Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~38~5~ 5987
OPTICAL SYSTEM FOR AUTOMATIC METER READER
.
This invention.relates to automatic or remote
~éter readers and, in particular, to an optical system
for.reading out meters containing coded, apertured discs.
In the power distribution and. measuri~g art,
5- there i9 a need fo~ a remotely readable meter. In a given
,
l ~: res:idential district, ~or exampLe, each house may have a
.. . ., . , . . . . . . i
:i . . méter for monitoring electriclty~ ga~, and water consump~
; tion, none o~ which m~y be owned by the same corporate
.: entity. M~ltiplying that by the num6er o residences in
.
.. the district, it bec~mes apparent that visually reading
.. every meter adds substantially; to the overhead of the
~. ,.,: . .. , - . . ,
; - . ~ ut~i ty supplying the particular service.
~onsider~ng as a specific example tke electrical
.
- power industry and the familiar watt-hour meter, a number
I . 15 . of mechanisms have been proposed for remotely reading
e~ectrical power consumption, For example, apertured
~ . . . . . .
. discs having a plurality of light sources and a plurality
. . o~ detectors ~or reading out the.rotationaL position o~
each disc has been proposed. Alternatively, it has been
.s~ggested that dLgital pulses proportional to power
consumed be generated and locally counted. Then, upon
suitabl~ command, the count is transmitted to a central
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RD-5987
1038~
station, typically by telephone link.
A difficulty with both of these proposals is
cost. A further difficulty with the first proposal is
the care required in assembling or positioning the optical
elements. A urther d.ifficulty with the second proposal
is that the information cannot be checked visually, i.e.
the system is not fail-safe, wherein fail-safe does not
. mean the power is shut off, rather that the information
~the meter reading) is lost.
As guidelines, the power companies ha~e
suggested that the remote reader have low cost, low
maintenance, and be :Eail sa:Ee. In addition, it is
desirable that the unit be no bulkier than present devices.
In Canadian patent 1,012,609 issued June 21, 1977
and assigned to the assignee of the present invention, a
fail-safe remote meter reading system is disclosed. The
remote meter reading system has a unique coded disc arrange-
ment for encoding the meter reading of a watt-hour meter.
The aperture disc arrangement described therein occupies
very little additional space. Accordingly, it is
desirable that the reading optics be comparably compact.
In view of the foregoing, it is therefore an
object of the present invention to provide an optical
system for reading out a plurality of aperture discs.
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~ ~0380$~3 . RD-5987
Another object of the present invention is to
. provide a compact optical system for use in reading a
:' multit'ude o~ ~hat position indicatorY in a si.ngle'system.
'. ' ' . . . A further object of the present invention is to
5 . provide a low co~t opticaL system for reading apertured
. discs'po~ltions' in a use meter.'
, :, . . ...................................... . .
.. ' . ' 'Another object of the present invention i9 to
;' ' ' provide an'opt.ical ay9tem ~or a remote reader 9ystem
.
, . . . . . . . . .
. ' , , . using', ap~rt,ure discs. ' , '
. A fu~ther ob~ect o~ the present invention is to
,, . , , .. , . :
' .. ' provide a high assembly tolerance optical system for
... . . ..
~ . auto~atic meter .readers. . .'
I: ' ' The foregoing objects are achie~ed in the
:. . . .
present'invention wherein there is provided a single
I5 . . light source, comprising an incandescent lamp, collimating -
opties9 comprisi~g a parabolic reflector, scanned aperture
. ' discs, collecting optics,'co~prising a pair of reflectors
form;ng a folded path optical system, and a photodetect'or.
. ' . A'more complete.understanding of the present
. . invention can be obtained by considering the following
. . ' detailed description in conjunction with the àccompanying
. drawings, in which: ' .
.FIGURE 1 illustrates a preferred embodiment o~
. the optical system in accordance with the present inven-
! 3
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tion. 1 0~ ~ 0 5 8
FIGURE 2 illustrates in perspective a full
. readout system, including the optical system of the
.
present lnvention .
.. .. , . . .
