Note: Descriptions are shown in the official language in which they were submitted.
~3L3~8~
BACKGROUND OF iq-~E INVENTION
The presen-ti i.nvention conce:rns the appl.icatiorl oL inlrflIed
thermometry -to -the measuremen-l Or the tempera-ture of w:ircs~ bars or
-tubes and me-tal sheets mova.ble in the direct:ion o~` thc-ir length (here-
5 arter tlle word "wire" will be used t.o designate also bars and tubes).
It also applies to the contro:L of thi.s temperature using such
a measurement.
French patent 2 109 406 fi.led on 15-th 0c-tober, 1970 by the
10 Laboratoires d'Electronique et de Physique Appliquée (L~P) and the
grant of which was published on 26-th ~lay~ 1972, describes a process
und a device for measuring the temperature Or wires, called long-limbed
cylindrical bodies in the patent, moving in the direction of their
length, in which the wire whose temperature it is desired -to measure
15 is caused to pass in front of a blaclc backgro~und at a uniform
temperature and a parallel beam emi-tted by the assembly of the black
focL~seci
A background and said wire is focusso-d on the sensitive element of an
i.nfrared detector, the output signal of the detector being representative
of the temperature of said wirc and substantially independent of the
20 movement of the wire in relation to the blaclc bachgro~u~d. The focusing
is achieved by means of a flat swinging mirror and a lens -transparent
to the infrared.
Though the use of a parallel beam scanning the wire and the
black background by means of the swinging mirror has the advantage Or
25 providing a measurement of the -temperature :irldependent of -the pOS:iti
of the wire in relation to the ~laclc background, thc device of paten-t
2 109 ~06 has the disadvalltage o~ limiting considerably the op-tical
efficicncy Or the system since a. very small I)roportioll of the inrrared
ray~s, name:ly ti~ose which are subs/antially plrallel to thc opticll a.~is
113'~81i
A of the system, are ~e~s~ed on the sensitive element o.E -the detector
and are -thell converted into a usable electrical signal, this signal
being ca.ncelled out moreover preferably when the -temporature Or the
wire is identical to that of the blaclc backg:round by using a differential
5 measurement between the emission of the black background alone and of
the blacls background on which a fraction of the wire is superimposed.
The presen-t invention aims at improving the process and the
device of the above-mentioned patent by using a much larger fraction
of the infrared rays coming from the wire and the black background.
10 ~or this, instead of focussing by means of a lens solely the infrared
rays substan-tially parallel to the optical axis reflected by at least
one flat mirror, a much greater par-t of the infrared radiation emitted
by the black baclcground and the wire or an edge of the metal sheet,
the temperature of which it is desired to measure, is collected for
15 example by means of at least one concave spherical mirror.
The invention provides then a process for measuring, by infra-
red thermometry, the temperature of a wire or a metal sheet moving in
the direction of its length in front of a black background at a constant
tomperature, according to which substantially the whole of the infrared
20 radiation emitted by a portion of said wire, or said metal sheet, at a
given solid angle is collected and applied to the sensitive element of
an infrared detector during certain periods of time.
The invention also provides a device for implementing this
process, this device comprising at least one fla-t swinging mirror,
25 which reflects in a certain direc-tion all the infrared radiation
emitted by a portion of said wire or metal sheet and the black bacl;-
ground within a given solid angle, and at least one concave spherical
mirror which collects -the infrared beam ref].ected by said flat swinging
11;~281~
mirror and directs this beam thus collected on to said sensitive
element.
It might be thought a priori that the fact of not
being limited to the infrared rays substantially parallel to
the optical axis emitted by the portion examined of the wire or
metal sheet and the surrounding black background would increase
the influence on the measurement of the movements of the wire
or metal sheet. Now, it has been established however - and
figures will he given in this connection in the detailed des-
cription which follows - that this influence is reduced if it
is arranged for the wire or metal sheet to oscillate about a
position of equilibrium and if means are provided for integrat-
ing the signal emitted by the infrared radiation detector so as
to have a statistical response in which the fluctuations due to
the movement of the wire or metal sheet are counterbalanced.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is
provided a device for measuring, by infrared thermometry, the
temperature of a body having in at least one direction a small
dimension, said device comprising: black body cavity means
having an aperture formed therein to permit the escape of
infrared radiation to be measured; infrared measuring means dis-
- posed for making a first set of measurements; each measurement
of said first set being a measurement of the sum of the total
amount of infrared radiation which is incident on a first solid
angle and which comes from a portion of the body that is inter-
cepted by said first solid angle and the total amount of in-
frared radiation which is incident on said first solid angle
and which comes from a first portion of the interior wall of
said cavity means that is intercepted by said first solid angle;
and said infrared measuring means being disposed for making a
second set of successive measurements alternating with said
~'
" ` 1~32811
first set of measurements, each measurement of said second set
being a measurement of the total amount of infrared radiation
which is incident in a second solid angle equal to said first
solid angle~ which radiation comes from a second portion of
said interior wall of said cavity means that is intercepted by
said second solid angle; and means for generating an electrical
signal representative of the difference between said sum and
said total amount of infrared radiation that is incident on
said second solid angle.
