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Патент USA US2411672

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Nov. 26, 1946.
JY, A. VAN DEN AKKER
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ELECTRICAL CONTROL SYS TEM
Original Filed Sept. ~ 2, 1941
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ELECTRICAL CONTROL SYSTEM
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2,411,672
UNITED STATES PATENT OFFICE
2,411,672
ELECTRICAL CONTROL SYSTEM
Johannes A. Van den Akker, Appleton, Wis., as
signor to The Institute of Paper Chemistry, a
corporation of Wisconsin
Original application September 2, 1941, Serial
No. 409,174. Divided and this application Octo
ber 2S, 1943, Serial No. 507,958
9 Claims.
(Cl. 25o-41.5)
1
My invention relates, generally, to apparatus
for measuring and recording concentrations of
2
tical apparatus for measuring and continuously
recording in an accurate manner the concen
substances which have the property of absorb
tration of certain gases, vapors, and solutes hav
ing light energy of certain wavelengths, the ap
ing the property of absorbing to an appreciable
paratus being particularly adapted to measure 5 extent light radiation of certain particular wave
lengths.
and record small concentrations of such sub
stances. As will hereinafter appear, the disclosed
A specific object of this invention is to pro
embodiment of the invention includes a new and
vide an inexpensive and practical concentration
useful light conversion and selection system,
recorder which is particularly adapted to ac
photometer, and electrical circuit, each of which 10 curately measure and record small concentra
serves as one of the component parts of the con
centration recording apparatus, but which are
not limited solely to use with this apparatus.
This application is a division of my co-pending
application, Serial No. 409,174, which was iiled
on September 2, 1941, and which is assigned to
the assignee of this application. My earlier ap
plication matured into Patent No. 2,356,001 on
May 30, 1944.
It is a known scientiiic fact that certain sub
stances have the property of strongly absorbing
light of certain wavelengths, particularly in the
ultraviolet region of the spectrum. Examples of
gases and vapors having such a property are
ozone, sulphur dioxide, mercury vapor, chlorine,
perchloroethylene, phosgene, and a fairly large
group of other gases and vapors. Examples of
solutes which in solution have the property of
absorbing light of certain wavelengths are potas
sium diohromate, amino disulfonic acids, and
sodium benzoate. In general, light energy ab
sorption by these various substances is propor
tional to, or bears a definite relation to, their
concentration.
The present invention, making use of this light
absorption principle, provides an inexpensive and
practical concentration recorder for- accurately
measuring and simultaneously recording con
centrations of substances having this particular
property of appreciable absorption for light
radiation of certain wavelengths. Although
tions of ozone.
Another object of this invention is the pro
vision of an inexpensive light conversion and se
lection system which makes possible the use of
a commercial light source or lamp which emits
light in a plurality of wave bands as a source of
light energy in a single one of the emitted bands.
This light conversion and selection system is par
ticularly adapted for use as part of my improved
20 concentration recorder but may be put to cer--
tain other important applications.
In obtaining maximum sensitivity of response
in the apparatus of the present invention, an
electrical bridge circuit has been provided which
produces large changes in wave form in response
to relatively small changes in light flux. This
bridge circuit is particularly adapted to control
gas-filled electric valves, and although it is par
ticularly adapted for use in connection with con
centration recorders embodying my invention, it
may be advantageously employed in connection
with other applications.
rI‘he nature and principles of my invention may
be more fully understood from the following de
tailed description of an ozone concentration re
corder which forms one embodiment of the in
vention. Extended tests have shown that this
ozone concentration recorder is commercially
practical and will accurately measure and record
small concentrations of ozone in a very satis
factory manner.
In the interests of simpliiication, the detailed
description of the selected embodiment of the
invention will be preceded by a brief discussion
certain substances, and some progress has been
made in developing apparatus for only meas
of the basic principles of operation thereof taken
uring or indicating the concentrations of such
in connection with suitable diagrammatic draw
ings.
substances depending upon their particular light
absorption property, it does not appear that there
In the drawings:
has been any substantial progress made in de
Fig. 1 is a diagram of a simple basic system by
veloping apparatus for both measuring and re 50 which the concentration of a substance may be
cording in a continuous manner the concentra
measured depending upon its property of ab
tions of such substances depending upon their
sorbing light radiation of a particular wave
there is some literature treating in a general
way on this phenomenon of light absorption by
light absorption properties.
length;
Accordingly, the object of my invention, gen
Fig. 2 is a diagram of a system similar to that
erally stated, is to provide an inexpensive, prac 55 shown in Fig. 1, but employing the light con
2,411,672
3
‘4
version and selection system of the present in
The extinction coefficient a is defined by the
equation:
vention instead of a monochromatic illuminator;
Fig. 3 is a comprehensive diagrammatic View
of a concentration recorder embodying the fea
tures of the'present invention;
Fig. 4 is a view taken generally on line 4--4 of
where I0 and I are, respectively, the intensities of
incident and transmitted radiation, a is the ex
Fig. 3;
tinction coefhcient, and h is the thickness of the
layer of ozone gas in centimeters. Thus trans
Fig. 5 is a diagrammatic View of a photometer
aperture forming an important part of the pres
ent invention;
Fig, 6 is a mathematical diagram by which the
principles of construction and design of the
photometer of Fig. 5 may be explained;
mittance T of a quartz cell containing ozone gas
may be expressed by the equation
where p is the mass of ozone per cubicAcentimeter,
Figs. 7, 8 and 9 are electrical diagrams or wave
form sketches by means of which certain electri
cal observations important in connection with the
and a is the absorption coeflicient per unit con
centration and per unit thickness of gas. Under
standard conditions of temperature and pres
sure, 13:0.00214 g./cc.; therefore
electrical bridge circuit of the present invention
may be explained;
Fig. 10 is a diagram of a light-sensitive elec
a--__a/p=149/0.00214=69,700 cm2/g.
trical bridge circuit adapted to produce large 20 From this, p may be expressed by the equation:
.changes in wave form in response to small rela
(3)
tive changes in illumination of a pair of photo
Vcells and forming an important feature of my
p=(1/ah> 10210 (l/T)
Applying the foregoing data, it will be seen
present invention;
that the system shown in Fig. 1 can be used to
Fig. 11 is a diagram or sketch showing changes 25 measure the concentration of ozone gas. Refer
in Wave form produced by the electrical bridge
ring to Fig, 1, a mercury arc, indicated diagram
circuit of Fig. 10;
matically at I0, is used as a source of 253.7 mmu
Fig. 12 is a diagram showing an electrical con
radiation. The radiation of 253.7 mmu wave
trol system by which a reversible motor may be
length is isolated from radiation of other wave
_controlled in response to changes in Wave form 30 lengths emitted from the arc IS by a quartz mono
produced by an electrical bridge circuit embody
ing the essentials of the bridge circuit of Fig. 10;
chromatic illuminator, indicated diagrammati
cally at I I. An absorption cell I2, through which
Figs. 13a and 13b are horizontal sectional views
of a successfully operated and tested ozone con
centration recorder instrument made in accord- .
ozone gas may be circulated, is placed in line with
the monochromatic illuminator i i so as to receive
253.7 mmu radiation transmitted therethrough.
ance with the principles of the present invention,
Figs. 13s~ and 13b together forming a complete
horizontal section through this apparatus;
Radiation passing through the cell I2 is received
line Ide-Mb of Fig. 13b;
pleted by a galvanometer, indicated diagrammat
ically at HI, having its terminals connected with
the terminals of the photocell I3.
by a photocell I3 adapted to be sensitive to ultra
violet light through the use of fluorescent screen
Fig. 14a is a vertical sectional> view taken on
(not shown) which may be prepared, for example,
A line Illa-Ida of Fig. 13a;
40 by dipping plain transparent Cellophane in a so
Fig. 14h is a Vertical sectional View taken on .
lution of Uranine B dye. The system is com
Fig. 15 is an elevational view of a mercury va
por lamp taken on line I5-I 5 of Fig. 13a;
Fig. 16 is a vertical sectional view taken on 45
In operation, as 253.7 mmu radiation passes
line Iii-I5 of Fig. 13a;
through the absorption cell I2 its intensity is
Fig. 17 is a circuit diagram of the electrical
reduced to an extent depending upon the concen
_control system for the ozone concentration re
tration of ozone therein. In turn, the photo-cur
corder instrument in Figs. 13a, 13b, 14s and 14h;
rent produced by the photocell depends upon the
and
50 intensity of the 253.7 mmu radiation incident
Fig. 18 is a diagram of a modiñed form of light
thereon. Accordingly, the amount of deíiection
sensitive electrical bridge which has been ad
of the galvanometer I4 Will depend upon the con
vantageously substituted for the electrical bridge
centration of the ozone circlulated through the
of the electrical control system shown in Fig. 17.
absorption cell I 2.
