JPH0641884B2 - Radiation detector - Google Patents

Description

TECHNICAL FIELD The present invention is capable of accurately quantitatively detecting radiation power in a wide range from the ultraviolet wavelength range to the infrared wavelength range, and is compact and lightweight as a portable device. The present invention relates to a radiation detector used in an irradiometer.

Conventional technology It has been a long time for detecting radiation power (for example, mW · cm ^-2 unit). Thermocouples and thermopile (thermopile), which have black sensitivity on the light receiving surface and have no wavelength dependence in sensitivity, have been used. It was used, but these have a large zero point drift,
The response time (time constant) is also large. In addition, it was difficult to practically use because sufficient sensitivity could not be obtained.

Recently, a radiation detection element utilizing the pyroelectric effect has been developed as an alternative to these. The pyroelectric effect is an effect in which the magnitude of spontaneous polarization of a certain type of ferroelectric crystal changes with the temperature of the crystal. Pyroelectric radiation detector
By utilizing this effect, a temperature change of the element due to absorption of radiation of gold black attached to the light receiving surface is converted into an electric output. Therefore, the pyroelectric type radiation detection element responds only to the temperature change of the element, that is, the differential variation of the incident radiation,
There is no sensitivity to steady incidence (constant intensity that does not change with time), because the polarization charge generated by spontaneous polarization leaks. Therefore, the pyroelectric radiation detecting element is often used for detecting a transient change phenomenon such as a fire occurrence or a change in radiation by an intruder.

Problems to be Solved by the Invention When it is intended to measure the amount of stationary light with a pyroelectric radiation detection element, the rotating sector is usually driven by a motor or the like to modulate the input radiation, and the pyroelectric radiation at this time is then modulated. The amount of incident light is obtained by integrating the AC output of the detection element. Since the pyroelectric radiation detection element is a thermal radiation detection element, temperature noise and Johnson noise are relatively large with respect to the detection signal of the input radiation.
Therefore, in this case, the signal-to-noise ratio of the detector must be improved by using a lock-in amplifier with a synchronous detection circuit, which is synchronized with the modulation of the input radiation by the rotating sector. However, the device becomes complicated, precise, and large-scaled, and the acceptance angle is narrowed. Therefore, it is not suitable to construct a portable irradiance meter with the above device.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above conventional problems and provide a small, lightweight and portable radiation detector that quantitatively and accurately detects irradiance in a wide wavelength range from the ultraviolet region to the infrared region. .

Means for Solving the Problems A radiation detector of the present invention comprises a pyroelectric radiation detecting element, an optical shutter for intermittently inputting radiation to the pyroelectric radiation detecting element, and a pyroelectric radiation detecting element. And a full-wave rectifier that full-wave rectifies the voltage signal, and an integrator that integrates the output signal of the full-wave rectifier in synchronization with opening and closing of the optical shutter. To be done.

Operation According to the above configuration, irradiance in a wide wavelength range from the ultraviolet region to the infrared region can be quantitatively and accurately detected by opening and closing the optical shutter once.

Example Hereinafter, as an example of the present invention, an output signal from a pyroelectric type radiation detection element is full-wave rectified and integrated in synchronization with an optical shutter that intermittently interrupts the input radiation to the pyroelectric type radiation detection element. An embodiment of the radiation detector is shown using the drawings.

FIG. 1 shows the configuration of the radiation detector of this embodiment. In the figure, 1 is a light source for giving radiation to be measured, 2 is a pyroelectric type radiation detection element, 3 is an optical shutter, 4 is an optical shutter 3
A shutter drive device 5 for opening and closing is a preamplifier for converting the photoelectric output from the pyroelectric radiation detection element 2 into a voltage signal,
6 is a full-wave rectifier for full-wave rectifying the voltage signal from the preamplifier 5 in synchronization with the optical shutter 3, 7 is an integrator for integrating the output signal of the full-wave rectifier 6 in synchronization with opening and closing of the optical shutter 3, Reference numeral 8 is a sample-hold circuit for holding the value at the end of the integration by the integrator 7, and 9 is a display device for displaying the hold value of the sample-hold circuit 8. Further, 10 is a first single-shot circuit that gives a signal synchronized with the opening of the optical shutter 3 to the full-wave rectifier 6 and the integrator 7.
Reference numeral 1 is a second single-shot circuit which gives a signal synchronized with the closing of the optical shutter 3 to the full-wave rectifier 6 and the integrator 7.