In accordance with the present invention, there is
also provided a process for measuring by infrared thermometry
the temperature of a body in front of a black background, the
body having in at least one direction a relatively small dimen-
sion, said process comprising the steps of: measuring the sum
of the total amount of infrared radiation which is incident on
a predetermined first solid angle and which comes from a portion
of the body intercepted by said first solid angle, and the total
amount of infrared radiation which is incident on said predeter-
mined first solid angle and which comes from a first portion of
2Q said black background which first portion is intercepted by
said first solid angle; then measuring the total amount of
infrared radiation which is incident on a second solid angle
equal to said first solid angle and which radiation comes from
a second portion of said black background that is intercepted
by said second solid angle, said second solid angle being such
that the body is entirely exterior to said second solid angle;
and determining the difference between the respective amounts
of infrared radiation measured by means of said two measuring
steps.
In a first type of embodiment:
~13Z81~
- the process consists further in causing the whole of the
infrared radiations to be reflected alternately and successively by
means of a flat swinging mirror and these radiations are collected by
means of a fixed concave spherical mirror ;
- the device is further characterized in -that said at least one
mirror is formed by a flat swinging mirror and in that said means for
collecting the infrared radiations are for,med by a concave spherical
mirror.
In a second type of embodiment : .
- the process consists further in causing -the infrared
radiations to be reflected by at least two flat fixed mirrors and
collecting the infrared radiations reflected by the flat mirrors by
means of two concave spherical mirrors, each spherical mirror being
: associated with a flat mirror,- and in interrupting alternately and
successively, on the one hand, the total infrared radiation emitted
or reflected by a portion of the length of said body and emitted by
: a zone of the black background which surrounds said portion and
; . reflected by one of said fixed flat mirrors and by one of said concave-~ mirrors and, on the other hand, the total infrared radiation emitted
solely by said zone or an equivalent zone of said black background,
without intervention by said body, and reflected by the other flat
mirror and the other spherical mirror ;
- the device is further characterized in that said at least one
flat mirror is formed by two fixed flat mirrors, in that said means for
collecting the total infrared radiations are formed by two concave
spherical mirrors~ each concave spherical mirror being associated with
a flat mirror, and in that means are provided ~or intercepting alternately
and successively, on the one hand, the total infrared radiation emitted
`` 113Z8~1
or reflected by a portion of the length of said body alld emitted by a
~one of the black background which surrounds said portion and reflected
by one of said fixed flat mirrors and by one of said concave mirrors
and~ on the other hand~ the total infrared radiation emitted solely
by said ~one or an equivalent zone of said background, without inter-
vention by said body, and reflected by the other flat mirror and the
other spherical mirror.
Since a great sensitivity of measurement should preferably be
provided when the wire or metal sheet temperature to be measured is
equal or close to that of the black background, it is recommended to
reduce to a minimum the noise generated in said detector and the pre-
amplifier into which this detector feeds.
To this end and in accordance with an additional feature of the
invention used preferably at the same time as the-main feature of the
invention mentioned above, there is provided in the electronic part of
the device into which said detector feeds means for making the voltage
from the detector symmetrical in relation to the reference potential,
means for providing positive or negative peak detection according as
to whether the wire or metal sheet is respectively hotter or colder
than the black background or conversely, means for detecting said
positive and negative peak voltages and means for determining the
algebraic sum of these positive and negative peak voltages thus
detected.
The above and other objects, features and advantages of the
present invention will become apparent from the following description
given solely by way of non-limiting illustration when -taken in
conjunction with the accompanying drawings.
DESCRIPTION OF TIIE DRAWINGS
113Z8il~
Fig. 1 shows schematically in partial sec-tion the whole Or
one embodiment of the device O.:r the invention for measurine the
temperature of a wire~ wi-th the exception of the electronic part.
Figs. 2 to 7 illustrate the electric signals used in this
embodiment.
Fig. 8 shows the electronic par-t of this embodiment.
Figs. 9 and 10 illustrate electric signals used in the circuit
of Fig. 8.
Fig. l1 is similar to Fig. 1 but it concerns the measurement
of the temperature of a metal sheet.
Fig. 12 illustrates the mechanical portion of the device of
Figs. 1 and 11.
Fig. 13 shows schematically in partial section another
embodiment o~ a device having imporovements in accordance with the
invention and being adapted especially to the measurement of the
temperature of a tube or a bar.
Fig. 14 shows, seen from the top, -the means for alternately
and successively reflecting two infrared radiations on to the sensitive
element in the embodiment of Fig. 13.
Figs. 15 and 16 show in two planes perpendicular to each other
the optical means used in the device of Fig. 13.
