GB2206205A - Viscosity measuring device particularly suited for measurements in boiling pans of sugar-making systems - Google Patents

Description

n 0 6 2 0 I'S .L/- d 1 230P56644 VISCOSITY MEASURING DEVICE PARTICULARLY

SUITED FOR MEASUREMENTS IN BOILING PANS OF SUGAR-MAKING SYSTEMS This invention relates to device for measuring viscosities and consistencies. which is particularly suited for the boiling pans of plant for making sugar.

The known system for measuring the viscosity and consistency of dense fluid masses such as massecuites, employs a drum rotating at a predetermined speed within the fluid mass in question. This rotating drum is driven by a driving shaft fitted with a torquemeter.

From the torque on the shaft, and the speed at which the shaft turns. the power absorbed by friction, as the drum rotates in the viscous fluid, can be calculated. By means of suitable calibrations. the consistency and viscosity of any such fluid can then be determined.

1 The torquemeter may be embodied by applying strain gauge sensors to the driving shaft. This embodiment is more suitable for relatively long and heavily loaded shafts, and where the forces involved are relatively 2 small it is preferable instead of measuring the unit deformations to measure the phase angle between the two ends of the shaft.

This phase angle can be measured in a single section of measurement, by fixing a first disk around a driving shaft (in the vicinity of the driving gear) and a second disk, alongside the first, but fixed to the end of a surrounding coaxial countershaft which. along its whole length in the absence of any torque. has the same angular orientation as the end section of the driving shaft, i.e. that section located nearest to the rotating drum to be.immersed in the fluid. In this way the phase angle between the two ends of the driving shaft is measured as a phase difference between two disks lying alongside one another.

According to known prior art. these two disks have circumferential teeth which, when the driving shaft of the rotating drum is at a standstill. are exactly in phase with one another. When the device is in operation, the angular displacement between the two ends of the driving shaft is manifested as an angular displacement between the two sets of identical teeth of said two disks, so that a suitable optical sensor can measure the circumferential amplitude of the openings visible between the teeth of the respective disks as a

1'1 0 3 measurement of the torque value. The optical sensor in question measures the duration of a period of illumination defined by the opening between the circumferentially adjacent teeth of different disks compares it with the period of darkness defined by the circumferential length of the two partially overlapping teeth.

This known type of measurement device.has disadvantages since the response of the optical sensor does not follow the same law when it passes from a obscurity to a illumination as it does in the reverse direction.Therefore, to obtain good precision it is necessary to calibrate the instrument continuously, which leads to additional expense.

The present invention sets out to overcome this problem, and in one aspect consists in a viscosity measuring device of the type provided with (a) two adjacent peripherally toothed discs fixed one in relation to each end of a rotary shaft carrying a drum for immersion into a fluid mass whose viscosity is to be measured. so that applied torque on the shaft to rotate the drum causes relative angular displacement of the discs in dependence upon the torque; (b) an optical sensor for light passing through both toothed disc peripheries to detect periods of illumination and 4 darkness varying with the changes of relative tooth position caused by the angular displacement: in which device the teeth on each disc are equally spaced and those on one disc have a circumferential extent less than the circumferential extent of the similarly equally spaced gaps between the teeth on the other discs, and at all torque values to be detected lie in a radial register within the circumferential extent of such gaps.

Measurement of the phase angle with such a device can be determined by the time lapse between two passages, each from a dark area to an illuminated area. and thus th.e same response curve of the optical sensor is used with a considerably greater precision. Therefore repetitive calibrations are no longer necessary.

The invention will be further described with reference to the accompanying drawings. in which:- Figure 1 is a diagram which shows the contours of the teeth of the first disk and of the second disk represented on a plane. in the known embodiment; Figure 2 shows the optical measurement output signal derived from the disks of Figure 1; J.

Figure 3 is a wiring diagram of a device according to the invention; Figure 4 is a diagram showing. in a manner corresponding to Figures 1 and 2 combined the situation resulting from the use of the invention.

In Figures 1 and 2, the dotted line 10 indicates the tooth contour of the first disk and the dotted line 20 indicates the tooth contour of the second disk.

The teeth of the first and of the second disk are shown staggered. a situation which corresponds to a torque being applied to the driving shaft. In known devices of this type, when no torque is being applied to the shaft the teeth of the two disks cover each other perfectly.

