JP2003014541A - Infrared detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive, high-performance, and reliable infrared detection circuit. SOLUTION: The DC voltage of a DC power supply 11 is inverted and amplified by an inverting amplifier 14 for changing amplitude according to the change in resistance in the radiation heat of the infrared rays in a sensitive resistor Rt, and the output voltage of the inverting amplifier 14 is added to the DC voltage of the DC power supply 11 to obtain a DC voltage according to the change in resistance due to the radiation heat of the infrared rays of the sensitive resistor Rt, thus eliminating the need for a correction circuit for making linear the amount of change in an input voltage to the change in resistance as in the conventional method, reducing costs, and miniaturizing the entire infrared detection circuit. Additionally, since the need for the correction circuit is eliminated, error affecting the accuracy in the correction circuit is eliminated, and the entire accuracy of the infrared detection circuit can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a presence detection type infrared detection circuit for detecting infrared rays.

[0002]

2. Description of the Related Art A conventional infrared detecting circuit is shown in FIG.
This infrared detection circuit detects infrared rays with an infrared sensitive resistor Rt serially connected to both ends of a DC power supply 11 via a reference resistor Rref, and the detected output is a difference from a comparison voltage 13 in a DC differential amplifier 12. The amplified voltage is the output voltage Vout
It is what

An infrared sensitive resistor (hereinafter referred to as a sensitive resistor) Rt is a resistor such as a thermistor whose resistance value changes in accordance with a temperature change. FIG. 22 shows a change in resistance value (so-called temperature characteristic) of a typical thermistor with respect to a change in temperature. Here, as the sensitive resistor Rt, one having a heat capacity as small as possible and a heat resistance as large as possible is used, so that the temperature of the sensitive resistor Rt itself rises and a resistance value change occurs even with a slight radiation heat. Is done.

The reference resistance Rref has a resistance value exactly the same as that of the sensitive resistor Rt and has a resistance change rate with respect to a temperature change which is exactly the same as that of the sensitive resistor Rt. However, it is completely shielded from radiant heat from the outside. That is, the radiant heat due to infrared rays is blocked by a method that does not affect the resistance value or the rate of resistance change, or a method that spatially insulates. Therefore, when the radiant heat is not incident on the sensitive resistor Rt, the divided voltage by the sensitive resistor Rt and the reference resistance Rref is kept constant even if the ambient temperature changes.

The comparison voltage 13 is the voltage of the DC power supply 11 E
Then, it is set to E / 2. The comparison voltage 13
Alternatively, as shown in FIG. 25, the voltage E of the DC power supply 11 may be obtained by dividing the voltage E by the resistors Rd ₁ and Rd ₂ .

In the above infrared detecting circuit, the sensitive resistor Rt
When there is no change in the resistance value due to the radiant heat, the resistance values of the sensitive resistor Rt and the reference resistor Rref are equal, and the divided voltage of the sensitive resistor Rt and the reference resistor Rref (the DC differential amplifier 1
Since the input voltage Vin of 2) matches the comparison voltage 13, the output voltage Vout of the DC differential amplifier 12 becomes 0V. When the resistance value of the sensitive resistor Rt changes due to radiant heat, the output voltage V corresponding to the difference between the divided voltage of the sensitive resistor Rt and the reference resistance Rref and the voltage E / 2 of the comparison voltage 13 is generated.
out is output from the DC differential amplifier 12. That is, the change in ambient temperature is canceled out, and only the value corresponding to the amount of radiant heat is output from the DC differential amplifier 12.

Here, when the gain of the DC differential amplifier 12 is A, the input voltage Vin and the output voltage Vout of the DC differential amplifier 12 are expressed by the following equations.

[0008]

[Equation 1]

FIG. 23 shows a case where the above infrared detecting circuit is applied to a human body detecting device. In this human body detecting device, an appropriate optical means L such as a lens is used to irradiate the sensitive resistor Rt with infrared rays, and a comparator 5 for comparing the output voltage Vout of the DC differential amplifier 12 with an appropriate reference voltage 6. Is provided, and high and low binary outputs (so-called ON and OFF outputs) are obtained for radiant heat above a certain level determined by the setting of the reference voltage 6.

FIG. 24 shows the operation of the human body detecting device when the human body X, which is an infrared radiation object, moves in the order of (A) .fwdarw. (I) .fwdarw. (U) in FIG. Here, it is assumed that the human body X has energy higher than ambient temperature by ΔT ° C. (lower in some cases), and (a) → (i) in FIG.
→ Fig. 2 shows the change of radiant energy in the detection field of view when passing through the detection field of view (→)
4 (a). Here, when the human body X does not exist in the detection visual field, it is assumed that the temperature in the detection visual field is equal to the temperatures of the sensitive resistor Rt and the reference resistance Rref.

When the human body X moves as described above, FIG.
The radiant heat in the detection field of view 4 (a) changes the resistance value of the sensitive resistor Rt as shown in FIG. As the resistance value of the sensitive resistor Rt changes, the input voltage Vin of the DC differential amplifier 12 changes as shown in FIG. Here, if the input voltage Vin of the DC differential amplifier 12 becomes higher than the reference voltage E / 2 by ΔVin as shown in FIG. 24C, the DC differential amplifier 12 shows the same as shown in FIG. The output voltage Vout is obtained. Now, when the reference voltage 6 of the comparator 5 is set as shown in FIG. 24 (d), the output of the comparator 5 is as shown in FIG. 24 (e).

As described above, the presence of the human body X in the detection visual field changes the resistance value of the sensitive resistor Rt, and the change in the resistance value is DC-amplified as a voltage value change, so that the human body X exists. Can be detected.

[0013]

However, the above infrared detecting circuit has the following problems. That is, in the above infrared detecting circuit, the DC voltage of the DC power supply 11 is divided by the series circuit of the sensing resistor Rt and the reference resistor Rref to obtain the input voltage Vin of the DC differential amplifier 12, so that the sensing resistor is used. Rt resistance change and input voltage Vin
The change is not proportional and becomes non-linear. Specifically, the change amount ΔVin of the input voltage Vin with respect to the minute resistance value change ΔRt of the sensitive resistor Rt is expressed by the following equation.

