READOUT DEVICE

• US 3,573,773 A
• Filed: 12/26/1967
• Issued: 04/06/1971
• Est. Priority Date: 12/26/1967
• Status: Expired due to Term

• Current Assignee: Edward W O'Hanlon
• Original Assignee: Edward W O'Hanlon
• Inventors: O'hanlon, Edward W.
• Application Number:
  US04/693,684
• Time in Patent Office: 1,197 Days
• US Class Current: 340/870.27
• CPC Class Codes: G01D 5/268 using optical fibres G01D5/28 - G01D5/38 take precedence
• CPC Class Codes: H03M 1/26 with weighted coding, i.e. the weight given to a digit depends on the position of the digit within the block or code word, e.g. there is a given radix and the weights are powers of this radix

Abstract

In a device for reading the position of a meter pointer or other indicator having a reflective portion and moving in a predetermined path, light is directed at such path from one side, for example, through the meter'"'"''"'"'s cover glass, for reflection back through the glass at the position of the pointer, a series of light receiving elements of light transmitting fibers have ends thereof arranged sequentially along the path to selectively receive the light reflected at the position of the pointer and to selectively illuminate photocells to which the other ends of such elements extend, and an electrical characteristic, such as the frequency, of a signal adapted for transmission to a remote station is determined in dependence upon the selective illumination of the photocells and hence according to the position of the pointer.

Claims

1. A readout device for optically sensing the position of an indicator member movable in a predetermined path and for producing an electrical signal corresponding to the sensed position, comprising means emitting light along the length of said path, a plurality of light receiving element each composed of light transmitting fibers and having first ends thereof arranged at sequential positions adjacent to the length of said path to selectively receive light from said light emitting means by way of said indicator member when the latter is at corresponding positions in said path, a plurality of photocells having the other ends of said light receiving elements extending thereto so as to be selectively illuminated when said member is disposed at said positions corresponding to the associated light receiving elements, and signal producing circuit means including said photocells to determine an electrical characteristic of the produced signal in dependence upon the selective illumination of said photocells and hence according to the position of said indicator member.

2. A readout device according to claim 1, in which said light emitting means and said first ends of the light receiving elements are disposed at the same side of said path, and at least a portion of said indicator member is reflective so that, in each of said positions of the indicator member, said portion thereof reflects light from said light emitting means into the correspondingly positioned first end of a light receiving element.

3. A readout device according to claim 2, in which said light emitting means includes a light source and a series of light emitting elements each composed of light transmitting fibers and having first ends simultaneously and equally receiving light from said source and their other ends directed toward said path and arranged sequentially therealong.

4. A readout device according to claim 3, in which said indicator member is a meter pointer movable in said path, and said path is in a plane between a coplanar dial face and cover glass, and said light emitting and light receiving elements respectively emit and receive light through said cover glass.

5. A readout device according to claim 4, in which said first ends of the light receiving elements are spaced from said other ends of the light emitting elements in directions transverse to said path by distances that substantially subtend an angle enclosed by light rays incident on said reflective portion from said light emitting elements and reflected from said portion toward said light receiving elements.

6. A readout device according to claim 4, in which said pointer is movable angularly so that said path of its reflective portion is a circular arc and said first ends of the light receiving elements and said other ends of the light emitting elements are arranged in similar areas of larger and smaller radii and then the radius of said path so as to be spaced radially by distances that substantially subtend an angle enclosed by light rays from said light emitting elements incident on said reflective portion and reflected from the latter toward said light receiving elements, whereby light rays from said light emitting elements impinging on said dial face are reflected radially away from said first ends of the light receiving elements.

7. A readout device according to claim 6, in which said reflective portion of the pointer is spaced radially inward from a free end of the pointer which cooperates with a scale on said dial face for visually indicating the position of said pointer, and said light source, light emitting and light receiving elements and photocells are contained in a cylindrical casing which is secured to said cover glass and diametrically dimensioned to be radially inside said scale, whereby to avoid interference with direct visual reading of the position of the pointer.

8. A readout device according to claim 4, in which said dial face is of relatively low reflectivity.

9. A readout device according to claim 1, in which there are at least two sets of said photocells and said other end of each light receiving element extends to a respective photocell in each of said sets, whereby the number of said light receiving elements and of said positions of the member that can be discriminately sensed is the product of the numbers of said photocells in said sets.

