JPH0579909A - Heat radiation detector - Google Patents

Abstract

PURPOSE:To prevent the fluctuation of the detection sensitivity by the leak current of a coupling capacitor in an amplifying circuit. CONSTITUTION:An amplifying circuit 1 having at least a coupling capacitor C1 amplifying the output of a heat ray sensor S and a comparator 2 comparing the output of the amplifying circuit 1 with a preset value are provided. Outputs of the amplifying circuit 1 are sampled at the preset cycle, and the average value of the sampled values is determined. The average value is used as the reference voltage, and the comparator 2 compares the amplified output with it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat ray detector for use in a human body detecting device for detecting a human body by detecting a heat ray emitted from the human body.

[0002]

2. Description of the Related Art A conventional heat ray detector is shown in FIG. In this heat ray type detector, operational amplifiers OP ₁ and OP ₂ for amplifying the output of the heat ray sensor S such as a pyroelectric element are used.
It comprises a stage amplifier circuit 1 and a comparator 2 for comparing the output of the amplifier circuit 1 with a predetermined value. Here, as shown in FIG. 6A, the comparator 2 has threshold values V _TH1 and V _TH2 set above and below the reference level (usually the origin level of the amplitude value) of the output of the amplifier circuit 1. When an amplified output exceeding 10 is obtained, a low level output is obtained from the comparator 2. The diodes D ₁ and D ₂ connected in series between the input terminals of the operational amplifier OP ₃ forming the comparator 2 are for operating the comparator 2 as a so-called window comparator. That is, in the comparator 2 of this embodiment, the amplifier circuit 1
The configuration is such that the output of the comparator 2 can be obtained when the vertical amplitude becomes about 0.6 V or more. The threshold of the comparator 2 are determined by the divided voltage of the resistors R ₅ to R _8.

[0003]

By the way, in this type of hot wire detector, a coupling capacitor C ₁ is used for coupling between the first stage amplifier circuit 1a and the second stage amplifier circuit 1b. , The DC component is cut by this capacitor C ₁ , but there is a leak current in the actual capacitor C ₁ , and the output of the amplifier circuit 1 is as shown in FIG.
It increases by ΔV _{0 in} (b). Here, ΔV ₀ is ΔV ₀ = I _c1l × R ₂ / R ₁ when the leak current of the capacitor C ₁ is I _c1l .

As described above, when the output of the amplifier circuit 1 is increased by ΔV ₀ , the potential difference between the upper threshold value V _TH1 and the output V ₀ of the amplifier circuit 1 becomes smaller, and the heat ray sensor S fluctuates in the positive direction. If the output changes, the malfunction tends to occur.
On the contrary, the potential difference between the lower threshold value V _TH2 and the output V ₀ of the amplifier circuit 1 becomes large, and it becomes difficult to detect the negative fluctuation of the heat ray sensor S.

If the leak current of the capacitor C ₁ is constant, the threshold value of the comparator 2 can be corrected by the potential generated by the leak current, but the leak current is equal to the capacitance of the capacitor C ₁ . There are variations due to variations, temperature, humidity, etc., which makes it difficult to correct the potential ΔV ₀ . Therefore, conventionally, the capacitor C
_A low leakage type with low leakage current was used as 1. However, such a capacitor C ₁ has a high unit price, and there is a problem that the cost is high even though the effect of preventing the fluctuation of the detection sensitivity cannot be expected.

The present invention has been made in view of the above points, and an object of the present invention is to provide a hot-wire type detector in which the detection sensitivity does not fluctuate due to the leak current of the coupling capacitor in the amplifier circuit. It is in.

[0007]

In order to achieve the above object, the present invention is provided with a reference voltage generating means for sampling an output of an amplifier circuit at a predetermined cycle and obtaining an average value of the sampled values. The output of the creating means is used as the reference voltage of the comparator. The reference voltage generating means is specifically an oscillation circuit that periodically generates a pulse output, an analog switch that is turned on by the pulse output of this oscillation circuit, and a charge that is output from the amplification circuit when the analog switch is turned on. It can be configured with an integrating circuit.

Further, in order to shorten the unattended time at power-on and prevent the occurrence of false alarms at power-on, the first charge for rapidly charging the capacitor of the integrating circuit of the reference voltage generating means at power-on. Means and second charging means for rapidly charging the capacitor of the amplifier circuit are preferably provided.

[0009]

The present invention has the above-mentioned configuration,
Even if the DC level of the output of the amplifier increases due to the leakage current of the coupling capacitor of the amplifier circuit, the reference voltage of the comparator can be increased by the amount of the increase of the DC level due to the leakage current. The reference voltage of the comparator can be corrected by following the fluctuation of the output voltage of the circuit, so that the fluctuation of the detection sensitivity is not caused by the leak current of the coupling capacitor in the amplifier circuit.

