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Description  |
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BACKGROUND OF THE INVENTION:
The present invention relates to a method and apparatus for a non-contact
measurement of a temperature of a body.
In non-contact measuring of a temperature originating from heat radiation
of a body, which is not the same as body temperature, since the body need
not be thermally equalized, a problem arises in that an ambient radiation
can drastically falsify a result of the measurement. The problem, actually
a problem of signal-to-noise ratio, becomes even more critical if
temperatures to be measured lie only slightly above or below an ambient
temperature, such as within several 100.degree. C.
In order to avoid the above noted problem, according to advantageous
features of the present invention, a chopper means is provided for
chopping or interrupting the heat radiation between the body and a
temperature sensor, and at least one ambient temperature of a sensor on
the side of the chopper means facing the sensor is taken into account in
evaluating the temperature detected by the sensor.
By virtue of the fact that the heat radiation between the body and the
temperature sensor provided is chopped up or interrupted, heat radiation
pulses detected by the sensor are produced, an amplitude of which is
provided by two heat radiation components, namely, by ambient radiation on
the sensor side of the chopper means and by heat radiation on the side of
the chopper means facing away from the sensor, which latter heat radiation
is composed of the ambient irradiation at that location and radiation of
the body the temperature of which is to be detected.
While the ambient radiation on the side of the chopper means facing away
from the sensor cannot be separated from the body radiation but can be
reduced to an insignificant amount by, for example, a selected minimum
distance between the chopper means and the body, and is practically
time-invariant, the ambient radiation on the sensor side of the chopper
means presents a more serious problem, especially when considering its
change in time as it occurs after actuation of the sensor and chopper
means, due to the electrical feeds as well as, generally, by the output of
the chopper means and the fact that the mounting elements for the sensor
and chopper means define relatively small-volume spaces wherein
temperature fluctuations result despite a stable larger-space temperature.
Due to the fact that at least one ambient temperature of the sensor on a
side of the chopper means facing the sensor is considered or taken into
account in the evaluation process, it is possible to effect a temperature
measurement which represents solely the temperature for the body radiation
even before the partial system on the sensor side of the chopper means has
become thermally stabilized which may take, in dependence upon the
structure, relatively long periods of time and independent of the
temperature where the partial system finally stabilizes on.
Commercially available temperature sensors for non-contact measurement of
heat radiation have been proposed with the sensor being disposed in a
housing and constructed as finished components, usually, with an
integrated amplifier. In this connection, the present invention further
proposes to utilize as the one ambient temperature, a temperature of the
sensor housing.
As can readily be appreciated, a heat radiation of the sensor housing
directly affects the actual sensor which, for example, may be constructed
as a semi-conductor chip and integrated into the housing.
A further source of heat radiation which should be considered is the
chopper means. Due to the work performed by the chopper means, especially
since it is a mechanically operated chopper means, it acts in the
surrounding air as a Joule's brake. In this connection, in accordance with
the present invention, it is further proposed to take into account, as one
ambient temperature, the temperature caused by the work performed by the
chopper means.
In accordance with further features of the present invention, the
temperature of the sensor housing is feedback-controlled so that it is at
a predetermined value and this approach can optionally also be done with
regard to the temperature rise resulting from the work of the chopper
means.
If the heat radiation is chopped or interrupted by a mechanically moved
chopper means, such as, for example, a disc with radiation-impermeable and
radiation-permeable segments, it is also possible in accordance with the
present invention, to provide a sensor for sensing a temperature in a
region of the travel path of the chopper means as an ambient temperature.
While the temperature can be predetermined by appropriate regulation or
control means, due to the bulk of the mechanical chopper means, such a
regulation for maintaining temperature equalization over the entire area
at the chopper means will be relatively sluggish or slow. For this reason,
in accordance with the present invention, it is proposed that the
temperature measured by means of the sensor is corrected as a function of
the temperature produced by the chopper means.
