JP3010814B2 - Infrared detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared detecting circuit, for example, detecting infrared energy radiated from a human body to detect the movement or presence of a human body, or detecting indoor radiant energy or room temperature. It is used to perform air conditioning control.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional infrared detecting circuit. In the figure, Rt is an infrared sensitive resistor. This is composed of a resistor (for example, a thermistor) that changes its resistance value according to a temperature change. Rin is an input resistance. This is a resistor for converting a change in resistance value of the infrared sensitive resistor Rt into a change in voltage. E is a DC power supply, which converts the DC voltage into a change in the input voltage Vin by dividing the DC voltage by the infrared sensitive resistor Rt and the input resistor Rin. The input voltage Vin is input to the AC amplifier 1 and the DC amplifier 2, and the AC component and the DC component are amplified respectively. When the above signal processing is expressed by an equation, Vin = E × Rin / (Rin
+ Rt).

FIG. 4 shows a typical resistance-temperature characteristic of the infrared sensitive resistor Rt. In the figure, the vertical axis represents the resistance value (Ω) of the resistor Rt, which is expressed in logarithm. The horizontal axis is the temperature (° C.) of the resistor Rt. By making the heat capacity of the resistor Rt as small as possible and making the thermal resistance as large as possible, the temperature of the resistor itself rises even with a small amount of radiant heat (infrared rays), and the resistance value can be changed.

FIG. 5 shows a configuration in the case where this infrared detection circuit is applied to detection of movement of a human body. In the figure, L is an optical system, for example, a convex lens or a concave mirror. F is a detection visual field, and has a size obtained by projecting the resistor Rt via the optical system L. When an infrared radiator (for example, a human M) enters the detection field of view F, the infrared ray is received by the resistor Rt via the optical system L, and the temperature of the resistor Rt rises due to radiation heat by the infrared ray. And the resistor Rt
Then, the input voltage Vin obtained by dividing the voltage of the DC power supply E by the input resistor Rin and the input voltage Vin is amplified by the AC amplifier 1, so that the movement of the human body can be detected as a change in the input voltage Vin.

FIG. 6 shows waveforms at various parts when an infrared radiator (for example, a human M) moves across the detection field of view F.
Shown in In the figure, (a) shows a change in radiation energy in the visual field when a person M having infrared radiation energy passes through the detection visual field F. (B) is a change in resistance value caused in the infrared-sensitive resistor Rt by the radiant heat from the person M. (C) is an infrared sensitive resistor Rt
Is a change in the input voltage Vin to the AC amplifier 1 due to a change in the resistance value caused by the above. (D) is the input voltage V
This is the change in the output voltage V1 when the change in is amplified by AC.

As described above, when the infrared detection circuit is applied to the detection of the movement of a human body, the resistance value of the infrared sensitive resistor Rt changes when the human M having infrared radiation energy passes through the detection field of view F. The movement of the person M can be detected by AC-amplifying the change in the resistance value as the change in the voltage value.

[0007]

In the above-described conventional infrared detecting circuit, the resistance value of the infrared sensitive resistor Rt greatly changes depending on the ambient temperature, so that the sensitivity changes depending on the temperature. . That is, the change dVin of the detected input voltage Vin with respect to the minute displacement dRt of the infrared-sensitive resistor Rt is as follows: Vin = E × Rin / (Rin + Rt), dVin / dRt = −E × Rin / (Rin + Rt) Therefore, dVin = −E × Rin × dRt / (Rin + R
t) For the above equation, Rt = 100 to 10 KΩ, Rin = 1K
Ω, E = 10 V, dRt (%) = 1%. However,
dRt (%) is defined as% change in resistance value at each temperature. Therefore, the amount of change (Ω) in the resistance value changes at each temperature.

FIG. 7 shows the result of calculating dVin under the above conditions. In the figure, the horizontal axis is normalized by dividing Rt by Rin. As is clear from the figure, d
Vin shows the maximum value when Rt = Rin, and Rt ≠ R
At "in", it can be seen that the sensitivity is reduced.

Further, in the above conventional example, the detected input voltage Vin contains information on the ambient temperature and the radiant heat, and it is difficult to extract the information on only the radiant heat or the ambient temperature. This is because the detection voltage Vin changes depending on both the amount of radiation heat and the ambient temperature. However, as shown in FIG. 5, if the detected input voltage Vin is AC-amplified, the ambient temperature change is generally very slow, so that it does not appear in the output voltage V1 of the AC amplifier 1 and only information due to radiant heat is obtained. Can be taken out. Normally, the detection of a change in the radiant heat information is used to detect the movement of the human body. However, it is difficult to extract only the DC information of the radiant heat for the above-described reason, and it has been difficult to detect the presence of the human body.