[0014]

[Equation 2]

That is, as shown in the above equation (2), the resistance value change ΔRt of the sensitive resistor Rt and the change amount ΔVin of the input voltage Vin are not in proportion to each other, and depending on the change width of the resistance value of the sensitive resistor Rt, ΔRt is changed. The input voltage change rate (ΔVin) changes greatly.

For example, at ambient temperature T ₁ , the resistance value of the sensitive resistor Rt and the resistance value of the reference resistance Rref are equal (Rt = Rref), but the radiation value is incident on the resistance value of the sensitive resistor Rt. If only ΔRt changes, the change ΔVin of the input voltage Vin in this case is expressed by the following equation.

[0017]

[Equation 3]

The above equation (3) shows that the resistance change ΔRt of the sensitive resistor Rt and the change Vin of the input voltage Vin have a proportional or linear relationship. However, this formula (3) is satisfied only when ΔRt1 is very small, and when the resistance value of the sensitive resistor Rt changes greatly, the relation of Rt = Rref collapses, and therefore the formula (3) above.
Does not hold, and the change amount Vin of the input voltage Vin with respect to the resistance value change ΔRt in the resistance value of each sensitive resistor Rt is Vin.
Must be calculated.

That is, it is assumed that the responsive resistor Rt is radiated by heat.
Assuming that the resistance value of the sensitive resistor changes until Rt = 0.5 × Rref, ΔRt in the resistance value of the sensitive resistor Rt.
The variation ΔVin of the input voltage Vin with respect to Rt = 0.5
Substituting × Rref into the equation (2), it is expressed as the following equation.

[0020]

[Equation 4]

Assuming that the rate of change of the sensitive resistor Rt with respect to incident radiant heat is constant, the resistance value change ΔRt of the sensitive resistor Rt with respect to the same change of minute radiant heat is Δ.
Since Rt2 = 0.5 × ΔRt1, the change Vin of the input voltage Vin in this case is expressed by the following equation.

[0022]

[Equation 5]

That is, the difference between ΔVin2 shown in the above equations (4) and (5) shows non-linearity. Therefore,
In the conventional circuit, it is necessary to provide a correction means for correcting the above-mentioned non-linearity, which results in an increase in cost or an insufficient output of the infrared detection circuit output (radiation There is a problem that an error occurs in the temperature measurement value in the thermometer).

The present invention has been made in view of the above points, and an object thereof is to provide an infrared detection circuit which is inexpensive, has high performance, and is highly reliable.

[0025]

In order to achieve the above-mentioned object, the invention according to claim 1 has the same resistance value and the same resistance value as the infrared sensitive resistor that receives radiant heat by infrared rays. A reference resistance that shows a change in resistance value with respect to temperature and does not receive radiant heat due to infrared rays, a DC voltage generating means that outputs a DC voltage, and a DC voltage generating means that uses the infrared sensitive resistor as a feedback resistance and the reference resistance as an input resistance. Inverting and amplifying means for inverting and amplifying the DC voltage, and adding means for adding the DC voltage of the DC voltage generating means and the output voltage of the inverting and amplifying means.

In order to achieve the above-mentioned object, the invention according to a second aspect is such that an infrared sensitive resistor which receives radiant heat by infrared rays and a resistance value which has the same resistance value as the infrared sensitive resistor and changes at the same temperature. Indicated by a reference resistance that does not receive radiant heat due to infrared rays, a DC voltage generating means that outputs a DC voltage, and one of the infrared sensitive resistor and the reference resistance as a feedback resistance and the other as an input resistance by the DC voltage generating means Inversion amplification means for inverting and amplifying voltage, addition means for adding the DC voltage of the DC voltage generation means and output voltage of the inverting amplification means, and the addition when the infrared sensitive resistor is not receiving radiant heat from infrared rays The present invention is characterized in that adjustment means for adjusting the addition ratio of the addition means or the gain of the inverting amplification means is provided so that the output of the means does not occur.

In order to achieve the above-mentioned object, an infrared sensitive resistor which receives radiant heat from infrared rays and a resistance change which has the same resistance value as the infrared sensitive resistor and the same temperature change. A reference resistance that does not receive radiant heat due to infrared rays, a first DC voltage generating means that outputs a DC voltage, and a second DC voltage that has the same absolute value as the first DC voltage generating means but an opposite polarity. DC voltage generating means, first infrared amplifying means for inverting and amplifying the DC voltage of the first DC voltage generating means by using the infrared sensitive resistor as a feedback resistance, and second DC voltage by using the reference resistance as a feedback resistance. The present invention is characterized by comprising second inverting amplification means for inverting and amplifying the DC voltage of the generation means, and addition means for adding the output voltages of the first and second inverting amplification means.

According to a fourth aspect of the invention, in the third aspect of the invention, when the infrared sensitive resistor is not receiving radiant heat from infrared rays, the addition ratio of the adding means or the inverting amplification is performed so that the output of the adding means does not occur. Means gain or first
And adjusting means for adjusting the DC voltage of any one of the second DC voltage generating means.

In order to achieve the above-mentioned object, an infrared sensitive resistor which receives radiant heat from infrared rays and an infrared sensitive resistor which has the same resistance value as the infrared sensitive resistor and changes the resistance value with respect to the same temperature. A reference resistance that does not receive radiant heat due to infrared rays, a first DC voltage generating means that outputs a DC voltage, and a second DC voltage that has the same absolute value as the first DC voltage generating means but an opposite polarity. Of the direct current voltage generating means, and the direct current voltage of the first direct current voltage generating means and the direct current voltage of the second direct current voltage generating means which are input via one and the other of the infrared sensitive resistor and the reference resistance, respectively. And an inverting and amplifying means for adding and inverting and amplifying, and when the infrared sensitive resistor is not receiving radiant heat from infrared rays, the addition ratio of the adding means or the And characterized by comprising providing an adjustment means for adjusting one of the DC voltage of the second DC voltage generating means.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 shows a first embodiment of the present invention. The infrared detection circuit of this embodiment is
The DC voltage of the DC power supply 11 is inverted and amplified by the inverting amplifier 14 whose amplification degree changes according to the resistance change of the sensitive resistor Rt due to infrared radiation, and the output voltage of the inverting amplifier 14 is added to the DC voltage of the DC power supply 11. Then, a DC voltage corresponding to the resistance change of the sensitive resistor Rt due to the radiant heat of infrared rays is obtained.

