JP3058295B2 - 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 detected input voltage Vin changes depending on both the amount of radiated 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 changes in ambient temperature with substantially the same temperature-resistance characteristics as the infrared sensitive resistor Rt, , A first DC current source It for flowing a constant current through the infrared sensitive resistor Rt.
A second DC current source Iref for supplying a constant current to the reference thermal resistor Rref, an AC amplifier 1 for AC-amplifying a first voltage Vin obtained at the infrared sensitive resistor Rt, The DC amplifier 2 includes a DC amplifier 2 for amplifying a second voltage Vref obtained from the thermal resistor Rref, and a DC differential amplifier 3 for amplifying a difference between the first voltage Vin and the second voltage Vref . Around output V3
The output V1 of the AC amplifier 1 is used as an ambient temperature detection output.
As a detection output of the change in infrared radiation energy,
The output V2 of the DC differential amplifier 3 is represented by infrared radiation energy.
The detection output of the absolute value of

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; A reference thermal resistor Rref which is sensitive to changes in ambient temperature with substantially the same temperature-resistance characteristics as the infrared sensitive resistor Rt, and a voltage-controlled first direct current for flowing a current through the infrared sensitive resistor Rt A source Ia, a second DC current source Ib of a voltage control type for flowing a current through the reference thermal resistor Rref, and the infrared sensitive resistor R
AC amplifier 1 that amplifies the first voltage Vin obtained at t, and a first amplifier that amplifies the difference between the second voltage Viv obtained at the reference thermal resistor Rref and the reference voltage Vref.
, The integrator 5 for integrating the output voltage of the first DC differential amplifier 4, and the output voltage V4 of the integrator 5 so that the second voltage Viv becomes equal to the reference voltage Vref.
With the voltage-controlled first and second DC current sources Ia, Ia
comprising a feedback circuit for feeding back a control voltage for b, and a second DC differential amplifier 3 for amplifying a difference between the reference voltage Vref and the first voltage Vin, the AC amplifier
1 output V1 is detected as a change in infrared radiation energy
Output, the output V4 of the integrator 5 is used to detect the ambient temperature.
And the output V2 of the second DC differential amplifier 3 is
The detection output of the absolute value of the radiation energy of the line is characterized.

[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 DC current is supplied to these resistors Rt and Rref, and an input voltage Vin obtained at the resistor Rt,
Since the difference from the reference voltage Vref obtained by the resistor Rref is amplified by the DC differential amplifier 3,
By removing the influence of the ambient temperature, the absolute value of the radiant heat can be independently detected, and even when the ambient temperature changes, the detection sensitivity of the infrared ray can be kept constant. The information on the ambient temperature can be independently detected by detecting a change in the resistance value of the resistor Rref due to radiant heat.

[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.

It is a direct current source which supplies a constant direct current for converting a change in the resistance of the resistor Rt into a voltage. The change in the resistance value of the resistor Rt is converted into the input voltage Vin by the DC current source It. Input voltage Vin
Is given by Vin = Rt × It, and for signal processing,
It is input to an AC amplifier 1 and a DC differential amplifier 3. The input voltage Vin is AC-amplified by the AC amplifier 1 to obtain an output voltage V1.

Iref is a DC current source, and a resistor Rr
A constant DC current for converting a change in the resistance value of ef into a voltage is supplied. The change in the resistance value of the resistor Rref is converted into the reference voltage Vref by the DC current source Iref. The reference voltage Vref is given by: Vref = Rref × Ire
f, and are DC-amplified by the DC amplifier 2 for signal processing to obtain an output voltage V3. The reference voltage Vref is the other input voltage of the DC differential amplifier 3. In the DC differential amplifier 2, the difference between the input voltage Vin and the reference voltage Vref is DC-amplified, and the output voltage V2
Is obtained.

