JPS63159727A - Detector for quantity of infrared light - Google Patents

Abstract

PURPOSE:To detect the quantity of infrared light more accurately by generating and outputting an intermittent infrared-light quantity signal which is constant in period and duty ratio. CONSTITUTION:A clock from an oscillator 8 is supplied to 1st and 2nd frequency dividers 9 and 10 and the clock supplied to the frequency divider 9 is outputted as a constant-period pulse signal. A pulse motor 7 rotates a semicircular disk 2 by a constant angle every time the pulse signal is supplied. Thus, the intermittent light quantity signal (a) is supplied from an infrared-ray lamp 1 to a thermoelectric infrared-ray sensor 4. The sensor 4 converts the signal (a) into an AC electric signal and supplies it to an amplifier 5, which outputs a saw-tooth electric signal (b) to an actuation start integration type A/D converter 11. An operation start command signal is supplied from the frequency divider 10 to the converter 11. The converter 11 integrates the signal (b) by its internal integrator throughout an integration period T1 and then calculates the mean value of the signal (b). The period T1 is set shorter than a period wherein a duty ratio [signal (a)/period] is small so that the period T1 is not present on both positive and negative sides of the signal (b).

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an infrared light amount detection device, and in particular to an optical chopper that detects the amount of infrared light after converting infrared light to be measured into intermittent infrared light. The present invention relates to an infrared light amount detection device that enables even more accurate detection of the amount of infrared light in the type of infrared light amount detection device.

(Prior Art) Conventionally, a method using a phototransistor or a photodiode is generally well known for detecting the amount of light. However, the phototransistor, photodiode, etc. cannot be used to detect the amount of infrared light with a wavelength longer than 2 μm, and instead, thermal lightning infrared sensors such as pyroelectric infrared sensors or thermopile infrared sensors are used. be done.

This thermoelectric infrared sensor converts an amount of infrared light into an amount of heat, and outputs an electric signal corresponding to the amount of heat.

However, this thermal lightning type infrared sensor is affected by its surrounding temperature, etc., so if it simply supplies infrared rays, the electrical signal that is its output will not correspond to the amount of infrared light. Therefore, conventionally, when detecting the amount of infrared light using a thermoelectric infrared sensor, it is necessary to convert the infrared light to be measured into intermittent infrared light and supply it to the sensor. Note that the frequency of this intermittent infrared light is called a chopper frequency.

FIG. 2 is a block diagram showing an example of the conventional infrared light amount detection device described above. In the figure, 1 is an infrared lamp, 2 is a semicircular plate, 3 is a motor that rotationally drives the semicircular plate 2, 4 is a thermal lightning type infrared sensor, and 5 is an electric signal that is the output of the thermoelectric type infrared sensor 4. An amplifier 6 is a detection circuit that detects the output of the amplifier 5 using an analog method.

The operation of FIG. 2 will be explained below using the waveform diagram of FIG. 3.

When the semicircular plate 2 is rotationally driven by the motor 3, the light emitted from the infrared lamp 1 is converted into intermittent infrared light and supplied to the thermoelectric infrared sensor 4, as shown in FIG. 3(a). . The thermoelectric infrared sensor 4 outputs an electric signal corresponding to the intermittent infrared light to the amplifier 5. As a result,
The amplifier 5 outputs a sawtooth electrical signal as shown in FIG. 3(b). The detection circuit 6 performs, for example, full-wave rectification on the sawtooth electric signal, then smoothes it and outputs it as an average level. In addition, at the subsequent stage of the detection circuit 6,
Based on the average value level, various signal processing, such as displaying the amount of infrared light, is performed. Incidentally, in recent years, in order to improve the accuracy of the signal processing, it is common to perform the signal processing digitally. For this purpose, the average level is converted into a digital signal immediately after the detection circuit 6 outputs it.

(Problems to be Solved by the Invention) The above-described conventional techniques had the following problems.