Specifically, as shown in FIG. 1, a DC power supply 11 is used as in the conventional example of FIG. 21, and a DC voltage of the DC power supply 11 is inverted and amplified by an inverting amplifier 14,
Further, the inverted and amplified DC voltage Vin and the DC power supply 1
The power supply voltage of 1 is added in the adding DC amplifier 15 to be amplified.

The inverting amplifier 14 is constructed by using the operational amplifier 14a as the input resistance of the reference resistance Rref and the sensitive resistance Rt as the feedback resistance. In the inverting amplifier 14, when the sensitive resistor Rt does not receive radiant heat, the resistance value of the sensitive resistor Rt is equal to that of the reference resistor Rref. A DC voltage whose absolute value is equal to that of the DC voltage of the DC power supply 11 and whose polarity is inverted is output. Therefore, when the DC voltage of the DC power supply 11 and the output voltage of the inverting amplifier 14 are added by the addition DC amplifier 15, they cancel each other out, and the output of the addition DC amplifier 15 becomes 0V.

On the contrary, when the sensitive resistor Rt receives radiant heat, the resistance value of the sensitive resistor Rt changes and the inverting amplifier 14
Since the absolute value of the amplification degree of is deviated from 1, the inverting amplifier 14
Output voltage changes, which causes a difference from the DC voltage of the DC power supply 11. Therefore, at this time, a DC voltage output Vout corresponding to the radiant heat received by the sensitive resistor Rt is obtained as the output of the adding DC amplifier 15.

That is, the relationship between the voltage Vin input to the addition DC amplifier 15 as the output voltage of the inverting amplifier 14 and the output voltage Vout of the addition DC amplifier 15 is as follows. Note that E is the DC voltage of the DC power supply 11, and A is the amplification degree of the adding DC amplifier 15.

[0035]

[Equation 6]

Therefore, from the above equation (6), the sensitive resistor R
Change Δ in input voltage Vin with respect to change in resistance value ΔRt of t
Vin is calculated by the following equation.

[0037]

[Equation 7]

As is clear from the above equation (8), according to the above configuration, the resistance value change ΔRt and the change amount ΔVin of the input voltage Vin are always in a linear relationship regardless of the resistance value of the sensitive resistor Rt. (Proportional relationship) can be maintained. Therefore, unlike the conventional case, a correction circuit for linearizing the variation ΔVin of the input voltage Vin with respect to the resistance value variation ΔRt is not required, so that the cost can be reduced and the infrared detection circuit as a whole can be downsized. . Further, since the correction circuit is not necessary, an error due to the accuracy of the correction circuit does not occur, and the accuracy of the infrared detection circuit as a whole can be improved. Further, in the case where a correction circuit is provided, in order to avoid the above error and ensure accuracy, conventionally, the correction circuit must be adjusted, which requires a great deal of time and effort (heat-up for adjustment). , Aging or fine adjustment of the correction value) are all unnecessary, and there is an advantage that the cost can be reduced also in this respect. Here, as described above, the inverting amplifier 1
The use of 4 has an advantage that the impedance of the entire infrared detection circuit can be lowered and the influence of external noise can be reduced.

Since the resistance value change ΔRt and the change amount ΔVin of the input voltage Vin can maintain a linear relationship, the temperature of the object can be measured in a non-contact manner by calculating the ambient temperature. This infrared detection circuit can be applied to a thermometer.

FIG. 2 shows a case where a radiation thermometer is constructed by using the infrared detection circuit of this embodiment. Structurally, similar to the presence detecting type human body detecting device shown in the above-described first to eighth embodiments, an appropriate optical means L such as a lens is used to irradiate the sensitive resistor Rt with infrared rays, and an operational amplifier is provided. 15
A DC output voltage Vout corresponding to the amount of infrared radiation is obtained from the adding DC amplifier 15 constituted by a. By calculating the output voltage Vout and the ambient temperature, the surface temperature of the measurement target can be measured in a non-contact manner.

FIG. 3 shows the operation of the radiation thermometer when the human body X, which is an infrared radiation object, moves in the order of (A) .fwdarw. (I) .fwdarw. (U) in FIG. Here, the change of the radiant energy in the detection visual field when the human body X passes through the detection visual field (detection area) as shown in (a) → (i) → (u) in FIG. 2 is shown in FIG. 3 (a). Like Therefore, as the human body X moves, the radiant heat in the detection field of view of FIG. 3A changes the resistance value of the sensitive resistor Rt as shown in FIG. As the resistance value of the sensitive resistor Rt changes, the input voltage Vin of the addition DC amplifier 15 changes as shown in FIG. 3C, and the output voltage Vout shown in FIG. 3D is obtained from the addition DC amplifier 15. To be The surface temperature of the human body X can be measured in a non-contact manner by calculating the output voltage Vout with the output corresponding to the ambient temperature obtained by another suitable means.

However, in the case of FIG. 2, since the adding DC amplifier 15 is composed of an inverting amplifier composed of the operational amplifier 15a, the polarity of the output voltage Vout is opposite to that of FIG. 3 (d).

(Second Embodiment) FIG. 4 shows a second embodiment of the present invention. In the present embodiment, instead of using the summing DC amplifier 15 in the first embodiment shown in FIG. 1, the output terminal of the inverting amplifier 14 and the positive electrode of the DC power supply 11 are connected via resistors Rd ₁ and Rd _2. It is characterized in that they are connected and are amplified by the DC amplifier 16. That is, the output voltage of the inverting amplifier 14 is added to the power supply voltage E of the DC power supply 11 by the resistors Rd ₁ and Rd ₂ , and these resistors Rd ₁ and Rd ₂ serve as addition means.

The operation of the above infrared detecting circuit is basically the same as that of the first embodiment except that the output voltage Vout drops (about half).
The description is omitted here.

