GB1604625A - Digital barometers - Google Patents

Description

(54) DIGITAL BAROMETERS (71) I, DENNIS CHARLES STAN LEY GORRINGE, a British Subject of 4 Carlyle Road, Staines, in the County of Middlesex, TW18 2PU, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is concerned with arrangements for the provision of an output indication which represents the angular position of an angularly rotatable shaft. The invention is particularly, but not exclusively, applicable to barometric instruments, for example of the aneroid type.

A typical known barometric instrument of the aneroid type comprises at least one evacuated flexible capsule of which at least a portion expands and contracts in, response to changes in the magnitude of the atmospheric pressure, that expansion and contraction being converted, by means of a mechanism, into angular rotation of an angularly rotatable output shaft upon which is mounted an indicating needle (pointer) for movement over a calibrated, circularly extending scale, to thereby give a continuous output-indication of analogue form. The power and the energy provided by the expansion and the contraction of the capsule(s), and available to drive the output shaft, are relatively small.

According to the invention there is provided a barometric instrument comprising an aneroid-barometer mechanism having an angularly-rotatable output shaft of which the angular position is a measure of the atmospheric pressure, an encoding disc carried by said shaft and arranged to differently intercept beams of electromagnetic radiation ac cording to said angular position to thereby provide for the generation of electrical sig nals representing, in a binary coded form, said angular position, and main display means responsive to said electrical signals to display the atmospheric pressure-reading in digital form as a sequence of decimal digits.

Conveniently, said main display means comprises at least one electro-optical device.

In one arrangement, the encoding disc is arranged for the direct generation of said electrical signals in a binary-coded-decimal coded form. In an alternative arrangement, the encoding disc is arranged for the generation of said electrical signals in the basic binary coded form, the instrument comprising also converter or translator means arranged to convert or translate said electrical signals into a binary-coded-decimal coded form, in which latter form the electrical signals are employed to control said main display means.

Conveniently, said electrical signals are provided in parallel, existing form.

Said radiation is conveniently infra-red radiation; or, it may be visible light, or ultra-violet radiation.

Conveniently, said encoding disc has an array of encoding elements of which some are of a first type and some are of a second type as regards their action upon said beams of radiation.

Conveniently, the instrument includes further display means arranged to alternatively display any one of three indications, for example of three different characters or of two different characters and an absence of indication and means responsive to the magnitude of the atmospheric pressure to cause different ones of those indications to be displayed respectively according as that pressure is increasing, is steady, or is decreasing.

The invention may be put into practice in a number of ways, but one specific em embodiment and a number of modifications thereof will now be described with reference to the accompanying drawings in which: Figure 1 is a block diagram illustrating one arrangement of an aneroid barometer in strument, arranged to display its pressurereading in digital form as a single corresponding sequence of decimal digits, together with an optionally provided additional external unit; Figure 2 is a front elevation, partly broken away, of the barometer of Figure 1; Figures 3A and 3B are incomplete plan views of the encoding disc used in the barometer of Figures 1 and 2 and relate respectively to the barometer arranged to read in millibars and in inches of mercury; Figures 4A and 4B are code rasters, illustrating respectively the basis of the coding arrangements used for the encoding discs of Figures 3A and 3B; Figure 5A is similar to Figures 3A and 3B, but shows the four sensing-head mounting members in mutually angularly-displaced relationship relatively to the encoding disc; Figure 5B shows the relative forms of the four sensing-head mounting members; Figure 6 is a longitudinal section of one of the sensing-head mounting members, taken along the line VI-VI of Figure 5A; Figure 7 is similar to Figure 4A, but relates to a modification of the invention; Figure 8 is similar to Figure 3A, but relates to the modification of the invention, and Figure 8A is similar to Figure 5B, but relates to the modification of the invention.

Referring to Figure 1, the normal, angularly rotatable output shaft 1 of a conventional aneroid barometer instrument 2 of generally known form is arranged to carry, instead of the usual indicating needle (pointer), an encoding disc 3 which acts to differently intercept a plurality of beams of infra-red radiation (see below) according to the angular position of the shaft 1. Thereby (see below), infra-red radiation-sensitive devices 4 provided for the beams, generate in parallel coexisting form a corresponding set of electrical signals 5 which represent, in the basic binary code form, the angular position of the shaft 1 and thereby the pressure-reading of the instrument 2.

