 in cluding the resilient members 103 is entirely housed in a tubular cover 111 of a large diamater which is fitted around the metering section 101.The opposite ends of the tubular cover 111 are fixedly fastened to the periph eral edge portions of the flanges of the con necting adaptors 110 by hexagonal bolts 11 2. The tubular cover 111 is provided with a connector 11 3 at a suitable position so that the voltage signal from a vibration signal processor 107 in the metering section 101 can be led out from the connector 11 3 through a lead wire 11 4.

With this construction, the conduit pipes 102 are rigidly coupled with each other thereto of unnecessary disturbing forces, coupled with the advantage that the mainte nance and service of the metering section as a whole is facilitated by the prevention of the intrusion of dust or other foreign matter.

It will be clear from the foregoing descrip tion that the accuracy of measurement can be improved to a considerable degree by the provision of the tubular resilient members which isolate the vibrations of the conduit pipe itself from the metering section when measuring the mass flow rate of particulate material by way of vibrations caused by colli sion of the particulate material.

Referring now to Figs. 1 6 and 17, there are shown frequency spectra in hammering tests using resilient members as shown in Fig. 15, of which Fig. 1 6 is a diagram showing the results of hammering on the metering section 101 and Fig. 17 the results of hammering on the conduit pipe 102 with the same force as in the case of Fig. 1 6. It will be seen that in the case of Fig. 1 6 the vibrations which occur in the metering section are clearly detected, in i contrast to Figure 1 7 in which the vibrations are almost undetectable due to absorption by the resilient members. Thus, the vibrations of the conduit pipe can be suppressed to a significant degree, so that it becomes possible to detect accurately only those vibrations which take place in the metering section.

Although the invention has been described in terms of specific embodiments, it is to be understood tjlat other forms of the invention may be readily adapted within the scope of the invention defined in the appended claims.

Claims

1. A method for measuring the mass flow rate of particulate material through a pipe by detection of vibrations caused by the collision of said particulate material, said method comprising: detecting said vibrations at a predetermined metering section of said pipe; forming a voltage signal related to the detected vibrations in a predetermined frequency range of the vibrations; calculating an effective value of said voltage signal to produce a voltage signal of the calculated effective value; feeding the calculated effective voltage signal to an arithmetic conversion circuit to produce a voltage signal indicative of the mass flow rate of said particulate material corresponding to said calculated effective voltage value on the basis of predetermined correlation between said mass flow rate and said calculated effective voltage signal.

2. The method as claimed in claim 1, comprising the step of detecting vibrations occurring at the surface of said pipe in a direction perpendicular to the flow direction of said particulate material.

3. The method as claimed in claim 1, comprising the steps of inserting at least one vibratory member across a flow passage at the metering section of said pipe and detecting vibrations of said vibratory member in the axial direction of said pipe.

4. The method as claimed in claim 3, wherein said vibratory member consists of a unitary rod-like structure.

5. The method as claimed in claim 3, wherein said vibratory member consists of a unitary tubular structure.

6. The method as claimed in any of claims 3 to 5, wherein a number of said vibratory members are inserted into the flow passage in said metering section at different positions and angles relative to each other.

7. The method as claimed in claim 3, wherein said vibratory member is provided with a number of radially extending rib portions.

8. The method as claimed in any of claims 1 to 7, comprising the steps of providing said metering section separately from said pipe and inserting said metering section at a suitable position along the length of said pipe with tubular resilient members at opposite ends of said metering section for vibrationally insulating same from said pipe.

9. The method as claimed in claim 8, wherein said resilient members are made of rubber-like material.

10. The method as claimed in claim 8 or 9, wherein said resilent members each consist of a bellows tube.

11. The method as claimed in claim 8, 9 or 10, wherein said resilient members are connected to said pipe and metering section by press4ifling.

1 2. The method as claimed in claim 8, 9 or 10, wherein said resilient members are securely fixed to said pipe and metering section by means of bolts and nuts.

