JPS6153760B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal processing circuit for an ionization smoke detector.

Conventional ionization smoke detectors apply a square wave voltage to the ion chamber, but because the ion chamber has a capacitor-like structure, spike voltages are generated when the voltage rises and falls superimposed on the output signal. Compensation adjustment for this spike voltage was necessary. In addition, since the magnitude of the output signal is constantly monitored, there is a risk of false alarms due to continuous noise, and because of analog signal processing, there is a risk of reliability as it is not completely stable against changes in the surrounding environment. There were some disadvantages.

The present invention was made in view of the above-mentioned drawbacks, and its purpose is to facilitate signal processing by removing spike voltages generated by the ion chamber, and to check the magnitude of the signal in a pulse manner. The present invention provides a highly reliable signal processing circuit for an ionization type smoke detector that performs digital processing and has good characteristics against noise and against the surrounding environment.

The present invention will be explained in detail below using examples. FIG. 1 shows a circuit configuration diagram of one embodiment. Reference numeral 1 denotes an oscillation circuit for generating a basic signal, and this oscillation circuit 1 inputs an oscillation output to a waveform generation circuit 2. In FIG. The waveform generating circuit 2 has three sets of output terminals A, B, and E, and the output terminal A connected to the electrode of the ion chamber 3 outputs a square wave voltage signal shown in FIG. A square wave voltage is applied between the electrodes of bar 3. Further, from the output terminal B connected to the gate of the field effect transistor FET ₁ connected between the output terminal of the amplifier 4 for amplifying the output signal of the ion chamber 3 and ground, a second A square wave signal of the same polarity whose falling point is delayed from that of the square wave signal shown in FIG. a is output. Further, from the output terminal E connected to the gate of the field effect transistor FET ₂ connected in series to the output terminal of the amplifier 4 via the integrating circuit 6, a second
A pulse signal having a width corresponding to the delay time width between the signal in FIG. 2a and the signal in FIG. 2b is output. The waveform generating circuit 2, the field effect transistors FET ₁ and FET ₂ , and the integrating circuit 6 constitute a sampling circuit section 7, and the output signal of the ion chamber 3 is outputted via the amplifier 4. It is controlled by the signal at end B and is output with negative polarity as shown in FIG. 2c, thereby eliminating the spike voltage. The signal shown in Fig. 2c is integrated by the integrating circuit 6, and when there is no smoke, the integrated output is shown as the solid line shown in Fig. 2d, and when there is smoke, the integrated output is shown as the dashed line in the same figure. An integral output is obtained, and this integral output is sampled by the signal at the output terminal E and extracted as a pulse signal having an analog voltage value as shown in FIG. 2f. This extracted signal is output to the voltage-gate time conversion circuit 8. This voltage-gate time conversion circuit 8 generates a gate time proportional to the input analog voltage value, and outputs the reference clock q for only this gate time.The reference clock output during the gate time is The number of reference clocks is counted by a counting circuit 9 consisting of a stage counter and a latch. When the counted value exceeds a preset value, the counting circuit 9 outputs and holds the detection signal. Thus, this counting circuit 9 and the voltage -
The gate time conversion circuit 8 constitutes a detection circuit section 10 . FIG. 2g shows input signals A and B of the voltage-gate time conversion circuit 8 in the absence of smoke, and input signals C and D of the voltage-gate time conversion circuit 8 in the presence of smoke. Further, 5 in the figure is a radiation source.

Note that instead of the voltage-gate time conversion circuit 8, a voltage-frequency conversion circuit that outputs a number of pulse signals proportional to the analog voltage value is used, the number of pulses for a certain time is counted, and this counted value and the set value are calculated. Of course, you can also compare them.

Since the present invention is configured as described above and is provided with a sampling circuit section, it is possible to remove the spike voltage superimposed on the signal output from the ion chamber, eliminating the need for compensation adjustment for the spike voltage. It has the effect of being easy to process, and since it checks the signal size in pulses and processes the signal digitally, it has good characteristics against noise and the surrounding environment, and is highly reliable. It has the effect of improving.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a waveform diagram of each part of the same. 3 is an ion chamber, 7 is a sampling circuit section, and 10 is a detection circuit section.

Claims (1)

[Claims] 1. The output signal of the ion chamber is extracted and integrated for a period from the rising point of the square wave voltage applied to the ion chamber to a predetermined point slightly delayed from the falling point, and during the integral output, the falling point of the square wave voltage is detected. a sampling circuit section that extracts only the signal from up to the predetermined time point; and a detection section that proportionally converts the analog voltage of the signal extracted from the sampling circuit section into a pulse number and compares and detects the counted value of the pulse number with a set value. 1. A signal processing circuit for an ionization smoke detector, comprising a circuit section.