The disc 3 is so arranged (see below) that the set 5 of electrical signals represents, in the basic binary code form the pressurereading in millibars. In a modification, the disc 3 is replaced by a similar disc 3' so arranged (see below) that the set 5 of electrical signals represents, in the basic binary code form, the pressure reading in inches of mercury.

In the arrangement of Figure 1, the numerical value of the instantaneous pressure-reading is displayed, as a set of four decimal digits, by a set of four low-power electro optical display devices 6, 7, 8 and 9 of known kind, each of which may be a so-called num erical indicator of the seven-segment type and conveniently of the liquid-crystal type.

Such a set of display devices requires tl be electrically controlled by a set 10 of electrical signals which are in parallel, coexisting form and which represent, in the binary coded-decimal code form, the angular posi tion of the shaft 1 and thereby the pressurereading of the instrument 2. The apparatus of Figure 1 therefore includes a converter (translator) 11 arranged to convert (translate) the set 5 of electrical signals in the basic binary code form, into the set 10 of electrical signals in the binary-coded-decimal code form and suitable for controlling the display devices 6-9.

A suitable three-position switch 12 may be provided at the input to the display devices 6-9 inclusive, whereby those devices may be arranged to display continuously, or may be switched off, or may be arranged to display during the period for which the switch is depressed to a temporary position.

Referring now to Figure 2, the barometer is enclosed within a casing having upper and lower halves 17 and 18 respectively, the casing being perforated for the provision of (suitably four) support rods of which two are indicated at 19 and 20, the support rods being threaded and being provided with domed nuts 21 by means of which the co-assembly of support rods and casing can be effected. The casing is provided with rubber feet 16.

A frame bottom-plate 22 is supported, within the casing, upon the support rods, by means of nuts 23. A frame top-plate 24 is supported, parallel to the bottom-plate 22, upon the support rods 19 and auxiliary support rods (of which one is indicated at 25), again by means of nuts.

The conventional aneroid barometer instrument 2 of generally known form is indicated in Figure 2 and comprises a single evacuated flexible capsule 26, a generally U-shaped contrd spring 27, and a mechanism indicated generally at 28 and arranged to cause angular rotation of the angularly rotatable output shaft 1 in accordance with the expansion and contraction of the capsule 26 and thereby according to the magnitude of the atmospheric pressure. This assembly, of generally known form, is secured to the frame bottomplate 22 by way of an adjustment base-plate 30.

The output shaft 1 is arranged to carry, near its outer end, the encoding disc 3 which is embraced by four relatively-angularlydisplaced, generally U-shaped bodies, in the form of blocks, which act as sensing-head mounting members 35, 36, 37 and 38 (see Figures 2, 5A, 5B and 6).

Each sensing-head mounting member has its lower limb 39 (Figure 6) bored at three spaced positions 41, 42 and 43 to respectively receive three infra-red radiation sources (not shown) which are respectively arranged to project their radiation towards three infrared detecting devices (not shown) respectively received in three corresponding spaced bores 44, 45 and 46 formed in the upper lirnb 40.

The bores 41-46 inclusive (Figure 6) are extended at their inner ends by small-diameter bores 141-146 respectively, which act as radiation guides for the infra-red radiation.

The base of each U-shaped sensing-head mounting member has a side extension 47 (Figure 6), and (Figure 2) the four sensinghead mounting members are secured to an adjustment plate 50 by means of countersunk screws of which one is indicated at 51, the adjustment plate 50 being adjustably secured to the frame top-plate 24 by means of bolts 48 and nuts 49.

In the arrangement indicated in Figures 6 and 5A, the total of twelve radiation-sources are thus all mounted at one side of the disc 3 (3'), while the corresponding twelve detecting devices are all mounted at the relatively opposite side of that disc. Obviously, any other convenient arrangement may be employed.

