JPS5932838B2 - photoelectric detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a photoelectric detector in which a light emitting part and a light receiving part are arranged separately, and the light emitting part and the light receiving part are synchronized to detect the blocking or attenuation of transmitted light due to smoke or the like. Regarding.

When trying to measure smoke density and transmittance in a space, the light from a light emitting part with a light source is detected by a light receiving part, and the transmittance or attenuation rate of light between the light emitting part and the light receiving part is determined. However, in addition to the light from the light source of the light emitting part, modulated light from fluorescent lamps and other sources enters the light receiving part as disturbance light, and unless this is removed, accurate transmittance or light attenuation cannot be measured. It has been known.

Conventionally, as a means to solve this problem, the first method is to modulate the light emitted from one light emitting section using a mechanical chopper or the like and demodulate it at the light receiving section.The light source of the two light emitting sections is driven at, for example, 1KH2, and the light emitted from the light receiving section is driven at 1KH2. The second method is to process the received light signal through a filter, in which the three light emitting parts are driven intermittently, while a signal synchronized with the intermittent pulse is sent to the light receiving part, and the light receiving part receives light in synchronization with the intermittent pulse. There is a third method of processing only the signal, etc. However, the first method has drawbacks such as being expensive and having a short lifespan due to the presence of mechanical elements.

Further, the second method generally has a drawback that the high frequency component of the disturbance light may be included in the pass band of the filter, and the S/N ratio of the received light signal with respect to the disturbance light is poor. On the other hand, in the third method, compared to the second method, the light emitting part emits light intermittently, and the light receiving part receives light in synchronization with the intermittent light. Good signal to noise ratio,
Generally widely used. However, when this is used in a fire detector, etc., the power for the light emitting part and the light receiving part is supplied from the fire alarm receiver, and a signal line for transmitting and receiving the intermittent pulses between the light emitting part and the light receiving part is required separately. In order to
There was a problem with the installation work. In other words, separate fire detectors are installed in warehouses, etc., and the distance between the light emitting part and the light receiving part is several meters.
The increase in the number of lines has become a major problem, as the line can extend up to 100 meters from the line. Further, regarding the power supply line from the light receiving section side to the light emitting section side, there is a problem in that the luminance of the light source decreases due to a voltage drop due to the line resistance. The present invention has been made in order to solve the above-mentioned problems, and the present invention charges the capacitor of the light emitting part by intermittently supplying power from the light receiving part to the light emitting part, and reduces the charging charge of the capacitor of the light emitting part when power is not supplied. The light source is intermittently emitted by supplying power from the
By switching the received light signal using the inverted output for the intermittent supply of the power supply and inputting it to the signal processing circuit, there is no need for a special signal line for transmitting and receiving intermittent pulses between the light emitting part and the light receiving part, and the intermittent supply of the light emitting part is eliminated. It is an object of the present invention to provide a photoelectric detector which can process a light reception signal in synchronization with light emission and can cause a light source to emit light at a predetermined brightness almost unaffected by line resistance. The present invention will be explained below based on an embodiment shown in the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a specific example of the light emitting section in the above embodiment.

The embodiment shown in FIG. 1 includes a power supply determination circuit 1, a charging circuit 2,
A light emitting section consisting of an oscillation circuit 3, a light source driving circuit 4, and a light source 5, and a light receiving section consisting of a photoelectric conversion circuit 6, an amplifier circuit 7, a filter circuit 8, a signal processing circuit 9, an intermittent power supply circuit 10, and a light receiving signal switching circuit 13. It consists of In addition, the light emitting part and the light receiving part are installed separately, and the power line 1
4 and 14, and optical signals are transmitted and received between the light source 5 and the photoelectric conversion circuit 6 via an optical system 15 such as a lens. The power supply determination circuit 1 includes, for example, an inverter 1a as shown in FIG. input. It goes without saying that this power supply determination circuit 1 can be omitted as long as it controls the operation of the oscillation circuit 3, and it can be omitted if the oscillation circuit 3 operates and stops depending on the presence or absence of voltage across the power supply line 14. do not have. As will be described later, since power to the light emitting section is intermittently supplied from the intermittent power supply circuit 10, this control signal is also output intermittently in synchronization with the power supply. As shown in FIG. 2, for example, the charging circuit 2 is composed of a capacitor 2a and a diode 2b, and charges the power supply current supplied intermittently, and discharges it when the power supply is not supplied, and serves as a driving power source for the light source 5. . In order to reduce the rush current to the charging circuit 2, a resistor or a constant current circuit may be provided in series with the diode 2b. Note that the diode 3a and capacitor 3b in FIG. 2 are used to prevent the power supply voltage of the oscillation circuit 3 from changing due to charging and discharging of the capacitor 2a. The oscillation circuit 3 and the light source/drive circuit 4 are circuits that cause the light source 5 to emit light at a specific frequency.