Fig. 17, finally, shows schematically the mcchanical unit of
the device of Fig 13.
DESCRIPTION OF THE PREF'~RRED E~ODI~ENTS
~ccording to the invention, desiring to carry ou-t a process
and construct a device for measuring by infrared thermometry the
temperature of a wire or a metal sheet, the following or similar is
the way to set about it.
Z~
In what l`ollows the descrip-tion will gcnerall~y be lirnitcd to
the ease Or a wire, but it should be understood -that l,he explanations
which follow ll].SO apply to the case o~ a me-taL shee-t allCL also
(particularly for Figs. 13 to 17) to the case Or a tube or a bar.
Reference is made first of all to Fig. 1 in which for the sake
of simplieity the opening through which the infrared radiation passes
has not been shown. In this Fig. there is shown at 1 the wire whose
temperature it is desired to determine and which is surrounded by a
body or a black background 2 formed -for example by a tube made from
graphite or from a material obtained by so-called "pyrox" fritting
having a high emissive power. A cylindrical insulating jacke1 3 made
bcr
~rom glass ~b~e surrounds body 2. The whole of the inFrared rays
emitted by wire 1 and of the infrared rays 5 emitted by the black body
are reflected during certain periods o~ time by a swinging flat mirror
6 as ray 7 on to a mirrox 8.
In accordance wiSh -the main feature of the invention, this is
a eoneave spherical mirror which collects finally~ after reflection by
swinging mirror 6 ( when it is in the position shown in Fig. 1) the
whole of the rays emitted by wire 1 and the region of -the black body which
surrounds it and not only the -rays subs-tantially para:llel to the optica]
axis which corresponds to axial ray ~c which is reflected a-t 7c by
swinging mirror 6 in the position occupied b,y -this la-t-ter sllown in
Fig. 1.
Spherical mirror 8 reflec-ts rays 7, as rays 9, on to the
sensitive element 10 Or infrared radiation detector l1. I-t will be noted
-that axial ray 7c is reflec-ted by mirror 8, as axial ray ~c, and that
spherical mirror 8 has i-ts axis o~fset in reLa-tion to the axis o~ infra-
red radia-tion 7c ; it is -then all "of axis" splleIical mirror.
113Z811
The advantage of the system which has just been described with
reference to Fig. 1 is that it is very efficient if compared with that
of a system using only the infrared rays emitted by wire 1 and the
surrounding black background in a direction substantially parallel to
the op*ical axis 4c. This may be shown in the case of a particular
example of an embodiment corresponding to Fig. 1. In this embodiment,
the spherical mirror may have a radius of 75 mm~ an opening whose
diameter is 40 mm and a magnification of 1, -the distance between the
wire and the swinging mirror being 53 mm, whereas the distance between
the centre 6c of the swinging mirror and the centre 8c of the spherical
- mirror is 97 mm. The slope o the mean ray in relation to the axis of
the mirror is 7 and the solid angle at which the wire is seen is
equal to 5.56 X 10 2 steradian.
By taking as window for detector 11, i.e. for the sensitive
element, a square surface with a side of 2 mm, it is a 2 mm portion
- of the length of the wire (in the direction perpendicular to the plane
of Fig. 1) which appears on the sensitive surface. Assuming that the
wire has a diameter of 1 mm, the ratio between the surface of the wire
and the surface of the black background, seen by the detector, is 50~o.
On the contrary, in the case of the device described in the
above-mentioned patent n 2 109 406, it is the surface internal to a
circle of 23 mm which is soanned, this surface being determined by
two diaphragms which limit and make more constant the length of wire
concerned (which would otherwise be variable, which would falsify the
measurements). In this case the ratio between the surface of the wire
and the surface Or the black background is no more than 4.35,' (instead
of 5 ~ in the case of the embodiment of the accompanying Fig. 1), which
corresponds to a very low optical efficiency, resulting from using only
'10
~13'~81i
rays parallel to the optical axis.
On the other hand~ as pointed out in -the preamble~ the system
of Fig. 1 presents in principle the disadvantages of being sensitive
to the position of the wire in the direc-tion oE the depth (i.e. when
the distance from the wire to mirror 6 and so to mirror ~ varies).
However~ calculation shows that a deviation of 5 mm forwards or
backwards leads to a relative variation Or wire surface 1 scanned by
detector 11 less than 2%~ which then causes a variation in the infrared
flux and so in the electric signal supplied by detector 11 of the same
order. ~lso as pointed out in the preamble~ the disadvantages of this
variation are reduced because the wire oscillates about a position of
equilibrium and because the elec-tronic means which follow detector 11
(as explained above) supply a statistical response which eliminates the
fluctuations by means of an integrator circuit. It is in fact the mean
posi-tion of wire 1 in relation to black background 2 which is important.