As mentioned above, the disc 3 (Figures 1 and 2) is so arranged that the set 5 of electrical signals represents, in the basic binary code form, the pressure-reading in millibars.

Assuming that the instrument range, for a 3600 rotation of the output shaft 1, is 917 to 1060 millibars, and assuming that the instrument resolution is to be one millibar, then the disc 3 is regarded as divided into a corresponding one hundred and forty-four equal sectors 56 (Figure 3A), each of which corresponds to a pressure-range of one millibar. Further, in order to express pressures of 917-1060 millibars in the basic binary code form, eleven binary digits are required (i.e. powers of 21 down to 20, inclusive).

The disc 3 (Figure 3A) is thus regarded as provided with a set of eleven corresponding concentric tracks 57, each in the form of a circular annulus. The intersection of the sectors 56 with the tracks 57 defines the encoding elements 58 of the encoding disc 3: thus, within each sector SC of the disc 3, there is located a set of eleven arcuate encoding elements 58 which are radially disposed. (For a purpose to be discussed below, an additional radially innermost twelfth track 57A is also provided and provides, within each sector 56 of the disc 3, a further twelfth encoding element 58A).

Conveniently, the disc 3, as a whole, is made of material which is suitably transmissive (i.e. translucent or transparent) to the infra-red radiation emitted by the radiation sources (not shown) located within the bores 41, 42, and 43 (Figure 6). Thus, the disc 3 is conveniently made of Perspex (Registered Trade Mark). Thus, those encoding elements 58 and 58A of the disc 3 which are left plain, will allow the transmission of such infra-red radiation from the sources to the corresponding detecting devices (not shown) located within the bores 44, 45 and 46 (Figure 6). According to the code (see below), the remainder of the encoding elements 58 and 58A are rendered non-transmissive (i.e. opaque) to the infra-red radiation, by any suitable means: conveniently, by a generally known photographic type of process, suitable material is deposited upon the disc 3 so as to form these non-transmissive encoding elements.

Figure 4A shows the code raster for the disc 3 (Figures 1, 3A). This is a simple, direct translation into the basic binary code, so that, for example, pressures of 1060 and of 917 millibars are expressed as 10000100100 and 01110010101 respectively-the blackedin portions of Figure 4A representing a binary 0 and the remaining clear portions representing a binary 1.

Since the diameter of the disc 3 is to be kept as small as convenient, there is a limitation upon the effective physical size of the infra-red radiation-sources and detecting devices. To provide more space for the latter, different sets (each of such a source and such a detecting device) may conveniently be relatively angularly displaced. In one convenient arrangement, indicated in Figures 5A and 5B, twelve such sets are divided into four angularly-separated groups: thus, the Ushaped sensing-head mounting member 35 is provided with three such sets corresponding to the first, the fifth and the ninth of the twelve tracks 57, the sensing-head mounting member 36 is provided with three such sets corresponding to the second, the sixth and the tenth of the twelve tracks 57, and so on (Figure 5B) In the arrangement shown in Figure 5A, the sensing-head mounting members 35 and 38 are located diametrically opposite to one another, while the sensinghead mounting members 36 and 37 are angularly displaced by 400 respectively from the sensing-head mounting members 35 and 38 and in relatively opposite directions.

In view of this angular separation of the sensing-head mounting members 35-38, the code raster of Figure 4A cannot be straightforwardly applied to the encoding disc 3, but must be appropriately modified to take account of the relative angular separations of those mounting members. Thus, for example, with the arrangement of sensing-head mounting members shown in Figure 5A, the actual raster applied to the disc 3 will have the form shown (in part) in Figure 3A.

As mentioned above, the alternative disc 3' (Figure 1) is so arranged that the set 5 of electrical signals represents, in the basic binary code form, the pressure-reading in inches of mercury. Assuming that the instrument range, for a 3600 rotation of the output shaft 1, is 27.00 to 31.31 inches of mercury, and assuming that the instrument resolution is to be 0.03 inches of mercury, then the disc 3' is regarded as divided into a corresponding one hundred and forty-four equal sectors 56' figure 3B), each of which corresponds to a pressure-range of 0.03 inches of mercury. Further, in order to express numerals in the range 2700 to 3131 in the basic binary code form, twelve binary digits are required (i.e. powers of 211 down to 20, inclusive). The disc 3' is thus regarded as provided with a set of twelve corresponding concentric tracks 57', each in the form of a circular annulus. The intersection of the sectors 56' with the tracks 57' defines the encoding elements 58' of the disc 3': thus, within each sector 56' of the disc 3', there is located a set of twelve arcuate encoding elements 58' which are radially disposed.