(1) In order to obtain the average level with less ripple, the detection circuit 6 needs to integrate it with a time constant that is relatively large enough compared to the chopper frequency after rectification. However, when the time constant is increased in this way, the response characteristics of the circuit deteriorate, and an accurate average level, that is, the amount of infrared light cannot be obtained.

(2) As described above, the thermoelectric infrared sensor converts the amount of infrared light into the amount of heat and outputs an electric signal corresponding to the amount of heat, and therefore is affected by the heat capacity of the sensor itself. Therefore, in order to obtain a highly sensitive output electrical signal from a thermoelectric infrared sensor, it is desirable to lower the chopper frequency. However, considering the problem of the response characteristics (1) above, the chopper frequency cannot be made too low, and therefore, it is not possible to obtain a sufficiently sensitive output electrical signal.

(3) As mentioned above, in the latter stage of the detection circuit, the signal is digitally processed to improve the accuracy of the signal processing, but in the previous stage of the detection circuit, the average Since the value level is obtained, only data with poor accuracy can be obtained as a result.

(4) As is well known, analog detection circuits have many adjustment points (and are inefficient), which makes them expensive.

The present invention has been made to solve the above-mentioned problems.

(Means and operations for solving the problems) In order to solve the above problems, the present invention provides means for generating and outputting an intermittent infrared light amount signal with a constant period and duty ratio;
means for converting the intermittent infrared light amount signal into an alternating current electric signal; means for integrating a predetermined range of the alternating current electric signal at a fixed timing synchronized with the intermittent infrared light amount signal; and an output of the integrating means. The present invention is characterized in that a means for generating and outputting a digital signal according to the integral value is provided, and the planned range for integrating the AC electric signal does not extend over both the positive and negative sides of the AC electric signal.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

In the figure, the same reference numerals as in FIG. 2 represent the same or equivalent parts. 7 is a pulse motor, 8 is a transmitter,
9 is a first frequency divider that divides the output clock of the oscillator 8 and outputs a pulse signal for driving the pulse motor 7; 10 is activated by dividing the output clock of the oscillator 8; This is a second frequency divider that outputs an operation start command signal to the start integration type A/D converter 11.

The operation of this embodiment will be explained below with reference to FIG.

In FIG. 1, the clock output from the oscillator 8 is
It is supplied to the first and second frequency dividers 9.1o. The clock supplied to the first frequency divider 9 is frequency-divided here and output as a constant period pulse signal. Pulse motor 7
rotates the semicircular plate 2 by a certain angle each time the pulse signal is supplied. When the semicircular plate 2 rotates in this manner, an intermittent light amount signal is supplied from the infrared lamp 1 to the thermoelectric infrared sensor 4. FIG. 4(a) shows the intermittent light amount signal.

The thermoelectric infrared sensor 4 converts the intermittent light amount signal into an alternating current electrical signal and supplies it to the amplifier 5 .

As a result, the amplifier 5 outputs a sawtooth electrical signal as shown in FIG. 4(b). The electrical signal is then supplied to the start-up integral type A/D converter 11.

On the other hand, the second
An operation start command signal is supplied from the frequency divider 10. Fourth
Figure (c) shows the operation start command signal. The start-up integral type A/D converter 11 performs the following operations based on the supplied sawtooth electric signal (b) and operation start command signal (c). In this operation example, the start-up integral type A/D converter 11 is I
This is the case of CL7109.

The start-up integral type A/D converter 11 starts after a delay time of a certain time TO from the rise of the operation start command signal (c).
The sawtooth electric signal (b) is integrated in the internal integrator during an integration period T1. FIG. 4(d) shows the constant delay time TO and the integration period T1. Note that the integration period T1 is a fixed period. Next, the start-up integral type A/D converter 11 inputs into the integrator a constant voltage EO having a polarity such that its output becomes zero, thereby making the output of the integrator zero. This input period of the constant voltage EO is called an inverse integration period T. Thereafter, the average value of the sawtooth electric signal (b) in the integration period T1 is calculated from the calculation of (EOXT)/TI. Note that the start-up integral type A/D converter 1
The setting of each period in 1 is performed, for example, by counting a clock signal generated internally or supplied externally by known means. Therefore, the average value can be obtained accurately. Thereafter, the start-up integral type A/D converter 11 outputs the average value as a digital signal. Then, the next operation start command signal (c) is awaited.