Preferably, in accordance with the present invention, a first signal,
dependent upon the temperature produced by the work of the chopper means,
is multiplied by a first coefficient and then the product is added to a
second coefficient in order to obtain a second signal. A third signal,
dependent upon the temperature detected by the sensor by the second signal
is divided in order to obtain a fourth signal, and the fourth signal is
added to the first signal in order to obtain a signal representative of a
body temperature or body radiation.
Advantageously, the sensor output signal, prior to being further evaluated,
is averaged over several chopper periods of operation of the chopper means
in order to eliminate incidental fluctuations of the sensor output signal.
The above noted coefficients for correcting the sensor output signal, based
on the temperature produced by the work of the chopper means, are
preferably determined experimentally from at least two measurements, at
predetermined body temperatures and respectively two values of the
temperature produced by the work of the chopper means and supplied to a
memory means.
As noted above, one can only consider representative body temperature if
the body has been thermally equalized. On the other hand, temperature
measurement of a body that has not been thermally equalized represents
only the thermal energy content of a body volume element lying directly
within the region of the measurement.
With the use of such temperature measurement, in order to obtain, in the
case of relatively large bodies an indication of the thermal energy
content of a maximally large volume element of the body, it is proposed in
accordance with the present invention that the temperature measurement be
conducted by a sensor in the zone of an already existing recess at the
body or a recess that has been provided for this purpose in order to
increase or enlarge a body volume element for the thermal energy content
of which the temperature measurement is representative.
In accordance with the present invention, the recess may, for example, be
an opening of a can or container to be measured as a body or, with bodies
not provided with a recess, such as, for example, metal ingots, the recess
may be provided such as in the form of, for example, a bore. In this
manner, the above noted temperature measurement becomes representative for
the thermal energy content of a substantially larger body volume element
since the provided recess acts similarly to a structure exhibiting black
body radiation, and emits a heat radiation corresponding to the heat
content averaged over a relatively large adjoining volume.
If, for example, the body is moved relative to the sensor such as, for
example, on a production line, in accordance with the present invention, a
period of operation of the chopper means is selected to be shorter than
the time span during which the geometric recess lies within the sensor
measuring range so that, during such measuring period, an adequate number
of measuring samples are available so as to enable averaging thereby
eliminating random variables.
According to the present invention, an apparatus or arrangement for
non-contact measurement of a temperature of a body is provided which
includes a first temperature sensor means, a heat radiation chopper means
connected in front of the heat input of the sensor means, and at least one
further temperature sensor means disposed at least chopper means and
adjacent the first temperature sensor means, and on the side of the first
sensor with respect to the chopper means.
Preferably, according to the present invention, first temperature sensor or
a further temperature sensor is thermally tightly coupled with a housing
of at least one of the first temperature sensor and the chopper means. It
is further proposed in accordance with the present invention to connect at
least one additional temperature sensor as a pick up for a controlled
variable into a temperature feedback control circuit for the temperature
of a zone or area wherein the pick up is located.
To provide for a simple construction of the arrangement or apparatus of the
present invention, it is proposed to use a mechanically moved chopper
means such as, for example, a chopper disc, provided with a plurality of
segments impermeable to heat radiation and segments permeable to heat
radiation, with the temperature sensor or, respectively, a further
temperature sensor, being arranged directly adjacent the path of movement
of the chopper.
It has been determined that, especially when providing a mechanical chopper
means, relatively large time periods of from one hour to several hours may
elapse due to the frictional work to the surrounding air until the air,
ambient in the chopper means and thus the heat radiation transmitted from
the zone of the chopper means to the first sensor means, has reached a
stable value.
Since it is extremely important in many applications to be able to perform
representative measurements directly after connecting the arrangement or
apparatus to power, the provision of an additional temperature sensor
means as proposed by the present invention adjacent the travel path of the
chopper means is extremely advantageous because, by correspondingly
considering the time-variable temperature detected by the additional
temperature sensor means for a measured result, it becomes inventively
possible to effect a representative measurement as soon as immediately
after the connection of the apparatus or arrangement to power.
Although, as noted above, the time variable behavior of the heat radiation
may be eliminated by the provision of one or more feedback control
circuits, as can readily be appreciated, the total overall expense for
such an arrangement is relatively high particularly when considering that
it is necessary to include, as temperature-adjusting members, heating
and/or cooling elements such as Peltier elements and, as noted above, such
control circuits have a relatively slow response time or are sluggish.