SUMMARY OF THE INVENTION The present invention has been made in view of the foregoing, and an object of the present invention is to provide an infrared detecting circuit capable of preventing the sensitivity from being changed by the ambient temperature. Another object of the present invention is to provide an infrared detecting circuit capable of individually detecting information on ambient temperature and radiant heat.

[0011]

In order to solve the above-mentioned problems, an infrared detecting circuit according to the first aspect of the present invention will be described with reference to FIG.
As shown in the figure, an infrared sensitive resistor Rt sensitive to infrared radiation energy and ambient temperature, a reference thermal resistor Rref sensitive to a change in ambient temperature with substantially the same temperature-resistance characteristics as the infrared sensitive resistor Rt, A DC power supply E for supplying a current to a series circuit of the infrared-sensitive resistor Rt and the reference thermal resistor Rref, and the resistors Rt and Rref;
Current detecting resistor Ri for converting a current flowing through the series circuit into a first voltage Viv having a sufficiently smaller resistance value than
v and a DC amplifier 2 for DC amplifying the first voltage Viv
And the infrared sensitive resistor Rt and the reference thermal resistor R
an AC amplifier 1 for AC-amplifying a second voltage Vin obtained at a connection point of the ref;
Reference voltage Vre corresponding to 1/2 of the difference from the voltage Viv
f = (E-Viv) / 2 and a DC differential amplifier 3 for amplifying the difference between the second voltage Vin, the DC amplifier 2
Output V3 as an ambient temperature detection output,
1 output V1 is detected as a change in infrared radiation energy
And the output V2 of the DC differential amplifier 3 is
The detection output of the absolute value of the radiant energy is used.

In order to solve the same problem, the infrared detecting circuit according to the second aspect of the present invention includes, as shown in FIG. 2, an infrared sensitive resistor Rt which is sensitive to infrared radiation energy and ambient temperature; In order to supply a current to a reference thermal resistor Rref which has substantially the same temperature-resistance characteristics as the infrared sensitive resistor Rt and which responds to a change in ambient temperature, and a series circuit of the infrared sensitive resistor Rt and the reference thermal resistor Rref. DC power supply E, and an input voltage Vin detected at a connection point between the infrared sensitive resistor Rt and the reference thermal resistor Rref.
An AC amplifier 1 for amplifying the input voltage Vin, a first DC differential amplifier 3 for amplifying a difference between a reference voltage Vref = E / 2 corresponding to a half of the power supply voltage of the DC power supply E and the input voltage Vin. A second DC differential amplifier 4 having a feedback resistor Riv for converting a current flowing through the series circuit into a voltage.
And the output V1 of the AC amplifier 1 is radiated by infrared radiation.
The first DC difference is used as the detection output for the change in energy.
The output V2 of the dynamic amplifier 3 is calculated based on the absolute value of the infrared radiation energy.
Of the second direct current by the feedback resistor Riv.
The voltage V4 obtained as the output of the
It is characterized in that it is a degree detection output .

[0013]

According to the first or second aspect of the present invention, the infrared-sensitive resistor Rt sensitive to infrared radiation energy and ambient temperature is provided.
In addition, the reference thermal resistor Rr which is sensitive to a change in ambient temperature with substantially the same temperature-resistance characteristics as the infrared sensitive resistor Rt.
ef, a current is supplied from a DC power supply E to a series circuit of these resistors Rt and Rref, and the resistors Rt and Rr
Since the difference between the input voltage Vin obtained at the connection point of ef and the predetermined reference voltage Vref is amplified by the DC differential amplifier 3, the influence of the ambient temperature is removed, and the absolute value of the radiant heat is independently detected. In addition, even if the ambient temperature changes, the detection sensitivity of infrared rays can always be maximized. Since the change in resistance of the resistor Rt due to radiant heat is sufficiently smaller than the change in resistance due to ambient temperature, the current flowing through the series circuit of the resistors Rt and Rref is changed to the resistance Ri.
If the voltage is converted into a voltage by v and detected, information on the ambient temperature can be substantially detected.

[0014]

FIG. 1 is a circuit diagram showing the configuration of the first embodiment of the present invention. In FIG. 1, Rt is an infrared-sensitive resistor, which changes its resistance value according to a temperature change. By making the heat capacity of the resistor as small as possible and increasing the thermal resistance as much as possible, the temperature of the resistor itself rises even with a small amount of radiant heat (infrared rays), and the resistance value can be changed. Next, Rref is a reference thermal resistor. This is a resistor having exactly the same resistance value and resistance change rate as the infrared sensitive resistor Rt. However, it is completely shielded from external radiant heat. That is, radiant heat due to infrared rays is cut off by a method that does not affect the resistance value or the rate of change in resistance or by a method that is spatially insulated. Therefore, when the ambient temperature changes, each resistor Rt, Rref
Changes with the same resistance value, and when radiation energy due to infrared rays enters, the resistance value of only the resistor Rt changes. Riv is a resistor for current-voltage conversion, and has a sufficiently smaller resistance value than the resistors Rt and Rref so as not to affect the current value of the entire circuit.