The operating principle of the above device is shown below. The pyroelectric radiation detection element 2 emits light E (t), which has a small temporal change as shown in FIG.
Incident on. At this time, when the optical shutter 3 is opened and closed with a time characteristic of Q (t), light of q (t) enters the pyroelectric radiation detecting element 2. In this case, the change q (t) of the incident light is as shown in FIG. 3 and expressed by the following equation.

q (t) = E (t) · Q (t) (1) The pyroelectric radiation detection element 2 is used to differentiate the incident light q (t) as shown in FIG. 4 (a). It produces a proportional output voltage R (t). R
(t) is expressed by the following equation.

R (t) = dq / dt (2) This output fluctuation is transient, and since it is a differential value, the voltage amplitude is not proportional to the incident intensity, so this voltage value Does not measure the amount of incident light. Here, when this differential voltage R (t) is integrated by an integrating circuit, an output S (t) proportional to the incident light q (t) is obtained by the integration. That is, This is shown in FIG. 4 (b). The amplitude of this restored signal is E (t)
It becomes proportional to (average of values between t ₁ and t 2 in FIG. ₂ ). Actually, this integration is performed by charging a capacitor or the like, but since the charge is gradually discharged and attenuated, it is held by the sample hold circuit 8 immediately after the end of the integration (t ₂ ).

In this device, the shutter opening time Δt = | t ₂ −t ₁ | is set sufficiently larger than the time constant of the differential response of the pyroelectric type radiation detection element 2.

When the integrator 7 integrates the differential signal from the preamplifier 5, the differential signal is full-wave rectified by the full-wave rectifier 6 as shown in FIG. At this time, the rising signal is integrated and shown in FIG.
As shown in (b), when the amplitude is held and the integration of the falling signal whose sign is inverted by full-wave rectification is superimposed on it, the amplitude becomes about twice, and the detection efficiency of the radiation detector is doubled. Can be

The shutter driving device 4 interlocks with the optical shutter 3 and outputs pulse signals of durations δt ₁ and δt ₂ through the first single shot circuit 10 and the second single shot circuit 11 when the shutter is opened and closed, respectively. generate. This waveform is shown in FIG.

In FIG. 6, (a) is the opening / closing drive waveform of the optical shutter, (b)
Is the output waveform of the first single-shot circuit 10, (c) is the output waveform of the second single-shot circuit 11, and (d) is the output waveform of the full-wave rectifier 6.

The pulse widths of δt ₁ and δt ₂ are each set to be larger than the duration of the differential signal of the pyroelectric radiation detection element 2. Full wave rectifier 6
Performs full-wave synchronous rectification by opening and closing the gate according to the rise and fall of the shutter synchronizing signals δt ₁ and δt ₂ . By synchronous rectification, noise input other than the differential signal, that is, the output signal of the pyroelectric radiation detection element 2 can be removed. This full-wave rectified output goes to the next stage integrator 7 and is restored to the source signal. Similarly, the integrator 7 also opens and closes the gate by the rise and fall of the shutter synchronizing signals δt ₁ and δt ₂ to eliminate an error due to a leakage current or the like.

The output of the end of integration of the integrator 7 is held in its amplitude by the next sample hold circuit, and its value is displayed on the display device 9. The display of the display device 9 is C · q (t), which indicates the temporal average of the input radiation during the shutter opening time period.

The measurement can be repeated any number of times by opening and closing the shutter at any time. Further, even if there is a variation in the operation of the shutter, if Δt is sufficiently large, the differential signal can be captured completely, so the integrated value, that is, the measured value does not change.