In the electrical bridge of Fig. 18 the photoelec 55
To calibrate the apparatus, a table of galva
tric cells are of the photo-emissive type, whereas
nometer deflections with corresponding ozone
in Fig. 17 the photoelectric cells are of the block
concentrations may be prepared for the system
ing-layer type.
of Fig. 1 as follows:
.
Ozone gas has the ability to strongly absorb
As above stated, the mass of ozone per cubic
ultraviolet light of certain wavelengths. In par 60
centimeter p is related to the transmittance T in
ticular, the absorption by ozone gas of light radi
accordance with Equation 3.
ation ín the 253.1 mmu line of the mercury spec
trum is exceedingly strong, the extinction coeñi
cient being 149 cnr-1, under standard conditions
p=(1/h) logio (l/T)
Now since a and h are constant, and T is Ipro
of temperature and pressure. That is, a layer of 65 portional to the deflection D of the galvanometer
ozone having a thickness of 1 cm. Will, under
standard conditions of temperature and pressure,
reduce the intensity of 253.7 mmu radiation to
1/10149. A Lauchli (Z. Physik, 53:92 (1929)), re
when I0 is constant, we have Equation .
(4)
p=k1 logic (l/D)
The value of k1 maybe determined -by observ
ported extinction coef?cients a for ozone gas un 70 ing the deflection D1 for a known concentration
der standard conditions of normal pressure and
p1 of ozone, then substituting these known val
temperature, as follows:
Table I
Wavelength: 237.8 248.2 253.7 265.2 280.4 296.7 312.5 324.1 mmu
,
a: 1130.5 141. 149. 123.
45.6
6.9
0.96
«107cm-1
ues in Equation 4 and solving for k1. Having de
termined k1, a calibration table for the system
,may be calculated by substituting diiferent values
75 `for D and solving for corresponding values for p.
2,411,672
6 .
Byusing absorption cells of different gas thick
neighboring lines inthe ultraviolet has a total of
only about 153. Computation shows that the
ness h, ozone concentrations -in different ranges
can be measured with good accuracy.
Although the ozone concentration indicating
system of Fig. 1 is successful in `operation from
a `scientific standpoint, it necessitates the vuse of
amount of excitation due to radiation emitted
from the lamp I5 in the neighboring lines of the
mercury spectrum is only 1.4 percent of that due
to 253.7 mmu radiation.
the monochromatic illuminator II. Accordingly,
to eliminate this piece of apparatus, .the system
As can be seen from
Läuchli’s data in Table I above, these neighbor
ing lines are somewhat absorbed by ozone but,
shown in Fig. 2 was provided.
assuming they suffered no absorption (this ena
Referring to Fig, 2, a mercury vapor lamp I5 10 bles computation of maximum error), an idea
is shown which serves as a source of ultraviolet
of the error involved can be obtained by taking
light for the system. A Westinghouse “Sterilamp”
a transmittance value T of the ozone in the ab
having an M-shape was found to serve very sat
sorption cell I6 as equal to 0.500. The observed
transmittance would then be
isfactorily a-s this mercury vapor lamp I5. Over
88 per `cent of the radiation from the lamp I5 is 15
concentrated in the 253.7 mmu line of the mer
cury spectrum and the detailed distribution of
the energy in the various lines thereof is given in
the following table:
Table II
Vtf avelength, mmu
Relative
energy
1l . 3
0.032
0.011
0. 016
0.065
0. 043
0. 34
0. 30
0. 36
1. 09
(l. 60
0. 13
(5)
M[11h00/21+ 153
T* "11,300+153 =0.5067
If this corresponds to a concentration of ozone
of 1.00 percent, the observed concentration would
20 be 0.98 percent. This is only an error of 2 per
cent of the value of the concentration itself.
When `the concentration of ozone 0:0.5 percent,
T=O.707; the observed T would be 0.711 and
Sc=-0.008, or about 1.6 percent of the concen
25 tration itself. These discrepencies are satisfac
torily small and may be compensated for in cali
bration of the instrument.
Fluorescent radiation from the plate I‘I, which
is most strong in the red portion of the spectrum,
30 is filtered through a filter I8 before it reaches a
photocell I9. The filter I8 may be a Wratten
No. 25 filter which excludes or absorbs all direct
radiation of wavelength less than 580 mmu, but
A quartz absorption cell I6 through which
ozone gas may `be circul-ated is disposed in front
freely passes radiation of longer wavelength.
Hence, the response of the photocell I9 due to
of the lamp I5, >and a glass plate I1 coated with
a 4thin layer or deposit of cadmium borate phos
phor is placed in line with the cell IB to receive
due to the visible spectrum of the mercury arc
the lines 578.0, 546.1, 435.9 mmu, etc., in the sys
tem, will be negligible. The residual response
radiation transmitted therethrough. The cad 40 will be due to the very feeble lines in the red and
near infra-red, If not accounted for, this radia
mium bor-ate phosphor is strongly excited Iby
tion in the red and near infra-red portions of
radiation »of 253.7 mmu wavelength, is weakly
the spectrum would give rise to a concentration
excited by near `ultraviolet light, and receives-no
excitation at all from visible light.
When ex
cited by ultraviolet ligh-t alone, «the cadmium
borate phosphor iluoresces in the orange and red
part of the spectrum.
According to R. N. Thayer and B. T. Barnes (J.
error of a smallness comparable with that under
2.0 percent discussed above in connection with
Equation 5. Instrument calibration may be re
lied upon to take care of this small error.
Ac
cordingly, the photocell I9 (which may be of the
blocking-layer
type) will give rise to a photo
Optical Soc. Am. 29:131 (March, 1939)), the
spectral excitation curve of cadmium borate 50 current which is primarily dependent upon and
responsive to the intensity of 253.7 mmu
phosphor is negligible for wavelengths -greater
radiation.
than approximately 380 mmu and, in going «to
The deflection of a galvanometer 20 connected
ward shorter wavelengths, rises very steeply, be
in series with the photocell I9 will be proportional
ing very substantial at a wavelength of 253.7
mmu. When the values for relative energy given 55 to the photocurrent produced thereby. With a
uniform amount of 253.7 mmu radiation being
in Table I are multiplied by the spectral excita
supplied to the absorption cell I6 from the mer
tion values given by Thayer and Barnes, the ex
cury
vapor lamp I5, the photocurrent will be
citation due to 253.7 mmu radiation, and excita
proportional to the intensity of the 253.7 mmu
tions vdue to neighboring lines are obtained as
radiation transmitted through the absorption
cell I6, and accordingly will vary inversely with
given in the following table:
the ozone concentration therein. To calibrate
the apparatus, a table of galvanometer deiiec
Table III
Wavelength, mmu
eììâläëi‘èì
tions and corresponding values of ozone concen
tration may be prepared for the system of Fig. 2
65 according to the method as described above in
11,300
connection with the system of Fig. 1.
25. 0
The systems described above in connection
6. 6
7. 5
with Figs, l and 2 of the drawings serve only to
25. 0
15. 0
6. 0
measure or indicate ozone concentrations.
Such
70 apparatus, while perhaps suitable for measuring
the concentration of ozone in various gas sam
ples from time to time, is inadequate since there
It will be seen from Table III that the relative
excitation of the fluorescent-plate I'I due rto_253.7
are many applications and instances where it is
necessary to measure and record the concentra
mmu radiation is 11,300, whereas that due to the 75 tions of ozone and other gases and vapors in a
2
@211,672
âontinuou's manner. In Figs. 3'and 4 of the draw
ings, such a system for measuring and record
-lower set so _as to prevent Ainterference due to
light leakage` therebetween.l
`
,
.
