Patent GB-779152-A (GB)
Title: Improvements in and relating to graphical recording apparatus
Inventor: MARGARY HARRY HERBERT
IPC: G01D15/14
Filed: 1954-04-03
Abstract: 779,152. Photo-electric control of recording apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. July 4, 1955 [April 3, 1954], No. 9825/54. Class 40 (3). Apparatus for graphically recording the movements of one or more instrument mirrors (e.g. of a galvanometer) comprises movable control means for causing or permitting light reflected from each mirror to face momentarily upon a photo-cell at intervals and an electric circuit for causing a stylus to make a mark on a recording strip each time light from a mirror faces on the photo-cell, the strip and stylus being moved relatively to one another in one direction to record a succession of marks each corresponding to the position of one mirror at one instant and being moved relatively to one another in a second direction so as to record a series of marks corresponding to the changed positions of each mirror at the end of each interval. 'In the apparatus shown in Fig. 1, light from an elongated filament 1a is reflected from each mirror 3 of a multi-channel galvanometer unit on to a plane mirror 6 and thence on to an opaque screen 5 containing a slit 5a behind which is a photo-cell 10. Mirror 4 is rotated about an axis 6 so that light from each mirror 3 faces in turn on the photo-cell. A recording strip 13 such as that known under the Registered Trade Mark " Teledeltos " is unwound from a roll 14, Fig. 2, and caused to take up a circular form with its axis of curvature coaxial with the rotary axis 12 of a stylus 11. This stylus is rotated by the means driving mirror 4 so that any one stylus moves from one side of the strip to the other during the time taken for all the galvanometer light spots to traverse the slit 5a. During this period the successive impulses from the photo-cell 10 are used to trigger a circuit whereby an instantaneous voltage is applied to the stylus in contact with the strip so as to make a mark thereon, each mark corresponding to the position of a mirror 3. The operations are repeated cyclically so that the marks made by each succeeding stylus correspond to the new positions of the mirrors. In this way there is built up in the form of a dotted trace a graphical record of the movement of each mirror 3. The styli 11 may in another form be attached to a sprocket driven endless belt. Fig. 4 shows a form which may be used as a multichannel strain gauge recorder. It comprises a rotatable mirror 20 adapted to reflect light from a source 1 on to a rotatable opaque screen 21 having therein several apertures 21a. Behind the screen is a photo-cell 10, and connected to the screen is a stylus 22 for making marks on a paper strip 23 on a recording drum, which is coaxial with screen 21 and rotatable relatively thereto. In operation, the output of one strain gauge bridge is connected through a selector circuit to the galvanometer having mirror 20 so that light is incident on the photo-cell when an appropriate slit coincides with the light beam and the resulting impulse is used to cause stylus 22 to make a mark on the paper 23. Another strain gauge bridge is now connected to the galvanometer and another mark made. When the readings from all the bridges have been recorded, the stylus is displaced axially of the drum 24 and a new set of readings is recorded. The sequence of operations is then repeated so as to build up on the paper a series of graphs, each showing the variations in the readings of one strain gauge.