E is a DC power source for converting a change in the resistance value of each of the resistors Rt and Rref into a voltage. The current flowing through the resistors Rt and Rref by the DC power supply E is converted by the current-voltage conversion resistor Riv into the current detection voltage Viv.
Is converted to This current detection voltage Viv is DC-amplified by DC amplifier 2 and output as output voltage V3. The input voltage Vin detected from the connection point between the resistors Rt and Rref is AC-amplified by the AC amplifier 1 to obtain an output voltage V1. Furthermore, in the DC differential amplifier 3, the difference between the input voltage Vin and the reference voltage Vref is DC-amplified, and the output voltage V2 is obtained. Note that the reference voltage Vref is a voltage for detecting only radiant heat information, and is given by Vref = (E−Viv) / 2.

The operation of the circuit shown in FIG. 1 will be described below. The current detection voltage Viv obtained from the resistor Riv is V
iv = E × Riv / (Rt + Rref + Riv). Since (Rt + Rref) ≫Riv, V
iv = E × Riv / (Rt + Rref). Here, since (Rt + Rref) is determined by the ambient temperature and the radiant heat, as the output voltage V3 of the DC amplifier 2,
Ambient temperature information and radiant heat information can be extracted. However, since the change in the resistance value due to the radiant heat from the human body is usually 1/100 to 1/1000 or less than the change due to the ambient temperature, in such an application, only the ambient temperature information can be obtained practically. become.

Further, the reference voltage V
By performing differential amplification between ref = (E-Viv) / 2 and input voltage Vin, only radiant heat information can be extracted as output voltage V2. Because, when there is no radiant energy from the outside, even if the ambient temperature changes, Rt = Rref, and Vin = (E−
Viv) / 2 = Vref holds, and V2 = Vin−Vr
This is because ef = 0. Therefore, even if the ambient temperature changes, the output voltage V2 constantly maintains 0V,
The output voltage V2 appears only when the resistance value of the resistor Rt changes due to radiant heat.

Further, as the output voltage V1, as in the prior art, the input voltage Vin is AC-amplified by the AC amplifier 1, whereby a change in radiation energy can be detected. The above three output voltages V1, V2,
By using V3, it is possible to independently detect the change in the radiant energy incident on the infrared sensitive resistor Rt, the absolute value of the radiant energy, and the ambient temperature.

FIG. 2 is a circuit diagram showing the configuration of the second aspect of the present invention. In FIG. 2, Rt is an infrared-sensitive resistor,
Rref is a reference thermal resistor, which is the same as each resistor Rt, Rref shown in FIG. Also, Riv
Is a resistor for current-voltage conversion. In the circuit of FIG.
Since this is used as the feedback resistance of the DC differential amplifier 4, it is not always necessary to make the resistance value sufficiently smaller than each of the resistors Rt and Rref as in the circuit of FIG. The non-inverting input terminal of the DC differential amplifier 4 is grounded, the inverting input terminal is connected to the output terminal via a feedback resistor Riv, and connected to the positive terminal of the DC power supply E via resistors Rref and Rt. ing. The negative electrode of the DC power supply E is grounded.
Input voltage V detected at the connection point between resistors Rt and Rref
“in” is AC-amplified by the AC amplifier 1 and is used as one input of the DC differential amplifier 3. A reference voltage Vref is applied to the other input of the DC differential amplifier 3. This reference voltage is a voltage for detecting only radiant heat information, and is given by Vref = E / 2.

The operation of the circuit shown in FIG. 2 will be described below. The DC differential amplifier 4 has a very high input impedance, and no input current flows into the inverting input terminal or the non-inverting input terminal. Also, since the amplification factor is very high, the inverting input terminal and the non-inverting input terminal have substantially the same potential. In the circuit shown in FIG. 2, since the non-inverting input terminal is grounded, the potential of the inverting input terminal becomes substantially 0V. Also,
Since the input impedances of the AC amplifier 1 and the DC differential amplifier 3 are also very high, no current flows from the connection point between the resistors Rt and Rref. For this reason, the resistors Rt and Rref
Is E / (Rt + Rref), and this current also flows through the resistor Riv. Therefore, the output voltage V4 of the DC differential amplifier 4 is V4 = −E × Riv / (Rt
+ Rref). Here, since (Rt + Rref) is determined by the ambient temperature and the radiant heat, the output voltage V4
As a result, ambient temperature information and radiation heat information can be extracted. However, the change in the resistance value due to the radiant heat from the human body is usually 1/100 to 1/1 of that due to the change in the ambient temperature.
000 or less, so in such an application,
In effect, only ambient temperature information is provided.

