GB2044931A - Instrument assembly - Google Patents

Abstract

In an instrument assembly (1) a current value indicator element (6) is rotatably mounted on a shaft (5) and a set value indicator element (12) controlled by a knob (14) and mounted in the glass face (10) of the instrument for rotation about the axis of the shaft (5) is mechanically connected by spur gears (9, 13) to a shaft (8) of means 7 e.g. a potentiometer, which provides a signal output corresponding to the set position of the indicator element. Current value indicator element 6 is rotated by a galvanometer 4 supplied with a signal proportional to the temperature of apparatus being controlled and the galvanometer signal and potentiometer signal are compared in electronic comparison circuitry. <IMAGE>

Description

SPECIFICATION Instrument assembly This invention relates to an instrument assembly.

It is often required that an instrument assembly should provide a visual indication of both the current value of a parameter and of the required value of the same parameter. The instrument assembly will usually also include the comparison devices, for example electronic circuitry, which serves to provide an input to the apparatus being controlled in accordance with the relationship of the current value of the parameter to the required value. For safety and aesthetic reasons it is desirable that the device should give as clear an indication as possible of the relationship of the current value and the required value at any instant in time and that the instrument assembly itself should be designed and constructed in such a way that there is as little potential obstruction to visibility as possible.

In accordance with the present invention there is provided an instrument assembly, comprising a scale and two value indicator elements mounted in said assembly for rotation independently of each other over the face of the scale about a common axis, one of the indicator elements being a current value indicator element and being operatively connected to means in said assembly for moving it to rotational positions around said axis in response to corresponding inputs, and the other of the indicator elements being a set value indicator element and being mechanically connected to means for providing a signal output corresponding to a given position thereof.

Preferably the output shaft of the current value indicator moving means and the input shaft of the signal output providing means do not both lie on said axis and it is particularly preferred that the current value indicator moving means have an output shaft lying on said axis and that the input shaft to the signal output providing means should lie parallel to and spaced from said axis, in which case it is further preferred that spur gear means should interconnect the said input shaft with the said value indicator element.

Where manual control of set value indicator element is to be provided on the instrument assembly of the invention it is further preferred that a control knob be fixed to the set value indicator element for rotation therewith about said axis.

In a particular embodiment of an instrument assembly according to the invention the current value indicator element moving means is a galvanometer and the signal output providing means is a potentiometer and the assembly may further comprise means for comparing the output from the potentiometer with the input to the galvanometer.

An instrument assembly in accordance with a more particular aspect of the invention comprises a housing having a fixed planar scale secured thereto and covered by a protective window, a galvanometer mounted in the housing mounted on the side of said scale remote from the window and having the free end of its output shaft protruding through the scale substantially perpendicularly thereto, a first indicator needle secured to the free end of said output shaft for rotation about the axis of said output shaft over the scale, a potentiometer mounted in the housing on the same side of the scale as the galvanometer and having an input shaft parallel to and spaced from the output shaft of the galvanometer and having a free end protruding through the scale, a set value needle lying between said window and said current value needle and having a support boss journalled in said window for rotation about the axis of the output shaft of the galvanometer, and drive means interconnecting the boss and said input shaft of the potentiometer.

Preferably said boss extends out through the window and has a control knob attached thereto, and, preferably also, said drive means is comprised of spur gears secured on said boss and said potentiometer input shaft.

One embodiment of the invention will now be described by way of example only, with reference to Figures 1 and 2 of the accompanying drawings in which: Figure 1 is a front view of an instrument assembly for indicating and controlling the temperature of apparatus; and Figure 2 is a schematic sectional view on line 2-2 of Figure 1.

The drawings illustrating the specific embodiment of the invention to be described are somewhat schematic and do not illustrate the electrical input and outputs to the mechanical devices of the instrument assembly and they do not show the electronic circuitry associated with the instrument assembly.

In the instrument assembly 1 illustrated in the drawings there is provided a housing 2 which includes a front plate 3 which comprises on its outer face a circular planar scale which extends through approximately 270 .

A galvanometer 4 is mounted in the housing and has an output shaft 5 which is coincident with an axis extending centrally of and perpendicularly to the front plate 3. A current value indicator needle 6 is secured to the free end of the shaft 5 protruding through the scale plate 3 and is of a length to pass over the numbered portion of the scale. The needle 6 is a current value indicator element since the input to the galvanometer 4 will be proportional to the temperature of the apparatus being controlled.

A potentiometer 7 is also mounted within the housing 2 but is arranged to lie spaced from the axis of the output shaft 5 of the galvanometer and with its input shaft 8 parallel to the shaft 5. The free end of the input shaft of the potentiometer 7 also extends through the scale plate 3 and has a spur gear 9 secured to that free end.