Reference is now made to Fig. 11 (in which are to be found the
references of Fig. 1) where there is shown at 1a the metal sheet which
moves through a narrow slot 3a machined in black body 2 and in cylindrical
jacket 3. The whole of the infrared rays 4 emitted by the edge 1b of
metal sheet 1a :as in the case of the wire, with the infrared rays
emitted by black body 2, are reflected during certain periods of time
by swinging mirror 6 as ray 7 on to spherical mirror 8. The plane of
metal sheet 1a forms an angle with the axial ray 4c so as to prevent
external rays, passing through slot 3a, from reaching sensitive element
10.
Up to now~ it has not been pointed out why mirror 6 was a
swinging mirror. Mirror 6 is caused to swing so as to send to detector
10 alterna-tely an infrared flux which comprises rays 4- emitted by wire
1~3'2811
1 at the same time as rays 5 emi-tted by the blaclc background, on the
one h&nd~ and solely rays 5 emitted by the black background~ on the other
hand. It will then be readily understood that if -the clifrerence is
taken between the first radiation~ on the one hand, and the second
radiation~ on the other hand~ a signal is obtained which is equal to
zero when wire 1 is at the same temperature as black body 2 and which
is positive or negative according as to whethçr the temperature of wire
1 is higher or lower that that of black background 2 (according to the
polarity, such a response or even the reverse response may be obtained
depending on the temperature difference between wire 1 and black body
2).
In Fig. 12 there is shown schematically the mechanical device
for causing flat mirror 6 to swing at the same time as the synchronizing
signal. A motor and step-down gear 81 drives at the same time a pulley
82 with its notched belt 83 and a disk 84 having a slot 85. Notched
belt 83 drives another pulley 86 integral with a cranked arm 88 and
link 87 system, of which the link 87 slides in a sleeve 89 rotatable
about a shaft 90 fixedin space. This shaft 90 is integral with flat
mirror 6, which swings due -to the movement of link 87 with an amplitude
adjustable by modifying the length of the crank-arm 88. In Fig. 12 are
to be found elements 1, 8 and 11 of Fig. 1. Disk 84 with the slot 85
passes under an optoelectronic detector 91 which detects the passing
of slot 85 by means of a light source 92 whose rays then reach detector
91. By changing the angular position of slotted disk 84 in relation to
drive pulley 82 the position of -the synchronous de-tec-tion is modi~ied.
So it can be seen that the electronic part which is not illustrated
in Fig. 1 must provide a grea-t sensitivity in -the measurement about the
detection of zero~ when wire 1 and blacls backgro~d 2 are at -the Sanle
113Z811
temperature. The result is then that the noise emitted by detector 11
and that emitted by the pre-amplifier into which the detector feeds
and which may be incorporated in the detector or placed thereagainst,
in a known way, assumes a very great importance.
In accordance with a feature of the invention means are
provided for making the voltage from detector 11 symmetrical in relation
to the reference potential, and this particularly by means of a high
impedance capacitive connection. Then the positive peak and the negative
peak are detected, one corresponding to the case where the wire is
hotter than the black background and the other to the opposite case,
then the positive and negative voltages about the "zero detection" are
detected and finally the algebraic sum of the positive and negative
peak voltages is made.
In Figures 2 to 7 there is illustrated the different corresponding
signals.
Thus a detected positive voltage 12 is obtained which is
illustrated in Figure 2 in which the amplitude a is shown as ordinate
and the time t as abscissa.
In Figure 4 is shown the negative voltage detected 13 using the
same ordinate a and abscissa t.
In Figure 6 there is shown with the same ordinate a and abscissa
t the signal 14 detected about ~ero and it can be seen that very good
sensitivity is obtained which is for example of the order of 0.5C for
a black background temperature of the order of 70 C, which means that
variations of half a degree of the temperature of the wire above or
below the temperature of the black body may be detected when this latter
is of the order of 70C.
Figures 3, 5 and 7 illustrate with the same ordinate a and
g
~13'~81~
abscissa -t -the positive voltages 12b, -the negative voltages 13b and the
algebraic sum 1~b corresponding to signals 12, 13 and 14 respectively,
after storage. In Fig~ 7 can be seen ln par-ticular tllc positive part
14p~ the negative part 14n and the part 140, which constitutes the
algebraic sum of the positive part 14p and the negative part 14n of
the integrated signal in the case where the temperature Or the wire
is respectively higher than, lower than or substantially equal to -that
of the black background.
With reference to Fig. 8 for the electronic circuit and to
Figs. 9 and 10 for the signals, there will now be described the circuit
of the electronic part according to a preferred embodiment of the
invention.
We will begin first of all by describing Fig. 9 so as to be
able to better follow the fuulctions of the components of the device of
Fig. 8.
In Fig. 9 there is first of all illustrated signal 15 which is
.~ " ~. //
the output signal of detector ~ and which represents then~ in the
system of coordinates a and t, the difference between the temperature
of wire 1 and the temperature of black body 2.