Figure 4B shows the code raster for the disc 3' (Figures 1, 3B). This, again, is a simple, direct translation into the basic binary code. If, as described above, the sensinghead mounting members are relatively angularly displaced, for example as in Figure SA, then, again the code raster of Figure 4B must be appropriately modified to take account of that displacement: for example, with the arrangement of sensing-head mounting members shown in Figure 5A, the actual raster applied to the disc 3' will have the form shown in Figure 3B.

The basic operation of the specific embodiment will now be described, with particular reference to Figure 1. The output shaft 1 of the conventional aneroid barometer instrument 2 rotates in accordance with the magnitude of the prevailing atmospheric pressure, and thereby rotates the encoding disc 3 (or 3') accordingly.

The disc 3 (or 3') is arranged to lie in the path of twelve similar beams of infra-red radiation, the beams being mutually displaced, radially of the disc, and being also conveniently (see above) mutually angularly displaced, and the beams conveniently being perpendicular (as shown) to the surface of the disc.

The arrangement is basically such that, for a given angular position of the disc 3 (3'), each beam co-operates with a corresponding one of the tracks 57 and 57A (or 57') and is intercepted by an encoding element, 58 or 58A (Figure 3A), (or 58', Figure 3B), of the disc. According as that encoding element is transmissive to, or is non-transmissive to, the infra-red radiation beam, so that beam is either transmitted through the disc, or is not so transmitted.

As described above, each infra-red radiation beam is generated by an infra-red radiation source (not shown) located within a bore (e.g. 41, Figure 6) in a sensing-head mounting member (e.g. 35). The transmission of the beam through the disc, is detected by a corresponding infra-red detecting device (not shown) located within a bore (e.g. 44, Figure 6) in the sensing-head mounting member, which detecting device accordingly pro vides the relevant one of the set 5 of electrical signals (Figure 1) which represent, in the basic binary code form, the angular position of the shaft 1 and thereby the pressurereading of the instrument 2.

The arrangement is thus such that, the electrical-signal output of each of the infrared detecting devices represents, in the basic binary form, either a digital 1 or a digital 0 according as the radiation beam in question is, or is not, transmitted through the relevant encoding element 58 (or 58') of the disc 3 or (3').

Each infra-red radiation beam is thus generated by a corresponding radiation source and is sensed by a corresponding detecting device. Sets, each comprising such a radiation source and such a detecting device, each of suitably small physical size, are commercially available, e.g. as a so-called "opto coupler and isolator" comprising a galliumarsenide L.E.D. (lightsmitting diode) infrared source together with an NPN silicon photo-transistor (detecting device).

The U-shaped sensing-head mounting members are selected to be suitably nontransmissive to the infra-red radiation employed, in order to avoid interference between the twelve radiation-beams, and may conveniently be blocks made of metal such as aluminium.

The converter (translator) 11 is commercially available, and is conveniently in printedcircuit-board form.

As previously explained, the converter (translator) 11 converts (translates) the set 5 of electrical signals in the basic binary code form, into the set 10 of electrical signals in the binarycoded-decimal code form and suitable for controlling the display devices 6-9. Thereby, the display devices 6-9 display the numerical value of the instantaneous pressure-reading, as a set of four decimal digits.