By the way, as in this embodiment, the operation start command signal (C)
In the integration period T1 corresponding to the sawtooth electric signal (b), when integrating the sawtooth electric signal (b) and obtaining a digital signal based on this integral value, ) and the intermittent light amount signal (a) for forming the sawtooth electric signal (b) have the following relationship: set the frequency division ratios of the first and second frequency dividers 9 and 10. There is a need to. That is, the repetition period of the integration period T1 is set to be an integral multiple or a fraction of the period of the intermittent light amount signal (a), and
It is necessary to ensure that the integration period T1 does not extend over both the positive and negative sides of the sawtooth electric signal (b). Also, in order to prevent the integration period T1 from extending over both the positive and negative sides of the sawtooth electric signal (b), the integration period T1 must be set from the period of the intermittent light amount signal (a), which has a smaller duty ratio of one cycle. also needs to be shortened. In this embodiment, since the duty ratio of the intermittent light amount signal (a) is 50%, the integration period T1 is made shorter than the half period of the signal (a), and the repetition period of the integration period T1 is set to the intermittent light amount signal. The period is the same as in (a), and the integration period T1 is a sawtooth electric signal (
It is clear that we are trying not to straddle both the positive and negative sides of b).

Therefore, according to this embodiment, the latest infrared light amount value can be obtained for each integration period T1.

Further, according to this embodiment, it is possible to obtain a low chijippa frequency, so it is clear that an accurate infrared light amount value can be obtained. However, the average value obtained as a digital signal in this embodiment is not obtained by full-wave rectification and then smoothing of the sawtooth electric signal (b) as in the conventional example, so the value is different. . Therefore, in order to obtain the same average value as in the conventional example, it is necessary to take measures such as multiplying the obtained average value by a predetermined correction coefficient.

FIG. 6 is a block diagram showing a second embodiment of the invention. This second embodiment differs from the embodiment (first embodiment) shown in FIG.
A free-running integrating type A/D converter 11a is used instead of the converter 11, and a second frequency divider 1 outputs an operation start command signal.
The only difference is that a third frequency divider 10a which outputs the operation clock of the free-running integrating type A/D converter 11a instead of 0 is used.

The free-running integrating type A/D converter 11a of this embodiment is made into a free-running integrating type A/D converter by switching the operating state of the ICL7109 manufactured by Intersil, Inc. of the United States. Hereinafter, operating portions different from those in the first embodiment will be explained using FIG. 5.

The self-running integrating type A/D converter 11a uses a known method to
A repeating operation of a fixed self-running operation period synchronized with the intermittent light quantity signal supplied to the thermoelectric infrared sensor 4 is started. FIG. 5(a) shows a repeating state of the free-running operation period, and the high-level period is the free-running operation period. In each free-running operation period, the free-running integral type A/D converter 11a integrates the sawtooth electric signal output from the amplifier 5 after a certain delay time TO has elapsed from the start of the period. It has T1. FIG. 5(b) shows the delay time TO and the integration period T1.

Now, in this embodiment, when the intermittent light amount signal is the same as in the first embodiment, the period of the integration period T1, its repetition period, and its phase are set in the same way as in the first embodiment. , the free-running integrating type A/D converter 11a integrates the sawtooth electric signal in the same period and timing as in the first embodiment, calculates the average value of the integration period T1, and converts the average value into a digital signal. Output as . Then, it waits for a scheduled period of time until the start of the next self-propelled operation period.