„
When the concentration recorder of Fig. 3 is
ing 'ozone concentrations in a continuous man-being used to measure and record ozone‘concen
ner is shown. The general arrangement and
broad principles of operation of my concentra 'Cil tration, the mercury vapor lamp 25 serves as a
source of 253.7 mmu radiation. The fluorescent
tion recorder may be conveniently understood by
plate 33 and filter 35 forming the upper. set, of
a brief, general description thereof taken in con
light conversion and selection elements, trans
nection with Figs, 3 and 4, while a detailed
description of the various operating parts
form the ultraviolet 253.7 mmu radiationinto
and elements thereof can be advantageously al!) visible light and isolate thegother neighboring
lines of the mercury spectrum, so that the re
given below.
sponse of the upper photocell 31 is substantially
Accordingly, referring to Figs. 3 Vand V4 of the
entirely due to the amount of 253.7 mmu radia
drawings, there is shown at 25 a mercury .vapor
l,tion passing the photometer. The manner, in
lamp, which may be in the form of an M-shaped
which this light conversion and isolation is ac
Westinghouse “Sterilamp,” and which serves as
complished is described above in connection with
a source of ultraviolet light. ’I‘he light energy dis
tribution characteristics of the vapor lamp 25
have been described above in connection with
the mercury vapor lamp I5 of Fig. 2. A pair of
quartz-window absorption cells 26 and 21 are `
placed to the right of the lamp 25 so as to receive
ultraviolet light therefrom. The rays of radia
tion from the lampy 25 to the cells 26 and 21 are
indicated in broken line. The upper absorption
cell 26 serves as the “active” cell through which
ozone gas may be circulated, When the concen
tration of ozone or other gas or vapor in air is
being measured it is not necessary to provide
the lower absorption cell 21. However, when the
Fig. 2. Likewise, the fluorescent plate 34 and
filter 36, forming the lower set of light conver
sion and selection elements, convert the ultra
violet 253.7 mmu radiation passing through
those elements into visible light, so that the re
sponse of the lower photocell 33 will be substan
tially entirely dependent upon the amount of
253.7 mmu radiation passing through the win
dow 36.
The photocells 31 and 33 comprise part of an
electrical control system for controlling a re
versible motor 45. The control system for the
motor 45 is indicated diagrammatically in Fig.
The details of this electrical
control system will be fully described below. The
electrical control system and the reversible mo
concentration of a solute in a solvent is being 30 3 by the box 46.
measured, the clear solvent should be placed in
the lower absorption cell 21.
A plate 28 is placed a short distance to the right
of the absorption cells 26 and 21, this plate hav
ing two rectangular openings or Windows 29 and
30 formed therein. The windows 26 and 36 reg
ister with the upper and lower absorption cells
26 and 21, respectively, so that light from the
lamp 25‘passing through> the absorption cells 26
tor 45 are energized from the source of alternat
ing current as indicated by the circuit diagram
in Fig. 3.
The reversible motor 45 operates the photom
eter by shifting the ‘ photometer member 3I
back and forth in different positions across and
in front of the upper opening 29.
The driving
and 21 alsov passes through the openings 29 and 40 connection between the motor-45 and the vari
able aperture member 3l is indicated in Fig. 3
36. A photometer member 3l, the construction
by
the broken line connection therebetween. Re
and design of which is described in detail herein
ferring particularly to Fig. 4, this driving rela
after, is shiftably mounted in front of the upper
between the motor 45 and the variable
opening 29. The photometer member 3| and the 45 tionship
aperture member'â'! is shown in detail. A Worm
opening 29 together form a variable photometer
41 provided on the end of the rotor vshaft 48
aperture for measuring light passing through the
of the reversible motor 65, serves to drive a worm
upper absorption cell 26. An adjustable shutter
wheel 49. A cord 56 runs over a pulley 5I on
member 32 is provided in the back of the lower
one side of the worm wheel 43 and a second
window 33 which serves to adjust the Width
50 pulley 52 mounted to the left of the photometer
thereof.
member 3I. One end of the cord 56 is fastened
A pair of the light conversion and selection
to the upper right hand corner of the photom
systems described in connection with the system
eter member 3I at 53, and the other end of the
of Fig. 2 of the drawings are incorporated in
>cord 56 is fastened to the upper left hand end
the concentration recorder of Fig. 3; that is to
of the photometer member 3l as indicated at 54.
say, the system or combination formed by the
The pulley 52 is carried on a bell-crank lever
fluorescent plate I1 and the ñlter I8 of Fig. 2.
55 which is pivotally supported at the point 56.
In Fig. 3, a cadmium borate phosphor coated
A spring 51 connected to the lower arm of the
plate 33 is positioned to the right of the upper
bell-crank 55 and a rigid part of the recorder,
opening 29, while a similar fluorescent plate 34 60 serves to tension the pulley 52 toward the left,
is positioned to the right of the window 36. The
thereby maintaining the cord 50 in a taut con
fluorescent plates 33 and 34 may have the same
dition.
excitation characteristics as the fluorescent plate
The record of the concentration recorder is
I1 described in connection with Fig. 2. 'A pair
made on a time-driven chart 58 by a stylus or
of red filters 35 and 36 are placed to the right 65 pen 59 carried on the end of an arm 66 extending
and in back of the fluorescent plates 33 and 34
from the left hand side of the photometer mem
respectively, so as to receive fluorescent light
ber 3I.
therefrom. The filters 35 and 36 may be of the
In operation, the concentration recorder- is
Wratten No. 25, or “A” ñlter type, having the
first adjusted for zero reading. When used to
absorption characteristics described in connec 70 .measure and record the concentration of ozone
tion -with filter I8 of Fig. 2. A pair of photocells
in air, this initial adjustment is made with the
31 and 3B are placed behind the filters 35 and 36,
upper and lower absorption cells 26 and 21 con
respectively, so as to receive light passing there
taining air only. It will be understood that the
through. A horizontal partition 36 ,serves to
4photometer member 3l has different positions
separate the upperfset Vof elements from the 75 ranging `from that, corresponding to zero ozone
2,411,672
10
concentration to that corresponding to the max
imum'` ozone concentration which the recorder
6|, 62, and 63 of exponential shape formed there
in. Three openings 6|, 62 and 63 are used soas
to reduce photometric error. _If -a single large
is .adapted Ítoîmea'sure.v In making the’zero ad
justment the width of the window 30 is regu
lated by the shutter 32 so that the system will be
balanced when the photometer member 3| is in
zero position. That is, the Width of the lower
window 30 is adjusted so that the amount of
253.7 mmu radiation passing therethrough is suf
ñcient to effectively balance the amount of 253.7
opening were used instead, it will be seen, on re
ferring to Fig. 3, that the points of fluorescence
on the plate 33 would move from a central area
to cover most of the plate 33 on shifting the mem
ber 3| from >its zero position shown in Fig. `4~-to
its opposite position where the greatest amount
of light is passed thereby. This fanning or wid@
ening out of the excited iiuorescent area might
give rise to a photometric error, since ,the ref
sponse of the upper photocell 31 to fluorescent
light of given source intensity depends upon the
mmu radiation passing through the photometer,
when the member 3| is in its zero position.
After this adjustment has been made, the re
corder is in condition to measure and Arecord
ozone concentration.
~
,
15
When the concentration recorder is'put into
operation and ozone is circulated through the
upper absorption cell 26, the intensity of 253.7
mmu radiation transmitted through this cell will
be reduced in accordance with the concentration 20
of ozone therein. As a result, the amount of 253.7
mmu radiation passing through the photom
eter will be correspondingly reduced, and with the
position of the source on the fluorescent plate
33. Theoretically this error would be minimized
to a negligible value if a large numberof equally
spaced openings having parallel axes'were _cutin
the photometer member 3|.
Since such an ar
rangement would be impractical, the three elon
gated openings 6|, 62and E3 were chosen. ’I‘he
photometric error with the three openings has
been found to be sufficiently small so thatv the
photometer member 3| in its zero position, will not
over-all accuracy of the recorder is not impaired.
be sufficient to balance the amount of the same 25
The calculation of the shape'of the openings
radiation passing through the lower window 30.