Calibration of measured values may be performed, for example, by using a light bulb of known radiation amount and opening and closing the shutter in front of it, and measurement of dark input may be performed in front of a dark curtain at the same temperature as the ambient temperature. Good.

The optical shutter is generally much lighter and thinner than a motor-driven rotating sector, and the angle of incidence from the pyroelectric radiation detecting element, which is a light receiving element, can be set larger than that of the rotating sector. . Further, unlike the rotating sector, it is not necessary to drive it constantly, and since the opening / closing operation is limited to only during measurement, power consumption is small. For this reason, the radiation detector using the pyroelectric radiation detection element and the shutter has excellent characteristics even for portable use.

EFFECTS OF THE INVENTION The present invention converts a photoelectric output from a pyroelectric type radiation detection element, an optical shutter for intermittently inputting radiation to the pyroelectric type radiation detection element, and a photoelectric output from the pyroelectric type radiation detection element into a voltage signal. The preamplifier, the full-wave rectifier for full-wave rectifying the voltage signal of the pre-amplifier, and the integrator for integrating the output signal of the full-wave rectifier in synchronization with opening and closing of the optical shutter have the following effects.

(1) An irradiance type that quantitatively and accurately detects irradiance in a wide wavelength range from the ultraviolet region to the infrared region can be configured by opening and closing the optical shutter once.

(2) When full-wave rectifying the signal, the gate signal is opened / closed by the rising and falling of the synchronizing signals δ ₁ t and δ ₂ t when the shutter is opened / closed to perform full-wave synchronous rectification. A noise input other than the output signal of the type radiation detection element can be eliminated, and radiation with a good SN ratio can be measured.

(3) The shutter is generally much lighter and thinner than the motor-driven rotating sector, and the angle of incidence from the pyroelectric radiation detection element, which is the light receiving element, can be set larger than that of the rotating sector. it can.

(4) The shutter does not have to be constantly driven like the rotating sector, and the opening and closing operations are limited to only during measurement, so power consumption is low. For this reason, the radiation detector using the pyroelectric radiation detection element and the shutter is small and lightweight, and has excellent characteristics even for portable use.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a radiation detector in one embodiment of the present invention, FIG. 2 is a diagram showing temporal changes of light incident on the radiation detector, and FIG. 3 is incident on a pyroelectric radiation detection element. FIG. 4 (a) shows the response output of the pyroelectric radiation detection element, and FIG. 4 (b) shows the response output of the pyroelectric radiation detection element integrated by an integrating circuit. Figure 5 shows the waveform
(a) and (b) are output waveform diagrams of full-wave rectifier and integrator, Fig. 6
(a)-(d) is a figure which shows the output pulse waveform of a 1st and 2nd single shot circuit. 1 ... Light source, 2 ... Pyroelectric radiation detection element, 3 ... Optical shutter, 4 ... Shutter drive device, 5 ... Preamplifier, 6 ... Full-wave rectifier, 7 ... Integrator, 8 ... ... Sample-hold circuit, 9 ... Display device, 10 ... first single-shot circuit, 11 ... second single-shot circuit.

Claims (1)

[Claims] 1. A pyroelectric type radiation detecting element, an optical shutter for intermittently inputting radiation to the pyroelectric type radiation detecting element, and a front end for converting a photoelectric output from the pyroelectric type radiation detecting element into a voltage signal. An amplifier, a full-wave rectifier for full-wave rectifying the voltage signal of the preamplifier, and an output signal of the full-wave rectifier to start integration in synchronism with opening and closing of the optical shutter. An integrator that integrates with an integration time larger than the duration of the photoelectric signal is provided, and when the optical shutter is opened or closed,
The integrated value of the photoelectric output of the pyroelectric type radiation detection element when the optical shutter is opened and the integrated value of the photoelectric output of the pyroelectric type radiation detection element when the optical shutter is closed are combined, and the measured light A radiation detector that outputs as energy.