According to the above configuration, the summing DC amplifier 15
Is not necessary, and a normal one-input DC amplifier 16 may be used, so that the cost can be reduced.

(Embodiment 3) FIG. 5 shows a third embodiment of the present invention. In the present embodiment, in the infrared detection circuit of the first embodiment (see FIG. 1), the addition DC amplifier 15 when infrared rays are not radiated to the sensitive resistor Rt
Of the feedback circuit 1 for controlling the addition ratio in the addition DC amplifier 15 so that the output voltage Vout of
The feature is that 7 is provided.

The feedback circuit 17 avoids the problems caused by the variation of the offset voltage / current of the adding DC amplifier 15 due to the temperature and the stability in the long-term range, or the instability of the resistance values of the sensitive resistor Rt and the reference resistor Rref. Work to do. That is, since the feedback circuit 17 is used for such a purpose, the time constant in the feedback control system may be a very large value (for example, several hours).

Incidentally, in the case of the present embodiment, although not shown, as in the case of the second embodiment, a detecting means for detecting whether or not radiant heat is applied to the sensitive resistor Rt is provided. In this detection means, for example, a short-term fluctuation of the output voltage Vout of the addition DC amplifier 15 is measured to detect whether or not radiant heat is applied to the sensitive resistor Rt. That is, if the human body is moving, a short-term fluctuation of the frequency component of about 0.1 to 10 Hz is measured, and it is possible to detect whether or not the radiant heat is applied to the sensitive resistor Rt depending on the presence or absence thereof. is there.

However, in order to more reliably detect whether or not the radiant heat is applied to the sensitive resistor Rt, a radiant heat shielding means such as an optical shutter is arranged in front of the sensitive resistor Rt and, if necessary, It is desirable to perform the above feedback control in a state where the radiant heat is cut off at different time intervals.

With the above-described structure, the DC voltage output Vout corresponding to the radiant energy incident on the sensitive resistor Rt can be obtained, and the resistance value change of the sensitive resistor Rt can be changed as in the first embodiment. ΔRt and addition DC amplifier 1
The linearity with the change ΔVin of the input voltage Vin of 5 can always be maintained. Moreover, in the adding DC amplifier 15, the input voltage Vin from the inverting amplifier 14 and the DC power supply 11
Since the DC voltage E from the above is added, the offset voltage, the fluctuation of the current value or the resistance value of the sensitive resistor Rt or the reference resistor Rref which has been a problem when the DC differential amplifier is used as in the conventional example. The DC error due to the drift due to the instability will not occur at all. That is, in the addition DC amplifier 15, the offset voltage and the current value fluctuation or drift as described above are canceled out and do not appear at all in the output. Therefore, the extremely high-precision performance required for the input offset as in the past is not necessary, and even if the adding DC amplifier 15 is configured by using a generally available inexpensive operational amplifier, it is sufficient. Stable characteristics can be obtained.

Further, in order to avoid the above-mentioned DC error, in the past, structural or circuit means for suppressing the temperature rise of the DC differential amplifier 12 or eliminating the temperature gradient may be taken. In the case of the present embodiment, there is also an advantage that it is not necessary to take such means for the adding DC amplifier 15. Further, in the past, it took a lot of time and labor to make adjustment for ensuring DC accuracy, but in this embodiment, since DC accuracy is not required, there is also an advantage that the adjustment work can be reduced.

Further, in the present embodiment, the radiant heat due to infrared rays is radiated by the feedback circuit 17 to the sensitive resistor Rt.
Output Vou of the adding DC amplifier 15 when not added to
Since t is set to 0, a DC error does not occur in this respect as well, and there is an advantage that reliability, that is, long-term stability can be improved.

In addition to this, in the present embodiment, the resistance value change ΔRt and the change amount Δ of the input voltage Vin are the same as in the first embodiment.
Since Vin can always maintain a linear relationship (proportional relationship) regardless of the resistance value of the sensitive resistor Rt, the variation ΔVin of the input voltage Vin with respect to the resistance value variation ΔRt is linear as in the conventional case. Therefore, the correction circuit is unnecessary, and the cost can be reduced, and the infrared detection circuit as a whole can be downsized. Further, since the correction circuit is not necessary, an error due to the accuracy of the correction circuit does not occur, and the accuracy of the infrared detection circuit as a whole can be improved. Further, in the case where a correction circuit is provided, in order to avoid the above error and ensure accuracy, conventionally, the correction circuit must be adjusted, which requires a great deal of time and effort (heat-up for adjustment). , Aging or fine adjustment of the correction value) are all unnecessary, and there is an advantage that the cost can be reduced also in this respect. Here, by using the inverting amplifier 14 as described above, there is also an advantage that the overall impedance of the infrared detection circuit can be lowered and the influence of external noise can be reduced.

FIG. 6 shows a case in which a presence detecting type human body detecting device is constructed by using the infrared detecting circuit of the present embodiment.
As in the configuration, as in the first embodiment, an appropriate optical means L such as a lens is used to irradiate the sensitive resistor Rt with infrared rays, and the output voltage V of the addition DC amplifier 15 is increased.
By comparing out with an appropriate threshold value, high and low binary outputs (on and off outputs) can be obtained with respect to radiant heat above a certain level exceeding a threshold value. Further, in FIG. 6, the sensitive resistor Rt is connected to the inverting amplifier 14
Is used as the feedback resistance, and the addition DC amplifier 1 for the DC voltage E from the DC power supply 11 is used.
A voltage control type resistor is used as the input resistor Rd ₂ of FIG. 5, and the resistance value of the resistor Rd ₂ is adjusted by the output of the feedback circuit 17, so that when the radiant heat due to infrared rays is not applied to the sensitive resistor Rt, the addition DC amplifier The output voltage Vout of 15 is kept at 0V.