The oscillation circuit 3 oscillates at a specific frequency when the control signal of the power supply determination circuit 1 is input, and its output is input to the light source 5 drive circuit 4. Further, the light source driving circuit 4 is connected to the charging circuit 2, and modulates the output of the oscillation circuit 3 using the charged electric charge to cause the light source 5 to emit light intermittently at a specific frequency. For example, as shown in FIG. 2, the light source drive circuit 4 is composed of a transistor 4a and a resistor 4b. By connecting the output of an oscillation circuit to the base of the transistor 4a, the charge in the charging circuit 2 is discharged. The light source 5 is modulated and driven at the oscillation frequency. Note that the light source 5 may be configured to be driven by a control signal from the power supply determination circuit 1, and in this case, the oscillation circuit 3 can be omitted. The light source 5 is made of, for example, a light emitting diode, and is turned on by the light source 5 drive circuit 4 described above.

Note that as the light source 5, a semiconductor laser or the like can be used.
The photoelectric conversion circuit 6 is composed of a Si photodiode or the like, and functions to convert the optical signal from the light source 5 into an electrical signal. The amplifier circuit 7 amplifies the optical signal (hereinafter referred to as a light reception signal) converted into an electrical signal by the photoelectric conversion circuit 6.
The filter circuit 8 functions to remove noise by passing only signals of a specific frequency from the amplified light reception signal. Further, the signal processing circuit 9 is a circuit that compares the light reception signal with a reference value and generates an alarm signal when the light reception signal is below a predetermined level. These are similar to those used in conventional transmittance measurement devices. Intermittent power supply circuit 10
This circuit consists of a pulse generation circuit 11 and a switch circuit 12, and has the function of intermittently supplying power to the light emitting section and generating an inverted output in response to the intermittent supply of the power. The pulse generating circuit 11 generates pulses having a constant pulse width and pulse interval in order to intermittently supply power to the light emitting section. The ratio of the pulse interval to the pulse width is determined from the impedance of the power supply line 14 and the interval of intermittent light emission of the light source, and is, for example, about 10:1. The switch circuit 12 sends out the pulse to the light emitting section side via the power supply line 14, and also generates a pulse having a waveform that is an inversion of the pulse. The pulse of this inverted waveform is input to the light reception signal switching circuit 13 as an inverted output for intermittent power supply. The light reception signal switching circuit 13 is inserted between the filter circuit 8 and the signal processing circuit 9, and has characteristics similar to, for example, an analog switch, and inputs the light reception signal to the signal processing circuit 9 in response to the inverted output. urge

The light reception signal switching circuit 13 operates by closing the switch while the inverted output is being input, and opening the switch when it is not being input. Note that the light receiving signal switching circuit 13 is not limited to the above-mentioned position, but may be inserted at any other position as long as it can switch the light receiving signal input to the signal processing circuit 9. Next, the operation of this embodiment will be explained.

FIG. 3 is an operating diagram showing the operating state of the photoelectric detector of the above embodiment, and A to F indicate voltage and current waveforms at points with the same symbols shown in the block diagram of FIG. 1, respectively. The intermittent power supply circuit 10 intermittently supplies power to the light emitting section via the power line 14.

FIG. 3A shows this power supply waveform. At the same time, the intermittent power supply circuit 10 sends an inverted output for the intermittent power supply to the light reception signal switching circuit 13. The waveform of this inverted output is shown in FIG. 3B. Note that the waveform in FIG. 3B shows that it is sufficient if the light reception signal switching circuit 13 is opened while the light source is being supplied to the light emitting section, and if this operation can be ensured, the third Diagram A
It does not need to be an inverted output. On the other hand, on the light emitting part side, the power supply determination circuit 1 detects the presence or absence of the intermittently supplied power, and also outputs a control signal synchronized with the inverted output when the power is not supplied, as shown in FIG. 3D. Output.

