GB2040050A - Meter - Google Patents

Abstract

A meter for recording maximum and minimum values of a quantity over a period of time has an indicating pointer (1), a maximum recording pointer (4), and a minimum recording pointer (5), all three pointers being pivotable about a common axis over a graduated scale (3). The indicating pointer has a stepped portion which passes between the two recording pointers and engages one or other of them as it moves over the scale. When the indicating pointer retreats from a maximum or minimum value, the respective recording pointer is held in a position corresponding to that value by frictional contact between a small magnet mounted on it and the rear surface of a steel reset plate (8). The reset plate is movable away from the recording pointers to release the frictional restraint by pressing a tab 20 whereupon they are moved automatically towards the indicating pointer by means of counterweights. A coil spring loading the bearings may be used in lieu of the magnetic means. <IMAGE>

Description

SPECIFICATION Meter This invention relates to a meter having one or more recording pointers arranged for movement relative to a scale.

It is often a requirement that, in the measurement of a quantity which varies with time, the measuring instrument, as well as indicating an instantaneous value of the quantity, should in addition be able to record a maximum or minimum value reached within a chosen period of time. Examples of such quantities are temperature, pressure, humidity, mains voltage, liquid levels, and rotational speed, all of which can conveniently be indicated by a pointer travelling over a calibrated scale.

For the recording of maximum and minimum temperatures in, for example, weather recording, a mercury thermometer having a U-shaped tube is well known. As the temperature rises a column of mercury moves down in one arm of the tube (due to the expansion of a column of alcohol in the arm) and up in the other. Floating on the top of the column of mercury in each arm ofthetube is an iron marker which moves up with the mercury but, due to frictional resistance, is left behind when the mercury retreats down the tube. One marker acts as a maximum temperature indicator and the other as a minimum temperature indicator, each arm of the U4ube being disposed in front of a graduated scale.

To reset the markers for another recording period, they are returned to their respective ends of the mercury column by drawing them down with a magnet. This known thermometer has the disadvantage that resetting can be awkward. In an alternative known construction, the frictional resistance between the markers and the tube is insufficient to hold them in position when the mercury retreats, unless a magnet is placed behind the tube to pull the markers against the wall of the tube. To reset the markers, the magnet, normally positioned close to the tube, is pushed away from the tube, whereupon the markers drift slowly down towards the ends of the column.

Both these types of mercury thermometer have disadvantages in that blowing a glass bulb in the end of one arm as an alcohol reservoir is a skilled operation, and that each individual tube has to be calibrated by marking each arm of the tube at a reference temperature and adjusting the position of each scale relative to the tube. Both these operations are time-consuming and therefore costly. Further, such mercury thermometers are relatively difficult to read due to the shortness of the scales, and are often unsuitable for transportation by air.

A meter having a circular or part-circular scale and a maximum value recording pointer is known. The recording pointer follows a main indicating pointer as it rises to a maximum. When the indicating pointer retreats, the recording pointer is held at the maximum value by a ratchet mechanism. To reset the recording pointer, a small knurled knob must be rotated by hand until the pointer is brought to the same position as the indicating pointer. This mechanism is relatively complicated and expensive.

It is an object of this invention largely to avoid the disadvantages mentioned above.

According to this invention, there is provided a meter having an indicating pointer pivotally movable relative to a scale in response to changes in a quantity to be measured, and at least one recording pointer also pivotally movable relative to the scale about the same axis as the indicating pointer, wherein the or each recording pointer is movable in a direction towards a respective end of the scale in response to movement of the indicating pointer in that direction, movement of the or each recording pointer in the respective opposite direction being resisted by frictional restraining means, the latter being releasable to cause the or each recording pointer to move under the influence of a resetting force.

According to another aspect of the invention, there is provided a meter for recording the maximum and the minimum values of a variable quantity during a period of time, wherein the motor includes a maximum recording pointer for recording said maximumvalue, and a minimum recording pointer for recording said minimum value, said pointers being movable relative to an arcuate scale about a common axis, and wherein the meter further includes frictional restraining means to hold said pointers against a resetting force when said quantity retreats from said maximum and minimum values respectively, said restraining means being releasable to allow the pointers to move under the influence of the resetting force to a position corresponding to prevailing value of said quantity.

In the preferred embodiment of the invention, which has two recording pointers, one for recording a minimum value and one for recording a maximum value, the frictional restraint means is provided by small magnets attached to each recording pointer.

These magnets are attracted towards a plate made of steel or another ferrous material. As the recording pointers are pushed by the indicating pointer, the magnets slide over the surface of the plate against the resistance due to the frictional force between the magnets and the plate created by the magnetic attraction force therebetween. To reset the pointers at the start of a new recording period, the plate is moved away from the pointers, whereupon the recording pointers immediately move to the position of the indicating pointer. Resetting is thus accomplished relatively quickly and simply.

