METHOD AND APPARATUS FOR MONITORING THE SPECIFIC GRAVITY OF A LIQUID

Abstract: Apparatus for monitoring the specific gravity of a liquid comprises a cantilevered load sensing beam (24) on which is suspended a displacer (15). The beam (24) is itself mounted on a support tube (19) extending from the wall of a vessel (10) holding the liquid whereof the specific gravity is to be monitored. Deflection of the beam (24), which is measured by strain gauges (27), provides a measure of any variation in specific gravity. The output of the strain gauges (27) is associated with processing means for providing information on specific gravity changes.

Description: METHOD AND APPARATUS FOR MONITORING THE SPECIFIC GRAVITY OF A LIQUID This invention relates to a method of and apparatus for monitoring the specific gravity of a liquid, especially but not exclusively a fermenting liquid such as beer. It is known that the specific gravity of a fermenting liquid such as beer decreases as sugars in the liquid are converted to alcohols and it is desirable that process workers operating the fermenting process be aware of such changes in specific gravity for efficient operation of the process. It is therefore an object of the present invention to provide a simple and effective method of and apparatus for monitoring, continuously or intermittently, the specific gravity of a liquid, especially a fermenting liquid. The present invention has particular but not exclusive application to the brewing industry. According to the present invention, therefore, there is provided apparatus for monitoring the specific gravity of a liquid, comprising support means on which is mounted a cantilevered load sensing beam associated with means for measuring deflection of the beam, and a displacement body heavier than the liquid supported by and depending from the beam. Also according to the present invention there is •provided apparatus as claimed in claim 1, wherein the beam is of rectangular cross-section and has two generally coplanar circular apertures in the plane of weight sensing deflection of the beam, and four strain guages are provided for monitoring deflection of the beam. Preferably, the connection between the weight-detecting sensor and the body is a pivotal one. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a fragmentary part-sectional side elevation of a process receptacle, for example a fermenting vat, with the specific gravity monitoring apparatus according to the present invention; Fig. 2 is a fragmentary side elevation of the specific gravity monitoring apparatus to an enlarged scale, but omitting details of the spray tube. Fig. 3 is a detail of the load cell used in the apparatus of Fig. 1; Fig. 4 is a view on the line IV-IV of Fig.3; and Fig. 5 is a modification of the beam deflection limiting means shown in Figs. 3 and 4. Referring to the drawings, a wall of the fermenting vat within which, for example, beer (B) is being fermented is indicated at 10. The wall 10 adjacent the bottom of the vat which may be of considerable height, say 50 to 60 feet, is apertured at 11 and has an integral tubular port 12 flanged at 13. The specific gravity monitoring apparatus of the present invention generally indicated at 14 is inserted through this port 12 into the vat and is partially accommodated within the port 12. The monitoring apparatus 14 comprises an elongate displacer 15 in the form of a closed tubular body of known volume and weight suspended in cantilever fashion within the beer contained in the vat. This displacer 15 is sufficiently substantial so as to have a sufficiently high moment of inertia so as to be generally unaffected by the movement of bubbles and suspended solids in a fermenting liquid. A bar or rod 16 is welded to one end of the displacer body 15 and is pivoted as indicated at 17 to one end of a load cell unit 18 (indicated in more detail in Fig. 3) forming part of a cantilever beam from which the displacer body 15 is suspended as aforesaid. The cantilever beam also comprises a support tube 19 welded to the load cell 18, the support tube 19 extending through, and out of, the port 12 and having a flange 20 whereby the cantilever beam 18, 19 is bolted as indicated at 21 to the port flange 13. A sealing disc 22 or similar is sandwiched between the flanges 13, 20. The signal cable of the load cell unit 18 is indicated at 