Note: Descriptions are shown in the official language in which they were submitted.
~.~8~
RD-16845
IMAGING PYROMETER
Background of the Invention
This invention relates to a system for measuring
the sur~ace temperature distribution of remote objects
above approximately 400C, such as metals during processing.
Numerous material joining, melting and heat
05 treating processes depend upon precise tempera~ure
control for success. Most often, _ontact temperature
sensors such as thermocouples are used when possible,
but such sensors only reveal the temperature at discrete
locations. Rapidly moving or otherwise inaccessible
parts cannot, in general, be instrumented in this manner.
Contact sensors may also introduce unacceptable impurities
in materials. Radiation pyrometers, such as the present
invention, often provide the most practical solution .
to these measurement problems.
Conventional "spot" radiation pyrometers provide
an effective and accurate means to remotely measure
the surface temperature of small areas and are intended
to replace contact sensors where the use of the latter
- is impractical. These instruments have been commercially
available from a number of vendors for decades. Spot
pyrometers will yield local temperature measurements
of a remote surface and will not reveal variation of
temperature over the surface unless the device is scanned
over the surface or several pyrometers are used.
Since the early 1970's, a few vendors have offered
ima~ing infrared radiometers (also known as Forward
Looking Infra~ed scanners or FLIR's) which generate
a television-like display of object radiance, i.e.
object temperature. These devices typically use cryo-
genically-cooled, single-element photoconductive or
--1--
~2 ~ ~ ~2 8 RD-1684;
photovoltaic detectors and mechanically-scanned optical
axes and operate in the 2-6 and 7-14 micrometer spectral
region. Neither spectral band is optimal for accurate
temperature measurements of most metals at typical
05 processing conditions since metal emissivity is generally
quite low at these wavelengths in comparison to the
near-infrared (0.7-2 micrometers). Further~ore, the
cooling systems and delicate scanning mechanisms required
by most thermal infrared imagers often preclude their
use in harsh industrial environments.
The present invention fills the gap in available
instrumentation between spot radiation pyrometers and
thermal infrared imaging radiometers for high temperature
measurement and process control industrial applications.
Summary of the Invention
An object of the invention is to combine the
thermal mapping and display capabilities associated
with thermal infrared imaging radiometers with the
accuracy, reliability and low relative cost of spot
radiation pyrometers.
Another object is to provide such an instrument
to supplement or replace contact temperature sensors
and other radiation pyrometers for industrial temperature
measurement, particularly to monitor and control metal
melting, heat treating and joining processes.
The imaging radiation pyrometer system is constructed
from an electronic or solid-state video camera
having a two-dimensional detector array which responds
to radiation wavelengths in the near~infrared range,
and operates in a fixed gain mode so to have a linear
response of video output signal to incident radiation intensit~
A lens or lens system with a known aperture forms an
image of the remote object on the detector focal plane~
--2--
~,7~8~7?,l~
RD-168~5
.~eans are provided to limit the spec~ral response of
the system to suppress erroneous measurements due to
extraneous light; an infrared filter is typically mounted
in the camera directly in front of the detector array.
05 The system further incl~ldes means for guantitatively
determining from the video signal the temperature at
any point on the object surface within the sensor's
field of view, and for displaying object temperature.
The instrument measures surface temperatures above
approximately 400C; neutral density filters are added
to extend the high temperature range.
A preferred embodiment uses a charge injection
devic~ (CID) solid-state video camera and internally
mounted infrared filter, and a standard television
camera lens with one or more reproducible aperture
settings. Spectral response of the instrument is restricted
to 700 to 1100 nanometers or any smaller portion of
this band. The video signal output from the sensor
head is processed by a video analyzer prior to display
on a black and white television monitor and provides
a continuous graphical display of temperature variations
along a user-positioned measurement cursor. A second
display option is to present the video signal to a
color synthesizer and show each temperature band as
a distinct color or hue on a color monitor. A third
alternative is a digital frame grabber to convert the
video output to digital form and signal intensity to
a temperature map.
Brief Description of the Drawings
Fig.l shows the imaging pyrometer system with
various display options.
Fig.2 illustrates the typical spectral responsivity
of an imaging radiation pyrometer with a CID detector.
8'~2~3
RD-16845
Fig.3 shows the display layout in a system having
a video analyzer and black and white television monitor;
the trace gives temperature variations along a user
positioned measurement cursor.
05 Detailed Description of the Invention
Referring to Fig.l, the imaginy pyrometer may
be constructed from any television ar video camer using
a detector which responds to radiation wavelengths
in the near-infrared, approximately 0.7 to 2.0 micrometers
or any portion thereof, and is capable of operating
in a fixed gain mode, i.e. the video signal output
by the camera is proportional to the radiant power
flux incident upon the detector. The preferred embodiment
is a solid-state video camera 10 having a charge injection
device two-dimensional silicon detector array 11, such
as the General ~lectric TN-250X series (2500, 2505,
2509 and variants) CID Solid-State Camera. All GE
cameras in this series may be operated ln the required
fixed-gain mode either by default or jumper configuration.
They are preferred for their superior stability, low
fixed-pattern noise and infrared anti-blooming charac~eristics
in comparison to other devices generally available.
Cameras based on alternative detector array architectures,
;~ including but not limited to charge coupled device
(CCD), diode matrix or vacuum tube Vidicon-like devices,
such as the Texas Instruments "Tivicon" tube could
also serve as the basis for this pyrometer.