It is to be understood that the beams are not necessarily of infra-red radiation, but may be beams of other forms of electromagnetic radiation, particularly but not exclusively beams of visible light or of ultraviolet light. In such modified arrangements, different radiation sources and detecting devices may be employed, in a manner obvious to a man skilled in the art: the disc 3 (3') may also be modified accordingly in such cases. It is also contemplated that the encoding elements 58 (58') of the disc 3 (3') might, in a modification, be arranged instead to reflect, or fail to reflect, the intercepted radiation beams: in such case, the necessary arrangements will be obvious to a man skilled in the art, in particular that in such case the radiation sources and detecting devices will all be located opposite the same one face of the disc 3 (3'). In a further modification, the encoding elements 58 (58') of the disc 3 (3') might, instead, be formed by the presence, or the absence, of corres ponding apertures formed in the disc, the material of the disc being in this case selected to be non-transmissive to the radiation employed.

Referring to Figure 1, the "mechanical setting adjustment" 4A comprises correct orientation of the sensing-head mounting members 35-38, relatively to the encoding disc 3 (3'), and is basically effected with the aid of the adjustment plate 50 (Figure 2).

Where the specific embodiment is located at a physical position above normal groundlevel, for example on a high mountain, it may be desired to introduce a corresponding off-set into the pressure-indication, so that the pressure-reading obtained is the corresponding reading at normal ground-level. As indicated in Figure 1 at 11A, such off-set may conveniently be effected by appropriate modification of the output of the converter (translator) 11, by manually-adjustable appropriate known electronic circuitry.

The specific embodiment also includes a further low-power display device 60 (Figure 1) similar to the devices 6-9 but arranged to display either "+", "0" (or no indication), or "--" respectively according as the magnitude of the atmospheric pressure is increasing, is steady, or is decreasing.

The display device 60 is controlled by a pressure sense discriminator 61 which comprises a digital store, of known general form, adapted at selected or preselected samplingtimes (see below) to store the instantaneouslyexisting set 10 of electrical signals which, in the binary-coded-decimal code form, and as the output of the converter (translator) 11, represent the instantaneous pressure-reading.

The discriminator 61 also comprises a comparator of known general form, arranged to compare the content of the digital store with the existing output of the converter (translator) 11 and, in response, to cause the appropriate display (see above) by the display device 60.

The discriminator 61 further comprises an electronic timer circuit 61A of known general form, arranged to automatically re-set the content of the digital store, after the expiry of a preselected time-period (e.g. 12 hours) variably preselected by means of an appro priately calibrated manual control knob 61B.

The timer circuit 61A is associated with over-riding re-set arrangements. Thus, firstly, the content of the digital store can be re-set at any selected time, by actuation of a manual re-set switch 62, so that the content of the digital store is immediately updated to ac cord with the magnitude of the existing atmospheric-pressure. Secondly, the discri minator 61 also includes a binary counter arranged to sense changes in the output of the comparator: if the change of that out put corresponds (see 63, Figure 1) to a posi tive or negative atmospheric-pressure change of 1 millibar (i.e. I 0.03 inches of mercury), then the resulting output of the counter is arranged to automatically re-set the content of the digital store, i.e. to automatically update the content of that store to accord with the magnitude of the existing atmosphericpressure.

Electric power for the operation of the apparatus so far described, is provided by a dry battery 66 (Figure 2), which may be of the re-chargeable type. The converter (translator) 11, control circuitry 11A, power supply circuitry, and discriminator 61 and associated circuitry, are provided on printed circuit boards 67 (Figure 2) which may con veniently incorporate large-scale integrated circuits (L.S.I.s).

It will be obvious to the man skilled in the art, that many modifications may be made to the arrangements described, within the scope of the appended Claims and particularly, but not exclusively, in respect of the electronic arrangements.

In particular, the encoding disc 3 (3') may be arranged to encode directly into the binarycoded-decimal system, i.e. the modified disc is so arranged that the radiation-beam sensing devices (4 Figure 1) generate directly, in parallel co-existing form, the set 10 of electrical signals which represent, in the binary-coded-decimal code form, the angular position of the shaft 1 and thereby the pressure-reading of the instrument 2. In such case, for a fourdigit output display of the pressure-reading, the set 10 of electrical signals comprises sixteen signals, and, correspondingly, the modified disc 3" is (Figure 8) arranged to intercept sixteen radiation-beams, the modified disc having a corresponding sixteen tracks instead of the eleven or twelve tracks 57 or 57' (Figures 3A, 3B). In such case, the converter (translator) 11 is omitted, and the set 10 of electrical signals is sup plied directly (or via known amplification means) to the display devices 6-9. For the modified disc, an appropriate sixteen-track raster can be constructed, as shown in Figure 7 (cf. Figures 4A, 4B): Figure 8 (corresponding to Figure 3A) shows the actual raster (in part) applied to the modified disc 3", for the case where the sensing-head mounting members have the relative angular separations shown in Figure 5A (the sensing-head mounting members in this case having each, however, four sets each of a radiation source and a corresponding radiation detecting device, to correspond to the sixteen tracks, as indicated in Figure 8A).

