Document gD82koZjQ5ejymrj7Xe7akOdV

^Photoelectric-Tube Symbols and Characteristic Curves 6.'A photoelectric scanrnnfl System focuses the HflKt The symbol for o vocuum photoelectric tubo whh o V(rn o Homo through a len`tcurved eoated-mctol cothode fton tho cothode of the tubo and `o verttcal wire onode "hr;- Tho symbol for photoelec* frk tube thot it gat* filled. Dot Indicates the pas as In a hot-cathode tube Clcmontory<lixuit dlo-*;* ram' uses tube. Positive terminal connects to anode, and negative to the cathode c c U'fHk 'rue#- -- 1^ ?Cot at/tat OS ,8 ( y v6e/v t.O lumtr (34 tumtn 1 I Relation between onode volts and current flow for a glven light Intensity In' vocuum and gat-filled photo tubes -0 know- r fuOt c. A OS 0.4 as 06 07 .06 09 L^irllvi.tvnwm 11 Relotion between light flux In lumens end Current flow for given voltage In vocuum and gas-filled photo tubes ^ hot close as long as beam is broken, Diffusion. Applications where the in?,eTer*e this application, the !`Shl, beam is directed aerosa a'door opening. When a person walks across ?*;beato a relay closes to energise the light beam is diffused include smokedensity indicators. Here, as the density changes, the amount of light reaching the photoelectric 'tube also changes. 2.**" to open the door. A timing This causes the emoke-densily indicator S*y folds It open a given period to let to function accordingly, and generally to pass; then the relay func- sound an alarm if a specified density is 5?Mo.1et U close. exceeded. A similar use is found in de jjkB' pother application a factory tecting turbidity In liquids. JaPr* approaching an electric-elevator Reflection. A mirror may reflect the v* V "i^rrupts a light beam. This ' light beam much aa tilting a mirror e^CTnlorttaW>,-<L a' Pfo,0><lcciric relay that makes a light beam race across a wall. cSm l machine to bring the Reflection is used to. measure speed of (`jj for when the doora open for fast-running shafts. A light beam re flected by a tiny mirror on the shaft's 0n * conveyr aw counted end acting through a photd-electric re li&rlJ^^ 11 they move through a lay gives accurate speed Indication.. 'ges * Obstructing this beam act* Photoelectric relay that causes l? / t0 !tinclw- A photoelectric recorder is another reflection application. Weak input signals cause the movement of a tiny B.vvVa . e iir . StpUmbar 1940 mirror. Reflected light from it controls a photoelectric-tube follow-up system that makes a permanent record of the weak electrical-input signal. A prism provides another method of reflecting or bending a light beam toward a photoelectric tube. In its simplest form a prism is merely a glass pyramid. Light entering the pyramid . from one side is bent toward the base as it passes through the glass, Fig. 3. Deflection. Fig. 2, which diagrams psrt of the optical system of a photo meter, gives a good illustration of how ` prisms and minors bend light beams In electronic metering devices. Light from the lamp is focused into a beam and di rected to the left to a prism. Here the beam first posses through a lens and into the prism where it is deflected and passes through another lens toward a (SSS) 101