By the way, when a sawtooth electric signal is integrated during the integration period T1 corresponding to the start of the free-running operation period and a digital signal is obtained based on this integrated value as in this embodiment, the same process as described above is performed. , the first and third frequency dividers 9 are arranged so that the repetition period of the integration period T1, the sawtooth electric signal and the intermittent light amount signal for forming the sawtooth electric signal have the following relationship. It is necessary to set the frequency division ratio of 10a and 10a. That is, the repetition period of the integration period T1 is set to be an integral multiple or a fraction of the period of the intermittent light amount signal, and the integration period T1 is
1 must not straddle both positive and negative sides of the saw-shaped electric signal.

Furthermore, in order to prevent the integration period T1 from extending over both the positive and negative sides of the sawtooth electric signal, it is necessary to make the integration period T1 shorter than the period with the smaller duty ratio of one period of the intermittent light amount signal. .

In this embodiment, as is clear from the above, the above relationship is set in the same manner as in the first embodiment.

Therefore, according to this embodiment, as in the first embodiment, it is possible to obtain the latest infrared light amount value for each integration period T1, and also to use a low chopper frequency, so that accurate infrared light can be obtained. A light intensity value is obtained. However, the average value obtained as a digital signal in this embodiment is different from that in the conventional example, as in the first embodiment.
In order to obtain the same average value as in the conventional example, it is necessary to take measures such as multiplying the obtained average value by a predetermined correction coefficient.

FIG. 7 shows an infrared light amount detection device similar to the embodiment (second embodiment) related to FIG.
on-DispersionInfra-Red G
FIG. 2 is a block diagram showing an example in which the present invention is applied to an NDIR gas analyzer (hereinafter referred to as an NDIR gas analyzer).

In the figure, the same reference numerals as in FIG. 6 represent the same or equivalent parts. Reference numeral 12 denotes a sampling cylinder through which the sample gas passes, and 13 an infrared bandpass filter whose passage wavelength band is set to an infrared wavelength that is absorbed by a specific gas component of the sample gas.

The operation shown in FIG. 7 will be explained below using FIG. 8.

When infrared rays are applied from the infrared lamp 1 to the sample collection tube 12 through which the sample gas is passed in the direction of arrow A to arrow B, there are different wavelengths of infrared rays passing through the tube 12 depending on the sample gas components. The light is absorbed by the sample gas component, the amount of light is reduced, and the sample is output from the sample collection tube 12. Note that the amount of infrared rays of a specific wavelength absorbed by a sample gas component is determined by the concentration of the gas component.

As described above, the infrared rays having a specific wavelength absorbed in accordance with the concentration of the gas component are supplied to the infrared bandpass filter 13 as an intermittent light amount signal by the rotation of the semicircular plate 2. The infrared bandpass filter 13 passes only infrared wavelengths of the intermittent light amount signal that are absorbed by a specific gas component of the sample gas. FIG. 8(a) shows the intermittent light quantity signal after passing through the infrared band pass filter 13. Thermal lightning type infrared sensor 4 converts the intermittent light intensity signal (a) into an alternating current electric signal and sends the signal to an amplifier 5.
supply to As a result, the output from the amplifier 5 is as shown in FIG. 8(b).
The saw-shaped electrical signal shown in is output. The electrical signal is then supplied to the free-running integrating type A/D converter 11a.

On the other hand, the free-running integrating type A/D converter 11a is supplied with an operating clock from the third frequency divider 10a. Accordingly, the free-running integral type A/D converter 11a changes the green return of the free-running operation period as shown in FIG. 8(C), and the integral period of each free-running operation period as shown in FIG. Set as shown. That is, in this example, the repetition period of the free-running operation period is set to 172 of the period of the intermittent light amount signal (a). Therefore, in this example, the self-running integrating A/D converter 11a integrates sections near the peak values on both the positive and negative sides of the sawtooth electric signal (b), and averages each section based on the integrated values. After that, the average value for each section is output as a digital signal.

