JPH0133879B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a crime prevention alarm device in which a light receiving part receives and detects pulse modulated infrared rays emitted from a light projecting part to activate an alarm circuit part.

<Prior Art> In this type of device, pulse-modulated infrared rays are used because they can be clearly distinguished from other light rays such as natural light, and a large signal can be obtained with small energy.

FIG. 1 is a block diagram showing a light receiving section of a conventional pulse modulation type infrared security alarm device. A near-infrared pulse beam with a wavelength of approximately 0.91 to 0.94 μm is emitted from an infrared light emitting diode connected to a waveform generating circuit, is reflected and focused by a reflecting mirror, and is emitted from a light projector. This infrared pulse beam is condensed by a condensing mirror 1 of a light receiving section, and is incident on a light receiving element 2 such as a phototransistor or a photodiode. The pulse signal converted into a voltage according to the amount of incident light by the light receiving element 2 is amplified by the selection amplifier 3 and enters the detection circuit 4. The detection circuit 4 has a predetermined trigger level set in advance according to the sensitivity of the light receiving element 2 and the intensity of white noise, and outputs a predetermined trigger signal only when the input signal exceeds this trigger level. It is configured. The monostable multivibrator 5 outputs a rectangular wave for a certain period of time when a trigger signal is applied, and when the intensity of this rectangular wave signal smoothed by the smoothing circuit 6 is higher than the switching level of the switching circuit 7, the switching circuit
When it turns on and does not exceed the switching level
It becomes OFF. When the switching circuit is turned OFF, the output circuit 8 is activated, the alarm circuit is activated, and an alarm is issued.

<Problems to be Solved by the Invention> In this type of device, the electrical output of the light receiving element 2 such as a phototransistor is amplified by the selection amplifier 3, so white noise generated by thermal disturbance within the light receiving element 2 is also amplified along with the signal. The problem arises that the signal is amplified and the S/N ratio decreases.

The white noise produced by phototransistors becomes louder when the temperature is high or when there is strong external light, and there are also differences in the level of noise inherent to each phototransistor. Therefore, when using a phototransistor as a light-receiving element in a security alarm device, it is important to select weather conditions that produce the most noise, or The sensitivity limit was set based on the phototransistor.

On the other hand, in the case of an outdoor infrared security alarm system,
Infrared rays are attenuated by weather conditions such as frost, fog, rain, and snow, so it is necessary to provide a sensitivity margin so that the device can operate normally even under the worst expected weather conditions. It was hot.

Therefore, in such a conventional device, the amplification degree of the selective amplifier 3 and the trigger level of the detection circuit 4 are uniquely set corresponding to the sensitivity of the light receiving element 2 and the maximum value of the intensity of white noise. It has been difficult to obtain satisfactory sensitivity even when truly high sensitivity is required due to the high attenuation rate of infrared rays in the optical path. In addition, if white noise with a stronger intensity than expected, that is, white noise that exceeds the trigger level of the detection circuit 4, occurs, the switching circuit 7 will be turned ON by the white noise alone, regardless of the presence or absence of a regular pulse signal.
There was a risk of equipment malfunction.

In this way, setting the sensitivity limit in consideration of the maximum noise and setting the sensitivity margin in consideration of the minimum amount of received light are contradictory matters when selecting the amplifier gain, and the best way to achieve this is to reconcile these contradictory matters. This is the first problem to be solved by the invention.

In order to solve this problem, the inventor of the present invention discovered that, as mentioned above, high sensitivity is required when there is a large attenuation of infrared rays in the optical path, such as frost, fog, rain, or snow, and the weather conditions in which these occur. Both are limited to times when the temperature is low and there is little influence from outside light such as sunlight.For this reason, when frost, fog, rain, snow, etc. occur and high sensitivity is required, white noise is low. I discovered that the condition is

The present invention was made based on this discovery, and when the white noise of the phototransistor etc. is small, that is, when the infrared rays are attenuated in the optical path and the signal level is low, the sensitivity is increased so that the device operates normally. On the other hand, when the white noise is large, i.e., when there is no infrared attenuation factor in the optical path and the signal level is high, such as on sunny days or high temperatures, we came up with the idea that this could be achieved by suppressing the sensitivity to prevent equipment malfunctions due to white noise. I came to the conclusion.

