GB1565895A

GB1565895A - Electrical indicators

Info

Publication number: GB1565895A
Application number: GB750777A
Authority: GB
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1977-02-22
Filing date: 1977-02-22
Publication date: 1980-04-23
Also published as: JPS53115276A; DE2806728A1; FR2381360A1; FR2381360B1

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRICAL INDICATORS (71) We, SMITHS INDUSTRIES LIMITED, a British Company of Cricklewood, London NW2 6JN, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to electrical indicators.

The present invention is concerned especially with electrical indicators of a kind in which an analogue representation in accordance with the value of an input variable is provided by selective bright-up along a reference scale (whether calibrated or otherwise) of a series of electricallyenergizable light-emitting elements.

Electrical indicators of this latter kind (referred to herein as "of the kind specified") have already been proposed; and in this respect it has been proposed to arrange that only one of the elements is selected for energization at any time, so that bright up occurs at only one point along the scale. The selection of the particular element energized, and thereby of the location along the scale of the bright up, is in this case made in accordance with the value of the input variable such that the displacement of the bright-up point from the scale zero or other datum provides a measure of that value. The indication provided is therefore analogous to that provided by a conventional mechanicalpointer instrument, but with the 'reading' against the scale signified in this case by the bright, energized element rather than by the pointer. Although such an indication may be entirely satisfactory there are circumstances in which it may be indistinct.

These circumstances in which it may be indistinct. These circumstances arise especially where significant accuracy of indication is required against the scale since the width of each element, and therefore its visual distinguishability when energized, is then necessarily limited.

The problem of ensuring adequate visual distinguishability can be over come by arranging that instead of energizing just the one element, all the other elements of the series up to that element are energized also.

The indication provided under this mode of operation is comparable with that provided by a conventional thermometer, the 'reading' in this case being taken by reference to the location against the scale of the readily distinguishable interface between the energized, bright elements and the unenergized, dark elements. However a very substantial increase in electrical-power dissipation in the indicator is in general required for this mode of operation, and this can present an electrical-supply or operating-temperature problem, or both.

Such problems become especially relevant where a large number of indicators are required to be operated together.

It is one of the objects of the present invention to provide an electrical indicator of the kind specified that enables adequate visual distinguishability to be achieved without the requirement for very substantial increase in electrical-power dissipation.

According to one aspect of the present invention there is provided an electrical indicator in which an analogue representation in accordance with the value of an input variable is provided by selective bright-up along a reference scale of a series of electrically-energizable light-emitting elements, wherein it is arranged that a predetermined plurality of consecutive elements of said series are energized so as to provide bright-up throughout only a correspondingly limited region of said series, the particular elements energized, and thereby the particular region involved and its displacement relative to a scale datum, being dependent on said value, and wherein it is arranged that the degree of bright-up varies along said region.

The fact that bright up is provided throughout a region embracing a plurality of light-emitting elements, readily enables adequate distinguishability to be achieved with the electrical indicator of the present invention. Because the region is of a limited extent, power dissipation can however be kept low, and the variation in the degree of bright up within the said region may be such that only one of the elements is fully energized to signify the appropriate location for the 'reading' against the scale. This one fully energized element may be the element which in the relevant region is furthest from (or nearest to) the scale zero or other datum: alternatively, the central (or some other intermediate) element of the region may be involved. Whatever the case, other elements of the region may be energized such that they are all of the same, lesser brightness or, alternatively, such that the brightness decreases progressively through the region away from the brightest element.

An electrical indicator in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of the electrical indicator; Figure 2 illustrates the form of display provided by the indicator of Figure 1; Figures 3 to 6 serve to illustrate to enlarged scale, modifications of the indicator of Figures 1 and 2; and Figure 7 is a graph showing the variation in brightness over a region of the display of Figure 6.

Referring to Figures 1 and 2, a multiplicity of light-emitting diodes or elements 1 are mounted side by side and in abutment one with the other, throughout the length of a straight, calibrated scale 2 of the indicator.