The operation of the circuit shown in FIG. 1 will be described below. In FIG. 1, the reference voltage Vref is Vref =
Rref × Iref, but the reference thermal resistor R
Since the resistance value of ref is determined only by the ambient temperature, only the information on the ambient temperature can be extracted as the output voltage V3 of the DC amplifier 2. Also, the reference voltage Vr
By performing differential amplification between ef and the input voltage Vin,
As the output voltage V2 of the DC differential amplifier 3, only information on radiant heat can be extracted. This is because when there is no radiant energy from the outside, even if the ambient temperature changes, Rt = Rref, and Vin = Rt ×
It = Rref × Iref = Vref holds, and V2 =
This is because Vin−Vref = 0. However, It
= Iref. Therefore, even if the ambient temperature changes, the output voltage V2 constantly 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 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. Ia denotes a voltage-controlled DC current source, which supplies a DC current for converting a change in the resistance value of the resistor Rt into a voltage. DC current source I
a, the resistance value of the resistor Rt changes with the input voltage Vin.
Is converted to The input voltage Vin is Vin = Rt × Ia
And input to the AC amplifier 1 and the DC differential amplifier 3 for signal processing. Ib is a voltage-controlled DC current source, which supplies a DC current for converting a change in the resistance value of the resistor Rref into a voltage. The change in the resistance value of the resistor Rref is converted into a detection voltage Viv by the DC current source Ib. This detection voltage Viv is expressed as Viv = Rref
× Ib, compared with the reference voltage Vref by the DC differential amplifier 4, and feedback-controlled so that Viv = Vref always. That is, the voltage Viv obtained from the reference thermal resistor Rref is fixed (= Vref
f), the DC differential amplifier 4 and the reference voltage Vre
f, an integrator 5 and a DC current source Ib form a feedback loop to control the output current from the voltage-controlled DC current source Ib so that the detection voltage Viv is constant. At this time, the DC current source Ia is simultaneously controlled by the output voltage V4 of the DC differential amplifier 4. Furthermore, a reference voltage Vr for detecting only information on radiant heat
ef is a reference input voltage of the DC differential amplifier 3 and is compared with the input voltage Vin.

The operation of the circuit shown in FIG. 2 will be described below. In FIG. 2, the detection voltage Viv is Viv = Rr
ef × Ib, but is fixed at Viv = Vref by the action of the feedback loop. Therefore, since the resistance value of the reference thermal resistor Rref is determined by the ambient temperature, the control voltage V4 of the DC current source Ib for keeping the detection voltage Viv constant can be treated as information on the ambient temperature. Further, in the DC differential amplifier 3, by performing differential amplification between the reference voltage Vref and the input voltage Vin, only information on radiant heat can be extracted as the output voltage V2. Because, when there is no external radiation energy, even if the ambient temperature changes, Rt = Rref, and Vin = Rt × I
a = Rref × Ib = Viv = Vref holds, and V2
= Vin-Vref = 0. Therefore, even if the ambient temperature changes, the output voltage V2 constantly maintains 0 V, and the output voltage V2 appears only when the resistance value of the resistor Rt changes due to radiant heat. Further, when there is no incident radiation energy, the input voltage Vin and the detection voltage Viv are kept constant by the action of the feedback loop even if the ambient temperature changes, and as a result,
A constant sensitivity is always maintained regardless of changes in the ambient temperature.

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.

[0022]

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 Vref Reference voltage Vin Input voltage 1 AC amplifier 2 DC amplifier 3 DC differential amplifier 4 DC differential amplifier 5 Integrator

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-5-45219 (JP, A) JP-A-5-45220 (JP, A) JP-A-5-45221 (JP, A) 155328 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01J 1/42-1/44 G01J 5/10-5/24 G01J 9/04

Claims (2)

(57) [Claims] An infrared sensitive resistor sensitive to infrared radiation energy and an 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 first direct current source for supplying a constant current to the sensitive resistor, a second direct current source for supplying a constant current to the reference thermal resistor, and a first DC current source obtained for the infrared sensitive resistor. An AC amplifier that amplifies the voltage of the reference thermal resistor, a DC amplifier that amplifies a second voltage obtained from the reference thermal resistor, and a DC differential amplifier that amplifies a difference between the first voltage and the second voltage. Of the DC amplifier
The output is the detection output of the ambient temperature, and the output of the AC amplifier
Is the detection output of the change in infrared radiation energy, and
The output of the DC differential amplifier is
An infrared detection circuit characterized by having a paired value detection output . 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 voltage-controlled first DC current source for flowing a current through the sensitive resistor, a voltage-controlled second DC current source for flowing a current through the reference thermal resistor, and an infrared sensitive resistor. An AC amplifier for AC-amplifying the obtained first voltage, a first DC differential amplifier for amplifying the difference between the second voltage and the reference voltage obtained for the reference thermal resistor, and a first DC differential An integrator for integrating the output voltage of the amplifier; and a feedback for feeding back the output voltage of the integrator as a control voltage of the first and second DC current sources of the voltage control type so that the second voltage becomes equal to the reference voltage. Circuit, the reference voltage and the The second that amplifies the difference from the voltage of 1
And the output of the AC amplifier is red.
The detection output of the change in radiant energy of the outside line
The output of the divider as the detection output of the ambient temperature,
The output of the differential amplifier is calculated as the absolute value of the infrared radiation energy.
An infrared detection circuit characterized by a detection output .