JPH04264698A - Photoelectric type intrusion detection system - Google Patents

Abstract

PURPOSE:To properly corresponds both to the level fluctuations of a signal component and to the level fluctuations of a noise component to automatically control a gain against,them. CONSTITUTION:A floodlight device 10 projects light only for a prescribed time To for every prescribed period Tp. The system converts the incident light signal with a photodetector 21, and inputs the converted electric signal into an amplifier 23 with a partial pressure circuit 22 constituted of a resistance R1 and diodes D1 and D2. The system compares the output signal Vi from the amplifier 23 with a reference signal Vr by using a comparator 24 to discriminate a signal component S. Then, the system samples a compared output V1 to a shift register 25 for every prescribed period Ts, adds the output of a prescribed column by using an adder 26, and sends it to a judgment circuit 27. The system also sends the output from the adder to a smoothing circuit 28 and feedbacks it to the above mentioned partial pressure circuit 22 as a gain control signal Vf. Thus, the system can automatically control the gain both against the level fluctuations of the signal component and against the level fluctuations of the noise component.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric intrusion detection system, and more particularly to an improvement of a light receiving device in a photoelectric intrusion detection system having a light emitting device and a light receiving device.

0002

[Prior Art] In this type of photoelectric intrusion detection system,
Because there is noise due to the reception of light other than light from the light emitting device (for example, light from an electric lamp), noise induced from the power line, etc., it is difficult to distinguish between the original signal component due to the light from the light emitting device and the noise component. It is necessary to discriminate in the light receiving side device.

Furthermore, the signal component level and the noise component level fluctuate due to the accumulation of dust, changes in the weather, and deterioration of the projector and receiver, so it is necessary to adjust the gain.

[0004] As a conventional device that automatically adjusts the gain, there is a device disclosed in Japanese Patent Application Laid-open No. 139298/1983, which detects a signal containing a mixture of signal components and noise components, and generates a smoothed voltage. The gain changes depending on the value.

[0005]

[Problems to be Solved by the Invention] However, as stated in the above-mentioned publication, the voltage value is substantially determined by the noise component, and the signal component hardly contributes. Although it is possible to deal with level fluctuations, there is a problem in that it cannot actually deal with level fluctuations of signal components.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a photoelectric intrusion detection system that can automatically adjust the gain in response to both signal component level fluctuations and noise components.

[0007]

[Means for Solving the Problems] A photoelectric intrusion detection system of the present invention has a light emitting side device and a light receiving side device, in which the light emitting side device has a predetermined cycle T.
The device emits light for a predetermined time To every p, and the light-receiving device includes a sensor means that converts an incident optical signal into an electric signal, an amplification means that can change the gain and amplifies the electric signal, and Comparing means for comparing the output of the amplifying means with a predetermined reference value; shift register means for sampling the output of the comparing means at predetermined intervals Ts and shifting the sampling value; and adding the outputs of predetermined digits of the shift register means. The present invention is characterized in that it comprises an adding means for adding, and a feedback means for feeding back the output of the adding means to control the gain of the amplifying means.

[0008]

[Operation] In the photoelectric intrusion detection system of the present invention, the output of the comparison means is sampled every predetermined time Ts, the value is held in a shift register, and the light emission period T of the light emission side device is
By adding each value synchronized with p, frequency selection characteristics for synchronized signals, that is, signal components, are improved. The gain of the amplifying means is automatically adjusted by feeding back the increase or decrease in the output of the adding means using the feedback means. Therefore, the gain can be adjusted even with respect to level fluctuations of signal components.

[0009]

EXAMPLES The present invention will be explained in detail below using examples. Note that this invention is not limited to this. FIG. 1 is a configuration diagram of a photoelectric intrusion detection system 1 according to an embodiment of the present invention. This photoelectric intrusion detection system 1
has a light emitting side device 10 and a light receiving side device 20, and detects intrusion by blocking the light L.

The light projecting device 10 applies a drive signal Do to the light emitting element 12 by means of a drive means 11. The drive signal Do is a pulse signal with a pulse width To and a period Tp (see FIG. 2). Therefore, the light L is intermittently projected. The pulse width To is, for example, 30 μS, and the period Tp is, for example, 960 μS.

In the light receiving device 20, the light L incident on the light receiving element 21 is converted into an electrical signal.

The electrical signal is transmitted through the resistor R1 and the diode D.
The signal is input to the amplifier 23 via the voltage dividing circuit 22 consisting of 1 and D2, is amplified by the amplifier 23, and is outputted as Vi. This output Vi consists of a signal component S based on the light L and a noise component N, as shown in FIG. As will be described later, a voltage dividing circuit 22 including a resistor R1 and diodes D1 and D2 and an amplifier 23 constitute variable gain amplification means.

The output Vi is compared with a reference value Vr in a comparator 24 and becomes a binary signal V1. The binarized signal V1 is sampled and shifted by the shift register 25 every cycle Ts of the clock signal CK. Period T
For example, s is To/4. Therefore, shift register 2
The value of the n-th digit of 5 represents the value of the binarized signal V1 at a time nTs hours before the current time. The binary signal V1 at the current time is also input to the adder 26.

The adder 26 adds outputs of predetermined digits of the shift registers selected so that the value of nTs includes at least one digit of the shift register 25 that is an integral multiple of the period Tp of the signal component, In the embodiment of FIG.
8th digit (nTs=Tp) and 256th digit (nTs=2Tp)
), ..., the 1024th digit (nTs=8Tp) are selected and added together with the binary signal V1 at the current time. The adder output signal Vs is sent to the determination circuit 27 and the smoothing circuit 2.
8 is connected.

The determination circuit 27 is a circuit that outputs an abnormality detection signal if a pulse signal larger than a predetermined determination criterion is not input within time TP+ΔT.

