Miscellaneous active electrical nonlinear devices – circuits – and – External effect – Temperature
Reexamination Certificate
1999-10-29
2001-11-20
Nuton, My-Trang (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
External effect
Temperature
C374S149000
Reexamination Certificate
active
06320450
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a temperature sensing circuit using a thermopile sensor and, more particularly, to a temperature sensing circuit using a thermopile sensor, which is able to detect temperature accurately with regard to an offset of an amplifier included therein.
2. Discussion of Related Art
In general, a thermopile sensor is a device which generates a voltage corresponding to the difference between a temperature of infrared rays incident from an object and a surrounding temperature of the sensor. This thermopile sensor is usually employed as a device for sensing the temperature of a food placed in the cooking room of a mircrowave oven. However, a signal detected by the thermopile sensor is too weak to be directly used for controlling cooking in the microwave oven. Accordingly, the signal is needed to be amplified to an appropriate level.
A conventional temperature sensing circuit is explained below with reference to the attached drawing.
FIG. 1
shows the configuration of a conventional temperature sensing circuit. Referring to
FIG. 1
, the conventional temperature sensing circuit is composed of a temperature detecting circuit
70
including a thermopile sensor
11
which generates a voltage value (Vb) corresponding to the difference between a temperature of infrared rays incident from an object and a surrounding temperature of the sensor, and a temperature amplifier
12
for compensating for an increase or decrease in voltage Vd with relation to the surrounding temperature within the output voltage of thermopile sensor
11
.
Temperature amplifier
12
is composed of an amplifier
12
a
for amplifying the output of thermopile sensor
11
, a temperature compensator
12
b
for amplifying output voltage Vb of thermopile sensor
11
and generating compensated voltage Vd, an adder
12
c
for adding an output of amplifier
12
a
to the voltage compensated by temperature compensator
12
b,
and an amplifier
12
d
for amplifying the output of adder
12
c
to generate a temperature sensing voltage Vo.
The operation of the conventional temperature sensing circuit is described below. Thermopile sensor
11
generates a voltage Va corresponding to the temperature of infrared rays incident from the object. Output voltage Va of thermopile sensor
11
varies with its surrounding temperature. The surrounding temperature is compensated using a temperature compensating device such as diode or thermistor which is arranged on one side of thermopile
11
or around it. The output value of the temperature compensating device corresponds to a resistance value when the temperature compensating device is a thermistor, and it corresponds to a voltage value when the device is a diode.
FIG. 1
shows a case where a diode is used as the temperature compensating device. Thermopile sensor
11
generates voltage Va corresponding to the temperature of infrared rays incident from the object. Amplifier
12
a
amplifies the output of thermopile sensor
11
, and temperature compensator
12
b
amplifies output voltage Vb of the temperature compensating device (not shown). Adders
12
c
adds output voltage Vc of amplifier
12
a
to output voltage Vd of temperature compensator
12
b.
Here, the output of adder
12
c
becomes a voltage corresponding to the temperature of the object, which is obtained by removing the effect of the surrounding temperature of thermopile from output voltage Va of thermopile sensor
11
. Amplifier
12
d
connected to the output terminal of adder
12
c
amplifies the output voltage of adder
12
c
and sends resulting value Vo to a microcomputer
80
. Microcomputer
80
detects the temperature of the object according to output voltage Vo of temperature amplifier
12
.
The aforementioned conventional temperature sensing circuit has the following problems. First of all, it requires the amplifier for amplifying the output of the thermopile sensor and the plurality of amplifiers for compensating for the variation in the surrounding temperature, resulting in complicated circuit configuration. Furthermore, the temperature compensating device and amplifiers are added, increasing the cost. Moreover, the output voltage of the thermopile sensor is amplified together with the offset values of the amplifiers so that it cannot be correctly calculated, deteriorating accuracy in temperature detection.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a temperature sensing circuit using a thermopile sensor that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a temperature sensing circuit using a thermopile sensor, which removes an error of an amplifier to accurately detect the temperature of an object.
To accomplish the object of the present invention, there is provided a temperature sensing circuit using a thermopile sensor, which includes a thermopile sensor generating a voltage corresponding to an incidence amount of infrared rays, means for amplifying the output of the thermopile sensor, means for compensating for an offset of the amplifying means, and means for removing the output of the offset compensating means from the output of the amplifying means, to detect the temperature of an object.
According to a preferred embodiment of the present invention, the offset compensating means is configured of a combination of resistors which is determined according to the offset value of the amplifying means. The amplifying means uses a voltage varying with a surrounding temperature as a reference voltage.
There is also provided a temperature sensing circuit using a thermopile sensor which includes a thermopile sensor generating a voltage corresponding to an incidence amount of infrared rays, surrounding temperature compensating means being placed adjacent to the thermopile sensor, for generating a compensation voltage for removing the effect of surrounding temperature, means for amplifying the output of the thermopile sensor using the compensation voltage generated by the surrounding temperature compensating means as a reference voltage, and offset compensating means for controlling the reference voltage of the amplifying means according to an offset of the amplifying means.
The offset compensating means is configured in such a manner that a resistor with a resistance value proportional to the offset of the amplifying means is connected between the reference voltage terminal of the amplifying means and a power supply terminal when the offset of the amplifying means has a negative value. The offset compensating means is configured in such a manner that a resistor with a resistance value proportional to the offset of the amplifying means is connected between the reference voltage terminal of the amplifying means and a ground terminal when the offset of the amplifying means has a positive value.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 4734554 (1988-03-01), Tateda et al.
patent: 5304950 (1994-04-01), Martin et al.
patent: 5826982 (1998-10-01), Schieferdecker et al.
patent: 5876120 (1999-03-01), Lee
patent: 6048092 (2000-04-01), Kimura et al.
Lee Koon Seok
Lim Jeong Hyun
Fleshner & Kim LLP
LG Electronics Inc.
Nuton My-Trang
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