In synchronism with the swinging of mirror 6 disk 84 with slot
85 (Fig. 12) rotates, which, whcn this slot lets the light beam from
source 92 passtowards photoelectronic detector 91, supplies an electric
pulse 16 which is synchroni~ed with signal 15. Tha-t means that to each
peak 15d of signal 15 there corresponds a pulse 16. By means which will
be described hereafter with reference to Fig. 8, there is obtained from
each pulse 16 two symmetrical pulses 17 and 18, one positive and the
other negative, of a given width (less than that of a pulse 16) and
whose leading edges are delayed in re]ation to the leading edge Or the
14
113'~
correspondil1g pulse 16. Furtl1ermore, stilL L'rom pulse -train 16 tilGre
is ob-tained a train Or pulses 19 each of which precccles -Ihc corrcsponding
pair of pulses 17, 18.
Reference is now made to Fig. 8 showing lhe general electronic
diagram. The output signal of the photoelectronic detec-tor which
receives the liglrt beam passing through the slo-t of said disk, i.e.
the succession of pulses ~6~ is applied to thé input 20 of the circuit
of Fig. 8. Pulses 16 are amplified by two operational amplifiers 21~ 22
molmted in cascade ; these pulses~ available at output 32~ are delayed
by circuit 23 comprising a capacitor 24 and an operationa] amplifier
25, said capacitor causing these pulses to be staggered between the
input ~nd the output of circuit 23 -through a phase-shift effec-t. The
ouput 26 of circuit 23 is connected~ on the one hand, -through
operational arnplifier 27 connected as an inverter~ to forward connected
diode 28 and~ on the other hand, directly to reverse connected diode
29. Thus -there is obtained a-t output 30 the train of positive pulses
17 and at the output 31 the succession of negative pulses 18 (symmetrical
with pulses 17), these pairs of pulses 17, 18 being delayed(because of
ciapacitor 24) in relation to the input pulses 16.
Furthermore, the OUtpllt pulses from amplifiel 22,-taken at 32,
are applied to the base of a tr~lnsistor 33 Or the PNP type ; there is
obtained at -the collector of this transistor 33 a negative voltage
when this transistor is disabled, i.e. whel1 its base is mQde negative
by outpu-t 32. So there is obtained at -the collector of -transistor 33~
a-t 34~ a negative pulse for each positive pulse 16. The duration of the
pulses appearing at 3~ is reduced by transislor 35 tlue to the conncc-tion
of the base ol' tr~lllsistor 35 to the output 26 of circuil; 23. ~rhen 0Utp-lt
26 provides a pulse (which will become a pair of positive 'l7 allcL
113Z811
negative 18 pulses), there appears a negative voltago which enables
transistor 35 and so puts the collector of this transistor to ground
which suppresses the portion oE the pulse available a-t 34 during the
durabion of pulses 17 and 18. This appears clearly in Fig. 9 in which
it can be seen that pulse 19 corresponds to the part of pulse 16 which
does not correspond to the pair of pulses 17, 18. In fact, at 36 wc do
not have positive pulses, as shown in Fig 9, but negative pulses, as
previously shown~ and it-is the operational amplifier 37 which effects
an inversion of polarity because of its mounting, pulses 19 bcing
efectively available at 38.
It can then be seen that the upper half of the circuit of Fig.
8 enables the successions of pulses 18 and 19 to be obtained
respectively at 30, 31 and 38 from the succession of pulses 16 applied
to input 20.
In the lower half of Fig. ~, the output of the infrared detec-
tor 11, i.e. signal 15d, is applied to input 39. The assembly formed by
capacitor 40 and re~sistor 41 forms a high impedance input which results
in signal 15 being made symmetrical in relation to ground while
distorting it as little as possible. The symmetrical signal available
at 42 is applied to an instrumental amplifier, having a very high
impedance input, formed by operational amplifiers 43, 44 and 45. At
the output~ at 46, a signal is obtained which will now be processed
as will be described hereafter with use of pulses 17, 18 and 19
available at 47, 48 and 49 respectively.
Transistors 50 and 51 are always enabled, except at the moment
when pulses 18 (arriving at 48) and 17 (arriving at 47) are applied
to their base. Thus~ modified signal 15 arriving at 46 is stopped by
these transistors 50 and 51 except during the duration of pulses 17
16
li3'~811
and 18. The circuit then comprises -two bloching circuits 52 and 53
each comprising two operational amplifiers O:r which the input operational
amplifier 52e, 53e amplifies in current the input puLse so as to
charge capacitors 52c, 53c respectively, whereas the output operational
amplifier 52s and 53s takes from capaci-tor 52c or 53c respectively a
very low current in order to supply a DC output voltage equal to the
nput pulse voltage.
Blocking circuits 52 and 53 are fed respectively by the
positive and negative parts of signal 46 through diodes 54 and 55 :
the positive parts pass into bloclsing circuit 52, whereas the negative
parts, after inversion of polarity in operational amplifier 56, pass
into blocking circuit 53. The result is that the signal stored in
capacitors 52c and 53c is always positive.