1 3. The method as claimed in any of claims 8 to 12, wherein said metering section is housed in a tubular cover.

14. A method as claimed in any of Claims 1 to 1 3 in which said predetermined frequency range is the entire frequency range.

1 5. A method as claimed in any of claims 1 to 1 3 in which said predetermined frequency range comprises a frequency range which is selected so as to produce a calculated effective voltage signal which has a high degree of correlation with the mass flow rate of the particulate material.

1 6. A method as claimed in claim 1 5 in which the frequency range is determined by a band pass filter.

1 7. A method as claimed in any of claims 1 to 1 6 in which k'ne calculated effective voltage signal is calculated by a process of square averaging.

1 8. A method as claimed in any of claims 1 to 1 7 in which the noise region of the voltage signal is eliminated by means of a bias adjusting circuit.

1 9. Methods for measuring the mass flow rate of particulate material through a pipe as claimed in claim 1 substantilly as hereinbefore described.

20. Apparatus for measuring the mass flow rate of particulate material through a pipe by detection of vibrations caused by the collision of said particulate material, said apparatus comprising means for detecting vibrations at a predetermined metering section of said pipe, means for forming a voltage signal relating to the detected vibrations in a predetermined frequency range of the vibrations, means for calculating an effective value of said voltage signal to produce a voltage signal of a calculated effective value, an arithmetic conversion circuit for receiving said calculated effective voltage signal to produce a voltage signal indicative of the mass flow rate of said particulate material corresponding to said calculated effective voltage signal on the basis of predetermined correlation between said mass flow rate and said calculated effective voltage signal.

21. Apparatus as claimed in claim 20 in which the means for detecting vibrations comprises means for detecting vibrations occurring at the surface of said pipe in a direction perpendieulal to the floors direction Qf said particulate material.

22. Apparatus as claimed in claim 20 in which the means for detecting vibrations comprises at least one vibratory member across a flow passage at the metering section of said pipe to detect vibrations of said vibratory member in the axial direction of said pipe.

23. Apparatus as claimed in claim 22 in which said vibratory member consists of a unitary rod-like structure.

24. Apparatus as claimed in claim 22 wherein said vibratory member consists of a unitary tubular structure.

25. Apparatus as claimed in claim 22 wherein a number of said vibratory members are inserted into the flow passage in said metering section at different positions and angles relative to each other.

26. Apparatus as claimed in claim 22 in which said vibratory member is provided with a number of radially extending rib portions.

27. Apparatus as claimed in any of claims 20 to 26 in which said metering section is separate from said pipe and is connected into the length of said pipe with tubular resilient members at opposite ends of said metering section for vibrationally insulating said metering section from said pipe.

28. Apparatus as claimed in claim 27 wherein said resilient members are made of rubber-like material.

29. Apparatus as claimed in claim 27 or 28 wherein said resilient members each consist of a bellows tube.

30. Apparatus as claimed in any of claims 27 to 29 wherein said resilient members are connected to said pipe and metering section by press fitting.

31. Apparatus as claimed in any of claims 27, 28 or 29 wherein said resilient members are securely fixed to said pipe and metering section by means of bolts and nuts.

32. Apparatus as claimed in any of claims 27 to 31 wherein said metering section is housed in a tubular cover.

33. Apparatus as claimed in claim 20 substantially as herein before described with reference to Figs. 1 to 5 or as modified in Figs. 6 to 1 7 of the accompanying drawings.

34. A method for measuring the mass flow rate of particulate material during transfer through a conduit pipe by detection of vibrations caused by collisional energy of said particulate material, said method comprising: detecting vibrations at a predetermined metering section of said conduit pipe.

extracting from detected vibrations a particular frequency of vibrational acceleration in the form of a voltage signal; calculating the effective value of said frequency range and producing a voltage signal of the calculated effective value; feeding the caculated signal to an arithmetic conversion circuit to produce a voltage signal indicative of the mass flow rate of said particulate material corresponding to said effective value on the basis of predetermined correlation between said mass flow rate and said effective value.