FIG. 7 shows the operation of the human body detection device when the human body X, which is an infrared radiation object, moves in the order of (A) .fwdarw. (I) .fwdarw. (U) in FIG. Where the human body X
The change of the radiant energy in the detection visual field (detection area) when passing through the detection visual field (detection area) as shown in FIG. 6 is as shown in FIG. 7A. Therefore, the resistance value of the sensitive resistor Rt changes as shown in FIG. 7B due to the radiant heat in the detection field of view of FIG. 7A accompanying the movement of the human body X. With the change of the resistance value of the sensitive resistor Rt, the input voltage Vin of the addition DC amplifier 15 changes as shown in FIG. 7C, and the addition DC amplifier 15 outputs the DC output voltage Vout shown in FIG. 7D. Is obtained. By comparing this output voltage Vout with the comparison voltage 6 of the comparator 5, the presence or absence of a human body is detected. In the case of this human body detection device, even if the human body X remains stationary for a long time in the state shown in FIG. 6B, it can be detected stably.

As shown in FIG. 8, the positive terminals of the DC power supply 11 and the output terminal of the inverting amplifier 14 are connected to the input resistors Rd ₁ and Rd.
The configuration may be similar to that of the second embodiment by connecting via d ₂ and connecting to the input terminal of the one-input DC amplifier 16.

(Embodiment 4) FIG. 9 shows a fourth embodiment of the present invention. The infrared detection circuit according to the present embodiment includes a DC power supply 11 ₁ that generates a DC voltage E, and a DC power supply 11 that generates a DC voltage E ′ (E ′ = − E) that has the same absolute value as the DC voltage E and an opposite polarity. ₂ , an inverting amplifier 14 ₁ having a resistor R ₁ as an input resistor and a sensitive resistor Rt as a feedback resistor, and a resistor R _1.
An inverting amplifier 14 ₂ having ₂ as an input resistance and a reference resistance Rref as a feedback resistance, and a summing DC amplifier 15 for summing and amplifying the input voltages Vin ₁ and Vin ₂ from the _two inverting amplifiers 14 ₁ and 14 ₂ are provided. DC to the inverting amplifier 14 ₁ power 1
The DC voltage E of 1 ₁ is input, and the DC voltage E ′ of the DC power supply 11 ₂ is input to the other inverting amplifier 14 ₂ . In addition,
Each inverting amplifier 14 _1, 14 input resistance R ₁ of _2, the resistance value of R ₂ is made equal.

The two inverting amplifiers 14 ₁ and 14 ₂ use the resistors R ₁ and R ₂ having the same resistance value as input resistors, and the sensitive resistor Rt and the reference resistor Rref as feedback resistors, respectively, and operational amplifiers 14 a ₁ and 14 a. It is configured using ₂ . Here, when the sensitive resistor Rt does not receive radiant heat, the resistance values of the sensitive resistor Rt and the reference resistor Rref are equal, so that the amplification degree of the inverting amplifiers 14 ₁ and 14 ₂ becomes −1, and the inverting amplifiers 14 ₁ and 14 ₂ respectively. _{From 1} and 14 ₂ Summing DC amplifier 1
Since the input voltages Vin ₁ and Vin ₂ input to 5 have the same absolute value and opposite polarities, the output voltage Vou of the adding DC amplifier 15 is increased.
t becomes 0V.

On the contrary, when the sensitive resistor Rt receives radiant heat, the resistance value of the sensitive resistor Rt changes and the inverting amplifier 14
_Since the absolute value of the amplification degree of 1 deviates from ₁ , a difference is generated between the amplification degrees of the _two inverting amplifiers 14 ₁ and 14 ₂ according to the change of the resistance value of the sensitive resistor Rt. That is, the output voltage Vout of the addition DC amplifier 15 is the input voltage Vin ₁ from the inverting amplifier 14 ₁ and the input voltage V ₁ from the inverting amplifier 14 _2.
It is represented by the following formula by in ₂ . In addition, A is the amplification degree of the addition DC amplifier 15.

[0060]

[Equation 8]

Therefore, from the above equation (9), the sensitive resistor R
Change Δ in input voltage Vin with respect to change in resistance value ΔRt of t
Vin is calculated by the following equation.

[0062]

[Equation 9]

[0063] As apparent from the above equation (10), according to the configuration described above, the resistance change ΔRt the variation .DELTA.Vin ₁ of the input voltage Vin _1, regardless of the resistance value of sensitive resistor Rt, always A linear relationship (proportional relationship) can be maintained. Therefore, a correction circuit for linearly correcting is unnecessary, cost can be reduced, and the infrared detection circuit as a whole can be downsized. Further, since the correction circuit is not necessary, an error due to the accuracy of the correction circuit does not occur, and the accuracy of the infrared detection circuit as a whole can be improved. Further, in the case where a correction circuit is provided, in order to avoid the above error and ensure accuracy, conventionally, the correction circuit must be adjusted, which requires a great deal of time and effort (heat-up for adjustment). , Aging or fine adjustment of the correction value) are all unnecessary, and there is an advantage that the cost can be reduced also in this respect. Here, as described above, the inverting amplifier 1
The use of 4 ₁ and 14 ₂ also has the advantage that the impedance of the entire infrared detection circuit can be lowered and the influence of external noise can be reduced.

The resistance value change ΔRt and the input voltage Vin ₁
Since it is possible to maintain a linear relationship with the change amount ΔVin ₁ of, the infrared detection circuit can be applied to a radiation thermometer that can measure the temperature of an object in a non-contact manner by calculating the ambient temperature. it can.

FIG. 10 shows a case where a presence detecting type human body detecting device is constructed by using the infrared detecting circuit of the present embodiment. FIG. 11 shows the human body X as (A) → (I) → (U) in FIG.
Shows the operation when is moved. When the human body X is present at the position (ii) in FIG. 10, the balance between the resistance values of the sensitive resistor Rt and the reference resistor Rref is lost as described above,
As shown in FIG. 6C, a difference occurs between the input voltages Vin ₁ and Vin ₂ from the inverting amplifiers 14 ₁ and 14 ₂ to the adding DC amplifier 15, and the infrared rays incident from the adding DC amplifier 15 are generated in accordance with the difference. A DC voltage output Vout proportional to the radiation amount of By comparing this output voltage Vout with the comparison voltage 6 of the comparator 5, the presence or absence of a human body is detected. In the case of this human body detection device, even if the human body X remains stationary for a long time in the state shown in FIG. However, in the case of FIG.
Since 5 is composed of an inverting amplifier composed of the operational amplifier 15a, the polarity of the output voltage Vout is opposite to that of FIG. 11 (d).