Provision of a feedback-control circuit may be basically eliminated by
providing an evaluating unit such as, for example, a data processing unit
for receiving the outputs of at least some of the temperature sensors and
generating and transmitting at an output side an output signal
representative of the body temperature.
Preferably, in accordance with the present invention, such an evaluating
unit for the performance of calculations on the output signal of the
additional temperature sensor disposed in a zone of the chopper means with
an output signal of the first temperature signal for the body temperature
may include a multiplication unit connected at on input to an input for
the further temperature sensor at the evaluating unit, with a signal of an
adjustable value being fed to the second input of the multiplication unit.
The output of the multiplication unit may be fed to a summation unit, with
an adjustable signal value being fed to the second input of such unit. The
output of the first temperature sensor may be transmitted at the
evaluating unit to a numerator input of a dividing unit, the denominator
input of which is fed with the output signal of the summation unit. The
output of the dividing unit as well as the output of the further
temperature sensor may be transmitted to a further summation unit the
output of which is connected to the output of the evaluation unit.
Additionally, in accordance with the present invention, storage elements
may be provided for storing the signals of the adjustable values, with the
storage elements being connected to second input of the multiplication
unit and to the summation unit connected thereafter. In situations
wherein, as noted above, a recess is provided in a body to be measured,
and the body is moved relative to the temperature sensor, in accordance
with the present invention, it is necessary to take into account certain
criteria indicating when a temperature measurement with respect to the
moving body takes place at a correct location, that is, in a region of the
recess and also to provide an indication as to when the temperature
measurement should not take place inasmuch as the recess is not located in
a predetermined position. Preferably, this difficulty is solved by
connecting, after the first sensor, a threshold-value-sensitive unit the
output of which operatively connecting the output of the first sensor with
the output of the arrangement or apparatus if the value of the sensor
output signal lies above or below a predetermined value according to the
threshold value.
Since, in a body provided with a recess such as described hereinabove, only
its surface radiation is effective for measurement, as long as the recess
is not located or disposed in the measuring range of the sensor and there
is a sudden change once the recess enters the measuring range, the above
noted threshold-value-sensitive unit makes it possible to detect the point
in time when the aforementioned recess lies within the measuring range of
the sensor.
Preferably, in accordance with the present invention, the sensor and
threshold-value-sensitive unit are constructed so that a response is
obtained to a predetermined change in the temperature or, respectively,
radiation per unit of time, detected by the first sensor. Thus, changes in
radiation and/or flanks trigger the measurement independently of the
prevailing temperature levels.
The above and other objects, features, and advantages of the present
invention will become more apparent from the following description when
taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS:
FIG. 1 is a schematic view of an arrangement of a temperature sensor for
non-contact measurement of the temperature of a body depicting effects of
ambient radiation;
FIG. 2a is a schematic representation of the arrangement of FIG. 1 during a
chopping or interruption of heat radiation between a body and a
temperature sensor;
FIG. 2b is a graphical illustration quantitatively illustrating sensor
output signal resulting from an arrangement of FIG. 2a in dependence upon
the various radiations;
FIG. 3 is a schematic illustration of an arrangement of a temperature
sensor for non-contact measurement of a temperature of a body in a zone or
area of the sensor-chopper means to be thermally controlled in accordance
with the arrangement of FIG. 2a;
FIG. 4 is a schematic representation of a temperature sensor for
non-contact measurement of a temperature of a body similar to FIG. 2a and
of the provision of further temperature sensors at significant locations
for controlling a temperature and, respectively, heat radiation conditions
in a zone or area such as shown in FIG. 3;
FIG. 5 is an arrangement according to FIG. 4 with a temperature control of
a housing for the body radiation sensor, and with a correction of the
measuring signal as a function of radiation produced by work of a chopper
means;
FIG. 6 is an illustration analogous to FIG. 5 but with a
temperature-controlled chopper means and with a correction of the
measuring signal as a function of the housing temperature of a body
radiation sensor;
FIG. 7 is a schematic view of the arrangement of FIG. 5 provided with an
evaluating unit represented by functional blocks; and
FIG. 8 is a partially schematic cross-sectional view of a body illustrating
the processing units for a sensor output signal for detection of a point
in time when the body to be measured, having a recess provided therein
enters a measurement-relevant position and for accurate measurement of the
body temperature.
