GB2182435A - UV sensor device - Google Patents

Abstract

A sensor device for detecting UV rays from a fire includes a discharge tube 1, a counter 3, a pulse generator 4, and a D/A converter 6 or a parallel-to-serial converter 5. The presence of UV rays causes the discharge tube 1 to discharge and produce pulses which are counted by counter 3. At fixed intervals the pulse generator decrements the count value of the counter by one by triggering both the count (C) and the up/down (UD) inputs. The converter 6 outputs a signal corresponding to the count value of the counter. <IMAGE>

Description

SPECIFICATION Sensor device The present invention relates to a sensor device for detecting ultraviolet rays or the like generated by a fire and which causes a discharge tube to discharge and in particular though not exclusively, to a sensor device which continuously detects the scale of a fire.

The invention also extends to sensors which incorporate tubes (e.g. Geiger-Muller tubes) sensitive to other forms of ionizing radiation.

In a conventional sensor device of this type, as shown in Fig. 3 of the accompanying drawings, a voltage generated by a high-voltage generator 2 comprising a voltage booster is applied to an ultraviolet discharge tube 1 via a resistor R, and a charging capacitor C,.

When the discharge tube 1 is irradiated with ultraviolet rays generated by a fire, local ionization occurs and an avalanch phenomenon causes discharge of the capacitor C,. However, since the impedance of the high voltage generator 2 is high, the voltage applied to the discharge tube 1 immediately falls below the discharge threshold voltage by discharge of the capacitor C1, and discharge is stopped.

When ultraviolet rays are continuously present, an output waveform as shown in Fig. 4 of the accompanying drawings appears at a resistor R2.

This output turns on a switch circuit 10 via a waveshaper 6 (e.g. a monostable multivibrator), an integrator 7, and a level detector 8 to generate an alarm signal.

In order to extract an output of such a conventional sensor device as an analog output corresponding to the intensity of ultraviolet rays, an output signal of the integrator 7 in Fig. 3 can be used. However, when the intensity of ultraviolet rays increases and the capacitor is frequently discharged, the magnitude of the discharge pulse differs from that of the output voltage of the high voltage generator, as shown in Fig. 4. In the circumstances the capacitor C1 is only partially charged to a different peak value. When the waveshaper 6 is used to control the peak value and pulse width, as shown in Fig. 3, a discharge pulse generated within the pulse width is omitted, and the intensity of ulraviolet rays cannot be sequentially extracted as linear analog outputs.

According to one aspect of the present invention, there is provided a sensor device comprising a discharge tube for detecting ultraviolet rays or the like generated by a fire and for discharging, a counter for counting a pulse output generated by the discharge tube, a pulse generator for decrementing a count value of the counter by one at a predetermined period, and converting means for outputting a signal corresponding to the count value of the counter.

By way of example only, one specific embodiment of sensor device will now be described in detail, reference being made to the accompanying drawings in which: Figure 1 is a circuit diagram of an embodiment of a sensor device; Figure 2 is a timing chart for the embodiment of Fig. 1; Figure 3 is a circuit diagram of a conventional sensor device; and Figure 4 is a timing chart showing a waveform of an important portion in Fig. 3.

Fig. 1 shows a sensor device according to an embodiment of the present invention, and Fig. 2 shows a timing chart for explaining the operation of the circuit in Fig. 1. In Fig. 1, a discharge tube 1 comprises e.g. an UV discharge tube. A high voltage is applied between the anode and cathode of the discharge tube 1 via a high-voltage generator 2 and a charging capacitor C,. A discharge pulse is extracted from a resistor R2 which is connected to the cathode K.

Reference numeral 3 denotes an n-bit up/ down counter, and the cathode electrode K of the discharge tube 1 is connected to a count terminal C of the up/down counter 3 via an inverter IC, and one input terminal of a NAND gate IC2. An output of a pulse generator 4 is supplied to the other input terminal of the NAND gate IC2 via one input terminal of the NAND gate IC3, and is connected to up/down input terminal U/D of the counter 3. Outputs of respective output terminals Co to Qn of the up/down counter 3 are supplied to the other input terminal of the NAND gate IC3 via an OR gate IC4. When an output of the up/down counter 3 is zero, the OR gate IC4 prevents the up/down counter 3 from further decrementation.