6|, 62 and 63, may be explained as follows, with
Accordingly, the control system will be unbal
reference to Fig. 6:
anced, and the reversible motor will be operated
g=width of the opening 29,
so asA to shift the photometer member 3| from
its zero position to a position where a sufiicient 30 w=total opening in member 3|,
Let œ=distance on recorder chart=distance oi'
amount of the 253.7 mmu radiation is passed to
motion of the member 3| from the origin or
balance that passing through the lower window
zero position.
30. Thereafter, as the concentration of the ozone
We know that the transmittance of the ozone is:
circulated through the absorption cell 26 changes
from time to time, the photometer member 3| 35 T’=10*“cf, where a=extinction coefficient=69,7[)0
cm.2/g.
will be shifted from one position to another so as
to keep the system in balance. The concentra
tion will be recorded on the chart 58 by the ele
ment >59 which shifts with the photometer mem
ber 3|. The details of the photometer and the
electrical control system are described below.
It will be seen that the photometer system, of
the concentration recorder is of the so-called
"null balance type.” That is, a definite relation
ship is maintained between the amount of 253.7 45
mmu radiation passing through the photometer
comprising the photometer member 3| and the
opening 29, and the amount of the same wave-`
length radiation passing through the adjustable
t=thickness of ozone in cm.
c=concentration of ozone in g./cm.'°`.
Since we desire a linear scale, c=lc2m~
The photometric method calls for constant flux
of 253.7 rnmu radiation going to the fluorescent
plate; hence, calling :rm the maximum displace
ment .in operation of the photometer member 3|,-`
we may «Write
'
'
Y
(6)
lower window or aperture 3U. The great advan-` '
tage afforded by the employment of the “null
balance type” of photometer system is that the'
accuracy of the concentration recorder is not af->
fected by changes in output of radiation from the
vapor lamp 25 due to changes in line voltage. f
The concentration recorder will thus accurately
measure and record independently of Variation
in output from the lamp 25.
Photometer system
where T'mn is the value of T’ at mm and at maxi
mum recorded concentration. The object is to
find a function of .r which will satisfy the above
integral equation. It is easy to show that the
solution is a simple exponential function:
Put f(:r)=AeBœ. Then, substituting and inte
grating, we obtain:
(7)
60
For accuracy and convenience, it was found
desirable to provide a photometer having a linear
scale so designed that the amount of shift of
or
(8)
the photometer member 3| from its zero position
required to balance the system should be a linear
and,
or straight-line function of the ozone concentra
tion in the absorption cell 26. Reference may be
made to Figs; 5 and 6 of the drawings for a de
therefore,
tailed description of the variable aperture mem
ber 3|. (Fig. 5 is a rear View of the photometer 70.
when
member 3| in respect to its position shown in
Figs. 3 and 4 with the opening 29 indicated in
broken outline.)
It will >be noted that the variable .aperture
member 3| has three similar elongated openings 75
,
¿80cm-m) =e2,303k2at(mm-m)
B=2.13037c2at
'
for) =`A1ok2m
2,411,672
1.1i
Finally, the equation >for the totalopening in
the exponential opening becomes v
vWe may select as the following values of con
stants, values which were actually used in the
design of the photometer member of a success
fully >operated ozone recorder instrument to be
described hereinafter:
'
:rmà3.5"=8.89 cm.
g'=2.00 cm.=(0.'788")
b‘='2.20 cm.
c1a,='(11.8).10-6g/cc. (equivalent to 1 per cent,
based on weight for dry air at 21° C‘., 'l5
cm. Hg pressure)
lc2=(1.'327).10-6g/cm.4
t'_=0.400 cm.
_ With these values, Equation 9 becomes:
(10)
f(:c) = (2.20) .10-0.-037/10-89-f)cm.
.Computations were made from Equation 10,`
12
ness (inside width) should be 0.98 of the theoreti
cal thickness. Thus, with a theoretical inside
cell thickness t of 0.400 cm., the actual inside cell
thickness should be
0.4 x 0.98 or 0.392 cm.=0.1543 inch
Electrical control system
The electrical control system employed in con
nection with the concentration recorder dia
grammatically shown in Figs. 3 and 4 constitutes
an important feature of the invention, and in
volves the use of a novel type of electrical bridge
circuit for controlling gas-filled electric valves.
The principles of my electrical control circuit are
15 described below in
connection with Figs. 7
through 12.
Referring particularly to Figs. 7, 8 and 9, the
following observation was made in experiments
with a single blocking-layer photocell on the in
20 put of an oscilloscope. With the photocell 65
connected across the input of the oscilloscope
56, as shown, and exposed to an intense source
of light showing a strong periodic variation in
intensity, a voltage wave of insignificant ampli
andthe results are presented in the following
table:
Ã
Table IV
25 tude was observed on the fluorescent screen 6l
of the oscilloscope. However, when the un
earthed terminal of the input was connected to
a: (cm.)
j' (I) (cm.)
a short antenna, as indicated by the broken line,
to pick up the sixty-cycle wave, the wave form on
--0. 5
0. 835
30 the vfluorescent screen 61 changed very markedly
0. 0
0. 871
1.0
0. 948
as sketched in Figs. 8 and 9. In Fig. 8 the sixty
2. 0
1. 031
cycle sine wave is shown which is obtained when
3. 0
1. 126
4. 0
1. 223
the photocell 65 is in the dark. However, when
5. 0
1. 332
the photocell 65 is exposed to low illumination
6. 0
1. 450
7. 0
1. 579
35 of either steady or fluctuating intensity, the sine
8. 0
l. 718
wave is materially changed in one half part of
9. 0
l. 872
10. 0
2. 038
the cycle as shown in the sketch of Fig. 9. The
11.0
2. 220
broken line part of the sketch in Fig. 9 indicates
12.0
2. 42
13. 0
2. 63
the normal- sine wave pattern. The explanation
40 off the‘change'in sine wave as shown in Fig. 9,
is that’illumination decreases the shunt resist
" The values given in Table IV are equally di
ant across the input terminals of the oscilloscope
vided between the three parallel elongated _open
ings B'I, 62 and 03. In the photometer member
designed for the working embodiment of Vmy in
vention, the axes of the openings 6I,'62 and 63
are each separated by a distance of 0.85 cm. The
Eßfduring one-half of the cycle.
Although it
was known that the internal resistance of a block
ing-layer cell depended upon the intensity of
light falling upon the photocell, it was surpris
ing to find 'that the sensitivity of change of wave
openings 6h62 and 63 are somewhat longer than
form to light was very much greater than the
3.5 inches (mm) so as to permitoverplay at zero
direct photoelectric eiîect, where a rapidly ñuctu
and maximum concentrations. (A distance on 50 ating source of light is involved, and one is inter
the recording chart of exactly 3.5 inches was
ested only in the alternating current component.
chosen for the range in ozone concentration of
from 0.0 to 1.0 percent.) As indicated in-the
By way of explanation, it appears that the direct
photoelectrio effect was impaired by the low im
foregoing theory, all calculations have been based
pedance of the blocking-layer photocell.
on concentration ofozone expressed in grams per 55. It lWas found that the above observation of
cubic centimeter. (g./cc.). Percentage composi
the. sensitivity of wave form to light of a block
tion, based on weight, is made relative to the
ing-layer photocell could be used to provide an
density of dry air at 21° C., 75 cm. Hg atmos
electrical bridge circuit which was very sensitive
pheric pressure.
Í
to small relative changes in light flux from two
In making the above calculations it has bee 60 light sources so as to produce large changes in
assumed that all of the rays of 253.7 mrnu radia
wave form. Such a bridge circuit is shown di
agrammatically in Fig. 10 of the drawings.. .