The information finally leaves bloclsing circuits 52 and 53 in
the form of a DC voltage and is used either directly at 57, or at 58,
after inversion in operational amplifier 59. The positive signal
available at 57 and the negative signal available at 58 are added and
applied to opcrational amplifier 59.
Capacitors 52c and 53c must of course have been previously
discharged and this is achieved by means of pulses 19 available at 49
and which are applied to the bases of transistors 52-t and 53-t of
blocl{ing circuits 52 and 53 respectively ; when these transistors 18
and 19 are enabled by pulses 19, the corresponding capacitors 52c and
53c discharge to ground through the emitter-collector circuits of these
transistors.
Consequently if there appears at 39, and so a-t 46, a positive
voltagc duLillg a pulse 18~ playing the role of a window~ it is stored
positive in capacitor 52c and il will appear in the rorm of a nega-tive
il3Z811
DC voltngo at the output 60 Or the mixer oporationaL amplifier 59 ;
on the other hand ir there appears at 39, and so at 46, a negative
voltage during pulse 17, also playing the role of a window, it is
stored positive in capacitor 53c and appears in the form of a negative
DC voltage at output 60 ; finally, if there appears at 39, and so at
46, a voltage both positive andnegative (this is the case of noise),
this voltage will be stored both in capacitor 52 and in capacitor 53c
and will appear at 60 in the form of the difference between these
negative and positive voltages, this difference itself being either
positive or negative.
In short it can be seen that the succession of signals 16
which is generated by the window of the disk not shown, in synchronism
with signal 15 of the detector, serves to produce pulses 19, forming
windows~ which discharge capaci-tors 52c and 53c ; after this discharge,
windows 17 and 18 allow signal 15 previously processed to be stored in
these same capacitors and a DC voltage to appear at output 60. This
voltage is positive or negative, depending on the polarity of signal
15 and so depending on whether wire 1 is hotter or colder than back-
ground 2, it being understood that the amplitude of this DC voltage
varies in the same direction as the temperature difference. We have
seen moreover that the influence of noise tends to be eliminated. The
positive or negative DC voltage appearing at 60 is renewed with each
group of pulses 18 and 19, the rate being for example ten repetitions
per second.
It should be noted that this DC signal may come from a small
positive or negative zone of the signal of the infrared detector or
from the algebraic sum of two positive and negative zones, if the noise
produces an amplitude information covering the zero axis of ground. This
~3Z8~1
arrnngemel1-t provides great sharpness of response in -lhe most interesting
zone, that where the temperature of the wire is close -to that of the
blaclc body.
The voltage available at 60 then passes into a low-pass filter
61 so as to eliminate certain random and rapid variations~ the time
constant of these filters being possibly ol` the order of 0.5 second.
It is finally at 62 that a positive and negative DC voltage is obtained
which is the signal representative of the difference between the
temperature of the wire and that of the black background.
In Fig. 10, finally, different signals are shown, on an
enlarged scale and with indication (in volts V or millivolts mV) of
polarities given by way of example (the grolmd potential being shown
by the level In) ~ namely :
- signal 63 which leaves the photoelectric de-tector cooperating
with the slotted disk which is actuated in synchronism with the
swinging mirror 6 to constitute a synchronisation device, this signal
63 comprising pulses 16 of Fig. 9, which arrive at 20 (Fig. 8),
- signal 64 available at 32,
- signal 65 available at 26,
- signal 66, with pulses 18, available at 31 and 48,
- - signal 67, with pulses 17, available at 30 and 47,
- signal 68 available at 34~
- signal 69 available at 36,
- and finally signal 70, with pulses 19, available at 38 and
49.
It can be seen that the embodiments described cnable very
accuratc measurcments to be made of the tempcrature of a wire or metal
sheet in relation to a black background at constant temperature, even
19
` 113'~811
when this wire or metal sheet oseillates in front Or -tho blaek back-
grolund and even whell the differenee of temperature is very small, e g.
less -tllan 1, betwoen 1ihe wire and the blaclc baclcground.
Ilowever, the use of a swinging mirror presents a number of
disadvantages :
- -the adjus-tment of the sighting axis must be very aceurate,
- transverse movement of the body produees variations in the
frequeney of the output signal of the sensi-tive element,
- the ra-tio be-tween the si~e of the optical sighting window
and the distanee between this window and the body must be maintained
small and so the size of the blaek background needs to be increased
when the diameter of the body seen by the flat mirror inereases,
- sensitivity diminishes if the above diameter is reduced.
This results -then in problems when the diameter of the body is
too great or too small and/or when -this body is subjeeted to transverse
movements in relation to the black backgro~d.