[0010]

【Example】

(Embodiment 1) FIG. 1 shows an embodiment of the present invention. In this embodiment, the charging circuit 3 including the resistor R ₁₁ and the capacitor C ₂ is connected between the output of the amplifier circuit 1 and the ground via the analog switch AS ₁ , and the voltage across the capacitor C ₂ is divided by the voltage dividing resistor R _4. , R ₅ is applied to the midpoint. The analog switch AS ₁ is turned on and off by the output of the oscillation circuit 4. The other configurations are the same as those of the conventional example shown in FIG.

The resistor R ₁₁ and the voltage dividing resistors R ₄ and R ₅ of the comparator 2 are, for example, 10 kΩ, R ₃ and R _{6 to} R _8.
Is 1 MΩ and the capacitor C ₂ is 220 μF. The oscillator circuit 4 periodically generates the pulse output shown in FIG. 1, and the duty of the oscillation period and the pulse width is set to be, for example, 10: 1. In the hot-wire type detector of the present embodiment, the capacitor C is connected via the resistor R ₁₁ when the analog switch AS _{1 which} is turned on by the output pulse of the oscillation circuit 4 is turned on in the standby state when the hot-wire sensor S has not obtained a sensing output. ₂ is charged periodically. As a result, the voltage across the capacitor C ₂ is maintained at approximately the average value of the output V ₀ of the amplifier circuit 1.

Since the input of the comparator 2 at this time does not fluctuate more than (reference voltage ± forward voltage of the diodes D ₁ and D ₂ ), the output of the comparator 2 is maintained at a high level. Next, when a sensing output is obtained by the heat ray sensor S, this sensing output is a component of about 1 Hz,
When the resistor R ₁₁ and the capacitor C ₂ forming the integrating circuit have the above-mentioned specific values, the time constant of the integrating circuit becomes about 2.2 seconds, and the fluctuation of the reference voltage is delayed with respect to the fluctuation of the detection signal. Therefore, when the detection signal is obtained, the detection signal that makes the output of the comparator 2 low level is obtained.

Then, the coupling capacitor C _{1 of the} amplifier circuit ₁
Even if there is a leak current in the capacitor C ₂ , the voltage across the capacitor C ₂ is corrected to the DC level of the output of the amplifier circuit 1 including the leak current after a predetermined period after the power is turned on. That is, since the reference voltage of the comparator 2 can be corrected according to the leak current, the problem that the detection sensitivity varies as in the conventional case does not occur.

Further, since the fluctuation of the output V ₀ of the amplifier circuit 1 according to the ambient temperature and humidity is about several tens of minutes, the voltage across the capacitor C ₂ changes following the fluctuation,
It is possible to prevent fluctuations in the detection sensitivity even depending on the ambient temperature and humidity. That is, in this embodiment, the oscillation circuit 4 and the integration circuit 3 including the analog switch AS ₁ constitute a reference voltage generating means for sampling the output of the amplification circuit 1 at a predetermined cycle and obtaining the average value of the sampled values. There is.

(Embodiment 2) FIG. 2 shows another embodiment of the present invention. In the case of the embodiment, the oscillation circuit 4 'configured by using an operational amplifier OP _4, is characterized in that the comparator 2 in that constructed by using transistors Q ₁ to Q _4. The comparator 2 ′ is an average output voltage V of the amplifier circuit 1 obtained by sampling the analog switch AS ₁ on and off and integrating it with the resistor R ₁₁ and the capacitor C _2.
When the output voltage V ₀ is _higher than _0ave by the base-emitter potential of the transistor Q ₂ , the transistor Q ₁ is turned on and the transistor Q ₅ is turned on.
A low level output is obtained as the output of the comparator 2.

[0016] Conversely, when the average output voltage V output voltage V ₀ than _0ave becomes lower by the potential amount between the base and emitter of the transistor Q ₃ are the transistor Q ₃ is turned on by turning on the transistor Q _3, transistor Q ₄ is turned on and a low level output is obtained as the comparator 2 output. The oscillator circuit 4'of the present embodiment operates substantially in the same manner as the oscillator circuit 4 of the first embodiment.

Also in the case of the present embodiment, the same effect can be obtained by operating in a manner substantially similar to the above-mentioned embodiment. (Example 3) By the way, in the case of each of the above embodiments, larger the duty of the oscillation circuit 4, 4 'is the voltage across the capacitor C ₂ after Therefore the power is turned on, i.e. the reference voltage is the voltage of the normal There was a problem that it took a long time until the power was turned on and the unguarded time was long. Further, there is a problem that a false alarm is always generated when the power is turned on due to the difference in the rise time between the amplifier circuit 1 and the reference voltage of the comparator 2.