V tion passed through the absorption cell in a direc
tion perpendicular to the quartz windows there
Referring to Fig. 10, it Will be seen that the
of. In any practical arrangement this condi
electrical bridge circuit comprises four legs con
tion cannot be completely met and, therefore, the 65 nected to provide two parallel branches. One
pair of the legs or one branch comprises adjust
incident rays are not perpendicular to the ab
able impedance devices indicated diagrammat
sorption cell but actually cover a range of angles
ically at 10 and ll, and the other pair of legs
from zero degrees to a certain maximum value
constitutes the other branch, each leg including
dependent upon the size of the light source, the
size of the absorption cell, etc. On the basis of 70 a blocking-layer photocell indicated diagram
matically- at 'l2 and 73. The-photocells 72 and
sound theory the error due to this deviation from
'i3 should be matched for sensitivity, internal re
the ideal picture may be calculated. Such calcu
sistance and capacitance. Each of the pairs of
lations have been made for the dimensions used
legs are connected in series circuit relation and
in the ozone recorder instrument described4 here
inafter. They showed that the _actual cell thick 75 the 'pairs of legs are then connected in parallel
2,411,672>
13;
to provide a circuit having> two parallel branches,
as shown. The conductors 14 and 15 serve to con»
neet the bridge with a source of alternating cur
rent indicated diagrammatically at 18. Adjust
able impedance devices indicated diagrammat
14
cuit was an important factor. When this volt
age was raised to a certain maximum value (two
or three volts), depending upon the particular
circuit involved, the circuit was no longer sen
5 sitive to changes in illumination on the photo
ically at 69 and 11 may be connected in shunt
cells 12 and 13, and an essentially sinusoidal wave
relation with the photocells 12 and 13 respec
form was observed on the screen of the oscil
tively. lThe adjustable impedance devices 69 and
loscope 8|. However, when the voltage was again
11 may each include an adjustable resistor and
reduced to a value t0 which the bridge became
an adjustable capacitor connected together either 10 sensitive, the wave forms shown in connection
in series or parallel circuitrelationship. The in
with sketch of Fig. 11 were again obtained.
put of an electronic amplifier indicated diagram
It is apparent that the wave form patterns
matically at 18 may be connected across the com
shown in the sketches in Fig. l1 are well suited
mon connections 19 and 80 between each of the
for direct control of electric valves of the gas
pairs of legs, as shown. The output of the am
iilled type (Thyratron or Grid-glow tubes). The
plifier 18 is connected to the input of an oscil
grids or control elements of the Thyratrons
loscope indicated diagrammatically at 8|.
should be operated together and the -plates op
Many interesting effects were observed in con
erated apart by 180 electrical degrees.
nection with this electrical bridge arrangement.
In Fig. l2 of the drawings one type of elec
When an alternating current voltage, within a
trical control system for the concentration re
range to which the electrical bridge circuit was
corder of Fig- 3 is shown, employing the elec
sensitive, was applied across the bridge from the
trical bridge circuit principles described above
source 16, and the bridge balanced through the
in connection with Fig. l0. Referring to Fig.
manipulation of the impedance devices 10, 1| and
12, the blocking-layer photocells 31 and 38 (Fig.
11, the bridge circuit became very sensitive to 25 3) are indicated diagrammatically at 85 and 86
small relative changes in light flux gathered by
in two legs of an electrical bridge circuit. The
one of the photocells. When the cells 12 and 13
are in darkness, the bridge circuit may be bal
anced so as to obtain the residual wave 82
sketched in Fig. 1l. This residual wave is indi
cated by the full line having loops of equal am
plitude above and below the reference line. The~
oretically, if the photocells 12 and 13 were iden
tical and completely matched for sensitivity, in
ternal resistance and capacitance, the residual
wave 82 .would be a straight line.
y
photocells 85 and 86 are connected in series cir
cuit relation in one branch of the electrical
bridge by a resistor 81, and the other branch of
the electrical bridge comprises a resistor 88. The
input terminals of an amplifier, indicated dia
grammatically at 89, are connected between the
electrical midpoints of the bridge circuit as in
dicated at 90 and 8|. Since the photocells 85
and 86 cannot ordinarily as a practical matter
be perfectly matched for internal resistance or
capacitance, an adjustable resistor 02 and a
variable capacitor 83 are connected in shunt cir
cuit relationship with one of the photocells 85
The change in wave obtained when one of the
photocells receives an increment in light flux or
illumination not accompanied by a similar in
or 86.
crement received by the other photocell, is indi
cated by tlie Waves 83 and 84, the wave 83 being
The bridge circuit may be energized from a
designated. with dots and dashes, whereas the
transformer, indicated generally at 94, having
wave 84 is designated with uniform dashes.
its primary winding 95 connected for energiza
Referring to the sketch of Fig. l1 it will be seen
tion from a 1l5-volt alternating current source,
from the waves 83 and 84 that peaks 360 electrical 45 and having a secondary winding 98 of few turns.
degrees apart, relative to the potential source‘16
The secondary winding 98 is connected across
connected across the parallel branches ofA the
the branches of` the bridge circuit through an
bridge circuit, increase, and alternate peaks (180°
adjustable resistor 91 whereby the voltage V im
phase difference) decrease, when one of the
pressed across the bridge may be regulated. The
photocells receives an increment in illumination 50 value or the voltage V is ordinarily adjusted to
about 0.25 volt.
`
and, vice versa, the alternate peaksv rise and the
first-mentioned set of peaks decrease when the
The resistor 91 is a low resistant potentiometer
other photocell receives an increment in illumi
rheostat having a resistance of the order of
nation. The wave 83 represents the wave ob
1000 to 2000 ohms, the exact value not be
tained when one of the photocells 12 or 13 re 55 ing critical. The resistors 81 and 88 may be
100G-ohm potentiometer rheostats, and the re
ceives the greater illumination, While the wave
84 represents the wave obtained when the other
sister 92 may be a 10,000-ohm rheostat. The
photocell receives the greater illumination. It
exact values of the resistance 92 and the capac
should be noted that peaks of the same potential
itance .93 depend upon the degree of difference in
are produced during each half cycle of the po „o impedances of the photocells 85 and 86. It will
tential source 16 when the relative illuminations
be understood that these details of the electrical
of the two photocells are at proper values. This
bridge circuit are not critical and that certain
other arrangements may be used.
is most unexpected, and as will hereinafter ap
pear, most useful phenomena. When light flux
As stated, the wave form pattern obtained with
to the two cells 12 and 13 is greatly increased, 85 the electrical bridge is well suited for direct con
but balance (through only change in relative
trol of gas-filled electric valves, of the type com
flux), the residual wave 82 shown in the sketch
mercially available as Thyratrons (General
of Fig. l1 docs not change greatly in either am
Electric) or Grid-glow tubes (Westinghouse).
plitude or phase, the change in phase being very
Accordingly, the output of the amplifier 89 is
small; moreover, the phenomenon is not sig 70 capacitively coupled to the control grids of two
nificantly altered when a strongly pulsating light
such electric valves |00 and |0|, as shown. The
source (l-tube G, E. Mazda fluorescent lamp) is
grid bias is supplied and the firing points of
used.
the electric valves |00 and |0| adjusted, by volt
It was found that the value of the alternat
age from a battery indicated diagrammatically
ing current voltage impressed on the bridge cir
75 at. |02 through suitable adjustable resistance,
2,411,672>l
as'shown. Only low ampliñcation 4is necessary,`
and the ampliñer 39 may be of the conventional
ment which is under the'ï'partition ||4 and back
of theV partition I|3. The recorder compartment
two-stage type.
includes that portion in front of the partition I I3
The tube y| 03 is connected in series with one of
the ñeld coils (not shown) of a reversible motor
E33 while- the other tube Iiìi `is connected in se
ries with the other neld coil oi' the reversible mo
tor. The ñlaments or heater elements of the
electric valves ||l|3 and Iûi are connected for
energization to the secondary winding |06 of a 10
and extends over the rectiñer compartment II 8.
The side walls (not shown) Vof the instrument
may be constructed with lightweight sheet steel, '
bent at the corners and bolted to the steel frame.