As shown in FIG. 12, the inverting amplifier 1
The output terminals of 4 ₁ and 14 ₂ may be connected via the resistors Rd ₁ and Rd _{2 and} may be connected to the input terminal of the one-input DC amplifier 16 to have the same configuration as that of the second embodiment.

(Embodiment 5) FIG. 13 shows a fifth embodiment of the present invention. In the infrared detection circuit of the present embodiment, the infrared detection circuit of the fourth embodiment is similar to the third embodiment.
Feedback circuit 17 that operates in the same manner as described in
It is characterized by the provision of. That is, in the feedback circuit 17 of the present embodiment, the output Vout of the adding DC amplifier 15 when infrared rays are not radiated to the sensitive resistor Rt.
The DC voltage E ′ of the DC power supply 11 ₂ is controlled so that the voltage becomes 0. This avoids problems due to instability of the DC power supplies 11 ₁ and 11 ₂ in the long-term range and instability of the resistance values of the sensitive resistor Rt and the reference resistor Rref.

FIG. 14 shows a human body detection apparatus using the infrared detection circuit of the present invention, and its operation is shown in FIG. In addition,
In the human body detection device of FIG. 14, a voltage control type resistor is used as the input resistance Rd ₂ of the summing DC amplifier 15 connected to the output end of the inverting amplifier 14 ₂ , and the feedback circuit 17 controls the voltage of the DC power supply 11 _2. Instead, by adjusting the resistance value of the resistor Rd _{2 by} the output of the feedback circuit 17, the output voltage Vout of the adding DC amplifier 15 is set to 0 when radiation heat due to infrared rays is not applied to the sensitive resistor Rt.
I keep it at V.

As shown in FIG. 16, the inverting amplifier 1
The output terminals of 4 ₁ and 14 ₂ may be connected via the resistors Rd ₁ and Rd _{2 and} may be connected to the input terminal of the one-input DC amplifier 16 to have the same configuration as that of the second embodiment. Further, instead of controlling the DC power source 11 and _second voltage and the input resistance Rd in the feedback circuit 17, using a voltage-controlled resistor as the reference resistor Rref, adjusts the resistance of the reference resistor Rref in the output of the feedback circuit 17 You may do it.

(Embodiment 6) FIG. 17 shows a sixth embodiment of the present invention. In the present embodiment, a DC power supply 11 ₁ that generates a DC voltage E, a DC power supply 11 ₂ that generates a DC voltage E ′ (E ′ = − E) that has the same absolute value as the DC voltage E and an opposite polarity, and A summing inverting amplifier 18 having a resistor Rt and a reference resistor Rref as input resistors and a fixed resistor R ₁ as a feedback resistor, and an input voltage Vin from the summing inverting amplifier 18.
And a feedback circuit 17 for controlling the DC voltage E ′ of the DC power supply 11 ₂ so that the output Vout of the DC amplifier 16 becomes 0 when infrared rays are not radiated to the sensitive resistor Rt. It has and.

The adding and inverting amplifier 18 is a DC power supply 11
The DC voltage E of _{1 and} the DC voltage E'of the DC power supply 11 ₂ are added and inverted and amplified via the sensitive resistor Rt and the reference resistor Rref, respectively. Therefore, in the addition inverting amplifier 18, when the radiant heat due to infrared rays is not applied to the sensitive resistor Rt, the DC power source 1 at each connection point of the sensitive resistor Rt and the reference resistor Rref.
When the output voltages E ₁ and E 1 of 1 ₁ and 11 ₂ are canceled and the resistance value of the sensitive resistor Rt is changed by radiant heat due to infrared rays, the balance of the resistance values of the sensitive resistor Rt and the reference resistor Rref is lost. Further, a DC output voltage corresponding to the unbalanced state is obtained as a potential change at the connection point between the sensitive resistor Rt and the reference resistor Rref, and the sensitive resistor Rt and the reference resistor Rref are obtained.
The addition output at the connection point is amplified.

FIG. 18 shows a human body detection apparatus using the infrared detection circuit of this embodiment, and its operation is shown in FIG. In the human body detection device shown in FIG. 18, the DC power supply 11 ₂
Instead of this, the voltage of the other DC power supply 11 ₁ is controlled by the output of the feedback circuit 17. Further, as shown in FIG. 20, the reference resistor Rref connected to the DC power supply 11 ₂ is a voltage control type resistor, and instead of controlling the voltages of the DC power supplies 11 ₁ and 11 ₂ by the feedback circuit 17, the reference resistance Rref is used. The resistance value of Rref may be adjusted by the output of the feedback circuit 17.
Alternatively, the feedback resistor R ₁ of the adding / inverting amplifier 18 may be a voltage control type resistor, and the resistor R ₁ may be adjusted by the output of the feedback circuit 17.

[0073]

According to the first aspect of the present invention, an infrared sensitive resistor which receives radiant heat from infrared rays, and an infrared sensitive resistor which has the same resistance value as the infrared sensitive resistor and shows a change in resistance value with respect to the same temperature, receive the radiant heat from infrared rays. A non-reference resistance, a DC voltage generating means for outputting a DC voltage, and an inverting amplifying means for inverting and amplifying the DC voltage of the DC voltage generating means using the infrared sensitive resistor as a feedback resistance and the reference resistance as an input resistance, It is provided with an adding means for adding the DC voltage of the DC voltage generating means and the output voltage of the inverting amplifying means, and a change in the output voltage of the inverting amplifying means with respect to a change in the resistance value of the infrared sensitive resistor due to the radiant heat of infrared rays. It is possible to make it independent of the infrared sensitive resistor, and this makes it possible to detect the change in the resistance value of the infrared sensitive resistor and the infrared detection output from the adding means. Since it is proportional to the force, the correction circuit that was required in the past to correct the non-linearity of both can be eliminated, and the infrared detection circuit can be made highly accurate and can be constructed at low cost. And downsizing can be achieved. Further, since the correction circuit is not required, the adjustment work by the correction circuit is not required, and the adjustment time and the time and labor required for the adjustment work are unnecessary, and the cost can be reduced in this respect as well.