23 and is housed in the support tube 19. The cable 23 egresses from the support tube 19 externally of the vat as shown and is coupled to amplifying means (not shown) and thereafter to a signal processing means giving, for example, a read-out in units of specific gravity. The cantilever beam 18, 19 is a sealed unit to prevent process product, for example, beer ingress, and it together with the displacer body 15 and bar or rod 16 are made of stainless steel, for example 316 stainless steel, to prevent process product contamination and corrosion. The cantilever beam connection or joint 13, 20 to 22 is leak-proof due to the provision of the sealing disc 22, and is rigid with the port 12 and consequently the vat. Referring now to Figs. 3 and 4, the load cell unit 18 will be seen to comprise a load sensing beam 24 with two generally circular cut-out 25 which open one into the other. Beam 24 is enclosed in bellows 26. A total of four strain gauges 27 are bonded (e.g. by welding) to beam 24 and each positioned above or below a respective circular cut out 25 as shown. The use of four strain gauges (mounted at the corners of a parallelogram) on the beam 24 means that deficiencies in the machining of the beam 24 are compensated and that accurate measurement of beam deflection is possible. As a variation, it would be possible to use only two strain gauges 27, (positioned diagonally opposite each other) but the measurement would not be so accurate. Obviously the strain gauges are associated with the necessary means for measuring the deformation of the beam. A rod 28 is screwed at one end into a support 29 (at the end of beam 24) and its free end locates in an elongate aperture 30 in a circular plate 31. Rod 28 serves to prevent excessive deflection of beam 24 (such as might occur by draining of the vat whilst leaving the displacer 15 freely suspended) by engaging against the ends of aperture 30 at a predetermined deflection of the beam. A modification for rod 29 and aperture 30 is shown in Fig. 4 in which the rod (designated here as 29) has a tapered end. This taper allows for calibration of the over-range limit adjustment. A platinum resistance thermometer 32 is bonded to beam 24 as shown. A further feature of the apparatus is a spray tube 33 extending beneath, and parallel to, the support tube 19. This spray tube is for use in sparging the apparatus and for this purpose is connected to a supply of cleaning liquid (e.g. water). The apparatus is used as a continuous on-line monitor for the specific gravity of a liquid, particularly a fermenting liquid (e.g. beer). The support tube 19 and displacer 16 are completely submerged in the liquid whereof the specific gravity is to be monitored. Ideally, the volume and/or weight of the displacer 15 is such that at the start of fermentation there is substantially no deflection of the beam 24. The load cell 18 detects apparent gains/losses in weight of the displacer body 15 due to changes in the specific gravity of the beer during fermentation signals generated by the load cell 18 are, as aforesaid, transmitted by the cable 23 to the amplifying means and the signal processing means to give the read-out in specific gravity units. The measurement is unaffected by bubbles and suspended solids which, as mentioned previously, do not cause movement of displacer 15. Thus the specific gravity is continuously monitored to permit a process worker to check and adjust the process operation if necessary. The platinum resistance thermometer 32 measures the temperature of the beer and allows a correction to be made for giving the specific gravity at a standard temperature, such as may be required for excise duty purposes. Due to the pivot connection 17 between the displacer body 15 and the cantilever beam 18, 19, it is a simple matter to remove the specific gravity monitoring apparatus 14 through the port 12 after releasing the connection or joint 13, 20 to 22 for maintenance, repair or replacement purposes for example. Re-insertion, or insertion of a replacement apparatus, is equally simple. Although the invention has been described with specific reference to a support tube 19 extending horizontally from the wall of the vessel, it is possible for the tube to be generally L-shaped with one vertical limb (supported above the vessel) and a horizontal limb on which the load sensing beam is mounted.

