JPS6148849B2 - - Google Patents

Description

[Detailed Description of the Invention] The ultraviolet detection tube is made of a metal such as molybdenum that emits photoelectrons when irradiated with ultraviolet rays inside an airtight container made of glass that transmits ultraviolet rays, such as fused silica. A cathode that collects electrons and an anode that collects electrons are provided in close proximity and are filled with several hundred torr of hydrogen gas, and the anode and cathode are connected to separate conductive wires that pass through the airtight container. When a voltage of, for example, 250 volts is applied between the anode and the cathode via the conductive wire, when ultraviolet rays are incident, photoelectrons are emitted from the cathode, and the photoelectrons ionize the sealed gas. A gas discharge occurs. Further, if a voltage of 300 volts or less is applied between the anode and the cathode, the gas discharge will also be interrupted when the incidence of ultraviolet rays is interrupted.

An ultraviolet detector tube connected to such a voltage source does not detect visible light, so if it is placed in a bright place, it will detect light from fire flames that also emit ultraviolet light, distinguishing it from other light. If the detection signal is used to operate an alarm lamp, it can be used as a fire alarm device.

However, the fire alarm device described above does not issue an alarm unless a fire occurs. On the other hand, in the above-mentioned fire alarm system, even if a crack occurs in the airtight container of the ultraviolet detection tube and air enters, no discharge will occur, so the ultraviolet detection tube It is not possible to determine whether it is working properly or is malfunctioning.

The present invention relates to an ultraviolet detection device equipped with a display device that indicates that an ultraviolet detection tube is operating normally while a fire alarm device is in operation.

The present invention utilizes the fact that the above-mentioned fire alarm device is energized by radiation existing in nature, such as cosmic rays, in the ultraviolet detection tube once every several tenths of time during operation. .

Next, the structure and operation of an ultraviolet detection device equipped with a normal operation display device for an ultraviolet detection tube according to the present invention will be explained using examples.

FIG. 1 is a circuit diagram of an ultraviolet detection tube device equipped with a normal operation display device for an ultraviolet detection tube according to the present invention.
1 is a power source that generates an electromotive force of 350 volts, and its cathode is grounded. 2 represents the internal resistance of the power supply 1 by an equivalent resistance, which is several tens of megohms.
3 is a 200 kilohm resistor, one end of which is connected to the positive terminal of the power source 1, and the other end connected to the positive terminal of the ultraviolet discharge tube 5. The ultraviolet light detection tube 5 is grounded through a 1 megohm resistor 6 at its cathode. 4 is a capacitor of 500 picofurad, 21 is a 1 megname resistor connected in series with capacitor 4, the other end of the capacitor is connected to the positive terminal of power supply 1, and the other end of resistor 21 is grounded. For example, 7 is a monostable circuit as shown in Figure 2, which is a retriggerable circuit that remains on for a certain period of time even if a trigger pulse is input while it is on, and its input terminal is exposed to ultraviolet light. It is connected to the connection point between the cathode of the detector 5 and the resistor 6. 8 is connected to the output terminal of monostable circuit 7
A 500 ohm resistor, 9 is a light emitting diode connected in series with resistor 8. Reference numeral 22 denotes a drive amplifier for driving the buzzer 23, the input end of which is connected to the connection point between the cathode of the ultraviolet detection tube 5 and the resistor 6. In this device, when ultraviolet rays generated from the flames of a fire are incident on the ultraviolet detection tube 5, if the ultraviolet detection tube 5 is normal, a gas discharge will occur within the tube, and the electric charge stored in the capacitor 4 will be transferred to the ultraviolet discharge tube 5. As a result, a voltage pulse with a peak value of 10 volts and a duration of about 100 microseconds is generated at the connection point between the ultraviolet discharge tube 5 and the resistor 6. Capacitor 4
is charged according to a time constant determined by the capacitance of capacitor 4 of 500 picofurad and the resistance of resistor 21 of 1 megohm, and as a result of the charging of capacitor 4 approaching saturation, the voltage at its anode increases. The discharge as described above is repeated every time the voltage reaches 250 volts. In other words, the capacity of capacitor 4
This produces pulses with a repetition rate higher than 2000 hertz, which is the reciprocal of 500 picofurad times the 1 megohm resistance of resistor 21.

This pulse is amplified by the drive amplifier 22 and drives the buzzer 23, so that a fire alarm can be issued.