DETAILED DESCRIPTION:
Referring now to the drawings wherein like reference numerals are used
throughout the various views to designate like parts and, more
particularly, to FIG. 1, according to this figure, a temperature measuring
sensor 1 such as, for example, a pyroelectric detector is arranged so as
not to contact a zone or area of a body 3. The temperature measuring
sensor 1 is adapted to act as a thermally electrical transducer and
transmit a signal S on an output side thereof, as a function of a
temperature of the body 3 or radiation .theta..sub.3 as well as the
ambient radiation corresponding to .theta..sub.U. If the radiation of the
body 3 is not substantially different from the ambient radiation, in that
its temperature is, for example, below 100.degree. C., with an ambient
temperature of 20.degree. C., then the ambient radiation unduly affects
measuring accuracy. This is particularly true if the ambient radiation for
reasons described more fully hereinbelow, is not constant but rather
varies with time.
As shown in FIG. 2a, a heat radiation chopper means 5 is, according to the
present invention, disposed between the body 3 to be measured having a
radiation corresponding to .theta..sub.3, and the temperature measuring
sensor 1. The chopper means is, for example, a mechanical chopper means
including segments 5a, 5b which respectively represent segments
impermeable to heat radiation and segments permeable to heat radiation,
with the segments being alternatingly moved between the temperature
measuring sensor 1 and the body 3 in the direction of the arrow P. The
ambient radiation with respect to the chopper means 5, on a side forward
the temperature measuring sensor 1 is represented by the character
.theta..sub.U1, with the ambient radiation with respect to the chopper
means 5, forward of the body 3, being denoted by the reference character
.theta..sub.U2.
FIG. 2b illustrates a qualitative output signal of the temperature
measuring sensor 1. If radiation between the body 3 and the temperature
measuring sensor 1 is interrupted by a segment 5a of the chopper means 5,
then the radiation level detected by the temperature measuring sensor 1
corresponds to the lower curve .theta..sub.U1 corresponding to a radiation
of .theta..sub.U1, illustrated in FIG. 2b. If the radiation between the
body and the temperature measuring sensor 1 is unimpeded because of a
segment 5b, then the detected radiation corresponds to a value resulting
from the ambient radiation corresponding to .theta..sub.U2 and the body
radiation .theta..sub.U3. While the ambient radiation .theta..sub.U2 on
the body side can be reduced by positioning the chopper means 5 as closely
as possible to the body 3, the ambient radiation .theta..sub.U1 on the
side of the temperature measuring sensor 1 causes substantially more
problems in controlling the same. Generally, an arrangement, as
schematically illustrated in FIG. 2a is accommodated in a schematically
illustrated housing 7 in such a manner that, when such arrangement is
placed into operation, relatively long periods of time may elapse until
the interior of the housing 7, which is generally poorly ventilated,
stabilize the radiation corresponding to .theta..sub.U1. This, as
indicated in FIG. 2b leads to a time variable amplitude characteristic of
the measuring temperature output signal S of the temperature measuring
sensor 1, even if the radiation of the body 3 corresponding to
.theta..sub.3 is constant. While the ambient radiation corresponding to
.theta..sub.U2 may, in many instances, be assumed to be constant with
adequate accuracy, this is not possible for the radiation corresponding to
.theta..sub.U1, especially during the thermal settling time and,
consequently, a time period for the settling time may last several hours.
For this reason, it is extremely important for an accurate temperature
measurement to know or ascertain the conditions on the sensor side of the
chopper means 5, to consider such conditions, or to affect such conditions
so that, as illustrated in FIG. 3, constant radiation conditions prevail
within the sensor-side zone B as defined or determined by the housing 7
or, if this is not the case, the most essential radiation contributions
from the space are known and may be taken into account when evaluating the
output signal S of the temperature measuring sensor 1.