Frictional resistance can be brought about without the magnets actually engaging the surface of the plate. Provided the attraction between the magnets and the plate is sufficiently strong, the transverse force on the recording pointer causes frictional resistance in the pivot bearing which mounts the pointers on the body of the meter.

Alternative non-magnetic frictional restraining means may take the form of a coil spring arranged coaxially with the pivot axis to apply a compression force on the pivot bearing, the spring being movable away from the recording pointers to allow resetting.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a perspective view of a maximum and minimum recording thermometer in accordance with the invention, with its front face removed; Figure 2 is a partly sectioned side view corresponding to Figure 1; and Figure 3 is a front view of the main indicating pointer, the two recording pointers, and the scale, of the thermometer of Figure 1.

Referring to the drawings, a maximum and minimum value recording thermometer has an indicating pointer 1 connected to a coiled bimetallic strip 2. The pointer 1 moves across a scale 3 about a horizontal axis which is generally perpendicular to the scale.

The thermometer includes a maximum recording pointer 4 and a minimum value recording pointer 5 which are also rotatable about the same axis as the indicating pointer 1. Rotation of the recording pointers is resisted by frictional restraint means comprising small magnets 6 and 7 attached to each pointer and a steel reset plate 8 which, in its normal static position, touches both magnets and, due to the attraction forces between the plate and the magnets, holds the recording pointers 4 and 5 in fixed positions relative to the scale, except in the presence of a sufficiently strong rotating force on the pointers.

The three pointers rotate in parallel adjacent planes, and the indicating pointer 1 has a portion bent at right angles as shown, which passes through the plane of each of the recording pointers, so that if, for example, the pointer 1 moves in a clockwise direction about the pivoting axis as the temperature increases, it pushes the recording pointer 4 ahead of it. If then the temperature reaches a maximum and subsequently begins to fall, the pointer 1 retreats down the scale and leaves the recording pointer 4 at a position corresponding to the maximum temperature, where it is held by friction between the magnet 6 and the inner, planar surface of the plate 8 which is perpendiculartothe pivoting axis.Similarly, if the temperature drops below the value at which the recording pointer 5 is held, the indicating pointer 1 will push the pointer 5 to a minimum value position, where it will be left when the temperature rises again.

Referring to Figure 3, each recording pointer has an arm portion 9 or 10, and a counterweight portion 11 or 12. Each counterweight portion is shaped in the form of a sector of a circle and has a magnet 6 or 7 attached to its surface in an outer corner of the sector on the opposite side of the pivoting axis from the respective arm portion 9 or 10. The shape of each recording pointer, which is formed from a single sheet of non-ferrous material, is such that its centre of gravity is positioned to one side of the axis so that the pointer is urged towards a "home" position in which its centre of gravity is vertically below the axis.Taking the maximum recording pointer 4 as an example, the centre of gravity, indicated in Figure 3 by the reference 13, lies between the two planes 14 and 15 which intersect along the pivoting axis and are at 135 and 45" respectively to a line 16 extending between the end of the arm portion 9 and the axis.

The optimum position of the centre of gravity 13 for operation over a maximum scale length is on a radius at 90" to the plane 16. In operation, as the indicating pointer 1 moves clockwise its right angled portion contacts the pointer 4 just below the step 17 in the edge of the pointer 4 and pushes the latter clockwise against both the frictional force mentioned above and a gravitational resetting force exerted by the counterweight portion 11.

Resetting of the recording pointers 4 and 5 is achieved as follows. By moving the reset plate 8 (Figure 2) away from the magnets 7 and 8, the frictional restraining force is removed and the recording pointers 4 and 5 immediately and automatically move towards their respective home positions until they each strike the indicating pointer 1. After resetting, the recording pointers both rest in a position coincident with that of the indicating pointer. The reset plate 8 is then returned to its normal position (Figure 2) (the plate is spring loaded towards its normal position by small foam pads 18 which press against the transparent front face 19 of the meter) and the meter is ready for another recording period.In the embodiment shown in the drawings the reset plate 8 can be moved away from the magnets by pressing a tab 20 which is attached to or forms part of the plate 8 and protrudes through a slot in the rear wall 21 of the thermometer casing.

This particular construction enables the meter, when mounted with its rear wall against a flat vertical surface, to be reset simply by pushing on the lower part of the front face 19. This action moves the thermometer towards the mounting surface, so that the tab 20 in contact with the mounting surface is pushed into the casing, compressing the foam pads 18 and releasing the frictional restraint on the recording pointers.

As an alternative to the provision of a gravitational resetting force using counterweights, other means, for example springs, may be used to bias the pointers towards their respective home positions.