An output of the up/down counter 3 is a binary digital signal and may be transmitted as a serial signal to a receiver (not shown) via a parallel-to-serial converter 5. Alternatively, in order to obtain an analog output value, an output of the up/down counter 3 can be supplied to a D/A converter 6.

The operation of this sensor device will now be described.

When ultraviolet rays are not present or are very weak, the discharge tube 1 applied with a high voltage does not discharge, and a pulse output of the pulse generator 4 is not applied to the count terminal C of the up/ down counter 3. The pulse generated by the pulse generator 4 is a pulse with a small duty ratio as designated by reference symbol P in Fig. 2. The pulse generator 4 oscillates at a predetermined period T.

Upon generation of a fire or the like, when a pulse as designated by reference symbol K in Fig. 2 is generated at the cathode K of the discharge tube 1, a pulse as designated by reference symbol C in Fig. 2 is applied to the count terminal C of the counter 3, and binary digital signals as designated by reference sym bols Qo to Qqn in Fig. 2 appear at the output terminals QO to C0 of the up/down counter 3.

A NAND output of outputs of the OR gate IC4 and the pulse generator 4 is supplied to the up/down input terminal U/D of the up/down counter 3. When the voltage is at low level, as designated by reference symbol U/D in Fig.

2, and a signal of high level is supplied to the count terminal C, the up/down counter 3 is decremented by one. Therefore, when no output is present at the output terminals QO to C0 of the up/down counter 3, i.e., at the OR gate IC4, the up/down counter 3 is no longer decremented. The number of bits of the output of the up/down counter 3 is determined in accordance with the number of discharge tube 1 generated within the output pulse period T of the pulse generator 4.

Reference symbol A in Fig. 2 denotes a graph showing analog values converted from digital values of the up/down counter 3, obtained in the manner described above.

In this embodiment, the n-bit up/down counter 3 is used; however, other up/down counters can be used to perform the same operation.

This embodiment has been described in particular relation to a sensor device for detecting ultraviolet rays generated by a fire, however, it is obvious that a sensor device such as a Geiger-Mulier tube for detecting radiation from which a discharge pulse corresponding to a detecting parameter is obtained can operate in the same manner.

The described embodiment of sensor device of the present invention can extract relatively linear analog outputs representing the intensity of ultraviolet rays of the like generated by a fire. In addition, since a digital processing circuit is used, the constituent components are free from temperature drift and deterioration over time.

Claims (7)

1. A sensor device comprising a discharge tube for detecting ultraviolet rays or the like generated by a fire and for discharging, a counter for counting a pulse output generated by said discharge tube, a pulse generator for decrementing a count value of said counter by one at a predetermined period, and converting means for outputting a signal corresponding to the count value of said counter.

2. A sensor device according to claim 1, wherein said counter comprises an n-bit up/ down counter having an up/down terminal, a count terminal and output terminals, and said converting means is a D/A converter which receives an output of a predetermined number of bits from said n-bit up/down counter and outputs an analog signal.

3. A sensor device according to claim 1, wherein said counter comprises an n-bit up/ down counter having an up/down terminal, a count terminal, and n output terminals, and said converting means is a parallel-to serial converter which receives a predetermined number of bits from said n-bit up/down counter and outputs a serial digital signal.

4. A sensor device according to claim 2 or claim 3, further including: an n-input OR gate, having input terminals to which are respectively connected said n output terminals; a first NAND gate, a first input terminal of which is connected to an output terminal of said n-input OR gate, a second input terminal of which is connected to an output terminal of said pulse generator, an output terminal of which is connected to said up/down terminal; and a second NAND gate, a first input terminal of which is connected to an inverted output from said discharge tube, a second input terminal of which is connected to an output terminal of said first NAND gate, and an output terminal of which is connected to said count terminal.

5. A sensor device according to claim 4, wherein said predetermined number of bits is determined in accordance with the number of discharge pulses generated within said predetermined period of said pulse generator.

6. A sensor device substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.

7. Any and all of the novel features or combinations thereof disclosed herein.