Thermal measuring and testing – Temperature measurement – In spaced noncontact relationship to specimen
Reexamination Certificate
2001-06-06
2003-05-20
Fulton, Christopher W. (Department: 2859)
Thermal measuring and testing
Temperature measurement
In spaced noncontact relationship to specimen
C374S133000, C374S181000, C136S224000
Reexamination Certificate
active
06565254
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a thermopile infrared sensing element and a temperature measuring device using the same.
2. Description of the Related Art
A known temperature measuring device uses an infrared sensing element which detects infrared radiation emitted from a heat source and converts it into an electric signal. Examples of known infrared sensing elements include a thermopile type, a pyroelectric type, a borometer, and the like. The thermopile infrared sensing element utilizes the Seebeck effect of a thermopile comprising a thermocouple or a plurality of thermocouples connected in series, for detecting a temperature change due to infrared radiation or absorption as thermo electromotive force. The pyroelectric infrared sensing element detects a temperature by using a change in floating charge due to polarization according to the infrared thermal energy, i.e. a pyroelectric effect, of a base material comprising ceramic or the like. The borometer comprises a thermosensitive resistor comprising a thin film or a thin wire of a metal or the like so that a thermal change in resistance value of the resistor is detected.
Of these sensing elements, the pyroelectric infrared sensing element requires a shutter provided on an optical path, for alternately measuring the temperatures of a surface to be measured and a reference point because polarization occurs only at the moment of application of thermal energy. Therefore, it is difficult to miniaturize the pyroelectric infrared sensing element and improve measurement accuracy. The pyroelectric infrared sensing element can thus be used for applications such as a “body sensing element” of an automatic door and the like, which are little required to have a small size or high measurement accuracy. However, the pyroelectric infrared sensing element is unsuitable for a temperature measuring device such as a clinical thermometer or the like, which is required to measure temperatures with high accuracy and have a small size and low cost.
Furthermore, the pyroelectric and thermopile infrared sensing elements require detecting a relative temperature difference from a reference temperature, while the borometer has the advantage that an absolute temperature can be measured. However, the barometer has many causes of error, such as self heating due to measuring current, current noise, etc., thereby causing difficulties in improving the measurement accuracy. The borometer also requires a bias current that complicates the structure, and thereby complicates handling.
On the other hand, the thermopile infrared sensing element does not use such a transient phenomenon as utilized by the pyroelectric type and such excess measuring current as flowing through the barometer, and thus the thermopile infrared sensing element can stably detect or measure temperatures. Furthermore, the thermopile infrared sensing element can be miniaturized by using the semiconductor manufacturing process at low cost, and is thus suitable for a temperature measuring device such as a clinical thermometer or the like, which is required to be small in size and inexpensive.
FIG. 21
shows an ear-type clinical thermometer
100
as a temperature measuring device using a thermopile infrared sensor or infrared sensing element. The ear-type clinical thermometer
100
comprises a body case
11
, an infrared receiving sensing unit
200
which receives infrared radiation from the ear to output a voltage signal according to the temperature of the ear, i.e. the temperature of the tympanic membrane, and a circuit board
3
on which various electronic parts and circuits are mounted. On the circuit board
3
, various electronic parts
4
C are mounted to form a temperature deriving circuit
400
for determining the temperature of the tympanic membrane based on the output voltage of the infrared receiving sensing unit
200
, or the body temperature based on the temperature of the tympanic membrane. Furthermore, LCD
5
for displaying the determined temperature, and the like, and a power source
6
for supplying electric power to each of the units are also mounted on the circuit board
3
.
The infrared receiving sensing unit
200
comprises a case
211
having a cylindrical shape which projects forward (to the right of the drawing) to permit the front end to be inserted into the lughole, a wave guide
206
contained in the case
211
, and an infrared sensing chip
210
arranged at the base of the wave guide
206
to face the front end of the case
211
. The front end of the case
211
is open, and covered with an infrared transmitting probe cap
25
, and the front opening of the wave guide
206
is covered with an infrared transmitting film
23
for preventing entrance of dust particles, etc, the film
23
being supported by a film holding O-ring
24
. Therefore, when the front end of the case
211
is inserted into the lughole, infrared radiation entering the infrared receiving sensing unit
200
is guided to the infrared sensing chip
210
by the wave guide
206
so that the infrared sensing chip
210
receives the infrared radiation corresponding to the temperature of the tympanic membrane to output a voltage signal according to the infrared radiation. Therefore, when a temperature measurement switch SW
4
of the ear-type clinical thermometer
100
is pushed, the body temperature can be measured by the infrared receiving sensing unit
200
through infrared radiation.
Namely, the clinical thermometer
100
is a wave guide type in which infrared radiation entering from a heat source (the lughole) S is transmitted through the wave guide
206
arranged in front of the infrared sensing chip
210
to be guided to the infrared sensing chip
210
, as shown in FIG.
22
. The temperature rise due to the infrared radiation is converted into a voltage by the thermopile of the infrared sensing chip
210
and then output.
FIG. 23
shows the infrared sensing chip
210
. The infrared sensing chip
210
comprises a thermopile infrared sensor
209
, and a thermistor
211
, both of which are mounted on a package substrate
212
. In the infrared sensing chip
210
, the thermistor
211
is used for determining the reference temperature of the thermopile formed in the infrared sensor
209
, i.e. the temperature of the cold junction. These components are contained in a package case
213
to unify the components. The package case
213
further comprises an infrared filter
208
composed of silicon or the like and provided in a window through which infrared radiation enters, for cutting-off visible light and transmitting infrared radiation.
FIG. 24
is a perspective view schematically showing the infrared sensor or infrared sensing element
209
. The infrared sensor
209
comprises a base
80
comprising a portion (thin film portion)
802
in which only a thin film is left by etching a silicon substrate to form a hollow at the center of the lower surface or the bottom of the silicon substrate, and a thick wall portion
801
in which the silicon substrate remains unetched. Namely, the infrared sensor
209
has a structure in which a hollow portion KW is formed at the center of the base
80
from the lower side to form a membrane at the top of the base
80
. Furthermore, gold black is deposited at the top of the thin film portion
802
by sputtering, evaporation, or the like to form an infrared absorber
81
comprising a black body for absorbing infrared radiation. The infrared absorber
81
absorbs infrared radiation to cause a change in temperature.
The infrared sensor
209
further comprises a plurality of thermocouples
82
with high sensitivity, which are provided on every side of the infrared absorber
81
. The hot junction
83
of each of the thermocouples
82
is arranged near the infrared absorber
81
or to be overlapped with it, and the cold junction
84
of each thermocouple
82
is arranged in the peripheral thick wall portion
801
in which the silicon substrate remains. Although electromotive force occurs between the hot junction
83
and the cold junct
Iwamoto Osamu
Oda Yuji
Sato Shigemi
Shiohara Yasuhiro
De Jesús Lydia M.
Fulton Christopher W.
Haro Rosalio
Seiko Epson Corporation
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