Only three of the series of elements 1 are, in this example, energized at any time so that there is bright-up against the scale 2 throughout only the limited region -- desig- nated in Figure 2 as region R - occupied by the three. The particular set of three elements 1', 1" and 1"', of the series energized, and thereby the particular region R of the scale 2 involved, is dependent on the value of the variable parameter to be indicated. In this respect the value of the input variable as signalled to the indicator from some external source, such as for example source 3 illustrated in Figure 1, determines the displacement along the scale 2 from the scale zero-datum of the bright region R.

More particularly the location along the scale 2 of the central element 1" of the set of three provides a measure, and thereby a 'reading', of the signalled value.

As illustrated in Figure 2, the central element 1" is distinguished from the other two elements 1' and 1"' of the region R by its increased brightness. The brighter element 1" accordingly defines a narrow 'pointer' against the scale 2 enabling accurate reading of the indicated variable to be made. The other two, less-bright elements 1' and 1"' of the set, one to each side of the central element 1", extend the area of brightness and in this manner enhance the visual distinguishability of the indication provided as compared with what would obtain if just the single element 1" were energized. Furthermore, because only three elements 1 are energized at any time the electrical-poza dissipation is substantially reduced as coi wared with what in general would apply if a 'thermometer-type' display - requiring energization of all elements 1 along the scale 2 from the zero-datum up to an including the element 1" (but not the element 1 were to be used. In addition, the electrical-power dissipation of the display is in general the same for all values (except those close to the zero-datum and those close to the full-scale reading) of the input parameter whereas, if a 'thermometertype' display were used, this dissipation would increase with increasing values of the input parameter as correspondingly more elements were energized.

Referring more particularly to Figure 1, the three light-emitting elements 1 that are to be energized in accordance with the value of the parameter signalled from the source 3, are selected under control of a multi-stage shift-register 4. The series of elements 1 along the scale 2 are individually associated with successive stages 5 of the shift register 4, and energization of any element 1 in the series is dependent on whether the stage 5 associated therewith contains 'ONE' or 'ZERO'. More particularly, only three consecutive stages 5 of the register 4 contain 'ONE', and these three 'ONE'-containing stages are shifted up or down in location throughout the register 4 under control of a shift-unit 6. The unit 6 is responsive to the input signal from the source 3 to locate the three-'ONE's pattern in the stages, 5', 5" and 5"', associated with the respective light-emitting elements 1', and 1" and 1"', appropriate to indication as illustrated in Figure 2, of the signalled value.

Each light-emitting element 1 has its own individual energizing circuit that comprises a diode 7 and transistor switch 8 connected in series with the respective element 1. The switches 8 each include two transistors 9 and 10 that have their emitter-collector current paths connected, via equal resistors 11 and 12 respectively, in shunt with one another. The emitter-collector path of the transistor 9 of the switch 8 is conductive to pass current to energize the respective lightemitting element 1 only if the particular stage 5 of the register 4 associated with that element 2, contains 'ONE'. More particularly an individual gate 13 is responsive to the condition in which the stage 5 contains 'ONE' to pass pulses (having a nominal repetition frequency of I kHz) from a common pulse-supply source 14 to the base electrode of the transistor 9, so as thereby to supply current pulses to the element 1. Energization of the element 1 in this way is supplemented by corresponding current pulses supplied via the emittercollector path of the transistor 10 if the immediately preceding and succeeding stages 5 both also contain 'ONE'. In the latter event an individual gate 15 connected to these two stages 5 is enabled to pass the pulses from the source 14 to the base electrode of the transistor 10, and thereby double the magnitude of current supplied to the individual element 1.

Thus with the example referred to above, where the stages 5', 5" and 5"' associated with the elements 1', 1" and 1"' all contain 'ONE', the gates 13', 13" and 13"' connected to those stages pass pulses from the source 14 to the transistors 9 of their associated switches 8', 8" and 8"'. Furthermore, the gate 15" is responsive to the condition in which the stages 5' and 5"' both contain 'ONE', to pass the same pulses to the transistor 10 of the switch 8". These pulses are not passed by gate 15' or gate 15"' since although the stage 5" contains 'ONE' the other stage 5 to which that gate is connected contains 'ZERO'. Thus although the three elements 1', 1" and 1"' are energized to emit light, via the transistors 9 of their respective switches 8, it is only the central element 1" of the three that is also energized via the transistor 10 of its switch 8, to provide the maximum brightness of emitted light.

