U.S. patent number 3,684,996 [Application Number 05/027,623] was granted by the patent office on 1972-08-15 for high-sensitivity, long-time-constant thermistor bolometer.
This patent grant is currently assigned to Barnes Engineering Company. Invention is credited to Frank Schwarz.
United States Patent |
3,684,996 |
Schwarz |
August 15, 1972 |
HIGH-SENSITIVITY, LONG-TIME-CONSTANT THERMISTOR BOLOMETER
Abstract
A high-sensitivity, long-time-constant thermistor bolometer
having a heat sink and two thermistor elements in the same plane
thermally connected to the heat sink through a path of high thermal
impedance including a cylinder of material of low heat
conductivity.
Inventors: |
Schwarz; Frank (Stamford,
CT) |
Assignee: |
Barnes Engineering Company
(Stamford, CT)
|
Family
ID: |
21838792 |
Appl.
No.: |
05/027,623 |
Filed: |
April 13, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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864842 |
Oct 9, 1969 |
3631434 |
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564391 |
Jul 11, 1966 |
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Current U.S.
Class: |
338/18; 338/22R;
250/338.1; 250/DIG.1 |
Current CPC
Class: |
G01J
5/20 (20130101); Y10S 250/01 (20130101) |
Current International
Class: |
G01J
5/20 (20060101); H01c 007/08 () |
Field of
Search: |
;338/17,18,19,22,25
;250/83R ;73/355 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Benjamin A.
Assistant Examiner: Kinberg; R.
Parent Case Text
RELATED APPLICATIONS
This application is a division of application Ser. No. 864,842
filed Oct. 9, 1969, now U.S. Pat. No. 3,631,434 which is a
continuation-in-part of application Ser. No. 564,391, filed July
11, 1966, and now abandoned.
Claims
I claim
1. A high sensitivity, long time constant thermistor bolometer
comprising, in combination,
a. a heat sink,
b. a hollow thermally insulating support mounted on said heat sink
with one edge of the support in contact with the heat sink,
c. a thin electrically insulating membrane mounted on the other
edge of the hollow support and therefore out of direct contact with
the heat sink,
d. a pair of thermistor flakes mounted on said thin membrane, the
flakes being electrically connected together,
e. externally extending electrical leads, the first of said leads
being connected to the electrical connection between the
extremities of the two flakes, second and third leads connected
respectively to the extremities of each flake opposite the
extremity connected to the other flake, whereby when the second and
third leads are connected to different polarities of a DC current
source, the thermistor flakes are in opposition, and thermal
connection of the thermistors to the heat sink is through a path
consisting of the membrane and the hollow support.
2. A thermistor bolometer according to claim 1 in which the
membrane is of a thin plastic and the hollow support of thermally
insulating material is a hollow cylinder.
3. A bolometer according to claim 1 in which the bolometer is
evacuated.
4. The thermistor bolometer according to claim 1 in which the thin
membrane is polyglycol terephthalate, and the hollow support is of
nylon.
5. A thermistor bolometer according to claim 4 in which the
bolometer is evacuated.
Description
BACKGROUND OF THE INVENTION
The problem of moving objects which are at a higher temperature
than their surroundings, or at least at a different temperature, is
one of great importance in warfare, and is also useful in
peacetime. The moving objects may be human beings, animals, or
vehicles which have relatively hot areas, such as the exhaust from
a motor vehicle. The problem may be considered as the detection of
a moving intrusion into or across a particular background. It is
also important, particularly when an instrument is to be carried,
to have an instrument that is light and does not consume any large
amounts of power and so can be operated for extended periods of
time with self-contained power sources, such as batteries, either
primary or secondary.
SUMMARY OF THE INVENTION
The present invention is directed to a high-sensitivity,
long-time-constant thermistor bolometer, in which the conventional
two thermistor flakes in opposition are mounted on a substrate on a
cylinder of material of low thermal conductivity, which in turn is
mounted on a conventional heat sink, the bolometer being evacuated.
It has very high sensitivity with a very long time constant,
typically of about 200 msecs.
The bolometer which can be operated with batteries and has very low
power requirements is particularly useful in passive intrusion
detectors, such as one pointed down a jungle path and which
responds to infrared radiations from intruders, such as human
beings, crossing the field of view of the intrusion detector. A
typical diagrammatic representation of such a detection system with
an illustrative form of electronic processing circuits is also
described, although the detector is claimed as such, regardless of
its use.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic representation of an intrusion detection
system, and
FIG. 2 is an enlarged section through the detector of the present
invention .
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows in diagrammatic form an intrusion detector system
using a detector of the present invention, and illustrative
electronic processing circuits. No mechanically movable parts are
required during operation. The instrument is provided with imaging
optics which is shown diagrammatically as a lens 10. The optics
images a particular field of view sharply in the plane of the
detector, with two sensitive thermistor flakes 4 and 5. The
detector flakes, the size of which is shown exaggerated, are
sufficiently far apart so that at ordinary distances an intruder
would be imaged as a sufficiently small image so that the image
would not cover both flakes at the same time.