Referring to Figure 1, the apparatus so far described is conveniently associable, as by appropriate leads, plugs and sockets, with an auxiliary unit 70 connectable by leads to an external power-source (providing more power than can the dry battery 66, Figure 2). The unit 70 includes an indicator unit 71 which comprises circuitry, of generally known form, for causing illumination of red, white and green lamps (by the external power-source) respectively according as the magnitude of the atmospheric pressure is decreasing, is steady, or is increasing, as indicated by the output of the discriminator 61 as described above.

The unit 70 further includes an alarm unit 72 arranged to give an audible alarm, and also to cause the red lamp of the unit 71 to repeatedly flash, if the atmospheric pressure is falling at a rate greater than a preselected rate. The alarm unit 72 is arranged to be actuated in response to the simultaneous occurrence of (A) an output signal from the discriminator 61 which indicates that the atmospheric pressure is falling (and which has caused illumination of the red lamp of the unit 71), and (B) a preselected change, within a variable preselected time, of the count represented by the set 10 of electrical signals.

It will be recalled that the disc 3 (Figures 1, 2, 3A) has a spare track 57A (Figure 3A) which comprises the encoding elements 58A.

Alternate ones of these encoding elements 58A may be left transmissive, and made non-transmissive, to the radiation beam associated with the track 57A: thereby, the electrical output of the radiation-detecting device associated with that beam will, in effect, as the disc 3 rotates, provide a count of which the rateof-change is an indication of the rate-ofchange of the magnitude of the atmospheric pressure, and which count can therefore be arranged, by generally known means not shown to establish the condition (B) referred to in the preceding paragraph.

In one modification of the invention, the display devices 6-9 inclusive and 60 may be located relatively remotely from the barometer 2 proper, or alternatively their indica tions may be duplicated by similar apparatus located relatively remotely from the baro meter 2 proper. It is clear that this may be easily effected, for example by supplying the set 10 of electrical signals and the output of the discriminator 61, to the remote location by means of appropriate circuitry (not shown).

WHAT I CLAIM IS: 1. A barometric instrument comprising an aneroid-barometer mechanism having an angularly-rotatable output shaft of which the angular position is a measure of the atmospheric pressure, an encoding disc carried by said shaft and arranged to differently intercept beams of electromagnetic radiation according to said angular position to thereby provide for the generation of electrical signals representing, in a binary coded form, said angular position, and main display means responsive to said electrical signals to display the atmospheric pressure-reading in digital form as a sequence of decimal digits.

2. An instrument according to Claim 1, wherein said main display means comprises at least one electro-optical device.

3. An instrument according to Claim 1 or Claim 2, wherein th

Claims (16)