. .A~ illustrated ln FIGURE.l, optical system 10
.. . . ..
:. . . comprises a light source 11 and collimating optics 12
; . .orméd by an annular solid L3 having a parabolic surace
: 14 formed thereon. Parabolic surace L4 i8 sUitAb ly
.. . , , , . ~
. . .sil~er or aluminum coated to pro~ide ~he necessary
LO re1ectance. . . . ~ :
' ' . ' ' , ' ' ' . , .
:` . .Optlcal system 10 further comprises collecting
' . ,
optics LS formed by a solid 16 having first and second
. ~e~lscting sur~ace 17 and 18. Surface 17 is preferably
.
: a parabolic reflector and is also suitably silver or
. . .
aluminum coated. Surface 18 is preferably hyperbolic
.
- and.serves to ~ocus the image of ligh~ source 11 onto
. - ,
; . photodetector l9,-which preferably contains a.semiconduc-
. tor photocell 21~ Reflec~ing surfaces 17 and 18 form a
.
. .folded optical path for the light image from light source
11. The combLnation o a parabolic and hyperbolic
reflector form what is known in the art as Cassegra~nian
optics. Other combinations of primary and secondary
. reflecting surfaces may be utilized, as for example,
. Dall-Kirkham optics, in which semi-elliptical and
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RD-5987
spherical surfaces are utilized as the primary and
secondary reflectors, or Newtonian optics, using a
parabolic reflector and a flat reflector.
Interposed between collimating optics 12
and collecting opkics 15 is a plurality of masks or plates
containing apertures. 'rhese plates, comprising code
discs such as disc 22, a scanning disc 23, and a fixed
aperture mask 24 provide the encoding of the rotational
position of the indici,a on the meter. The encoding o:E -the
rotational position of the indicia on the meter is more
fully described in the abo~e-identiEied Canad.ian p~tent
1,012,609.
Briefl~, each code plate contains a plurality of
arcuate apertures that are sequentially scanned by scanning
disc 23, Fixed plate 2~ contains a plurality of slits,
one for each of code plates 22. In order for light to
pass through plates 22, 23 and 24, it is necessary that
the apertures therein be aligned so that the light may pass
from collimating optics 12 to collecting optics 15. The
slits in fixed plate 24 serve to ensure that only one
of discs 22 is read at a time. The positioning of the
slits in disc 22 provides a coded output signal as it is
scanned by the apertures in scanning disc 23. As scanning
disc 23
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~3805~ RD~5987
eraverses the arc containing each of code. discs 22, a
plurality of shaft position signals are ob~ained seriatum
,
' as the light from source 11 is interrupted or passed to
' , collecting optics 15 and thence to photodetector"l9.
. . .. . .
' '"5 ' '~ There is thus provided a compact optical system
, for reading out a plurality of coded discs to provide an
,.' ''electrical signal indicative of the rotational position
, ' o a plurality'o~ shat~ by way o~ a,single optical
! ~, ' ' gy9tem having a single light source and a single photo-
.
,10 ,, . d'etector. The optical system i~ stationary and securely
fixed in place, yet a plurality of code disc~ can ~'e
' ' ,, scanned, depending' upon'the dlameter of the code discs ,'
" as compared to the diameter of the scanning disc.
' , ,Light source 11 preferably comprises a filament
.
-' 15 , or incandescent type lamp having a reiatively large
filament. For exampie, a General Electric type #3026
, lamp operating at a power dissipation of 3 watts has been
found suitable. The light output from this lamp is far
~n excess of that required to read'the discs. The large
~ilament is utilized to obtain a large lmage on the
,............ detector side of the optics. In so doing, alignment
' tolerances are greatly increased (loosened) so tha~ the
optical syste~ may be readily assembled on a mass produc-
tion basis. '
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- 103805B RD-5987
As previously noted, reflector elements 12 and
15 are formed from a clear plastic, such as acrylic,
(methyl methacrylate) or Lexan polycarbonate, having
.
. suitably silver or aluminum coated surfaces to provide
.
