Patent GB-801772-A (GB)
Title: Improvements in or relating to remote metering arrangements
IPC: G01D5/39
Filed: 1953-10-06
Abstract: 801,772. Photo-electric indicating systems. BERRIDGE, D. R., and MARTIN, R. E., and CENTRAL ELECTRICITY GENERATING BOARD. Jan. 6, 1955 [Oct. 6, 1953], No. 27409/53. Class 40 (3). A remote metering arrangement comprises (i) a gauge whose length is divided in accordance with the quantity to be measured into two portions having different optical effects on an incident beam of light; (ii) a photo-electric element for receiving a narrow beam of light emergent from the gauge; and (iii) a mechanical scanning device whereby such narrow beam is caused repeatedly to traverse the gauge. The photo-electric element receives light only during that part of the scanning cycle .associated with one of the two portions of the gauge and means are provided responsive to the electrical output of the photo-electric element for indicating at a remote point or points the duration of energization of such element in each cycle and thereby also the value of the quantity to be measured. The gauge may comprise one portion which refracts, transmits or reflects the incident light on to the photo-electric element whilst the other portion cuts off the light or refracts or transmits the light away from the photo-electric element. The invention is described with reference to apparatus for remote indication of water level in a steam boiler gauge. The latter is of the kind having flat windows in opposite walls inclined at an angle to one another so as to provide a prismshaped space containing the water column. The remote indicating means may comprise a second scanning device which operates to produce on an indicating screen a strip of light whose length varies with the water level in the steam boiler gauge. In Figs. 1 and 2 a drum B<SP>3</SP> has a helical slot B<SP>4</SP> and surrounds a tubular light B<SP>5</SP> and condenser lens B<SP>7</SP> and the drum B3 is rotated by a motor C whereby a narrow beam of light emerging through slot B<SP>4</SP> repeatedly traverses the length of the gauge A. The narrow beam of light is refracted differently by the prisms of water and steam A3, A4 and a photo-electric cell D is so located as to receive only the beam emerging from water column A<SP>3</SP>. The cell D through an amplifier E and relay &c. devices (not shown) delivers voltage impulses to a receiver-scanner, Fig. 3, synchronized with and similar to the transmitter-scanner so that a tubular lamp G<SP>5</SP> in the receiver-scanner is alight only when cell D is energized and correspondingly a light beam emerging through helical slot G<SP>5</SP> traverses indicating screen F. The scanning frequency is chosen so that the image on the screen F appears as a permanent strip of light whose length varies with that of the water column A<SP>3</SP>. The helical slot in each scanning drum may be replaced by a helical row of equally spaced holes or by two or more similar helices or helical rows of holes. Fig. 4 shows provision for reference images on screen F; prisms J<SP>1</SP>, J<SP>2</SP> refract beams from steam and water columns A<SP>4</SP>, A<SP>3</SP> so that screen F has a top light band and a bottom dark band corresponding to top and bottom datum points on gauge A. The light from the water column may be focussed (Figs. 7 and 8, not shown), by using a parabolashaped transparent block having a conical hole with a polished surface which reflects the light beams sideways out of the block on to the photo-electric cell. Alternative forms of scanning devices are described or mentioned and these are as follows: (i) a spiral slot in a rotating disc in conjunction with a fixed source of light; (ii) a cam-driven oscillating mirror throwing reflected light on to the gauge, Fig. 6 (not shown); (iii) a conveyer carrying a fixed light along the gauge; (iv) a spiral or, Fig. 9 (not shown), helically-shaped rotating discharge tube; (v) neon lamps forming the shape of a helix around a rotating cylinder.