The smoothing circuit 28 detects, smoothes, and converts the impedance of the adder output signal Vs, and feeds back the gain control signal Vf to the voltage dividing circuit 22.

Next, the operation will be explained. The electric signal received by the light receiving element 21 is passed through the resistor R1 in the voltage dividing circuit 22.
and the internal resistance value of the parallel circuit of diodes D1 and D2, and the divided voltage is input to the amplifier 23.

The output V1 of the amplifier 23 is connected to the comparator 2
4, the signal component S and the noise component N are compared with the reference value Vr.
is discriminated and output as a binary signal V1.

Next, the binary signal V1 of the comparator 24 at the current time is input to the adder 26, and is input to the shift register 2.
It is added to the binarized signal V1 of an integral multiple of the period Tp of 5,
It is output as the adder output signal Vs. In this example, the 128th digit, the 256th digit, the 384th digit, and the 51st digit are
2 digits, 640th digit, 768th digit, 892nd digit,
The 1024th digit is added to the binary signal V1 at the current time. As a result, the level difference between the synchronous signal and the asynchronous signal is expanded, and the synchronous signal component S is detected. Judgment circuit 2
8 does not output an abnormality detection signal because the adder output signal Vs is regularly inputted at the period Tp.

When the intruder interrupts the light L, the pulse signal is no longer output and a state occurs in which the time between pulses is greater than or equal to TP+ΔT, so the determination circuit 27 outputs an abnormality detection signal. Further, the adder output signal Vs is output from the smoothing circuit 2
8, the signal is detected, smoothed, and impedance converted, and fed back to the voltage divider circuit 22 as a gain control signal Vf.

The gain control signal Vf is a signal generated from the signal component S obtained from the adder output signal Vs, and is hardly affected by the noise component N contained in the received light signal.

Now, as shown in FIG. 1, the constants of the voltage dividing circuit 22 are set so that an appropriate gain is determined when the signal component S of the electric signal Vi is at a standard level. Then, constants of the smoothing circuit 28 are set so that an appropriate gain control signal Vf can be obtained.

At this time, the waveform of the gain control signal Vf at point P4 is as shown in FIG. Next, if the level of the signal component S has fallen for some reason and the output signal Vi of the amplifier 23 for the signal component S has fallen below the reference value Vr, then the binarized signal V1 of the comparator 24
is almost "0". Therefore, the adder output signal V
Since s decreases, the level of gain control signal Vf decreases. As a result, the value of the current flowing through the diodes D1, D2 decreases, and the internal resistance value of the diodes D1, D2 increases. Therefore, the voltage division ratio with the resistor R1 increases, raising the level of the electrical signal at the P1 point. In other words, the gain of the amplifying means consisting of the voltage dividing circuit 22 and the amplifier 23 increases.

If the gain increases too much, the output signal Vi of the amplifier 23 with respect to the noise component N will rise above the reference value Vr, so the binary signal V1 of the comparator 24 will be almost
1". Therefore, since the adder output signal Vs increases, the level of the gain control signal Vf increases. the result,
The current value flowing through the diodes D1 and D2 increases, and the internal resistance value of the diodes D1 and D2 decreases. Therefore, the voltage division ratio with the resistor R1 decreases, lowering the level of the electrical signal at the point P1. In other words, the gain of the amplifying means consisting of the voltage dividing circuit 22 and the amplifier 23 decreases.

After all, the output signal Vi of the amplifier 23 for the signal component S is above the reference value Vr, and
Equilibrium occurs when the output signal Vi of the amplifier 23 with respect to the noise component N reaches a gain such that it is lower than the reference value Vr.

As described above, in this photoelectric intrusion detection system 1, the gain can be automatically adjusted in response to both the level fluctuation of the signal component and the noise component. Further, since the level difference between the synchronous signal and the asynchronous signal is expanded by the shift register 25 and the adder 26, it is also possible to prevent the gain from fluctuating due to sudden noise.

[0027]

According to the photoelectric intrusion detection system of the present invention, the gain can be automatically adjusted in response to both signal component level fluctuations and noise components. Further, the gain can be stably controlled without being affected by sudden noise. Furthermore, since it has excellent frequency selection characteristics for synchronizing signals, it is possible to more stably detect signals even for signals such as interference. Therefore, the reliability of the system can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of essential parts of an embodiment of a photoelectric intrusion detection system of the present invention.

FIG. 2 is a signal waveform diagram of each part of the photoelectric intrusion detection system shown in FIG. 1.

[Explanation of symbols]

1 Photoelectric intrusion detection system 10 Light emitting side device 11 Drive means 12 Light emitting element 20 Light receiving side device 21 Light receiving element 22 Voltage dividing circuit 23 Amplifier 24 Comparator 25 Shift register 26 Adder 27 Judgment circuit 28 Smoothing circuit Do Drive signal L Optical Vi Electrical signal Vr Reference value V1 Binary signal Vs Adder output signal Vf Gain control signal D1 Diode D2 Diode R1 Voltage dividing resistor CK Clock signal

Claims (1)

[Claims] Claim 1: A photoelectric intrusion detection system having a light emitting side device and a light receiving side device, in which the light emitting side device emits light for a predetermined time To at every predetermined period Tp, and the light receiving side device detects light from the incident light. a sensor means for converting the optical signal into an electric signal; an amplification means whose gain is changeable and amplifies the electric signal; a comparison means for comparing the output of the amplification means with a predetermined reference value; shift register means for sampling the output at every predetermined period Ts and shifting the sampled value; addition means for adding the outputs of predetermined digits of the shift register means; and feeding back the output of the addition means to adjust the gain of the amplification means. A photoelectric intrusion detection system characterized by comprising a control feedback means.