The general level of brightness of the display provided by the energized three elements 1 of the indicator may be readily regulated by varying the repetition frequency of the pulses supplied from the source 14.

Although the indicator described above with reference to Figures 1 and 2 has a straight scale, the light-emitting elements 1 may alternatively be arranged in an arc or circle around a correspondingly arcuate or circular scale 22, as illustrated in Figure 3.

Furthermore, other display modes may be utilized as illustrated in Figures 4, 5 and 6, the implementation of such different modes merely requiring appropriate changes in the gating-logic associated with the switches 8 and their control from the shift register 4.

Referring to Figure 4, four elements I are in this case energized at the same time, the two elements 1' and 1" furthermost from the zero-datum of the scale 1 being energized to the maximum degree of brightness whereas the other two elements 1"' and 1"" are energized to the lesser degree. A four 'ONE's pattern is in this case used in the register 4, and the display produced is comparable with a 'thermometer-type' display. In the latter respect, reading is taken from the interface between the furthermost element, 1', and the dark region beyond it.

More than the four light-emitting elements 1 may be energized at any time and in this respect Figure 5 illustrates an extension of the arrangement of Figure 4 in which a further pair of elements 1 are energized but at a reduced degree of brightness with respect to the other two pairs of elements. This is achieved by providing for three possible degrees of energization-brightness utilizing, say, a further transistor and resistor connected in shunt with the transistors 9 and 10 in each switch 8, and extending both the gatinglogic and the 'ONE's-pattern in the register 4, appropriately.

The gradual decrease in the brightness of the elements away from the reading interface, as achieved more especially in the case of the indicator-display of Figure 5, can be readily extended further to give a more pronounced 'comet-tail' appearance directing the eye towards the interface.

The forms of displays described with reference to Figures 4 and 5 suffer from the disadvantage that, as the value to be indicated increases, the next element in the display is brightened suddenly, in a fashion which can be visually distracting to an observer. If the value to be indicated is oscillating slowly then this can cause a particularly distracting winking of the element furthermost from the zero-datum.

This effect can be reduced in the display shown in Figure 6. In this display, when the value of the parameter to be indicated corresponds exactly with the element n, this element will be brightened to the greatest degree and the adjacent element n+l, above element n, will remain unbrightened, as in the displays of Figures 4 and 5. However, if the value of the parameter rises to a level lying between those levels corresponding respectively with the elements n and n+l then, instead of element n+l remaining unbrightened, as in the previous displays, it is partially brightened (as shown in Figure 6) in accordance with the degree to which the parameter overlaps this element.

The brightness of the element n+l is most conveniently controlled in a step-by-step manner as shown in Figure 7. The graph in Figure 7 shows the way in which the brightness of each element of the display in Figure 6 changes as the value of the parameter to be indicated increases. The display is of the 'comet-tai!' type having its leading two elements n and n-I of the same brightness and its seven trailing elements n-2 to n-8 at successively lower brightness levels. As the value of the parameter increases, it can be seen that the element n+l in front of the leading element n is brightened to a level corresponding to that of element n-8 and that, as the parameter further increases, the element n+l is brightened in a step-by-step manner to successively brighter levels corresponding with those levels applied to the trailing elements n-8 to n-2. The brightness of element n+l rises until it is the same as the brightness of element n, and therefore becomes the new leading element, at which point the brightness of elements n-I to n-8 are correspondingly reduced as shown.

Increase in the value of the parameter, therefore, is represented on the display by a relatively gradual increase in brightness of the element above the leading element rather than the previous sudden brightening. Similarly, decrease in the value of the parameter causes a corresponding gradual reduction in brightness of the topmost element; in this way, winking of this element is avoided upon oscillatory fluctuations in the value of the parameter.

WHAT WE CLAIM IS: 1. An electrical indicator in which an analogue representation in accordance with the value of an input variable is provided by selective bright-up along a reference scale of a series of electrically-energizable lightemitting elements, wherein it is arranged that a predetermined plurality of consecutive elements of said series are energized so as to provide bright-up throughout only a correspondingly limited region of said series, the particular elements energized, and thereby the particular region involved and its displacement relative to a scale datum, being dependent on said value, and wherein it is arranged that the degree of bright-up varies along said region.