There are primarily two sources of radiation responsible for the ambient
radiation corresponding to the temperature .theta..sub.U1 on the sensor
side of the chopper 5. First, the temperature measuring sensor 1, with a
conventionally integrated amplifier, customarily supplied, as shown in
FIG. 4, by way of supply or feed cables 9 with electricity, and thus the
housing 11, and, second, the chopper means 5, if a mechanical chopper
means is involved as illustrated by the arrow P. While the housing of the
integrated temperature measuring sensor 1 radiates toward the inside onto
a pyrotechnical sensitive semiconductor element, the mechanical motion of
the chopper means 5 produces a frictional heat in the ambient air which
can lead, in a more or less closed relatively small-space system with
mechanical mounting elements and a casing, analogous to the housing 7 of
FIGS. 2a and 3, to result in a temperature rise of several degrees within
the first few hours following an activation of the apparatus or
arrangement.
Consequently, as shown in FIG. 4, according to the present invention, a
first correctional temperature sensor 13 is closely thermally coupled with
the housing 11 of the temperature measuring sensor 1, and an additional
correctional temperature sensor 15 is coupled with the chopper means 5, in
the case of a mechanical chopper means 5 so that the additional
correctional temperature sensor 15 is located in an immediate vicinity of
a path of motion of the chopper means 5 in such a manner that the
additional correctional temperature sensor 15 measures the temperature of
the ambient air of the chopper means 5.
The first correctional temperature sensor 13 and additional correctional
temperature sensor 15 include, for example, thermal electric transducers
which produce output signals S.sub.11, S.sub.5, representing the housing
temperature and the ambient air temperature for the chopper means 5,
respectively.
FIG. 5 schematically illustrates a first version as to the manner by which
signals of the temperature measuring sensor 1, the first correctional
temperature sensor 13, and the additional correctional temperature sensor
15 are evaluated.
The temperature measuring sensor 1 is embedded, as schematically shown, in
a relatively large-volume thermally well-conductive body 17 made, for
example, of a metallic material to which is thermally closely coupled the
first correctional temperature sensor 13 and a temperature setting member
19 such as, for example, a Peltier element. The output signal S.sub.11 of
the first correctional temperature sensor 13, dependent upon housing
temperature of the housing 11, is optionally processed and amplified in a
unit 21 and then introduced, as a control variable X into a differencing
or subtracting unit 23. The differencing or subtracting unit 23 is fed, at
a correcting variable input W, with an adjustable desired or governing
value W, adjustable at an adjustable signal source 25 of conventional
construction. A control differential signal .DELTA. is introduced through
a controller 27 to the temperature adjusting member such as a Peltier
element so that the temperature of the conductive body 17 is set at a
value corresponding to a desired value W controlled or set by the
adjustable signal source 25. Consequently, the housing temperature of the
housing 11 is constantly feedback controlled with respect to time and is
known.
Due to a relatively low inertia of the housing 11 and conductive body 17
with respect to temperature fluctuations, the thermal stability of the
housing 11 can be rapidly achieved so that, after activation of the
illustrated arrangement, a relevant measurement can soon be conducted with
regard to errors caused by thermal instabilities of the housing 11.
Preferably, in accordance with the present invention, for reasons
described more fully hereinbelow, the output signal S.sub.5 of the
additional correctional temperature sensor 15, detecting the change in
temperature resulting from operation of the chopper means 5, is introduced
together with the output signal S of the temperature measuring sensor 1
into an evaluating or data processing unit 29 at the output of which a
signal S (.theta..sub.3) appears which represents the radiation of the
body 3 and is determined from a calculation of the measuring sensor output
signal S and the output signal S.sub.5 of the additional correctional
temperature sensor 15. The controller 27 may be of the type disclosed, for
example, in Elsevier's Dictionary of Computers Automatic Control and Data
Processing or described on pages 670-681 in the German Handbook of
Electrical Engineering.