Therefore, the second problem to be solved by this invention was how to determine the magnitude of white noise and control the sensitivity margin of the amplification system.

Incidentally, AGC circuits such as those disclosed in Japanese Patent Application Laid-Open No. 56-29790 have been known for a long time, but this conventionally known AGC circuit controls the amplification degree of the amplifier according to the strength of the signal. It is a thing,
As will be explained later, the present invention is different in that it focuses on the magnitude of white noise.

<Means for Solving the Problems> The present invention focuses on the fact that white noise is high in sunny weather and high temperatures and low in bad weather, and conversely, the sensitivity of pulse modulation type infrared security alarm devices is particularly required in bad weather. , white noise is several KHz
It was developed with the focus on the fact that it contains a wide frequency component from 10KHz to several tens of kilohertz, has a relatively large duty of 1/2 to 1/10, and that a large DC component can be obtained by detection and smoothing.

In the pulse modulation type infrared security alarm device of the present invention, a light receiving element receives a pulse modulated infrared beam emitted from a projector, and a variable gain amplifier amplifies the electrical signal of the light receiving element, and a first trigger level is set. In a device that detects a wave by a first detection circuit that passes only components equal to or higher than el and then introduces the signal into the alarm circuit section, an input is taken in from a circuit from the variable gain amplifier to the first detection circuit, and A second trigger level AGC that is set lower than the first trigger level of the first detection circuit.
a second detection circuit having a second detection circuit, a smoothing circuit that smoothes the detected output of the second detection circuit, and automatic gain adjustment means that changes the gain of the variable gain amplifier according to the magnitude of the output of the smoothing circuit. It is characterized by having the following.

<Function> When frost, fog, etc. occur and the white noise is small, the white noise is lower than the trigger level el of the first detection circuit, and the intensity of the white noise on the amplified signal line is lower than the trigger level el of the first detection circuit. , and the second detection circuit outputs a trigger pulse corresponding only to the regular pulse signal. At this time, the DC output of the smoothing circuit is very small, and the gain of the variable gain amplifier hardly decreases.

On the other hand, when the white noise is large under clear skies and high temperatures, the intensity of the white noise is higher than the trigger level el of the first detection circuit, and therefore the output of the second detection circuit also contains a lot of white noise. As a result, the DC output of the smoothing circuit becomes large, so that the automatic gain adjustment function becomes effective and the gain of the variable gain amplifier decreases. However, since the level of the pulse signal to be received is also high, there is no fear that the signal introduced into the alarm circuit section will be insufficient, and only the noise component can be suppressed.

<Example> FIG. 2 is a block diagram showing the configuration of a light receiving section according to the present invention.

The infrared light collected by the condensing mirror 1 is transmitted to the light receiving element 2
It is converted into a pulse signal with a voltage corresponding to the amount of incident light and transmitted to the selective amplifier 3. A detection circuit 9 for automatic gain adjustment (hereinafter referred to as AGC detection circuit) and a smoothing circuit 10 (hereinafter referred to as AGC smoothing circuit) are added to the selection amplifier 3, and the selection amplifier 3, the AGC detection circuit 9 and The AGC smoothing circuit 10 constitutes an automatic gain amplification circuit 11 (hereinafter abbreviated as AGC amplification circuit). The selection amplifier 3 is a variable gain amplifier, and the gain decreases as the DC output of the smoothing circuit 10 increases. The detection circuit 9 passes components above the first trigger level el and does not pass components below it. The AGC detection circuit passes components above the second trigger level agc and does not pass components below it. The trigger level agc of this AGC detection circuit 9 is appropriately set in accordance with the level of white noise of the light receiving element 2, but does not exceed the trigger level el of the detection circuit 4.

FIG. 3 shows signal waveforms at points a to g in FIG. 2, where (1) shows when white noise is small and (2) shows when white noise is large.