An infrared filter 12, more particularly a long
pass type, is placed in such a manner as to limit the
camera's spectral response to the convolution of the
filter's transmission and the responsivity limits of
the detector array 11. A filter with an abrupt
--4--
~34~8
RD-16845
"cut on" wavelength of between 700 and 900 nanometers is
preferred. This filter serves to eliminate most of the
extraneous radiation from sources other than the intended
target without significantly reducing the sensitivit~ of
05 the pyrometer. Its use is optional, bu~ highly re~orn-
mended. The infrared filter 12 is in the optical pa~h
between a lens systerl 13 and the detectori the illustrated
filter is internally mounted in the cam~ra and is placed
in a holder positioned immediately in front of the
sensing surface of detector array 11. A working prototype
of the instrument was constructed with a ~oya IR-~ON
infrared long-pass filter. Typical detector and filter
limits as utilized in the preferred embodiment are
shown in Fig.2. The speçtral responsivity of a charge
injection device silicon detector array typically extends
from about 400 to 1100 nanometers. Above this upper
limit silicon becomes increasingly transparent to infrared
radiation. Light wavelengths shorter than approximately
800 nanometers are blocked by the filter 12. The spectral
response of the system is intentionally limited to
about 700 to 1100 nanometers or a smaller portion of
this band in order to suppress erroneous measurements
due to room lighting and the like sources.
Lens system 13 has one or more fixed, known
apertures and forms an image of the radiating object
on the detector focal plane. Virtually any standard
television camera lens with precision, reproducible
aperture settings can be employed in this system.
A good general choice is a 50 millimeter focal length,
f/1.4 telephoto "C" mount lens with "click adjustable"
aperture settings which are changed by rotating ring
14. An instrument in te factory that repetitively
performs a given measurement task may have only one
preset, known aperture, whereas a laboratory instrument
should have several aperture settings to fit it for
a variety of tasks.
-5-
The three components of the sensor head that
have been described are the solid-state video camera
10, infrared filter 12, and lens system 13 (a single
lens is adequate for some systems). The imaging pyrometer
with such a sensor measures the surface temperature
distribution of remote o~jects above approximately
400 Celcius. Neutral density filters are added to
extend the high temperature range of the instrument.
One good location is to place theM in front of the
infrared filter 12. At the lower end of the temperature
range the f/1.4 lens aperture is used, and to measure
higher temperatures a smaller aperture is selected.
The video signal output from camera 10 can be
directly displayed on a television monitor resulting
in a continuous grey scale depiction of temperature
variations of the target object. The basic signal
is most often processed further to yield more inEormative
displays. The video output signal of the GE CID Solid-
State Camera is a standard EIA RS-170 composite signal
(525 line, 60 Hz, 2/1 interface). The camera could,
of course, be built to output a European standard signal.
In a preferred embodiment of one display option, the
video signal from the sensor is processed by a video
analyzer 13 prior to display on a black and white televi~ion
monitor 16. A Colorado Video ~Boulder, CO) Model 321
Video Analyzer, for instance, provides a continuous
graphical display of signal intensity, i.e. object
temperature, along a user-selected cursor as well as
additional signal outputs useful for further processing.
A sketch of the imaging pyrometer's display, as modified
by the foregoing Video Analyzer, is seen in Fig.3 where
the black and white display layout is illustrated.
A user positioned measuremen~ cursor 17 is adjustable
left and right, passing through or intersecting the
RD-16845
target object 18. Trace 19 at the left on the dis?lay
grid gives the temperature variations along the measurement
cursor line.
M~re elaborate video signal processors are rea~ily
05 added to the system. As shown in Fig.l, a video recorder
20 is fed the object temperature signals from television
monitor 16. A second display option is to have a cGlor
synthesizer 21 and color ~onitor ~2. ~ach te~perature
band then has a distinct color or hue. If a step display
is desired, the temperature bands have different colors
in a continuous display the bands are various hues
of the same color. A third display option, expecially
suitable if the instrument is tied into a control system,
is to have a digital frame grabber 23. The video signal,
frame by frame, is converted into digital form and
a look-up table converts the digitized signal intensity
int a temperature map.
The most basic calibration of the imaging pyrometer
system entails obtaining the relationship between video
signal voltage and blackbody absolute temperature for
each aperture and filter combination used for any given
lens and camera (detector plus infrared filter). This
procedure is most readily accomplished utilizing a
laboratory blackbody radiation source, such as the
Infrared Industries Model 464 Blackbody, while making
use of the video analyzer D.C. video signal. The cali-
bration curve is well described by the relation
A
exp(B/T)-1
where
V = Video Signal Voltage,
T = Blackbody Absolute Temperature [Kelvin]
and A,B,C = calibration constants.
The pyrometer may be focused by illuminating the target
with a bright floodlamp. This lamp must be turned
--7--
.
Z8
RD-16845
off when temperature measurements are taken. Although
the infrared filter provides some protection against
errors due to erroneous background radiation, the operator
must insure that the target area is shielded from any
05 bright sources of external radiation prior to use.
It is seen that a properly calibrated imaging pyrorneter
system quantatively determines from the video signal
the object temperature at any point in the field of
view o~ the sensor over the sensitivity range of the
System.
Among the many applications of the imaging pyrometer
are monitoring and controlling metal heat treating,
melting and joining processes used to manufacture precision
components. This instrument is intended to supplement
15 ` or replace contact temperature sensors and other radiation
pyrometers for industrial temperature measurements.
~hile the invention has been particularly shown
and described with reference to preferred embodiments
thereof, it will be understood by those skilled in
the art that various changes in form and details may
be made without departing from the spirit and scope
of the invention.
--8--