To avoid these disadvantages, a deviee may be constructed in
accordance with the invention by causing the infrared radiation to be
reflected~ not by means of a single flat swinging mirror~ but with two
fixed l'lat mirrors and by causing the infrared radiations to be colleeted
not by means Or a single eoneave sphcrieal mirror but with two eoncave
spherieal mirrors~ each spherieal mirror being associated with a flat
mirror, in combination with means for intercepting alternately and
successively~ on the one hand, the total in:frared radia-tion emitted or
reflected by a portion of the length of said body and emitted by a
i30ne of the blaek baclcground which surrounds said portion and reflected
by one of said fixed flat mirrors and by onc o~ said concave mirrors
and~ on thc o-ther hand~ tho total infrared radiatioll emitted solely
113Z811
by said zone~ or an equivalent zone, of said blaclc background~wi-thou-t
interven1ion by said body alld refleeted by the other flat mirror and
the other spherica] mirror.
The scanning of -the radiation emit-ted~ on -the one hand~ by the
elongated body (particularly a wire, bar or -tube in the embodiment
illustra.ted) and, on the other hand~ by -the black background is then
achieved (Figs. 13 to 17) no longer by means Or one flat swinging
mirror and one concave spherical mirror (as in -the embodiments of
Figs 1 to 11), but by using two fixed sightings each using a fixed
flat mirror and a concave spherical mirror, disposed so that the parts
used of the radiation emitted not only by the wire, bar or tube, but
also by -the black baclcground~ are reflected by the f].at mirror and
collectcd by the concave mirror of each sighting towards -the same
sensitive zone of the detector, and this at the same angle, means
being provided for stopping alternately and successively the
radiations forming each of the two sightings.
This embodiment applies pa.rticularl.y to the measurement of the
temperature Or bars or tubes.
More particularly, referring to Fig. 13, thc in-frared radiation
4 of body 1 is reflected by a fixed flat mirror 6a on to a concave
spherical mirror 8a which collects all the in-frared radiation reflected
by flat mirror 6a and concentrat~s it at the sensitive zone 10 of a
detector 11.
Black background 2a is formed in the embodiment illustra-ted by
copper plates covered wi.th colloidal graphite having a high emissive
power, copper having the advantage of havillg good thermal conductibility.
This blaclc baclcground is heated by electrical resistances 101 embedded
~ ,~c~s
in a cylindrical insulating jaclcet 3a (made from glass -f~}~s for
1~3Z8~1
examp]e). A temperature detector 102 ( sucl1 as a resistance probe
or a thermo-eloctric couple), whose output wires aro shown at 103,
enables the -temperature of resis-tances 101 and so ot black body 2a to
be regulated by means Or a thermostat (not shown).
In this embodiment~ black background 2a has been given a
rectangular sec-tion so as to facilitate construction thereof and to
achieve the sighting of a portion 104 of the black background on a
flat surface and so at a constant angle.
The sighting of portion or zone 104 is achieved by means of a
flat mirror 6b which reflects the infrared radiation 5 e~itted by this
zone 104 on to a concave spherical mirror 8b which collects all the
infrared radiation reflected by mirror 6b and coming from zone 104 on
the same sensitive zone 10 of detector 11~ the radiations coming from
concave mirrors 8a and 8b reach sensitive zone 10 at the same angle.
It is also arranged for the optical path to be the same for the infra-
red radiation from zone 104 and for the infrared radiation from wire 1.
Such an arrangement leads to a doublc shift of the optical axis,
one shift being regulated by flat mirrors6a and 6b and the other by
concave mirrors 8a and 8b.
~eferring now also to Figs. 15 and 16~ corresponding respectively
for example to a view in a vertical plane (irom the front) and a view
in a horizontal plane (from the top) respectively~ it can be seen that
ii the sighting on wire 1 is efi`ected vertically, flat mirrors 6a and
6b control the shirt of the infrared rays in a ver-tical plane~ whereas
concave mirrors 8a and 8b provide this shif-t in -tho horizontal plane.
In a par-ticu]ar non limiting example, mirrors 8a and 8b are spherical
mirrors l1aving a rocal leng-th Or 1 lo mm and an aper-lure of 40 mm, the
distance hctwoen wire 1 and the centre of flat mirror 6a being 110 mm
~13'~811
and the distance between the centres of flat mirror 6a and spherical
mirror 8a beillg also 110 mm.
In Fig. 14 there are shown the references for radiations 7 and
9 reflected by the flat mirrors~ on the one hand~ and the spherical
mirrors~on the other~ as well as the central rays 4c~ 7c and 9c
corresponding to radiations 4, 7 and 9, namely the same references
as in Figs. 1 and 11.
The slope in the ver-tical plane which is controlled by flat
mirrors 6a and 6b is then 82, whereas the slope in the horizontal
plane which is controlled by spherical mirrors 8a and 8b is 59 for
both mirrors. Finally the solid angle at which wire I is seen is
6.28 X lO s-teradian.
In Figs. 15 and 16 are shown the angles of slope in the vertical
plane and in the horizontal plane.