The input voltage Vin detected from the connection point between the resistors Rt and Rref is given by E × Rref / (Rt +
Rref), the DC differential amplifier 3 differentially amplifies the reference voltage Vref = E / 2 and the input voltage Vin to obtain the output voltage V2 of the DC differential amplifier 3 as radiant heat information. Only can be taken out. Because, when there is no external radiation energy, even if the ambient temperature changes, Rt = Rref
And Vin = E / 2 = Vref holds, and V2 =
This is because Vin−Vref = 0. Therefore,
Even if the ambient temperature changes, the output voltage V2 always maintains 0 V, and the output voltage V2 appears only when the resistance value of the resistor Rt changes due to radiant heat.

Further, as in the case of the conventional example, the output voltage V1 is subjected to AC amplification of the input voltage Vin by the AC amplifier 1 so that a change in radiation energy can be detected. The above three output voltages V1, V2,
By using V4, it is possible to independently detect the change in the radiant energy incident on the infrared sensitive resistor Rt, the absolute value of the radiant energy, and the ambient temperature.

[0023]

According to the infrared detecting circuit of the present invention, the sensitivity is not changed by the ambient temperature, and the constant sensitivity can be constantly maintained. There is an effect that the variation of the incident radiation energy, the absolute value of the radiation energy, and the ambient temperature can be detected independently.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of the invention according to claim 1;

FIG. 2 is a circuit diagram showing a configuration of the invention according to claim 2;

FIG. 3 is a circuit diagram showing a conventional infrared detection circuit.

FIG. 4 is a characteristic diagram showing a typical resistance-temperature characteristic of an infrared sensitive resistor.

FIG. 5 is a diagram showing a schematic configuration of a human body movement detection device using an infrared detection circuit.

FIG. 6 is a waveform diagram showing an operation of the human body movement detection device using the infrared detection circuit.

FIG. 7 is a diagram showing a change in sensitivity according to the ambient temperature of a conventional infrared detection circuit.

[Explanation of symbols]

 Rt Infrared sensitive resistor Rref Reference thermosensitive resistor Riv Resistance for current-voltage conversion Vref Reference voltage Vin Input voltage Viv Current detection voltage 1 AC amplifier 2 DC amplifier 3 DC differential amplifier 4 DC differential amplifier E DC power supply

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shinji Kiribata 1048 Kazuma, Kadoma, Osaka Prefecture Matsushita Electric Works, Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) G01J 1/00-1 / 46 G01J 5/00-5/62

Claims (2)

(57) [Claims] An infrared sensitive resistor sensitive to infrared radiation energy and ambient temperature; a reference thermal resistor sensitive to a change in ambient temperature with substantially the same temperature-resistance characteristics as the infrared sensitive resistor; A DC power supply for flowing a current through a series circuit of the sensitive resistor and the reference thermal resistor; and a DC power supply for converting a current flowing through the series circuit into a first voltage having a sufficiently smaller resistance value than each of the resistors. A current detection resistor, a DC amplifier for DC-amplifying a first voltage, an AC amplifier for AC-amplifying a second voltage obtained at a connection point between the infrared sensitive resistor and the reference thermal resistor, and an AC amplifier for the DC power supply. A DC differential amplifier for amplifying a difference between a reference voltage and a second voltage corresponding to a half of a difference between the power supply voltage and the first voltage , wherein an output of the DC amplifier is provided as a detection output of an ambient temperature;
And the output of the AC amplifier is
The output of the DC differential amplifier is red
An infrared detection circuit, wherein a detection output of an absolute value of radiant energy of an outside line is used . 2. An infrared sensitive resistor sensitive to infrared radiation energy and ambient temperature; a reference thermal resistor sensitive to changes in ambient temperature with substantially the same temperature-resistance characteristics as the infrared sensitive resistor; A DC power supply for passing a current through a series circuit of the sensitive resistor and the reference thermal resistor, and an AC amplifier for amplifying an input voltage detected at a connection point between the infrared sensitive resistor and the reference thermal resistor; A first DC differential amplifier for amplifying a difference between a reference voltage corresponding to a half of a power supply voltage of the DC power supply and the input voltage; and a feedback resistor for converting a current flowing through the series circuit into a voltage. and a second DC differential amplifier having the AC amplifier
Output of the detector to detect changes in infrared radiation energy
And the output of the first DC differential amplifier is
A detection output of the absolute value of the energy
The voltage obtained as the output of the second DC differential amplifier.
An infrared detection circuit, which has a detection output of an ambient temperature .