`Septn 1o, 1946. . E. J. MARTIN ETA». LIGHT l 2,407,564 METER < ` Filed Margn s, 1944 ' zza \ ¿ya ¿i ê: “515% 1 Cíttorneg; Patented Sept. 10, 1946 2,407,564 unirse srres etant seres 2,407,564 LIGHT METER Edward> J. Martin, Pleasant Ridge, and carl E. Grinstea‘d, Detroit, Mich., assignors to General Motors Corporation, Detroit, Mich., a corpora . tion of Delaware Application March 6, 1944, Serial No. 525,318 1 Claim. l This invention relates: to measuring’means and more speciñcally to means for measuring minute quantities of light rays or the glow provided by phosphorescent material which has previously been activated bylsome activating means. ‘ There are of course many instances in which (Cl. Z50-41.5) 2 there is shown therein a multiplier pho'totube 2 having a cathode ‘4 and a series of multiplier anodes 6, 8, Il?, |21 i4, |‘t,.l8, 2U, 22 and 24. This phototube is the means »which is exposed to the i radiation to be measured and is mounted inside of a small box (not shown) having a Window `therein through which the rays may reach the cence or ray emitting value. of a body or surface head of the phototube. The cathode 4 is con and as one example'of this may be cited means nected through line 25 tothe anode12'8- of a rec for'printing on sensitized paper’ from some phos 10 tifier tube 30, the cathode 32` or filament of which phorescent source. There are in use processes is connected across a secondary winding'Sd of> a . utilizing a layer of phosphorescent paintv or radiat compound‘transformer 36. , l ing material applied to a` backing means which The primary 38 of this transformer is con has imposed‘thereon certain configurations which it isv desired to know the strength of phosphores nected to a suitable source of `commercial cur it is desired to reduce, such asdrawings, prints, 15 rent such as a 115 volt power‘ line. A second etc. One method of accomplishing this drawing secondary coil 40 of the transformer 36 provides reproduction'hasbeen to expose the phosphores power` for a filament or cathode ¿i2` of a second cent material to a strong activating means which rectiíier tube :lll` whose anode 45 is connected may be either X rays or light, depending upon through line 48 to a third transformer second the character of the phosphorescent means, and 20 ary 59. A line 52 connects one end of the sec then removing, theysource‘ of` activation and,` ap ondary 40? to ground. Connected across lines plying tothe member‘a sheetof sensitized mate 2li andc52v are two condensers Eiland` 5t` which rial for printing. ` > ` are in series, the’midpoint of these condensers . However, the rat'e‘ofdecay of glowor radiation lbeing connected by line 5BA to a` second terminal A of the phosphorescent means varies considerably 25 of secondary 5u. These two' half Wave rectiñers and it is known that if the temperature is low, ' 30: and M `therefore provide across-the two' con this decay in radiation strength can be slowed densers 54, 5S a relatively stable voltage for `the down considerably. However, `before applying the various anodes of the photomultiplier tube 2. sensitized sheet to make a print or reproduction In order, however, to have the extreme accu of the configuration on the phosphorescent 30 racy‘` necessary and to` provide the voltage ap means, it is desirable to know Whether or not plied to each'anode of the same proportion, it is there is suiiicient ray activity present in the phos necessary to provide additional‘means for main phorescent means to provide printing and also taining these individual voltages constant over as to the length of time it will be necessary to ñuctuationsin theline voltage. The output volt maintain the sensitized sheet in contact for eX age applied to lines 2B', 52 from the rectiiier is posure to obtain a satisfactory print. `It will be applied across a plurality of resistors 6e, S2', 64, evident that the amounts of light or activated B5, 68, is, l2, 1li, 15 and 18, al1 ’connected in rays under consideration herein is small.` „ It is therefore an “object of our invention to provide sensitive means for accurately measur ing small amounts of radiation in the light spec trum. , . It is a further object of our invention to pro vide means for measuring rays in the light spec trumÍ which is relatively small, portable, sensitive and rugged.` . l series, which formons> large resistance for the' total voltage. However, the various interconnect ing lines feeding> the anodes 6, 8, Hl, I2,` lli', It; 58, 2li, 22 andi@ are `all connected-to‘intermedi ate positions between these resistances, thus ap plyingto each anode aproportionate part oi- the total voltage `across the output; In order to pro. ' vide a. satisfactory voltagei'regulaton for each smallresistance; a voltage regulator tube', such as With these and other objects in view which B8, is connected in parallel across each of the will become apparent as the speciiication pro resistances Eìâl, 62, Bil, 5S, E8, 1i), 12, 14, 'l5 and ceeds, the embodiments of our invention will be lil. These tubes are well known in the art, are best understood by the following speciñcation 50 gas-filled and maintain the voltage across the and claim and the illustrations in the accompany same constant under varying supply. As an eX ing drawing, in which the -ñgure is a circuit dia example, the voltage tube used in the pres gram showing the electrical system embodying our ent instance has the commercial designation invention. “VR-105-30.” . Referring now more speciñcally to the ñgure, `As the electrons are bombarded Within the mul 2,407,564 3 4 tiplier tube, they are passed on from one anode to another and as such acquire greater speed and number as they proceed until they reach the last anode, therefore developing or multiplying the energy'therein. The last anode or output 24 is connected through line 82 to a series