The more detailed description of the new type of detector can be
understood best in connection with FIG. 2. This detector, which has
a conventional metal base 1 is equipped with a window 2 of suitable
infrared transmitting material, such as KRS5 or germanium, which
will transmit infrared in the wavelengths around 10.mu.. The two
thermistor flakes 4 and 5 are mounted on a thin insulating layer 9
of polyglycol terephthalate, which is cemented across the top of a
hollow cylinder or ring 3 of nylon resting on the base 1 of the
thermistor bolometer. The three pins of the bolometer 6, 7, and 8
are connected to one end of flake 4, the junction of flakes 4 and
5, and the opposite end of flake 5 respectively. The bolometer is
evacuated, and shows a high sensitivity with a fairly long time
constant of about 200 msecs.
As will be seen from FIG. 1, pins 6 and 8 are connected to the
positive and negative sides of a D.C. potential of about 13 volts.
Pin 7 is connected to the input of an amplifier 24 which shows good
low-frequency response. The input circuit of the amplifier is shown
outside the amplifier symbol in schematic, and is a differentiating
circuit of 1 .mu.f capacitor with 10M.OMEGA. resistor. It has a
time constant of approximately 10 seconds. The amplifier 24 should
preferably respond down to about 0.2 cycle.
The amplified output from 24 is coupled through a 150 .mu.f
tantalum capacitor into an integrating circuit with a 10k resistor
and two 15.mu.f tantalum capacitors connected back to back. This
leads to the input of an amplifier 11 which should have good
low-frequency characteristics. The output of amplifier 11 is
connected in parallel to two monostable multivibrators 12 and 15.
The outputs of the multivibrators are connected to an AND gate 13
and AND gate 16 respectively. The other connections to the AND
gates is the common input to the multivibrators. Each AND gate
actuates its own alarm 14 and 17 respectively.
The operation of the instrument is as follows:
An ordinary background in which there is no motion of the image of
an intruder from flake 4 to flake 5 within the time constant of the
input to amplifier 24 will not result in a signal to amplifier 24
unless the image on one or other flake moves on and off the flake.
For example, if a tree in the background having different
temperature than the average of the background sways in the wind,
there may be a signal, if the image sways on and off one flake.
This would result in amplifier pulses from the amplifiers 24 and
11, but the pulses would have the same polarity. Thus if the image
of the moving object only went on and off of flake 4, there would
be only positive pulses reaching the multivibrators. Let us assume
that multivibrator 12 responds only to positive pulses, and places
a negative pulse on the AND gate 13. The multivibrator 15 would not
be acted on by a positive pulse, and therefore it would not put any
signal on the gate 16. In a similar manner, if the image of an
object moved on and off flake 5, the resulting negative pulses
would cause the multivibrator 15 to operate, but not the
multivibrator 12. In either case there would be no alarm signal
given, because neither AND gate 13 nor 16 would have received
signals of proper polarities in both of their inputs.
Now let us assume that a man walks across the field of view, his
image first striking flake 4 and then a second or so later leaving
flake 4 and striking flake 5. The moving signal on flake 4 would
put out a positive pulse from amplifier 11 which would cause
multivibrator 12 to put a signal on gate 13 but would not trigger
off alarm 14 as there would be no negative signal in the other
input of gate 13. However, as soon as the man's image comes onto
flake 5, a negative signal will be generated in the output of
amplifier 11. This will reach AND gate 13 and since the gate now
has signals of the proper polarity on both of its inputs, its
output will set off the alarm 14. The negative pulse from flake 5
through the amplifiers will, of course, cause the multivibrator 15
to operate, but it will not cause the AND gate 16 to pass on the
signal because the other input to this gate will not have a signal
of the right polarity. Therefore, alarm 17 will not be actuated,
and the alarm signals will show that a moving target moved from the
left (looking at the flakes 4 and 5 on FIG. 1). If a man moved
across the field of view from the opposite direction, the pulses
would be reversed, multivibrator 15 would be activated by the first
negative pulse, and then the following positive pulse would cause
AND gate 16 to pass its signal on to the alarm 17, whereas gate 13
would not have received the signals of the proper polarity in both
its inputs and so alarm 14 would not be actuated.
Monostable multivibrators and AND gates are conventional electronic
devices, and therefore they have been shown purely diagrammatically
in block diagram form. Of course the multivibrators must have the
proper time constants so that there will be an alarm if a man moves
across from one flake to another in a reasonable time. Also, of
course, the gates must have the proper circuitry for the functions
which they are performing and which have been described above.
Similarly, the amplifier preceding the logic circuits may
incorporate automatic gain control features and clamp circuits of
conventional form in order to function optimally in detecting
targets at any distance within the limit of the instrument and
varying in intensity with the background, depending on particular
background conditions.
After an alarm is given, the operator of the instrument, if it is
being monitored by a human operator, can reset the alarm. As this
is a conventional electronic operation, its circuit is not shown.
It is possible to have the alarm unattended, or record at a remote
location, and in some such cases it is desirable to have the
multivibrators clear themselves after the expiration of a
predetermined delay, their preset time constant. This also is a
conventional type of electronic circuitry, and is not specifically
shown in schematic form.
The new detector, which is extremely sensitive (though slow, which
does no harm and actually is an advantage in the present use),
permits operation with fairly low voltages and very moderate power
inputs. It is possible to use primary batteries and run an
instrument for a week or more. Also, because there are no moving
parts and no need for the expense of immersion optics, the new
bolometers can be built very economically in comparison to their
high sensitivity. Other types of detectors, such as thermocouples
and thermopiles, may also be used, but they do not lend themselves
as well to the compact construction with good sensitivity which is
made possible with the slow, highly sensitive, unimmersed
bolometers shown particularly in FIG. 2.
* * * * *