According to the second aspect of the present invention, an infrared sensitive resistor which receives radiant heat from infrared rays, and a reference which has the same resistance value as that of the infrared sensitive resistor and shows a change in resistance value with respect to the same temperature and which does not receive radiant heat from infrared rays. A resistor, a DC voltage generating means for outputting a DC voltage, and an inverting amplifying means for inverting and amplifying the DC voltage of the DC voltage generating means with one of the infrared sensitive resistor and the reference resistance as a feedback resistance and the other as an input resistance. And an adding means for adding the DC voltage of the DC voltage generating means and the output voltage of the inverting amplifying means, and when the infrared sensitive resistor is not receiving radiant heat from infrared rays, the output of the adding means does not occur. An adjusting means for adjusting the addition ratio of the adding means or the gain of the inverting amplifying means is provided, and the adjusting means adjusts the DC voltage of the DC voltage generating means and the infrared radiation heat. By adding the output voltage of the inverting amplification means that changes with the addition means, the influence of the DC error of the DC amplifier constituting the addition means is canceled so that it does not appear in the output of the addition means at all. , The infrared detection circuit can be constructed at low cost, and the output of the addition means is not affected by the DC error of the DC amplifier forming the addition means, thereby ensuring high performance and high reliability. be able to. Furthermore, when the infrared sensitive resistor does not receive the radiant heat from the infrared rays due to the resistance values of the infrared sensitive resistor and the reference resistance changing with age,
The output of the adding means can be prevented by the adjusting means, so that the stability and reliability of the operation during long-term use can be ensured. If the infrared sensitive resistor is used as the feedback resistor and the reference resistor is used as the input resistor, the output voltage change of the inverting amplification means with respect to the change of the resistance value of the infrared sensitive resistor due to the radiant heat of infrared rays is infrared sensitive. Since it does not depend on the resistor, the change in the resistance value of the infrared sensitive resistor is proportional to the infrared detection output output from the adding means, eliminating the need for a correction circuit conventionally required to correct the non-linearity of both. It is possible to improve the accuracy of the infrared detection circuit, can be inexpensively configured, and can be downsized, and since the correction circuit is unnecessary, the adjustment work by the correction circuit is unnecessary. The adjustment time and the time and labor required for the adjustment work are unnecessary, and the cost can be reduced in this respect as well. On the other hand, if the infrared sensitive resistor is used as the input resistance of the inverting amplification means and the reference resistance is used as the feedback resistance, the overall impedance of the infrared sensing circuit can be lowered and the influence of external noise can be reduced.

The invention according to claim 3 is an infrared sensitive resistor which receives radiant heat from infrared rays, and a reference which has the same resistance value as the infrared sensitive resistor and shows a change in resistance value with respect to the same temperature and which is not radiant heat due to infrared rays. A resistor, a first direct current voltage generating means for outputting a direct current voltage, a second direct current voltage generating means for outputting a direct current voltage having the same absolute value and a reverse polarity as the first direct current voltage generating means, First infrared amplifying means for inverting and amplifying the direct current voltage of the first direct current voltage generating means by using the infrared sensitive resistor as a feedback resistance, and inversion amplification of the direct current voltage of the second direct current voltage generating means by using the reference resistance as a feedback resistance. Second inverting amplification means, and the first and second
And an adding means for adding the output voltage of the inverting amplifying means, so that the output voltage change of the inverting amplifying means with respect to the resistance value change of the infrared sensitive resistor due to the radiant heat of infrared rays does not depend on the infrared sensitive resistor. Therefore, the change in the resistance value of the infrared sensitive resistor and the infrared detection output output from the adding means are proportional to each other, which eliminates the need for a correction circuit conventionally required to correct the non-linearity of both. Therefore, the infrared detection circuit can be highly accurate, can be inexpensively configured, and can be miniaturized. Further, since the correction circuit is not required, the adjustment work by the correction circuit is not required, and the adjustment time and the time and labor required for the adjustment work are unnecessary, and the cost can be reduced in this respect as well. Since the infrared sensitive resistor and the reference resistor are used as the feedback resistors of the first and second inverting amplification means, respectively, the impedance of the whole infrared sensing circuit can be lowered, and the influence of external noise can be reduced. You can

According to a fourth aspect of the present invention, the addition ratio of the adding means, the gain of the inverting amplifying means, or the first and the second and the first and second infrared receiving resistors are so arranged that the output of the adding means does not occur when the infrared sensitive resistor is not receiving radiant heat from infrared rays. Since the adjusting means for adjusting the direct current voltage of any one of the second direct current voltage generating means is provided, the infrared sensitive resistor is radiated by infrared rays due to changes in the resistance value of the infrared sensitive resistor or the reference resistance due to aging. It is possible to prevent the output of the adding means from occurring when not receiving, by the adjusting means, and therefore, it is possible to ensure the stability and reliability of the operation during long-term use.

The invention according to claim 5 is an infrared sensitive resistor which receives radiant heat from infrared rays, and a reference which has the same resistance value as that of the infrared sensitive resistor and shows a change in resistance value with respect to the same temperature and which is not radiant heat due to infrared rays. A resistor, a first direct current voltage generating means for outputting a direct current voltage, a second direct current voltage generating means for outputting a direct current voltage having the same absolute value and a reverse polarity as the first direct current voltage generating means, Inverting amplification means for inverting and amplifying the direct current voltage of the first direct current voltage generating means and the direct current voltage of the second direct current voltage generating means that are added via one and the other of the infrared sensitive resistor and the reference resistance, respectively. Any of the addition ratio of the adding means or the first and second DC voltage generating means so that the output of the adding means is not generated when the infrared sensitive resistor is not receiving radiant heat from infrared rays. Since is provided with adjusting means for adjusting the DC voltage, the DC voltage of the first DC voltage generating means,
The DC voltage of the opposite polarity of the second DC voltage generating means is added via one and the other of the infrared sensitive resistor and the reference resistance, respectively, and inverted amplification is performed, so that the DC amplifier of the DC amplifier constituting the adding means is operated. Since the influence of such an error is canceled so that it does not appear in the output of the addition means at all, the infrared detection circuit can be constructed at low cost, and high performance and high reliability can be ensured. Furthermore, by changing the resistance values of the infrared sensitive resistor and the reference resistance with aging, it is possible to prevent the output of the adding means from occurring when the infrared sensitive resistor is not receiving radiant heat from infrared rays, by the adjusting means, Therefore, the stability and reliability of operation during long-term use can be ensured. Further, since the infrared sensitive resistor and the reference resistor serve as the input resistance of the inverting amplification means,
It is possible to reduce the overall impedance of the infrared sensing circuit and make it less susceptible to external noise.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment.