When a torque is applied to the shaft. as shown in Figures 1 and 2, there is a phase angle corresponding to distance 31 between the two disks. proportional to the torque applied to the driving shaft and thus to the consistency to be measured.

The optical sensor used to define the ratio between the circumferential length of the opening and the circumferential length of the overlapping teeth placed 6 between two successive openings does not however give an instantaneous response on passing from an obscured area to an illuminated area, but transmits this information after a small but not negligible time interval 34. Similarly. the response of the optical sensor when an obscured area is followed by a light area is not instantaneous but lasts an interval of time 35.

The time intervals 34 and 35 (shown enlarged in the figures for the sake of clarity) are generally not identical due to the different behaviour of the optical sensor as the sense of the information received, i.e. light/dark.or dark/light varies. (Temperature variation can also affect the readings).

It follows that the time intervals derived by using segments 34 and 35 are not identical to those time intervals 37 and 38 which correspond exactly to the obscuring and illumination time respectively.

According to the embodiment of the present invention shown at the top of Figure 4. the teeth 110 of the first disk have a circumferential width substantially equal to the opening defined between their edges.

The teeth of the second disk. however. have a much smaller circumferential width. in other words they are 9 -1 7 much narrower than teeth 110. and with the two disks at a standstill. with no torque applied. each "narrow" tooth 120 falls within the opening between two adjacent teeth 110 of the first disk.

The mechanical dimensions of the system are such that even at maximum torque. the narrow teeth 120 always remain in front of the opening defined between two teeth 10 of the first disk. The signaL emitted by the optical sensor therefore has the shape illustrated by the diagram 130 in Figure 4. The phase difference between the two disks is thus defined by measuring the distance between the- ascending edge of any pair of adjacent peaks. This eliminates the need for repeated calibration of the device, since the ascending edges of the signal emitted by the optical sensor all have the same linearity error. which is thus compensated for.

The same principles applies if the phase difference is measured by means of a pair of descending edges of the signal emitted by the optical sensor.

To complete the above information. 131 and 132 (Figure 3) indicate respectively the generator of a beam of light which passes between the peripheral double teething of the disks and an optical detector which 8 receives the light emitted by the former, in correspondence with the opening existing between circumferentially adjacent disks. 41 indicates a pulse clipping device. 142 indicates a monostable circuit and 143 a phase displacement detector.

144 indicates an integrating amplifier, and 145, 146, 147 and 148 are respectively (a) a root extractor (b) a converter, (c) an optoinsulator (c) an output stage.

Since the treatment of intermittent signals is well known, no further information need be given concerning the general layout of Figure 3.

In Figure 4. diagram (A) shows the contour of the teeth of the first disk. diagram (B) shows the contour of the teeth of the second disk, diagram (C) shows the signal generated by the optical detector but already clipped after passing through the clipper 41. and finally diagram (D) shows the same signal after further treatment in the phase difference detector 143.

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Claims (2)

Claims.

1.A viscosity measuring device of the type provided with (a) two adjacent peripherally toothed discs fixed one in relation to each end of a rotary shaft carrying a drum for immersion into a fluid mass whose viscosity is to be measured. so that applied torque on the shaft to rotate the drum causes relative angular displacement of the discs in dependence upon the torque; (b) an optical sensor for light passing through both toothed disc peripheries to detect periods of illumination and darkness varying with the changes of relative tooth position ca.used by the angular displacement: in which device the teeth on each disc are equally spaced and those on one disc have a circumferential extent less than the circumferential extent of the similarly equally spaced gaps between the teeth on the other discs. and at all torque values to be detected lie in a radial register within the circumferential extent of such gaps.

2. A viscosity measuring device according to claim 1. further comprising control electronics. of a type known per se, capable of measuring the time interval between the passing of the incoming edge of a tooth of the first disk and the passing of the incoming edge of the first tooth of the second disk.

3 A viscosity measuring device as claimed in claim 1 or 2 and substantially as herein described with reference to the accompanying drawings.

-j Published 1988 a, 1-he Patent Office, State House, e671 High Holborn. London WC1R 4TP. Further copies may be obtained from The Patent Office, Sales Branch. St Marv Cray. OrDinOtc-n. Kent BR5 3RD Printed bv Multinlex tpchmciues ltd. St Max.v Crav. Kent, Con. 1!87.