The back wall should be hinged so that free ac
cessrto- the recorder and rectifier compartments
II1v and I|8 may be had. The front wall should
transformer |37, having its primary winding |08
contain an opening so as to permit ready access
connected across a 115-volt alternating current
source. The motor |33 may be of the direct
to the recording chart. Y
current, fractional horse power type and has
_
ings, it will be seen that the vertical partition I II
has a pair of beveled-edged upper and lower open
ings or apertures |23 and |2I', respectively,
one terminal of one' of its field-coils connected
to one side ci“ the secondary winding I G4 of a
transformer indicated generally at |35, While
one terminal of the other ñeld coil is connected
to the oppositeV side of the secondary winding
|04. Each of the other terminals of the ñeld 20
coils is connected through one of the tubes |00
or EûI and through the armature of the motor
|33 to the center tap of the secondary Winding
'
Referring to Figs. 13a, 14a, and 16 of the draw
formed therein. A variable aperture, photometer
member |22, constructed according to the theory
described above in connection with Figs. 5 and 6,
is shiftably supported on the right hand side (re
ferring to Fig. 16) of the upper opening |26. The
photometer member |22 is supported by a pair
of upper and lower ñanged rollers |23, and an
arm |24 fastened to the right hand end thereof
-It will be seen that the control grids of the 25 which passes through a hole in the vertical par
I4.
‘
-
electrontubes lilû'and IBI are operated together
while the plates thereof are operated 180 elec
trical degrees apart. As described in connection
tition |I2. The arm |24 is supported and guided
between a pair of guide rollers |25 (Figs. 13b and
14h) mounted on the side of the partitionl I2.
with Figs. 10 and l1, small changes in light ñuX
A quartz-window ozone absorption cell I 26 is
to, for illumination of,` either of the blocking 30 mounted in front of the photometer member |22.
layer photocells 85 and 85 will distort the
The absorption cell |26 is supported by a pair of
residual-balance `wave of the bridge circuit so
conduits |21 which also serve to conduct ozonated
as to »produce either the wave form 83 or 84
air to and from the absorption cell |26 for- cir
(Fig. 11), depending upon` which o‘f-the photo
culation therethrough. A dummy, quartz-Win
cells receives the greater illumination. Accord 35 dow absorption cell |28 (Fig. 16) is supported in
ingly, when the balance between the illumina
front of the lower window |2| by a pair of sup
tion of the photocellsl 85 and 83 is changed in
port members |29. Since the recorder is intend
one direction 'one of the 'tubes' I8 or IIlI will
ed to measure the concentrations of ozone in air,
ñre, while if the illumination is 4unbalanced in
it is not necessary to circulate air through the
the opposite direction, the other tube will fire. 40 dummy absorption cell I 28. However, if the con
Since each of the ñeld coils of -thevreversible
centration' of a solute in a solvent were beingmotor |33 is connected with one of the electric
measured, conduits would be connected with the
valves IUS or Ißl, the motor will run in one
dummy absorption cell |28 so as to circulate the
direction or the other depending upon which of
clear solvent therethrough.
the tubes is caused to iire. Referring back to 45
The rectangular separator |33 for the absorp
the operation of the concentration recorder as
tion cell |26 may be cut out of a brass plate and
shown diagrammatically in Figs. 3 and 4, it will
the two faces thereof ground so as to be parallel
be seen that the bridge circuit will continue to
and
as smooth as possible. The reduced diam
be unbalanced and one of the tubes IBI) orV IGI
will `fire until the motor I|l3 has driven the 50 eter. nipples |34 entering the top of the frame
|33, may be soldered into the couplings |35 and
photometer member to a point where the bridge
the
separator |33. No organic material should
circuit is again balanced.
be present in the conduits |2'I or the absorption
' Employing the principles of my invention de
cell |26 since such material will cause a rapid
scribed above, an ozone concentration recorder
adapted to measure the concentration of ozone- 55 absorption of ozone and lead to an error in
reading. The quartz-windows |38 may -be ñrmly
in air up to 1.0 per cent was constructed. The'de
held in place to the opposite sides of the separa
tails of this recorder are described below in con
tor |33 »by pinch clamps (not shown), and the
nection with the remaining ñgures of the draw
ings.
Design of ozone recorder
cell may be sealed by molten paraiîin painted
around the edges thereof and allowed to solidify.
60 The lower absorption cell |28 may be constructed
in the same manner as the absorption cell |26.
Referring to Figs. 13a, 13b, 14a and 14h, the re
In order to adjust the Width of the lower win
cording instrument is housed in a box the frame
dow
|2| so as to adjust the recorder for zero read
elements of which comprise angle iron members
|||i welded together at the eight corners of the 65 ings, a shiftable shutter |40 is provided having a
supporting arm I4I (Fig. 14a) extending there
box. The box is 29 inches long, 10 inches wide,
from. The arm |4| is supported between‘a pair
from front to back, and 13 inches high. Three
of capped-pins |42 and the position of the shut
vertical partitions |||, H2 and IIS, and one hori
ter |40 may be adjusted by a screw |43 project
zontal partition I I4 divide the interior of the box
into four compartments. The four compart 70 ing into the internally threaded end of the arm
|4|. The head of the screw |43 extends through
ments may be designated as “light source com
the partition ||2 so that it may be reached with
partment” H5, “photocell compartment” I I6, “re
a screw driver and the position of the shutter |40
corder compartment” IIl, and “rectiñer com
adjusted vby turningthe same..v A spring I 44 com
partment” | I8. It will be noted that the rectifier
compartment I I8 is4 that .portion of the instru
75 pressed between the partition I I2 and a. collar | 45
17
2,411,672
18
on the end of the arm I4I serves to securely bias
and hold the shutter |40 in position.
As shown in Figs. 13a, 15 and 16, an M-shaped
same elevation as the center of the upper absorp
mercury vapor lamp |50 may be used as a source
tion cell |26 and the photometer, whereas the
of the mercury vapor lamp |50 is so adjusted
that the center thereof is at approximately the
of 253.7 mmu radiation. The lamp |50 may be
dummy absorption cell |28 is arranged at some
of the type commercially available on the market
distance (approximately 2 inches) below the line
as the Westinghouse “ Vterilamp.” The charac
of centers of the lamp |50 and the photometer.
teristics or“ the radiation of such a lamp have
This arrangement is made so as to obtain good
been described above in connection `with the sys
photometric accuracy since the radiation should
tem of Fig. 2 of the drawings. The lamp |50 is lil pass through the absorption cell |26 and pho
supported on a backing member |5| by a pair
tometer in as nearly parallel rays as possible.
of bands |52 (Fig. 15) which are spring tensionecl
On the other hand, it is not a matter of impor
by a pair of tension springs |53 inserted between
tance if the radiation from the lamp |50 strikes
the back |5| and retaining washers |54, as shown
in Fig. 13s. The backing member |5| is sup- .
ported from the bottom plate of the instrument
box by a pair of uprights |55 fastened at their
lower ends in a pair of blocks |56. The front
face of the backing plate I 5I, which may be made
of Bakelite, is smoked with magnesium oxide as
indicated at |51 so as to substantially increase
the amount of 253.7 mmu radiation radiated to
the photometer part of the instrument. An
opaque metal screen |58 (Figs. l5 and 16) is
placed around the lamp I y5I) so as to block out all
ultraviolet rays originating in the light source
excepting those which proceed to the photometer
assembly. The purpose of the screen |58 is to
prevent unnecessary deterioration of wire cover
ings and other organic material in the light
the lower iluorescent plate |12 at an oblique angle
after passing through the dummy absorption cell
|28, and the lower Window |2|. This is due to
the fact that it is only necessary that the per
centage change in light flux passing through
the Window |2| and incident upon the lower ñuo
rescent plate |12 due to change in output from
the lamp |50, be the same as for the correspond
ing percentage change in flux passing through the
absorption cell |26, the photometer, and inci
dent upon the upper ñuorescent plate |'I I.