In this example, the difference between the two positive and negative digital values is taken at the subsequent stage of the free-running integrating type A/D converter 11a to obtain an average value corresponding to one period of the intermittent light amount signal (a). As a result, in this example, even if the center line of the sawtooth electric signal (b) output from the amplifier 5 is biased with respect to the original center line position shown by the broken line B, the average value is not affected by the bias. can be obtained. However, this average value is twice the same average value in the first and second embodiments. Therefore, it is clear that in order to obtain the same average value as in the conventional example, it is sufficient to take measures such as multiplying the obtained average value by a corresponding planned correction coefficient.

According to this example, even if the center line of the sawtooth electric signal (b) is biased, it is possible to detect an appropriate amount of infrared light corresponding to the expected gas component of the sample gas without being affected by the bias. be.

FIG. 9 is a block diagram showing another example in which the infrared light amount detection device of the second embodiment is modified and applied to an NDIR gas analyzer.

In the figure, the same reference numerals as in FIG. 7 represent the same or equivalent parts. 13a to 13d are infrared bandpass filters 4a to 4d and 5a to 5d each having a pass wavelength band set to pass four infrared wavelengths absorbed by different gas components of the sample gas, respectively;
are thermoelectric infrared sensors and amplifiers provided corresponding to the infrared bandpass filters 13a to 13d, 14 is a changeover switch circuit for switching and transmitting the outputs of the amplifiers 5a to 5d, and 15 is a switch circuit of the transmitter 8. This is a frequency divider that divides the frequency of the output clock and supplies a switching signal to the changeover switch circuit 14. In this example, the semicircular plate 2, four infrared band pass filters 13a to 13d, and a thermoelectric infrared sensor 4a provided corresponding to these filters are used.
~4d are installed on concentric circles as shown in FIG.

The operation shown in FIG. 9 will be explained below using FIG. 11.

In this example, as can be easily understood from the explanation regarding FIG. Of the respective infrared wavelengths, only certain infrared wavelengths are allowed to pass through.

Therefore, the infrared bandpass filters 13a to 13d
As is clear from Fig. 10, Fig. 11(a)
Intermittent light amount signals (d), (g), and (j) are output, respectively. Thermal lightning type infrared sensors 4a to 4d convert the intermittent light intensity signals (a), (d), (g), and (j) into alternating current electrical signals, respectively, and supply the signals to amplifiers 5a to 5d. As a result,
From the amplifiers 5a to 5d, Fig. 11(b), (e), and (h)
Saw-shaped electrical signals shown in (k) are output. Is the selector switch circuit 14 a frequency divider? Each internal switch 14a to 1 is switched according to the switching signal supplied from 5115.
4d is selectively turned on. Figure 11(c)(f)
(L) (1) shows the on-state period of each of the switches 14a to 14d, where the high-level period represents the on-state period, and the 1 attached to the high-level period
The numbers 8 to 8 represent the order in which the switches 14a to 14d are turned on. Therefore, the self-running integral type A/D converter 11a receives saw-shaped electric signals (b), (e), and (h).
) (k), switches 14a to 1 according to the above order.
A signal for a period in which 4d is in the on state is supplied.

On the other hand, the free-running integral type A/D converter 11a repeats the free-running operation period as shown in FIG. 11(m), and the integration period in each free-running operation period is as shown in FIG. 11(n). is set to . That is, in this example, the self-running operation period is set to be repeated eight times in two periods of the intermittent light amount signal. Therefore, in this example, the self-running integral type A/D converter 11a converts sections near the peak values on both positive and negative sides of the sawtooth electric signals (b), (e), (h), and (k) into Each of the switches 14a to 14d is integrated in accordance with the order in which they are turned on, an average value for each section is determined based on the integrated value, and then the average value for each section is output as a digital value.

In this example, the difference between the two positive and negative digital values of each of the sawtooth electric signals is taken at the subsequent stage of the free-running integrating type A/D converter 11a, and the average value corresponding to one period of each intermittent light amount signal is calculated. I'm trying to get it. As a result, in this example, an effect similar to that described in connection with FIG. 7 can be obtained, and there is also an effect that the amounts of infrared light corresponding to the four gas components of the sample gas can be detected simultaneously.