of resistances 86, 88, 90 and 92 in series, the last of which is connected to line Y52 and thus to ground. The intermediate points of connection between these ` Y sistances 60, 62, 64, 66, 68, 10, 12, 14, 16 and 18. There are then taken from this total voltage, volt age steps applied to the anodes 6, 8, I0, l2, I4, I6, I8, 20 and 22 which are carefully regulated so that each will be the same as the other and that they >will be maintained as nearly constant as possible so that no errors will be introduced due to fluctuations in line voltage. Thus when _light is directed on the photo-multiplier through to any one of the series of taps provided between ' radiation from a phosphorescent surface, an elec tron stream will flow from cathode 4 to anode 6; This will dislodge additional electrons from anode 6 and cause the original stream tov be reflected on the anode 8. Thus a larger group will impinge on anode 8 and this will continue to multiply around'the tube to provide a useable amount of energy from a small excitation. Thus voltage will the resistances 86, 88, 90 and 92, depending upon the sensitivity available or desired. amount of excitation of the phosphorescent sur resistances are connected to taps and are capable of cooperation with an adjustable contact con nected to line 94 which in turn is connected to a limiting resistance 96 andthence through line 98 to control electrode |00 of the `power ampliñer |02. Line 98 is also connected through condenser |04 to ground. ~Thus tap 94 may be connected A second source of power is provided for the 20 be developed in the line 82 proportional to the face. Y This voltage will be applied through one 'o power ampliñers | 02, |06 which form a portion the taps associated with one of the resistances 86, of lthe bridge Vacuum tube voltmeter system pro 88, 90 and 92 and to the control grid|00 of power vided to measure the output of the photoelectric amplifier-|02. This will change the relationship tube -2. This power- supply comprises a second multi-winding transformer |08 having a single 25 in the balanced bridge composed of power ampli' ñers |82, |06 and resistances |20 and |22 in two primary ||0 and two secondary windings ||2 and arms and resistances |66,` |56 and |58 which may I I4. Windingrl I4 provides a small voltage for the be `balanced by the position of the tap V|54 »on |56. heater circuit ||6 of the tubes |02 and |06, and is shown as connected through by arrows to sim At this time of course power is being supplied to bridge input connection between two resistors|20 and |22 which are connected to cathodes |24 and scribed circuit incorporating transformer |08.> In this case also the‘output of the full-wave recti plify the wiring diagram. Secondary I|2 -has a 30 the balanced bridge and speciflcallyrto the power ampliiiers |02 and |06 through the previously de center tap- connected through line ||8 with a |26 of the power tubes |02 and |06, respectively, ñer is regulated by Voltage regulator tube |50 to tubes. The two ends of the secondary coill ||2 the power supplied to the bridge, and any vari ation in the supply to the amplifier tubes is ap plied equally to bothV and since they are situated in adjacent bridge arms, the’ effect will cancel and also to a further grid |28 and |30 of the same 35 eliminate as much as possible any ñuctuatìon in are connected through lines |32 and |34 to the electrodes |36 and |38 of a full-wave rectification tube |40. ' An electrode |42 of the tube |40 is connected 40 Thus as the current flow through one leg of the to resistors |44 and V|46 in series, which form a bridge varies due to the output of tube 2, current portion of a filter circuit in combination with out. capacity |48 and. with voltage regulator tube |50 which is similar to tubes 80, above described, provides a regulated output from Vthe Vfull-Wave rectifier to the bridge Vcircuit incorporating the vacuum -tube voltmeter for measuring means. Line |52 connects resistor |48 and one side of the voltage regulator |50 to a variable tap |54 on Vresistor |56. Resistor |56 has one terminal con- » nected through a second resistor |58 to line |60 to form a third bridge arm which line is com monly connected to the "plate |62 of the power amplifier |02V and also to a third grid |64 of the same tube. The oppositek end of resistor |56 is in like manner connected through a third resist ance |66 to connecting line |68 to complete the bridge, which line is jconnected to plate |10 and the third grid |12 of the power amplifier |06. Y v » ` will flow across the bridge through the milliam meter |14 vand this current will be directly prof portional to the amount of unbalance as intro duced by flow through power amplifier |02. Thus milliammeter |14 may be calibrated to read di-V rectly in terms of radiation from the surface of the phosphorescent layer. We claim: - In means for measuring the luminescent radia tion of small quantity from a phosphorescent sur Íface, a source of alternating current, means for rectifying said current connected Vto said source, tapped resistance means connected across the rectifier output, said'tapsV dividing said resistor into a plurality of substantially equal parts, a , photosensitive multiplier tube having a plurality of electrodes sequentially engagedV by electron Connected across the bridge between lines |60 and 60 streams, means for connecting each of the elec trodes to a tap andvoltage regulation means con |68 is a milliammeter |14 in series with a vari able resistance |16. , In the operation of the system as disclosed, the Vpower supply for transformer '36 provides alter nating current which is rectified and developed as ` Vdirect current across the -resistor formed of re nected across each adjacent pair of taps topro-` vide constant voltage to each electrode. EDWARD J.ÜMARTD.\I. CARL E. GRINSTEAD. '