There has been found to be an optimum sepa
ration between the upper fluorescent plate I1I
and the photometer member |22. This optimum
separation eliminates error and the necessity for
a perfect uniformity of the coating of cadmium
borate phosphor on the plate. This will be un
source compartment I | 5.
derstood on reference to Fig. 16 where it will be
Referring again to Figs. 13a, 14a, and 16 of the
drawings, it will be seen that the light conversion
seen that there is a Wide divergence or spread of
and photocell system is mounted as a unit on the
partition | I I on the opposite side thereof from
the rays passing through any one of the three
narrow elongated openings in the photometer
member |22. Thus, the diagrammatic rays fan
the photometer member |22 and the absorption
out in passing through the photometer member
cells | 26 and |28. The unit is enclosed in an out
|22, so as to cover approximately one-half of the
side band |60 ñtting over four square posts ISI
area ofthe fluorescent screen or plate |1I. This
which project from the partition ||I. The front
wide distribution and overlapping of the rays
of the box is closed by a plate |62 having open 40 serves to reduce error due to variation in thick
ings to accommodate a pair of upper and lower
ness of the film of cadmium borate phosphor.
photocells I 63 and |54, respectively. The pho
The reversible motor |80 for shifting the pho
tometer member |22 in opposite directions, is
shown in Figs. 13a and 14h mounted upon a plat
gage the plate |62, and two sets of clips |61 (Fig. 45 form |8| supported by posts |82 extending up
13e). The photocells |63 and |64 are of the
wardly from the bottom of the instrument box.
blocking-layer, iron-selenium type. A pair
The armature shaft |83 extends from the left
tocells I 63 and |65 are held in place in the plate
|62 by the ilanges |65 and |66 thereof which en
of terminals I 6B and I 69 project from the rear
of each of the photocells |63 and |64, respec
hand side of the motor |80 and carries a worm
|84 which engages and drives a worm wheel |85.
tively.
50 The worm wheel |85 is mounted on a horizontal
Each of the photocells |63 and |64 is covered
shaft |86 supported at one end in a bearing |81
with a red ñlter |10. The absorption properties
and at the other end in a bearing in the vertical
of the filters |10 correspond to those of the red
partition | | I. A pulley |90 is secured to the shaft
ñlters I8 described in connection with Fig. 2
|86 adjacent the vertical partition | I I over which
of the drawings. As stated, these iìlters may 55 a driving cord I9I runs. One end of the cord
be of the type known as Wratten No. 25.
|9| is secured to the upper left hand corner of
A pair of fluorescent glass plates |'|I and |12
the photometer member |22 as indicated at |92,
are mounted in front of each of the photocells
While the other end of the cord is secured to the
|63 and |64, respectively, and supported in the
upper right hand corner of the photometer mem
thin metal frame |13. The fluorescent plates I1I
ber |22 as indicated at |93. The driving cord ISI
and |12 are coated with a ñlm or deposit of
passes from |92 around the pulley |90 and thence
cadmium borate phosphor and have the excita
around an idling pulley |94 carried on a pin pro
tion characteristics describe-d in connection with
jecting from the upper end of an L-shaped lever
the fluorescent plate |1 of Fig. 2 of the draw
|95. The pin on which the pulley |94 is sup
ings.
Horizontal separators |14 and |15 (Fig.
I6) are provided in the unit to prevent fluores
cent light from either of the fluorescent plates
|1| and |12 from reaching the photocell |63
or |64 associated with the other nuorescent
plate. The interior surfaces of the enclosing
members |60 and |62 and the surfaces of the
frame |13 and separators |14 and |15 should
be painted in ñat black so as to minimize the
ported passes through a window |96 cut through
the Vertical partition I||, and the lever |95 is
pivotally supported to the partition III at |01.
A spring |98 serves to bias the idling pulley |94
toward the right and keep the cord |9| under a
tension substantially greater than that required
to move the photometer plate |22 and the re
cording pen or stylus 200 (Fig. 13b). In this
manner, friction is minimized and dimensional
effects of stray light.
changes in the length of the driving cord I 9|
From Fig. 16, it will be noted that the position 75 are automatically compensated for.
annoia
'Referringto Figs. 13s and'láß, for a'l descrip,
tion of the recording‘apparatus, it will be seen
that a synchronous Amotor 28! is mounted .on top
of the rectifier compartment i l2; A small pinion
gear 202 (Fig. 14h) is carried on the driveshaft
of the motor 22| and meshes with a‘large gear
wheel 203 mounted on one end of a shaft 222; The
are' connected >in -parallel across the terminalsof ,
the secondary winding 231 of a step-‘down trans
former 238. The'primary windingV 2391s' con
nected for energization across the 1l5-volt line,
as shown. The transformer 232 is approximately
the size andcapacity of a small door-bell ringe
ing transformer, and a secondary 231 consists'
of only» a few turns so that the voltage V im
left’hand’end of the shaft 222 is journaled in a
pressed across the bridge circuit will be in the
bracket 225 which also supports the synchronous
motor 2G I, and the right hand end is journaled in l0 order of 0.25 volt. Since the photocells M53 and
itil cannot ordinarily be perfectly matched for
a b1ock'265 carried on a bracket 22?. The shaft
204 >also carries a worm 268 which serves to drive
_ a worm Wheel 2m keyed to the reduced end 2II
impedance, an adjustable resistor 2d@ and a
variable capacitor 2li! are connected in shunt
circuit relation with at least one of the photo~
(Fig. 13b), of a stub shaft 212. The stub shaft
2 I 2 is journaled in a bearing 2 I 3 carried on top of 15 cells so as to balance them for difference in
the bracket 120'!V as shown.
internal resistance and capacitance. The photo
A collar member 2id' having a large diameter
cells E63 and Milt may be thus balanced for in
flange 255 is carried on the front end of the
ternal resistance and capacitance by proper ad
shaft 2l2. The flange 2i5 serves as a back sup
justment of the resistor 22d and capacitor 2M.
port to which a chart disc 2 l5 is held. The chartv 20
The input of an electronic amplifier, indicated
disc ZIBv ñts over the end of the shaft 2I2 and
diagrammatically at 2fi5, is connected across the
may be secured to the flange 2 I5 by screws pass
electrical mid~points of the bridge circuit, as ina.
ing therethrough. Chart paper may be held
dicated. The ampliñer 225 may be energized
against the chart disc 2l?) by a large nut 2i?. A
from the llö-voit current source through a pair
thin metal plate 22€) having allarga circular open~
of conductors or leads 2F56> and '222. The out
ing therein to accommodate the chart disc 2I6 is
put of the ampliner 2Ái5`is'capacitively coupled
vertically supported around the disc 2lb. Ears
to the control «elements or grids 2&2 and 229 of
or tabs 22I are bent out from the> thin sheet
a pair of gas-ñlled electric valves 252 and 25|.l
222 at diiîerent positions therearound‘and serve
The tubes 252 and 251 are of the four-element
to retain alchart paper 222. in vertical position 30 type and are presently classified as FG-QS (Gen
on the disc ZIS.
eral Electric). The grid bias of the control ele
The synchronous motor 20! drives the chart
ments 228 and 229 may be adjusted from a “B”
disc 2I6 at avconstant` speed and a record of
battery indicated diagrammatically at 252,v
ozone concentration is made thereon by the stylus
through suitable adjustable resistance. The
223 of the recording pen 222. The stylus 223 OJ Cil heated filaments 252 and 25? of the electric
is carried in a receiver 22:2> having a removable
valves are connected for energization with the
cap 225. A weak spring 226 within the receiver
secondary 252 of a transformer. indicated gen
22d serves to pressk the stylus 223 gently against
erally at 259.
the chart paper on the chart disc 216. The
One of the field coils 222 of the reversible
recording pen 22iâ‘isv adjustably mounted on the
motor i8@ is connected in'series circuit relation
end of the square arm'22álby a pin 221. The
with the electric-valve 252, while the other ñeld
pin 22'! is adjustablewithin a socket in the end
coil 255i is connected in series circuit relation with
of the arrn 222» and may be fastened.v imposition
the other electric valve 25i. As will be seen, the
by a set'screw 223..