As this control signal is input, the oscillation circuit 3 intermittently oscillates at a specific frequency (for example, several KHz). FIG. 3E shows the output waveform of this oscillation circuit. Further, the charging circuit 2 is charged by the power supplied intermittently, and is discharged through the light source drive circuit 4 when the power is not supplied.

FIG. 3C shows this change in charge/discharge voltage. As is clear from the figure, charging and discharging are performed in synchronization with the intermittent supply of power. The charging time constant of the charging circuit 2 is the capacitor 2a.
Since it is determined by the capacity of the capacitor 2a and the line resistance of the power supply line, if the pulse width when power is supplied is made sufficiently long compared to the pulse width when driving the light source, the capacitor 2a will be Can accumulate charge. In the light source drive circuit 4, the light source 5 is connected to the capacitor 2a by the output of the oscillation circuit 3.
Since it emits light by receiving power from the charged charges, it emits light intermittently and intermittently with the same waveform as the output of the oscillation circuit 3.

In this case, most of the power consumption of the light source is consumed by the capacitor 2a.
Since the light emitted from the light source 5 is supplied from the charged charge, the luminance of the light source 5 does not change due to the influence of the line resistance. In addition, in this embodiment, the charge in the capacitor 2a gradually decreases from the start of driving the light source, and the luminance of light emission also decreases with the passage of time. The transistor 4a may be driven with a constant current. The optical signal from the light source 5 passes through a photoelectric conversion circuit 6, an amplifier circuit 7, and a filter circuit 8, and reaches a light reception signal switching circuit 13.

This light reception signal switching circuit 13 is closed in synchronization with the inverted output of the intermittent power supply circuit 10, as shown in FIG. 3F, and the intermittent light emission of the light source 5 is also synchronized with the inverted output. , only the light reception signal from the light source 5 is processed by the signal processing circuit 9.
, and noise caused by other unsynchronized disturbance light is blocked. Therefore, when the photoelectric detector of the present invention is used in a dimming separation type fire detector, the influence of ambient light can be minimized, so the S/N ratio is significantly improved.
Attenuation of optical signals due to smoke can be detected with high accuracy.

Furthermore, when used in an infrared intrusion detector, the influence of disturbance light incident from sources other than the light source can be removed, and intrusion detection can be performed with high precision as described above. Note that, in addition to causing the light source to emit light intermittently, as in the above embodiment, the light source is modulated by the output of the oscillation circuit to cause it to emit light intermittently and intermittently at a specific frequency, which increases the influence of ambient light. It is more effective in places. As explained above, by having the above configuration, the present invention charges the power source intermittently supplied from the light receiving section side in the light emitting section, and causes the light source to emit light intermittently using the discharging current when the power is not supplied. At the same time, the light reception signal can be input to the signal processing circuit in response to the inverted output with respect to the intermittent supply of the power supply, so there is no need for a special signal line for transmitting and receiving intermittent pulses between the light emitting part and the light receiving part. The light receiving signal can be processed in synchronization with the intermittent light emission of the light emitting section, and the light source can emit light at a predetermined brightness without being affected by the line resistance of the power supply line.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific example of the light emitting section of the above embodiment, and FIG. 3 is an operation diagram showing the operating state of the present invention. 1...Power supply determination circuit, 2...Charging circuit, 3...Oscillation circuit, 4...Light source drive circuit, 5...... Light source, 6...Photoelectric conversion circuit, 9...Signal processing circuit, 10...
Intermittent power supply circuit, 13... Light receiving signal switching circuit, 14... Power supply line.

Claims (1)

[Claims] 1. A photoelectric detector in which a light-emitting part having a light source and a light-receiving part that detects light from the light-emitting part are installed separately, and the light-receiving part detects changes in the amount of transmitted light due to blocking or attenuation of the light beam from the light-emitting part. In the light emitting unit, a power supply determination circuit detects whether or not power is supplied from the light receiving unit side and outputs a control signal when power is not supplied; and a charging circuit that charges when power is supplied and discharges when power is not supplied; a light source drive circuit that receives a control signal from the power supply determination circuit when power is not supplied, discharges the charging circuit based on the control signal, and causes the light source to emit light using the discharge current; an intermittent power supply circuit that intermittently supplies power to the light emitting section and generates an inverted output in response to the intermittent supply of the power; and a light reception signal is input to the signal processing circuit in response to the inverted output of the intermittent power supply circuit. A photoelectric detector comprising a light receiving signal switching circuit.