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`Septn 1o, 1946.
.
E. J. MARTIN ETA».
LIGHT
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2,407,564
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Filed Margn s, 1944
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Patented Sept. 10, 1946
2,407,564
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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.
'
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