.
circuit for the i'leld coil 2S@ is completed through
In order that the ozone vconcentration may be ' one~half of the secondary winding’ 262 of the
conveniently read at any time, a scale 22Sv (Fig.
transformer 25%, the armature of the motor |83,
14s) is supported. beneath the. arm £24, and a
and the tube 25€), the armature being connected
pointer d@ is vcarried below the arm |24 so as
to the center-tap of the secondary winding 262.
to passover the divisions ofthe scale 22S. The
rilhe circuit for the field 'coil 265 is completed
scale229 is calibrated-in percentage ozone con
through the other half of the secondary 222;V the
centration from 0.0 to 1.0 per cent, as shown.
armature of the motor |80; and the other tube
ri‘he electrical system'flrst used in my ozone
25E. The primary winding. 253. of the trans
concentration recorder is shown in-Fig. 17 of
former 229 is connected’ for venergization across
the drawings, to which `reference may be had for
the 11E-volt source, as shown. A toggle switch
a description thereof. The recording instrument
222 is provided in the 1l5-volt linewhich serves
may be energized from 115-volt alternating cur
to control the> energizationof‘the recordingin'-l
rent source, as indicated. The synchronous mo
strument except for the “Sterilamp” lamp lei!
tor 2ûI which drives the chart disc 2I6 of the
and the synchronous recorder motor 2S! i
recorder' is connected for energization with the
The fourth elements 265ïand~2âfâ ofthe tubes
115'-volt line through aA toggle switch 230 so that 60 252 and 25E serveto give stea'dier operationV of
itmay be controlled independently of the other
the electrical system. It willbe seen that the
elements in the apparatus.V The mercury Vapor
ground output terminal of the amplifier 265,» the
lamp i553 is connected across the secondary 23!
fourth tube elements Ziìtìand '266, and the center
of a step-up transformer 232. The primary 233
taps of the secondary transformer windingsv 258
of this transformer is connected across the 115 65 and 222 are interconnected or grounded.
volt line through a toggle» switch 232, as shown.
In operation of my ozone concentrationV re
The blocking-layer photocells Iâä and Iâß (Fig.
16) are connected> in one branch of an electri
corder, the electrical ycircuit control system is
ñrst adjusted, conveniently with the help cf an
cal bridge circuit corresponding substantially to
oscilloscope. With the mercury-vapor lamp I5@
the electrical bridge described in connection with 70 turned off, the electrical bridge circuit including
12. One branch of the bridge comprises the
the photocells H53 and Ilëä> is balanced so as to
two photocells ISS and Iâálinterconnected in se
obtain a balanced residual waveform as described
in connection with Figs. l0 andllof the draw
ries circuit relation by a resistor 235, andthe
other- branch~ comprises a potentiometer type
ings. Then, the mercury vapor lamp >I ätjis turned
rheostat 225i.l The two branchesofthe bridgef 75 on and with the absorption cell |25 -entirelyffree
2,411,672
22
of ozone, the width of the lower window I 2| is
adjusted >with the shutter |49 so that the system
including the reversible motor |38 is balanced
trical mid-point of the bridge circuit, as indid
cated. Except for the modification of the elec
trical bridge as described, the electrical control
system by which the Thyratrons or gas-filled
When the photometer member |22 is in its zero
position. As a check (probably necessary only C11 valves 255 and 25| are controlled is the same
in the original test oi the instrument) the in
as the control system shown in Fig. 17.
tensity or output of radiation from the vapor
The residual Wave obtained with the bridge
lamp :|59 is varied through wide limits so as to
of Fig. 18 is very similar to that observed when
ascertain that the recorder gives a constant read
blocking-layer photocells are employed (Fig. l1),
ing in spite of these variations.
10 although the dependence of the amplitude of the
`After the recorder has been thus initially ad
residual Wave on light level is much stronger.
justed, the ozone-air mixture is circulated through
When the phototubes 27d and 275 are in total
the absorption cell |25 by suitable pumping ap
darkness, the residual Wave may be made zero;
paratus. As 253.7 mmu radiation is absorbed by
then, when the light level on the tubes is brought
the ozone on passing through the cell |26, the 15 up and balanced, the residual Wave comes into
system becomes unbalanced and one of the tubes
existence, and increases with increasing light
250 or -25| will nre over a longer portion of the
level.
cycle than the other. Accordingly, the reversible
The use of phototubes of the photo-emissive
motor |80 will rotate in such a direction as to
type as described in connection with Fig. 18,
shift the photometer member |22 to a position
has led to much more satisfactory operation of
permitting more 253.7 mmu radiation to pass
the recorder, since sensitivity is appreciably great
and thereby vbring the vsystem back into balance.
er and the stability or freedom from drift has
Conversely, in the event that the concentration
been greatly increased. Furthermore, it is easier
to obtain photctubes of the photo-emissive type
of ozone in the absorption cell |28 decreases,
thereby ypermitting an increased amount of 253.7
which are matched because it is only necessary
mmu radiation to pass, the firing period oi the
that these tubes be similar in the current-volt
tubes 250 and 25| will again become unbalanced,
age characteristic, Whereas photocells of the
but 4in'an opposite- direction, so as to rotate the
blocking-layer type must match in current-volt
motor |50 in an opposite direction. In turn, the
age characteristic, internal resistance and ca
'
photomete'r member |22.will be shifted so as to 30 pacitance.
decrease the amount- of radiation passing through
As another modification of the electrical bridge
the' photometer. and bring the system b-ack in
of the invention, the photocells employed therein
may be a pair of the early type selenium cells.
' As described, -the'motion of the variable aper
This type of cell is of the photo-conductive type
ture, photom'eter member |22 in 'following the 35 and involves ordinary conduction through a thin
concentration of ozone in the absorption cell |28
ñlm of selenium, which exhibits a change in re
is translated ‘to the recording pen 20D. ' In this
sistance when illuminated.
mannen'the pen makes a record of the ozone
Although I have described an embodiment of
concentration on the chart paper 222 (Fig. 14e).
my invention speciñcally adapted to measure and
'f Although my ozone concentration recorder, as 40 record concentrations of ozone in air, it will be
described above, operated satisfactorily in a prac
understood that modiñcations and adjustments
tical manner, it was found that even much more
may be made so that by applying the same prin
satisfactory operation of the recorder could be
ciples of invention, instruments may be made for
obtained by modifying the electrical bridge of the
measuring and recording concentrations of other
balance.-
'
i
electrical control system of Fig. 17. This modifi-l
cation consisted in substituting light-sensitive
tubes or >photocells of the photo-emissive type
(vacuum or gas-iilled phototubes) for the photo
45 gases and vapors, as Well as certain solutes in
solvents.
'
It will be understood that in apparatus of this
nature, involving as it does a relatively largeA
number of parts and elements organized into dif
ferent systems, certain changes, ' modiñcations
and other arrangements may be made without
departing from the principles and scope of the
cells |63and |64 (Fig. 17) which, as stated, were
of the blocking-layer type.
The modiñed bridge circuit is shown diagram
matically in Fig. 18 of the drawings as electri
cally interconnected between a transformer 210
invention. Accordingly, all matter described
and the ampliiier 245 (Fig. 17). The transformer
above or shown in the accompanying drawings is
210 corresponds in function to the transformer 55 intended to be interpreted as illustrative and not
238 (Fig. 17), but the transformer ratio thereof
in a limited sense.
is greater than that of the transformer 238 so as
I claim:
to impress a greater voltage across the bridge
l. Means adapted to control the operation of
circuit. Whereas it was found that the bridge
electrical apparatus in response to small changes
circuit of Fig. 17 had its greater sensitivity when 60 in light iiux from a light source, comprising a, gas
a voltage in the order of 0.250 was impressed
ñlled valve having control and plate elements, an
across it, it has been found that the bridge cir
electrical bridge circuit having four legs, one pair
cuit of Fig. 18 should have an impressed voltage
of said legs each including an impedance device
in the order of 3 to 5 volts.
and the other pair each including 9, polarized
One branch of the modified bridge circuit of 65 photocell, one of the photocells being adapted to
Fig. 18 is provided with a potentiometer type
receive light iiux from said light source, the legs
rheostat 273 while the other branch of the bridge
of each pair being connected together in series
is comprised of two phototubes 214 and 275 of
circuit relation, said polarized photocells being
the photo-emissive type interconnected in series
connected with unlike electrodes connected to
circuit relation. A small variable capacitor 271 70 gether, and said pairs of legs being connected in
isconnected in shunt relationship with each of
parallel circuit relation, a low voltage source of
the phototubes 214 and 275, as shown, so that
alternating current connected across the parallel
any slight difference in capacitance of the two
connected pairs or legs, a high voltage source of
tubes may be corrected. The input of the elec
alternating current which is of the same fre
tronic amplifier 245 is connected across the elec-v 75 quency as, and which is in phase with, said low
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