Claims: CLAIMS : 1. Apparatus for monitoring the specific gravity of a liquid, comprising support means on which is mounted a cantilevered load sensing beam associated with means for measuring deflection of the beam, and a displacement body heavier than the liquid supported by and depending from the beam. 2. Apparatus as claimed in claim 1 wherein the means for measuring deflection of the beam comprise strain gauges on the beam. 3. Apparatus as claimed in claim 2 comprising two strain gauges on the beam diagonally opposite each other. 4. Apparatus as claimed in claim 2 comprising four strain gauges on the beam at the corners of a parallelogram. 5. Apparatus as claimed in any one of claims 1 to 4, wherein the beam is of rectangular cross- section and has two generally circular apertures, and a first strain gauge is mounted above one aperture and a second strain gauge is mounted below the other aperture. 6. Apparatus as claimed in claim 1 wherein the beam and the means for measuring deflection of the beam are provided by a load cell. 7. Apparatus as claimed in any one of claims 1 to 6 provided with means for limiting the deflection of the beam. 8. Apparatus as claimed in claim 7 wherein the means for limiting the deflection of the beam comprises a rod fixed at one end relative to deflection of the beam and locating at its other end in a deflection limiting aperture associated with the beam. 9. Apparatus as claimed in claim 8 wherein the deflection limiting aperture is provided in a flange around the beam. 10. Apparatus as claimed in any one of claims 1 to 9 provided with a platinum resistance thermometer. 11. Apparatus as claimed in claim 10, wherein the thermometer is mounted on the beam. 12. Apparatus as claimed in any one of claims 1 to 11 wherein the support means is an elongate cantilever support for insertion through, and support by, the wall of a vessel containing liquid. 13. Apparatus as claimed in claim 12 having a spray tube extending parallel to the cantilever support. 14. Apparatus as claimed in any one of claims 1 to 13 in which the connection between the load sensing beam and the body is a pivotal one. 15. Apparatus as claimed in claims 12 or 13 in which the cantilever support comprises a support tube connectible, at one end, to the receptacle wall and having, at its other end, the load sensing beam. 16. Apparatus as claimed in claim 15 in which a signal-transmission cable from the means for measuring deflection of the beam is housed within the support tube. 17. Apparatus as claimed in claim 15 or 16, in which the support tube is adapted to extend through and be flange-connected to a port in the receptacle wall. 18. Apparatus as claimed in claim 17, in which the flange connection incorporates liquid sealing means. 19. Apparatus as claimed in claim 16, in which the signal transmission cable externally of the receptacle and support tube is connected to signal-amplifying means and signal-processing means. 20. Apparatus as claimed in claim 19, in which the signal-processing means provides a read-out of the apparent body weight gains/losses in terms of specific gravity units. 21. Apparatus as claimed in any one of claims 1 to 20 wherein the displacement body is an elongate body. 22. Apparatus as claimed in claim 21 wherein the elongate body is a sealed hollow tube of known weight and volume. 23. A vessel for holding a liquid and provided with apparatus as claimed in any one of claims 1 to 22. 24. A method of monitoring the specific gravity of a liquid, especially a fermenting liquid, comprising suspending in the liquid a displacement body heavier than the liquid, said body being dependent from a load sensing beam, measuring deflection of the beam as a result of apparent gains/losses in the weight of the body, and providing a presentation of such apparent weight gains/losses. 25. A method as claimed in claim 24 comprising the step of presenting the apparent weight gains/losses in the form of a read-out in specific gravity units. 26. A method as claimed in any claim 24 or 25 comprising the step of providing a body of known weight and volume. 27. A method as claimed in claim 26 comprising providing a body in the form of a hollow closed tube. 28. Apparatus for monitoring the specific gravity of a liquid substantialy as hereinbefore described with reference to Figs. 1 to 4 of Fig. 5 of the accompanying drawings. 29. Method for monitoring the specific gravity of a liquid substantially as hereinbefore described with reference to Figs. 1 to 4 or Figs. 5 of the accompanying drawings.

Inventors: DUTTON W JOHN, DUTTON, W., JOHN
Applicants: PCA ASSOCIATES CONGLETON LIMIT, PCA ASSOCIATES (CONGLETON) LIMITED
Application year: 1988
Main classification: G01N9
IPC codes: G01N9