FIG. 2 is a circuit diagram when the same is used in a radiation thermometer.

FIG. 3 is an operation explanatory diagram of the radiation thermometer of the same.

FIG. 4 is a circuit diagram of a second embodiment.

FIG. 5 is a circuit diagram of a third embodiment.

FIG. 6 is a circuit diagram when the same is used in a human body detection device.

FIG. 7 is an operation explanatory diagram of the human body detection device of the above.

FIG. 8 is a circuit diagram when a part of the configuration of the human body detection device is different.

FIG. 9 is a circuit diagram of a fourth embodiment.

FIG. 10 is a circuit diagram when the same is used in a human body detection device.

FIG. 11 is an operation explanatory diagram of the human body detection device of the above.

FIG. 12 is a circuit diagram when a part of the configuration of the human body detecting device is different.

FIG. 13 is a circuit diagram of a fifth embodiment.

FIG. 14 is a circuit diagram when the same is used in a human body detection device.

FIG. 15 is an operation explanatory diagram of the human body detection device of the above.

FIG. 16 is a circuit diagram when a partial configuration of the human body detection device of the above embodiment is different.

FIG. 17 is a circuit diagram of a sixth embodiment.

FIG. 18 is a circuit diagram when the same is used in a human body detection device.

FIG. 19 is an operation explanatory diagram of the human body detection device of the above.

FIG. 20 is a circuit diagram in the case where a part of the configuration of the human body detecting device is different.

FIG. 21 is a circuit diagram of a conventional example.

FIG. 22 is a temperature characteristic diagram of a thermistor as an infrared sensitive resistor.

FIG. 23 is a circuit diagram when a conventional example is used in a human body detection device.

FIG. 24 is an operation explanatory view of the human body detection device of the above.

FIG. 25 is a circuit diagram when a part of the configuration of the conventional example is changed.

[Explanation of symbols]

11 DC power supply 14 Inverting amplifier 15 Summing DC amplifier

Claims (5)

[Claims] 1. An infrared sensitive resistor which receives radiant heat from infrared rays, a reference resistance which has the same resistance value as the infrared sensitive resistor and shows a change in resistance value with respect to the same temperature, and which does not receive radiant heat due to infrared rays, and a DC voltage. DC voltage generating means for outputting, the infrared sensitive resistor as a feedback resistance and inverting amplification means for inverting and amplifying the DC voltage of the DC voltage generating means with the reference resistance as an input resistance, and the DC voltage of the DC voltage generating means. An infrared detection circuit comprising: an addition means for adding the voltage and the output voltage of the inverting amplification means. 2. An infrared sensitive resistor that receives radiant heat from infrared rays, a reference resistor that has the same resistance value as the infrared sensitive resistor and shows a change in resistance value with respect to the same temperature, and that does not receive radiant heat from infrared rays, and a DC voltage. A DC voltage generating means for outputting, and an inverting amplifying means for inverting and amplifying the DC voltage of the DC voltage generating means with one of the infrared sensitive resistor and the reference resistance as a feedback resistance and the other as an input resistance,
An adding means for adding the DC voltage of the DC voltage generating means and the output voltage of the inverting amplifying means, and an adding means for preventing the output of the adding means from being generated when the infrared sensitive resistor is not receiving radiant heat of infrared rays. An infrared detecting circuit, characterized in that it is provided with adjusting means for adjusting the addition ratio of or the gain of the inverting amplifying means. 3. An infrared sensitive resistor which receives radiant heat from infrared rays, a reference resistance which has the same resistance value as the infrared sensitive resistor and shows a change in resistance value with respect to the same temperature, and which does not receive radiant heat due to infrared rays, and a DC voltage. First to output
DC voltage generating means, second DC voltage generating means for outputting a DC voltage having the same absolute value and opposite polarity to the first DC voltage generating means, and the infrared sensitive resistor as a feedback resistance for the first DC voltage generating means. First inverting amplification means for inverting and amplifying the DC voltage of the DC voltage generating means, and second inverting amplification for the DC voltage of the second DC voltage generating means using the reference resistance as a feedback resistance.
2. The infrared detecting circuit, comprising: the inverting amplification means of 1. and the addition means for adding the output voltages of the first and second inverting amplification means. 4. The addition ratio of the adding means, the gain of the inverting amplifying means, or the first and second DC voltages so that the output of the adding means does not occur when the infrared sensitive resistor is not receiving radiant heat by infrared rays. 4. The infrared detecting circuit according to claim 3, further comprising adjusting means for adjusting the DC voltage of any one of the generating means. 5. An infrared sensitive resistor which receives radiant heat from infrared rays, a reference resistance which has the same resistance value as the infrared sensitive resistor and shows a change in resistance value with respect to the same temperature, and which does not receive radiant heat due to infrared rays, and a DC voltage. First to output
DC voltage generating means, second DC voltage generating means for outputting a DC voltage having the same absolute value and opposite polarity to the first DC voltage generating means, and one of the infrared sensitive resistor and the reference resistance. The infrared responsive resistor is provided with addition inverting amplification means for adding and inverting and amplifying the DC voltage of the first DC voltage generating means and the DC voltage of the second DC voltage generating means input via the other and respectively. When there is no radiant heat from the infrared rays, an adjusting means is provided for adjusting the addition ratio of the adding means or the DC voltage of either the first or second DC voltage generating means so that the output of the adding means does not occur. An infrared detection circuit characterized by being formed.