Therefore, in the present embodiment, the above-mentioned non-alert time is shortened and no false alarm is generated when the power is turned on. Note that FIG. 3 shows the present invention applied to the first embodiment, and FIG. 4 shows the same applied to the second embodiment. Specifically, the oscillator circuit 4,
The oscillating operation of 4'is stopped and the outputs of the oscillating circuits 4 and 4'are kept at the high level. Therefore, analog switch A
S ₁ is turned on, and the capacitor C ₂ is rapidly charged through the resistor R ₁₁ , which shortens the unattended time after power-on.

Here, the oscillation stop control of the oscillation circuits 4 and 4'is performed by the differentiation circuit 5 including the capacitor C ₃ and the resistor R _12.
And the analog switch AS ₂ are used. Also, the first-stage amplifier circuit 1a and the second-stage amplifier circuit 1b feedback resistor (in the case of the second-stage amplifier circuit 1b resistor R _2, also corresponding to the resistor R ₂ at the first stage of the amplifier circuit 1a resistance) A capacitor C ₁ that determines the rising edge of the output V ₀ of the amplifier circuit 1 by connecting analog switches AS ₃ and AS ₄ to both ends.
Etc. is designed to be charged rapidly. The on / off control of the analog switches AS ₃ and AS ₄ is performed by the output of the differentiating circuit 5. In this way, the rise time between the amplifier circuit V ₀ and the capacitor C ₂ after the power is turned on does not deviate, so that a so-called malfunction in which the output of the comparator 2 is inverted can be prevented.

[0020]

As described above, the present invention is provided with the reference voltage generating means for sampling the output of the amplifier circuit in a predetermined cycle and obtaining the average value of the sampled values, and the output of the reference voltage generating means is used as the reference of the comparator. Since it is a voltage, even if the DC level of the output of the amplifier increases due to the leakage current of the coupling capacitor of the amplifier circuit, the reference voltage of the comparator can be increased by the amount of the increase in the DC level due to the leakage current, That is, the reference voltage of the comparator can be corrected by following the fluctuation of the output voltage of the amplifier circuit, and therefore, the fluctuation of the detection sensitivity does not occur due to the leak current of the coupling capacitor in the amplifier circuit.

If the first charging means for rapidly charging the capacitor of the integrating circuit of the reference voltage generating means is provided when the power is turned on, the capacitor of the integrating circuit is charged rapidly when the power is turned on, and it is necessary to charge the capacitor. If the second charging means for speeding up the time to shorten the time required to start the alarm state and shortening the no alarm time when the power is turned on and providing the capacitor of the amplifier circuit with rapid charging is provided, the output of the amplifier circuit and It is possible to prevent the reference voltage from being in the same state at the time of detecting the heat ray, and thus to prevent the occurrence of a false alarm when the power is turned on.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of another embodiment.

FIG. 3 is a circuit diagram of an embodiment in which the embodiment of FIG. 1 is further improved.

FIG. 4 is a circuit diagram of an embodiment in which the embodiment of FIG. 2 is further improved.

FIG. 5 is a circuit diagram of a conventional example.

FIG. 6 is an explanatory diagram showing the above problems.

[Explanation of symbols]

1 Amplification circuit 2 Comparator 3 Integration circuit 4 Oscillation circuit 5 Differentiation circuit S Heat ray sensor AS _{1 to} AS ₄ Analog switch R ₁₁ Resistor C ₁ and C ₂ Capacitor

Claims (3)

[Claims] 1. A hot-wire detector comprising: an amplifier circuit having at least a coupling capacitor for amplifying the output of the hot-wire sensor; and a comparator for comparing the output of the amplifier circuit with a predetermined value. A hot-wire detector characterized in that a reference voltage generating means for sampling the average value of the sampled values is provided and the output of the reference voltage generating means serves as the reference voltage of the comparator. 2. An oscillation circuit that periodically generates a pulse output, an analog switch that is turned on by the pulse output of this oscillation circuit, and an integral that is charged by the output of the amplification circuit when the analog switch is turned on. The hot-wire detector according to claim 1, wherein the hot-wire detector comprises a circuit. 3. A first charging means for rapidly charging the capacitor of the integrating circuit of the reference voltage generating means when the power is turned on, and a second charging means for rapidly charging the capacitor of the amplifying circuit. The heat ray detector according to claim 2.