In the embodiment of FIG. 6, the temperature is controlled in a zone or
area of the path of motion of the chopper means 5. More particularly, a
chopper disc 5' including segments 5a impermeable to heat radiation and
segments 5b permeable to heat radiation is usually employed and is driven
by means of a motor 31 as the chopper means for obtaining high chopper
frequencies not only in the illustrated embodiment but also if a
mechanical chopper means is used in the remaining embodiments. In the
embodiments of the present invention the output of additional temperature
correctional sensor 15, measuring the temperature directly in the region
of travel path of the chopper disc 5' is transmitted, optionally, after
amplification and processing in a unit 21a, as the control variable signal
X to a differencing or subtracting unit 23a, the second input of which,
analogous to FIG. 5 is fed with a governing or desired value signal W
settable at an adjustable signal source 25a, the control difference signal
.DELTA. appearing on the output side of the differencing or subtracting
unit 23a is then transmitted through a controller 27a to a temperature
adjusting member 19a such as, for example, a Peltier element acting on a
disk shaft 33 closely thermally coupled with the chopper disk 5'. The
control circuit is more inert than the circuit shown in FIG. 5 to the
thermal transfer inertia between the shaft 33 and the periphery of the
chopper disk 5' where, due to the high peripheral velocity, the highest
ambient temperature arises so that a quick response of the control circuit
is limited in order to provide stable control.
In certain applications and with a corresponding reduced dimensioning of
the chopper arrangement, the last described embodiment may be optionally
selected in addition to a control according to FIG. 5 especially in a
situation where, for example, a Kerr cell is employed as an optoelectric
chopper.
In such an arrangement and as illustrated in FIG. 6, the output S.sub.11 of
the first correctional temperature sensor 13 measuring the temperature of
the sensor housing 11, is fed with the output signal S of the temperature
measuring sensor 1 to an evaluating or data processing unit 29a and, at
the output of the evaluating or data processing unit 29a a signal S
(.theta..sub.3) appears, which is representative of the body radiation.
The evaluating or data processing 29 is schematically illustrated in FIG. 7
and is based on the embodiment described hereinabove in accordance with
FIG. 5.
The following relationship represents at least in a first approximation, of
the body temperature .theta..sub.3 corresponding to the body radiation:
##EQU1##
wherein: .theta..sub.3 =a temperature prevailing at the location of the
sensor 1 due to the heat radiation of the body 3,
.theta..sub.1 =a temperature measured by the sensor 1, corresponding to S,
.theta..sub.5 =a temperature measured by means of the sensor 15 in the
immediate range of the path of motion of the chopper 5, corresponding to
S.sub.5,
a,b=coefficients and, respectively, constants to be empirically determined,
in dependence upon the character of the body 3 as well as the arrangement
of chopper means 5, temperature measuring sensor 1 and further facilities
provided in the zone or area of the sensor and/or chopper means.
In accordance with the above relationship, the output signal of the
additional temperature correcting sensor 15 at the evaluating or data
processing unit 29 is first introduced into a multiplication unit 35 and,
as a second input to the adding unit 45, the adjustable coefficient b is
transmitted as the amplification factor. The coefficient b is adjusted at
a setting unit 37 and stored therein. The output of the multiplication
unit 35 is introduced into an adding unit 39 and, as a second input of the
adding unit 39, the variable adjustable at an adjusting unit 41, is
transmitted. The output of the adding unit 39 is transmitted to the
denominator input of a dividing unit 43, with the numerator input of the
dividing unit 43 being fed with the output signal of the temperature
measuring sensor 1. Finally, the output signal of the dividing unit 43 is
added in an adding unit 45 to the output signal of the additional
temperature correction sensor 15, and, on the output side of the adding
unit 45, an output signal S(.theta..sub.3) representing the temperature
.theta..sub.3 corresponding to the radiation of the body 3 is generated.
The coefficients a and in the above noted relationship, set at the
evaluating or data processing unit 29, are empirically determined, for
example, in such a manner that, with at least two predetermined, constant
body temperatures of the body 3 at respectively two different temperatures
in zone of the chopper means 5, detected by the additional tem | | |