2. An electrical indicator according to Claim 1, wherein a central element within said region is arranged to be energized to one bright-up level and elements in said region to either side of said central element are arranged to be energized to one or more lower bright-up levels.

3. An electrical indicator according to Claim 1, wherein an outermost element of said region is arranged to be energized to one bright-up level and elements in said region to one side or said outer-most element are arranged to be energized to one or more lower bright-up levels.

4. An electrical indicator according to Claim 3, wherein some at least of the elements in said region are arranged to be energized such that adjacent elements are brighted-up to successively lower levels away from said outermost element.

5. An electrical indicator according to Claim 1, wherein an outermost element of said region is arranged to be energized in accordance with the extent to which the value of the input variable occupies said outermost element.

6. An electrical indicator according to Claim 5, wherein each of the elements within a part at least of said region to one side of said outermost element are arranged to be energized to a different one of a predetermined number of discrete levels such that the brightness of the part of said region decreases progressively along its length.

7. An electrical indicator according to Claim 6, wherein said outermost element is arranged to be energized at one of said predetermined number of discrete levels in accordance with the extent to which the value of the input variable occupies said outermost element.

8. An electrical indicator according to any one of the preceding claims, wherein each of said elements includes a lightemitting diode.

9. An electrical indicator according to any one of the preceding claims wherein each of said elements is arranged to be energized by a pulsed electrical input.

10. An electrical indicator according to any one of the preceding claims wherein each of said elements has associated therewith a respective energizing circuit, each said energizing circuit including a serial-connected switching circuit, and wherein each said switching circuit includes first switching means connected in series with a first resistor, and second switching means connected in series with a second resistor, the said first switching means and said first resistor being connected in parallel with the said second switching means and said second resistor such that each said resistor can be switched into or out of said energizing circuit so as thereby to control energization of said element.

11. An electrical indicator according to Claim 10 wherein said switching means includes a transistor.

12. An electrical indicator according to Claim 10 or Claim 11 including first and second gate means associated respectively with each said first and second switching means, a second gate means associated with one switching circuit being connected to receive signals as supplied to an input of first gate means associated with another switching circuit such that said second gate means is responsive to control switching of its associated switching means in accordance with the existence of a predetermined input signal to said first gate means.

13. An electrical indicator according to any one of the preceding claims including a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. to n-8 at successively lower brightness levels. As the value of the parameter increases, it can be seen that the element n+l in front of the leading element n is brightened to a level corresponding to that of element n-8 and that, as the parameter further increases, the element n+l is brightened in a step-by-step manner to successively brighter levels corresponding with those levels applied to the trailing elements n-8 to n-2. The brightness of element n+l rises until it is the same as the brightness of element n, and therefore becomes the new leading element, at which point the brightness of elements n-I to n-8 are correspondingly reduced as shown. Increase in the value of the parameter, therefore, is represented on the display by a relatively gradual increase in brightness of the element above the leading element rather than the previous sudden brightening. Similarly, decrease in the value of the parameter causes a corresponding gradual reduction in brightness of the topmost element; in this way, winking of this element is avoided upon oscillatory fluctuations in the value of the parameter. WHAT WE CLAIM IS:

1. An electrical indicator in which an analogue representation in accordance with the value of an input variable is provided by selective bright-up along a reference scale of a series of electrically-energizable lightemitting elements, wherein it is arranged that a predetermined plurality of consecutive elements of said series are energized so as to provide bright-up throughout only a correspondingly limited region of said series, the particular elements energized, and thereby the particular region involved and its displacement relative to a scale datum, being dependent on said value, and wherein it is arranged that the degree of bright-up varies along said region.

shift register for storing at a plurality of locations therein signals representative of elements to be energized, and means for displacing said signals within said shift register in accordance with the value of the said input variable.

14. An electrical indicator according to Claim 12 and Claim 13, wherein said gate means are arranged to receive at an input thereof signals output from said shift register.

15. An electrical indicator substantially as hereinbefore described with reference to Figure 1 and any one of Figures 2 to 6.