This alternative means would enable a scale subtending an angle of greater than 1800to be used.

With gravitational resetting, 1800 is the largest theoretical scale angle that can be used, and in practice an angle of less than 1800 is used to allow for tilting of the meter when mounted.

Claims (17)

1. A meter having an indicating pointer pivotally movable relative to a scale in response to changes in a quantity to be measured, and at least one recording pointer also pivotally movable relative to the scale about the same axis as the indicating pointer, wherein the or each recording pointer is movable in a direction towards a respective end of the scale in response to movement of the indicating pointer in that direction, movement of the or each recording pointer in the respective opposite direction being resisted by frictional restraining means, the latter being releasable to cause the or each recording pointer to move under the influence of a resetting force.

2. A meter according to claim 1 wherein the frictional restraining means is releasable to cause the or each recording pointer to move to a position substantially coincident with that of the indicating pointer.

3. A meter according to claim 1 or claim 2, having a maximum recording pointer and a minimum recording pointer movable respectively in a clockwise and an anti-clockwise direction relative to the scale in response to movement of the indicating pointer in the respective corresponding direction.

4. A meter according to any preceding claim, wherein the or each recording pointer is subject to a transverse force acting in a direction generally parallel to the pivoting axis causing the pointer frictionally to engage a stationary part of the meter, the transverse force being largely removed when the frictional restraining means is released.

5. A meter according to claim 4, wherein the transverse force is the result of magnetic attraction between the or each pointer and a static part of the meter.

6. A meter according to claim 5, wherein the frictional restraining means comprises a permanent magnet forming part of the or each recording pointer and a ferrous plate having a planar surface perpendi cular to the pivoting axis and adjacent the or each magnet, the restraining means being releasable in that the plate is movable away from the or each magnet.

7. A meter according to claim 6, wherein the ferrous plate constitutes the stationary part of the meter and the or each recording pointer frictionally engages the said planar surface.

8. A meter according to any preceding claim, wherein the resetting force is gravitational.

9. A meter according to claim 8, wherein the pivoting axis is substantially horizontal when the meter is in its normal operating position, and the or each recording pointer comprises an arm portion and a counterweight portion and has a centre of gravity which is spaced from the axis so that the or each pointer is urged towards a respective home position in which its centre of gravity is vertically below the axis; and wherein, for the or each pointer, the axis and the centre of gravity define a respective first plane, and the axis and that part of the arm portion which is adjacent the scale define a second plane, the angle between the first and second planes being in the range 450 to 135 .

10. A meter according to claim 9 when appendank to claim 6 wherein, in respect of the or each recording pointer, the arm portion and the counterweight portion are formed from a single sheet of non-ferrous material, the counterweight portion being shaped in the form of a sector of a disc centered on the pivoting axis with the magnet positioned in an outer corner of the sector on the opposite side of the axis from the arm portion.

11. A meter according to claim 9 or claim 10, wherein the or each recording pointer is movable in response to movement of the indicating pointer by engagement of the indicating pointer with the respective recording pointer arm portion.

12. A meter according to claim 11 when appendank to claim 3, wherein the scale, the arm portion of the maximum recording pointer, the arm portion of the minimum recording pointer, and an outer portion of the indicating pointer lie in separate, adjacent parallel planes substantially perpendicular to the pivoting axis, and wherein an inner portion of the indicating pointer intersects the planes of the two recording pointers.

13. A meter according to claim 6, wherein the pointers, the scale and the ferrous plate are housed in a closed casing, the ferrous plate being resiliently mounted in the casing and having a resetting member which projects through an aperture in the rear wall of the casing.

14. A maximum and minimum recording thermometer according to any preceding claim.

15. A meter for recording the maximum and the minimum values of a variable quantity during a period of time, wherein the meter includes a maximum recording pointer for recording said maximum value, and a minimum recording pointer for recording said minimum value, said pointers being movable relative to an arcuate scale about a common axis, and wherein the meter further includes frictional restraining means to hold said pointers against a resetting force when said quantity retreats from said maximum and minimum values respectively, said restraining means being releasableto allow the pointers to move under the influence of the resetting force to a position corresponding to the prevailing value of said quantity.

16. A meter having an indicating pointer and a scale; which pointer and scale are movable relative to each other in response to changes in a quantity to be measured, and at least one recording pointer which is movable towards a respective end of the scale in response to relative approaching movement of the indicating pointer and that end of the scale, movement of the or each recording pointer being resisted by frictional restraining means to hold the or each recording pointer stationary relative to the scale when the indicating pointer and the respective end of the scale move apart, the restraining means being releasable to cause the or each recording pointer to move automatically under the influence of a resetting force.

17. A meter constructed and arranged substantially as herein described and shown in the drawings.