On the other hand, when cosmic rays or radiation enter the ultraviolet detector tube 5, if the ultraviolet detector tube 5 is normal, a gas discharge will occur within the tube, and a peak value of 10 volts will be generated at the connection point between the ultraviolet discharge tube 5 and the resistor 6 for a period of time. A voltage pulse approximately 100 microseconds wide is generated. Since cosmic rays or radiation are incident at a rate of approximately once every several tens of minutes, only a single pulse is generated, and no alarm is generated as in the case of a fire as described above.

The voltage pulse is input to the monostable circuit 7, which switches the output voltage from, for example, 0 volts to 5 volts according to the voltage pulse, and maintains this state for one hour. Therefore, the light emitting diode 9
A current of 10 milliamps or less flows, and the light emitting diode 9 emits light, indicating that the ultraviolet detection tube 5 is operating normally. The monostable circuit 7 is a retriggerable monostable circuit, that is, when a voltage pulse is input and the output voltage reaches 5 volts, when a voltage pulse is input again, the second voltage pulse is received. It operates to maintain the output signal at volts for an additional hour.

The monostable circuit 7 is, for example, a monostable multivibrator as shown in FIG. That is, when the transistor 14 is in an on state and the transistor 13 is in an off state in advance, and a positive voltage pulse is input to the input terminal 11, the inverter 12 generates a negative voltage pulse, and the negative voltage pulse is input to the base of the transistor 14. At this time, the transistor 14 is turned off, a high level voltage is generated at the output terminal 16, and the transistor 13 is turned on, starting to charge the capacitor 17.

When the base voltage of the transistor 14 reaches a level at which the transistor 14 is turned on due to the above charging, a low level voltage is generated at the output terminal voltage 16 and the transistor 13 is turned off. The time for sending out the high level voltage is proportional to the product CR of the capacitance C of the capacitor 17 and the resistance R of the resistor 18. Again while producing high level voltage,
When a positive voltage pulse is input to the input terminal 11, the transistor 15 becomes conductive and discharges the accumulated charge in the capacitor 17, so that the time for sending out a high level voltage starts from that point. Large CR by design
If the value of is not obtained, connect multiple monostable multivibrators 10 shown in FIG. 2 in series as shown in FIG. When input to the circuit 20, the output terminal of the OR circuit 20 is connected to each monostable multivibrator 10...
...It is possible to obtain a high-level state with a time width corresponding to the sum of the time widths of 10 high-level states.

The device described above does not display a normal display from the time the fire alarm starts operating until cosmic rays first enter the system, but if necessary, it will emit light for a short time in conjunction with the switch that starts the fire alarm. What is necessary is to provide an ultraviolet lamp within the detection field of the ultraviolet detection tube.

As can be understood from the above description, the present invention can be applied to dozens of devices such as fire alarm systems using ultraviolet detection tubes that do not normally perform a discharge operation and only generate a discharge when a special condition occurs. A retriggerable monostable circuit that has a holding time of more than several tens of minutes and is capable of retriggering the output pulse of the ultraviolet detector tube due to the discharge of the ultraviolet detector tube caused by cosmic rays or radiation incident on the ultraviolet detector tube once every minute. The output signal is used to operate a display device such as a light emitting diode to indicate that normal operation is in progress.

As described above, the normal operation display device of the ultraviolet detection tube in the ultraviolet detection device of the present invention does not require any operation to confirm normal operation.
It checks the normal operation of the ultraviolet detection tube every few minutes and displays the results.It is especially useful for checking whether the ultraviolet detection tube is operating normally even after being in operation for a long time, such as in a fire alarm system. This is extremely effective for detection devices that use ultraviolet detection tubes, which are cumbersome.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an ultraviolet detection device equipped with a normal operation display device for an ultraviolet detection tube according to the present invention.
FIG. 2 is a diagram showing a monostable multivibrator circuit used in the monostable circuit 4 of FIG. 1. FIG. 3 is a block diagram of a monostable circuit in which a plurality of monostable multivibrators used in the monostable circuit 4 of FIG. 1 are connected.

Claims (1)

[Claims] 1 Ultraviolet detection tube circuit, an alarm means that is activated when the output pulse of the ultraviolet detection tube circuit is applied and the output pulse is applied continuously, a monostable circuit that is triggered by the output pulse of the ultraviolet detection tube circuit, and a monostable circuit. An ultraviolet detection device equipped with a means for indicating normal operation of an ultraviolet detection tube driven by a circuit.