First, the third method is when high sensitivity is required, that is, when frost, fog, etc. occur and the white noise is small.
This will be explained with reference to FIG.

a indicates a pulse signal voltage-converted by the light-receiving element 2; Although some white noise can be seen, its intensity is very weak and the detection circuit 4
Therefore, the intensity of the white noise of the amplified signal b is lower than the trigger level agc of the AGC detection circuit 9, and the AGC detection circuit 9 detects the trigger pulse c only in response to the regular pulse signal. Output. As a result, the level of the signal d smoothed by the AGC smoothing circuit 10 does not activate the automatic gain adjustment function of the AGC amplifier circuit 11, and the signal b amplified by the selection amplifier 3 is directly transmitted to the detection circuit 4. . The detection circuit 4 applies a trigger signal e corresponding only to the pulse signal to the monostable multivibrator 5, and the monostable multivibrator 5 outputs a rectangular wave f delayed by a predetermined time. Since the smoothed output g of this rectangular wave f is higher than the switching level sw of the switching circuit 7, the switching circuit 7 is turned on and the output circuit 8 is not activated.

FIG. 3 shows a case where the intensity of white noise is high under sunny weather and high temperature, and the intensity of the regular pulse signal is also high, but the intensity of the white noise is also higher than the trigger level el of the detection circuit 4. Therefore, if an intruder blocks the infrared rays between the emitter and receiver in this state and there is no regular pulse signal, if the wave is amplified and detected as it is, the switching circuit 7 will be activated due to white noise. It becomes ON, and the output circuit 8 becomes inoperable. This is a fatal flaw as a security alarm system. However, according to the present invention, in the case of the light receiving section, the output of the AGC detection circuit 9
Since the smoothed output d' of c' becomes larger, the automatic gain adjustment function is activated, and the output of the AGC amplifier circuit 11 becomes like b', and after detection, only the trigger pulse e' corresponding to the regular pulse signal is output. be done. The following is the same as in FIG. 3, 1, and therefore the switching circuit 7 is ON/OFF controlled only in response to a regular pulse signal, so that the device will not malfunction due to white noise.

Although Fig. 3 is expressed as a model, the infrared pulse modulation signal actually emitted from the projector has a frequency of about 1 KHz and a duty of about 1/100, and is smoothed by the AGC smoothing circuit 10. The DC component becomes very small. Compared to this,
As mentioned above, the duty of white noise is 1/2.
Since it is relatively large at ~1/10, the AGC smoothing circuit 10
The voltage value of the DC output is 30 to 50 times that of the pulse modulation signal.

<Effects of the Invention> According to the present invention, the gain of the amplifier circuit is controlled according to the strength of noise on the output line of the light receiving element, and the gain is increased when the noise is weak and suppressed when the noise is strong. Despite changes in weather conditions, we succeeded in constantly suppressing noise components while maintaining stability in the magnitude of the pulse modulation signal introduced into the alarm circuit. According to tests, while the conventional device was only able to detect phototransistor outputs up to about 8 mV, the present invention was able to detect up to 0.8 mV, achieving an approximately 10-fold increase in sensitivity.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a light receiving section of a conventional pulse modulation type infrared security alarm device, FIG. 2 is a block diagram showing a light receiving section according to the present invention, and FIG. 3 is a block diagram showing signals at points a to g in FIG. It is a figure showing a state. 1... Focusing mirror, 2... Light receiving element, 3... Selection amplifier, 4... Detection circuit, 5... Monostable multivibrator, 6... Smoothing circuit, 7... Switching circuit, 8... Output Circuit, 9...AGC detection circuit, 10...AGC smoothing circuit, 11...AGC amplifier circuit, el...Trigger level of detection circuit, agc...
...Trigger level of AGC detection circuit, sw...Switching level of switching circuit.

Claims (1)

[Claims] 1. A light receiving element receives a pulse-modulated infrared beam emitted from a projector, and the electric signal of the light receiving element is amplified by a variable gain amplifier, and a first detection method passes only the components higher than the first trigger level el. In a device that detects a wave by a circuit and then introduces it into an alarm circuit section, an input is taken in from a circuit from the variable gain amplifier to the first detection circuit, and the input is lower than the first trigger level of the first detection circuit. Second trigger level AGC also set low
a second detection circuit having a second detection circuit, a smoothing circuit that smoothes the detected output of the second detection circuit, and automatic gain adjustment means that changes the gain of the variable gain amplifier according to the magnitude of the output of the smoothing circuit. A pulse modulation type infrared security alarm device characterized by being provided with.