10. A readout device according to claim 1, in which said circuit means includes a series arrangement of resistance elements connected with said photocells so as to have the resistance values thereof selectively switched out of said series arrangement in turn upon selective illumination of said photocells, whereby the total resistance of said series arrangement corresponds to the position of said indicator member, and means to vary said electrical characteristic of the signal in accordance with changes in said total resistance.

11. A readout device according to claim 10, in which said circuit means includes an RC oscillator having said signal as the output thereof, and said total resistance of the series arrangement constitutes a resistance component of the oscillator, whereby the frequency of said output is the electrical characteristic of the signal which is varied according to the position of said indicator member.

12. A readout device according to claim 1, in which said circuit means includes resistance elements associated with said photocells and each having a diode in parallel therewith to freely conduct current in one direction so that the resistance effect of each resistance element is substantially eliminated when current flows in the respective diode, said resistance elements and parallel diodes are connected in at least one series string, a source of electrical potential is applied to junctions between successive resistance elements through said associated photocells so that, upon illumination of a selected photocell corresponding to the position of said member, the potential at the corresponding junction is varied in relation to the potentials at the other junctions to cause current to flow through all of the diodes which are between said corresponding junction and one end of said series string for effectively eliminating from the total resistance of said string those resistance elements in parallel with the current conducting diodes, the values of said resistance element are selected to correspond to increments of movement of said member between said positions thereof, and means to vary said electrical characteristic of the signal in accordance with changes in said total resistance of the series string.

13. A readout device according to claim 12, in which there are first and second sets of said photocells each having resistance elements and diodes associated therewith in respective series strings as aforesaid, said series strings are connected with each other in series, the diodes in one of said series strings are conductive in the direction opposed to that in which the diodes of the other series string are conductive so that the diodes of each of said strings are uninfluenced by the state of the diodes in the other string, the value of each resistance element associated with a photocell of said second set is substantially equal to the sum of the values of the resistance elements associated with the photocells of said first set, and said other end of each light receiving element extends to a respective photocell in each of said first and second sets, whereby the number of positions of said member that can be discriminately sensed is the product of the numbers of said photocells in said first and second sets.

14. In combination with a meter having a pointer with a reflective portion movable in a predetermined path lying in a plane which is between a parallel dial face and cover glass to provide, a visual indication of a condition sensed by the meter:

a readout device for providing an electrical signal corresponding to said visual indication and suitable for transmission to a remote station, said readout device comprising a casing secured against said cover glass of the meter, means emitting light from said casing through said cover glass toward said path along the length of the latter so as to be reflected back through said glass by said reflective portion of the pointer only at the position of the pointer, a series of light receiving elements in said casing each composed of light transmitting fibers and having first ends thereof arranged in sequence to selectively receive the light reflected through said glass from said reflective portion of the pointer when the latter is at corresponding positions in said path, a plurality of photocells in said casing having the other ends of said light receiving elements extending thereto so as to be selectively illuminated only when said pointer is disposed at the positions corresponding to the associated light receiving elements, and signal producing circuit means having said photocells included therein to determine an electrical characteristic of the produced signal in dependence on the illumination of said photocells and hence according to said visual indication.

15. The combination according to claim 14, in which said pointer is movable angularly so that said path is a circular arc, said light emitting means includes a light source and a series of light emitting elements each composed of light transmitting fibers and having first ends equally receiving light from said source and their other ends directed toward said cover glass and arranged in sequence, said sequentially arranged first ends of the light receiving elements and other ends of the light emitting elements lying along similar arcs of larger and smaller radii than said arc of the path so as to be spaced apart radially by a distance that substantially subtends the angle at which light rays from said light emitting elements are reflected by said reflectiVe portion of the pointer.

16. The combination according to claim 15, in which said scale is traversed by a free end of said pointer from which said reflective portion is substantially spaced, and said casing is disposed radially inward with respect to said pointer end and scale to permit reading of said visual indication with said casing secured against the cover glass.

17. The combination according to claim 14, in which said dial face is of relatively low reflectivity.

18. The combination according to claim 14, in which there are at least two sets of said photocells and said other end of each light receiving element extends to a respective photocell in each of said sets, whereby the number of said light receiving elements and of said positions of the pointer that can be discriminately sensed is the product of the numbers of said photocells in said sets.

19. The combination according to claim 14, in which said circuit means includes a series arrangement of resistance elements connected with said photocells so as to have the resistance values thereof selectively switched out of said series arrangement in turn upon selective illumination of said photocells, whereby the total resistance of said series arrangement corresponds to the position of said indicator pointer, and means to vary said electrical characteristic of the signal in accordance with changes in said total resistance.