In addition, in the above description, in each case, a sawtooth electric signal is integrated over a predetermined integration period to obtain an integral value, and based on the integral value, an average value of the sawtooth electric signal during the integration period is calculated. This was a case in which the average value was digitized and outputted, and the amount of infrared light was detected based on the digital average value through subsequent signal processing. However, in the present invention,
It is not necessarily necessary to do as described above; for example, the integral value is divided by one period of the sawtooth electric signal, the quotient is calculated, the quantity is digitized and output, and the digital quotient is obtained through subsequent signal processing. Alternatively, the integrated value may be digitized and output without averaging, and in subsequent signal processing, the infrared light amount may be detected based on the digital integrated value. Good too.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following effects are achieved.

(1) In the present invention, since the amount of infrared light is obtained without response delay based on the integral value obtained by integrating the scheduled period of the sawtooth electric signal, accurate amount of infrared light can be obtained.

(2) In the present invention, as a result of being able to use a low chopper frequency, it is possible to obtain a sufficiently sensitive output electrical signal, and therefore an accurate infrared light amount value can be obtained.

(3) In the present invention, since the amount of infrared light is obtained without using an analog type detection circuit which is significantly inferior in stability and accuracy, the accuracy of the obtained amount of infrared light is high.

(4) In the present invention, since there is no need to use an analog detection circuit that requires many adjustment points, work efficiency can be improved and the cost can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a block diagram showing an example of a conventional infrared light amount detection device, Fig. m3 is a waveform diagram for explaining the operation of Fig. 2, and Fig. 4 is the first
5 is a diagram for explaining the operation of FIG. 6, which will be described later. FIG. 6 is a block diagram showing the second embodiment of the present invention, and FIG. 7 is a diagram for explaining the operation of FIG. A block diagram showing an example in which an infrared light amount detection device similar to that of the second embodiment is applied to an NDIR gas analyzer, FIG. 8 is a diagram for explaining the operation of FIG. 7, and FIG. 9 is a diagram showing the operation of the second embodiment. A block diagram showing another example in which the infrared light amount detection device of the embodiment is modified and applied to an NDIR gas analyzer, FIG. 10 is a block diagram showing the semicircular plate of FIG.
A diagram showing the positional relationship between two infrared bandpass filters and thermoelectric infrared sensors provided correspondingly,
FIG. 11 is a diagram for explaining the operation of FIG. 9. 2... Semi-circular plate, 4... Thermal lightning type infrared sensor, 7...
- Pulse motor, ... Transmitter, 9... First frequency divider, 10... Second frequency divider, 10a... Third frequency divider, 11... Start-up start integral Type A/D converter, lla...
... Self-propelled integral type A/D converter Patent attorney Michito Hiraki and 1 other person Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Time closed 116 Figure 8 Time Figure 7

Claims (3)

[Claims] (1) means for generating and outputting an intermittent infrared light amount signal with a constant period and duty ratio; means for converting the intermittent infrared light amount signal into an alternating current electrical signal; and at a constant timing synchronized with the intermittent infrared light amount signal. , comprising means for integrating a predetermined range of the alternating current electrical signal, and means for generating and outputting a digital signal according to an integral value that is an output of the integrating means, the predetermined range for integrating the alternating current electrical signal is An infrared light amount detection device characterized in that it does not straddle both the positive and negative sides of an electrical signal. (2) The intermittent infrared light amount signal generation/output means includes a pulse motor, and means for converting the incident infrared light into an intermittent infrared light amount signal having a constant period and duty ratio by being rotated by the pulse motor and outputting the signal. An infrared light amount detection device according to claim 1, characterized in that: (3) The integrating means and the digital signal generation/output means are comprised of one of a start-up integrating type A/D converter and a free-running integrating type A/D converter. An infrared light amount detection device according to claim 1 or 2.