**WARNING** start of CLMS field may overlap end of DESC **. comprises circuitry, of generally known form, for causing illumination of red, white and green lamps (by the external power-source) respectively according as the magnitude of the atmospheric pressure is decreasing, is steady, or is increasing, as indicated by the output of the discriminator 61 as described above. The unit 70 further includes an alarm unit 72 arranged to give an audible alarm, and also to cause the red lamp of the unit 71 to repeatedly flash, if the atmospheric pressure is falling at a rate greater than a preselected rate. The alarm unit 72 is arranged to be actuated in response to the simultaneous occurrence of (A) an output signal from the discriminator 61 which indicates that the atmospheric pressure is falling (and which has caused illumination of the red lamp of the unit 71), and (B) a preselected change, within a variable preselected time, of the count represented by the set 10 of electrical signals. It will be recalled that the disc 3 (Figures 1, 2, 3A) has a spare track 57A (Figure 3A) which comprises the encoding elements 58A. Alternate ones of these encoding elements 58A may be left transmissive, and made non-transmissive, to the radiation beam associated with the track 57A: thereby, the electrical output of the radiation-detecting device associated with that beam will, in effect, as the disc 3 rotates, provide a count of which the rateof-change is an indication of the rate-ofchange of the magnitude of the atmospheric pressure, and which count can therefore be arranged, by generally known means not shown to establish the condition (B) referred to in the preceding paragraph. In one modification of the invention, the display devices 6-9 inclusive and 60 may be located relatively remotely from the barometer 2 proper, or alternatively their indica tions may be duplicated by similar apparatus located relatively remotely from the baro meter 2 proper. It is clear that this may be easily effected, for example by supplying the set 10 of electrical signals and the output of the discriminator 61, to the remote location by means of appropriate circuitry (not shown). WHAT I CLAIM IS:

1. A barometric instrument comprising an aneroid-barometer mechanism having an angularly-rotatable output shaft of which the angular position is a measure of the atmospheric pressure, an encoding disc carried by said shaft and arranged to differently intercept beams of electromagnetic radiation according to said angular position to thereby provide for the generation of electrical signals representing, in a binary coded form, said angular position, and main display means responsive to said electrical signals to display the atmospheric pressure-reading in digital form as a sequence of decimal digits.

2. An instrument according to Claim 1, wherein said main display means comprises at least one electro-optical device.

3. An instrument according to Claim 1 or Claim 2, wherein the encoding disc is arranged for the direct generation of said electrical signals in a binary-coded-decimal coded form.

4. An instrument according to Claim 1 or Claim 2, wherein the encoding disc is arranged for the generation of said electrical signals in the basic binary coded form, the instrument comprising also converter or translator means arranged to convert or translate said electrical signals into a binarycodeddecimal coded form, in which latter form the electrical signals are employed to control said main display means.

5. An instrument according to any preceding Claim, wherein said electrical signals are provided in parallel, coexisting form.

6. An instrument cccording to any preceding Claim, wherein said radiation is infra-red radiation.

7. An instrument according to any one of Claims 1-5, wherein said radiation is visible light, or ultra-violet radiation.

8. An instrument according to any preceding Claim, wherein said encoding disc has an array of encoding elements of which some are of a first type and some are of a second type as regards their action upon said beams of radiation.

9. An instrument according to any preceding Claim, wherein said beams are generated by stationary radiation-emitting sources, and said electrical signals are generated by stationary radiation-sensitive devices.

10. An instrument according to Claim 8 or Claim 8 and 9, wherein the encoding elements of the first and the second type respectively allow, and prevent, the passage of the said beams through the encoding disc.

11. An instrument according to Claim 8 or Claim 8 and 9, wherein the encoding elements of the first and the second type respectively reflect, and do not reflect, the said beams.

12. An instrument according to any preceding Claim, which includes further display means arranged to alternatively display any one of three indications, for example of three different characters or of two different characters and an absence of indication, and means responsive to the magnitude of the atmospheric pressure to cause different ones of those indications to be displayed respectively according a that pressure is increasing, is steady, or is decreasing.

13. An instrument according to Claim 12, wherein said further display means comprises at least one electro-optical device.

14. An instrument according to Claim 12 or Claims 12 and 13, wherein the said means

responsive to the magnitude of the atmospheric pressure comprises a digital store arranged to store the said electrical signals as supplied to the main display means at a selected or preselected time-instant, comparator means arranged to compare the content of the store with the said electrical signals as presently supplied to the main display means and in response to control the operation of the said further display means, and re-setting means for re-setting the content of the digital store automatically and/or at will.

15. An instrument according to any preceding Claim, in combination with a separate unit operable from an external power-source and comprising alarm means arranged to be automatically operated if the atmospheric pressure is falling at a rate greater than a preselected rate.

16. An aneroid barometric instrument arranged to display the pressure-reading in digital form, substantially as specifically described herein with reference to the accompanying drawings.