The dcvice which has just been described comprises means
illustrated in Figs. 13 and 14 for stopping alternately and successively
the infrared radiation 4 from wire 1 and the infrared radiation 5 from
the black background. By way of example these means aro formed by a
disls 105 illustrated in a plane view in Fig. 14~ which is rotated at
constant speed by a motor 100.
This disk comprises :
- on the one hand~ two apertures 106 limi-ted by two orthogonal
diameters 107 and by four quarters of a circle 108 and 109 ;
- on the other hand~ two recesses 110 also limited by the
orthogonal diameters 107 and by two quarters of a circle 111 and 112.
Apertures 106 cooperate wi-th the window 113 provided in black
body 2a and the insulating jackot 3a so as to let -through, when one of
them is a-t the level of this window 113, the infrared radiation 4
1~3'~8~1
emitted by the body or wire 1 towards flat mirror 6a and so towards
sensitive element 10 of deteetor 11 after colloe-tion by concave
mirror 8a.
Similarly the apertures or reeesses 110 cooperate with a
similar window 114 through which passes the infrared radiation 5
emitted by zone 104 to let this radiation through towards flat mirror
6a then towards eoneave eolleeting mirror 8b so that it reaehes the
sensitive element 10 when one of these reeesses is opposite window
114.
Beeause of windows 113 and 114 and apertures 106 and 110 whieh
follow eacl1 other alternately ( because they are limited by the same
diameters 107), it ean be seen that sensitive element 10 reeeives
al-ternately and sueeessively and at the same angle the infrared
radiations from wire 1 and from the blaek body (zone 104) after they
have been refleeted by flat mirrors 6a and 6b and collected by concave
mirrors 8a and 8b.
Detector 11 is advantageously a pyroelectric detector sensitive
to all the infrared radiation emitted by the wire or other body 1 and
the black background (zone 104) at all temperatures, particularly for
~xample around 150C.
The final detection ~ in the embodiment having two fixed flat
mirrors and two eoneave spherieal mirrors, is achieved for example
as above with reference to figures 2 to 10, i.e. by synchronous detection.
Sinee the rrequeney of the radiation is stable~ ror the sightings are
fixed without using a swinging mirror, an excellent synehronous
deteetion may be obtained.
It will be noted that with -the device of Fig. 13 to 17 the same
electronic system may be used as with the devices of Figs. 1, 11 and
24
113'~8~1
12~ ~or the foliowing reasons :
- in the system with a swinging mirror (Figs. 1, 11 and 12),
we pass progressively because of the swinging of the mirror from
sighting the wire to that of the black background and conversely ;
- in the device with two pairs of fixed mirrors (Figs. 13 to
17) we go progressively from sighting the wire to that of the black
background and conversely for, when apertures 106 progressively
uncover window 113, the opaque zones 115 progressively replace apertures
110 ; for this reason the radiation from body 1 progressively replaces
the radiation from zone 104 on the sensitive element 10 of the
detector ; going over from one radiation to the other is then gradual ;
simila~ly, when apertures 110 are substituted for opaque zones 115 in
front of window 114, the infrared radiation from zone 104 is progressively
.
substituted for the infrared radiation from wire 1 on the sensitive
zone 10 of detector 11.
Itwill be noted that this sensitive zone 10 also receives the
;~ radiation reflected by the opa~ue zones 115 and 116. So as not to
disturb the measurement it is necessary for these zones to be at the
same temperature and for this purpose disk 105 is made from a heat
- 20 conducting material so that its temperature is uniform. Disk 105 may
~ for example be made from copper.
:
In Fig. 17 there is shown schematically in space the whole of
the device having two pairs of fixed mlrrors with a practical example
~ of the drive for disk 105 effected by means of a motor 100 which drives
-- 25 shaf-t 117 of the disk not directly but through a belt device 118, the
shaft 119 of motor 100 being staggered in relation to axis 117 which
enables motor 100 and flat mirrors 6a and 6b to be disposed witllout
problem.
` ` 1132811
; As previously indicated~ the device of figures 13 to 17
.
~ presents a number of advantages with respect to the devices of figures
:;
1, 11 and 12~ in particular the improvement in sensi-tivity~ the ease
.. ., i ~
of adjustment, the`possibility of measuring the temperature of the
;.,
~5 body, such as tubes and bars, having even a relatively large section,
, :: ,
without needing to use a large-siæed black background and finally
;~ -the use, under the best conditions, of synchronous detection because
of the stability of the frequency of the detected infrared radiation.
However, the devices of figures 1, 11 and 12 are also suitable for
~ ~10 some sizes of wire or metal sheet.
.. ' :
It is apparent that within the scope of the invention,
modifications and different arrangements can be made other than are
here disclosed. The present disclosure is merely illustrative with
the invention comprehending all variations thereof.
. . .
.
.
;
, ~ .
:
- 26
' - .