A window plate 10 is mounted over the scale plate 3 and encloses the free ends of the output shaft 5 of the galvanometer 4 and of the input shaft 8 of the potentiometer 7. A stepped boss 11 is mounted centrally of the window plate 10 and isjournalled therein for rotation about the axis of the shaft 5 of the galvanometer 4. A set value indicator needle 12 is formed integrally with the boss 11 and has a length substantially equal to that of the needle 6 so that it is also rotatable about the axis of the shaft 5 over the scale on the scale plate 3. A spur gear 13 is also secured to the boss 11 axially inwardly of the set value indicator 12 and is in engagement with the spur gear 9 on the input shaft 8 of the potentiometer 7. A control knob 14 is fixed on a portion of the boss 11 which protrudes through to the outside with respect to the window plate 10.

In operation of the instrument assembly shown in the drawings and described above, an electrical signal corresponding to the temperature of the apparatus being controlled is applid to the galvanometer 4 and the needle 6 moves into a corresponding position on the scale plate 3 by rotation about the axis of the shaft 5 and under the control of the shaft 5 of the galvanometer 4. The desired value of the temperature of the apparatus being controlled is set by manual rotation of the knob 14 until the set value indicator needle 12 lies in the desired position on the scale plate 3.Rotation of the knob 14 and the boss 11 deflects rotation of the spur gear 13 and attached thereto and corresponding rotation of the spur gear 9 and the input shaft 8 to the potentiometer 7 so as to establish a signal output from the potentiometer 7 corresponding to the position of the set value indicator 12 over the scale plate 3. The instrument assembly contains electronic comparison circuitry which is not illustrated which produces an output from the instrument assembly for control of the apparatus in question related to the input to the galvanometer and the output from the potentiometer 7 and therefore to the relative positions of the current value indicator needle 6 and the set value indicator needle 12.

The instrument assembly as described provides for ready and accurate setting of the set value indicator element and ready comparison of this value with the current value indicator element 6 since they both rotate about the common axis and their position of coincidence is easily discernible. In addition, the boss 11 has to support only the control knob 14 and the set value indicator needle 12 so that it does not have to be of large cross sectional dimensions and does not therefore present a substantial obstacle to the all round visibility of the current and set value indicators.

The use of spur gears provides a useful element of versatility within the instrument assembly since the reduction ratio can be varied from the 1:1 ratio shown in the present drawings to other ratios suitable for particular elements of the assembly.

Claims (11)

1. An instrument assembly, comprising a scale and two value indicator elements mounted in said assembly for rotation independently of each other over the face of the scale and about a common axis, one of the indicator elements being a current value indicator element and being operatively connected to means in said assembly for moving it to rotational positions around said axis in response to corresponding inputs, and the other of the indicator elements being a set value indicator element and being mechanically connected to means for providing a signal output corresponding to a given position thereof.

2. An assembly according to claim 1,wherein an output shaft of the current value indicator moving means and an input shaft of the signal output providing means do not both lie on said common axis.

3. An assembly according to claim 1 or claim 2, wherein the current value indicator moving means has an output shaft lying on said axis and an input shaft to the signal output providing means lies parallel to and spaced from said axis.

4. An assembly according to claim 3, wherein spur gear means interconnect the said input shaft and a shaft carrying the said value indicator element and said output shaft carries said current value indicator element.

5. An assembly according to any preceding claim, wherein a control knob be fixed to the set value indicator element for rotation therewith about said axis.

6. An instrument assembly according to any preceding claim, wherein the current value indicator element moving means is a galvanometer and the signal output providing means is a potentiometer.

7. An assembly according to claim 6 further comprising means for comparing the output from the potentiometer with the input to the galvanometer.

8. An instrument assembly comprising a housing having a fixed planer scale secured thereto and covered by a protective window, a galvanometer mounted in the housing on the side of said scale remote from the window and having the free end of its output shaft protruding through the scale substantially perpendicularly thereto, a first indicator needle secured to the free end of said output shaft for rotation about the axis of said output shaft over the scale, a potentiometer mounted in the housing on the same side of the scale as the galvanometer and having an input shaft parallel to and spaced from the output shaft of the galvanometer and having a free end protruding through the scale, a set value needle lying between said window and said current value needle and having a support boss journalled in said window for rotation about the axis of the output shaft of the galvanometer, and drive means interconnecting the boss and said input shaft of the potentiometer.

9. An assembly according to claim 8 wherein said boss extends out through the window and has a control knob attached thereto.

10. An assembly according to claim 8 or claim 9, wherein said drive means is comprised of spur gears secured on said boss and said potentiometer input shaft.

11. An instrument assembly substantially as hereinbefore described with reference to the accompanying drawings.