:: 5 the necessary reflection. The curvature of the reflecting
.
- ;~ur$aces is provided by casting or pressing the plastia
. . .to the desired shspe and then coating the reflecting sur-
i . . . faces.
. . ', ,'
De~ector lg mAy comprise any sui~able photo-
. detector. It i8 préferred howe~er.that the.photosensltive
~ . area of the detector.be relatively.small so as to provide
¦~a hlgh sensitivity, low noise detector... One commercially
¦ ~ avaLlable detector ~ound suitable for the present invention
a type 2N5777-80 photocell, also manufactured by the
General Electric Company. This particular photocell has
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.an active area of about 0.015 inches square. In theory,
.
I any photocell may be utilized. In practice, an active
: element whose diameter is less than 0.10 inch is preferred.
The combination o~ large filament light source and small
1 20 detector enables a wide assembly tolerance while maintain-
.
. ing a high Qensitivity, lo.w noise detection system ~or
. producing an error ree output signal.
The overall operation of the present invention in
I combination with a plurality of coded discs may best be
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1~3~0S8 RD-5987
understood by considering FIGURE 2 in which a watt-hour . .
me~er is illustrated having a plurality of coded discs
22a-e attached one each to the shafts connected to a
. , ' plurality of indicia used in obtaining' a visual meter
.'.:. '' . . . . !
, 5 ' .. reading. As previously noted 9 scanning disc 23, in
;, . ., ;
:. . ' combination with the slits'in fixed plate 24, scans each
' , of codéd discs 22 individually and'provides a series of
,,...' , . . ..o~put. pul~es proportional to. the rotational position oE
.. . . . . .
, .' ' .each of ~he lndicia ad~acent Eront plate 25. Scanning
', ,,10 dise 23 may be turned by any su'itable mechanism such a~
.
' .,, ~ynchronous motor 26. The optical system of the present
., ,
. ' . , lnven.tion has a diameter equal to or slightly greater than
't~e working diameter of scanning disc,23, i.e. the diameter
, . , to t~e outermost,aper~ure. ' '.
I5. . , ' In opera~ion, in response to a signal ~rom the
.centra~,station, light source 11 is turned on and synchro-
;, nou~.motor 26 is activated. Starting from a rest position
.. . .
,!, , ' , scanning disc ~3 sequentially scans the coded discs
, '. atta,ched to each of the indicia adjacent plate 25. .Scanning
disc 23 i9 turned at a suitable rate, for example one
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; . revolut,ion per second, to. provide a beam path interruption
rate well within the response time of photodetector 19,
. yet not so long as to unduly prolong the reading operation.
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~o~380s8 RD-5987
If telephone transmission lines are used as the
link betweén the remote meter reader and the central
station, it is most likely that the meters would be read
at ~ight when the telephone lines are relatively unused,
5; as for example from 12 midnight to 6 a.m. Assuming a
rçading time of 1 ~econd per meter, then 21,600 meters
can be read Ln the six haur inter~al when the telephone
' ,',' ' ' , ' . . . .
lines are rel~tively inactlve. Ob~iousl~, iE the situatloh
.. .. .
r~uired it, the ~e~er may be resd at ~n~ ti~e.
- WhiLe not shown in either FIGURE 1 or FIGURE 2,
a light shield surrounding the optical system may be
provided so as to obviate erroneous readings of outdoor
meters during the daytime.
There i~s thus provided by the present invention
. 15 an inproved meeer reading optical-system in which a
- plurality of coded discs are illuminated by a single light
: . - . . . .
source and scannedg in effect, by a ~ingle pho~odetector.
Further~ the optical system of the present invention is
compact and readily its wlthin the meter movement and
coded diqcs utilized for remote reading. By virtue of the
present invention the entire optical system is-stationary
~hile a plurality of rotating coded dlscs are scanned by
an additional rotating scanning disc.
In view of the foregoing, it will be apparent
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58 RD-5987
to those of ~kill in the art that various modifica~ions
c~n be made w~thin the spirit and scope of t~e present
. . .
. . invention. . . `
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