JPS5930204B2 - A device that converts the amount of light into a digital amount of electricity - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for converting the amount of light into a digital amount of electricity, and in particular, a photometric amount conversion device that eliminates temperature effects in photoelectric conversion elements, amplifiers, etc., and provides a digital amount that is correctly proportional to the amount of incident light. Regarding.

For example, in devices such as spectrophotometers that use light to analyze samples, the amount of light is converted into electrical signals by photoelectric conversion means (e.g., phototubes, photoconductive cells, etc.), and then processed by electrical signal processing. For example, the transmittance and absorbance of a sample are determined. However, with the development of digital technology in recent years, it is sometimes more convenient to handle the electrical signal processing described above in digital quantities rather than in analog circuits.
Photometric conversion, which converts photometric quantities into digital quantities, has come to be widely used. In such a case, an analog-to-digital converter (hereinafter abbreviated as an AD converter) is used that converts the analog electrical signal amount from the photoelectric conversion means described above into a digital amount. Counting type and comparison type converters are widely used as A-D converters, depending on the required accuracy and simplicity of the circuit, but in either case, in order to handle the amount of light, an absolute value proportional to the amount of light is used. It is necessary to obtain the digital quantity of Furthermore, especially in absorbance measurement of high concentration samples, Raman spectroscopy, fluorescence spectrophotometry, etc., a wide dynamic range is required, and even weak light needs to be converted with excellent linearity. From this point of view, the photometric quantity conversion using the A-D converter, which has been conventionally used, has several disadvantages as described below. In particular, when dealing with weak light, excellent linearity in the weak signal range is required, but linearity is generally required in the voltage-frequency converter, which is often used in A-D converters, where the input is small. There are many bad things.

Furthermore, in the case of weak light, the input signal to the AD converter may contain a lot of noise due to noise generated by the photoelectric conversion element itself, noise in peripheral circuits, and the like. On the other hand, an A-D converter that handles positive electrical signals ignores electrical signals that are below zero level and contains a lot of noise, so it is not correctly proportional to the amount of light. Digital quantities cannot be obtained. In addition, when comparing the sawtooth voltage and the input voltage and measuring the time until they match, such as with a one-time voltage conversion type A-D converter, or when inputting the voltage after integrating the input voltage with an integrator for a certain period of time, If the method of applying a reference voltage of opposite polarity to the integrator and measuring the time until the output voltage returns to the reference level does not work, the input signal may fall to zero level during A-D conversion due to noise etc. If the level does not exceed 1, the level detector does not operate, which is extremely inconvenient. Above ↓ Una A-
In addition to the problems with the D converter, there were also some problems caused by the photoelectric conversion means.

For example, in phototubes and photomultiplier tubes, there is an undesirable DC signal component such as dark current that is added to the signal amount proportional to the amount of light, and furthermore, this undesirable DC signal component is dependent on temperature etc. Since the amount changes, it has been difficult to obtain a digital amount proportional to the amount of light.
Furthermore, in the case of weak light, the offset voltage of the amplifier that amplifies the electrical signal from the photoelectric conversion element and its temperature drift also have a serious adverse effect. Furthermore, in a photoconductive element such as a PbS cell, the change in dark resistance due to temperature is extremely large, 20 to 30% for a temperature change of 10°C, and the DC signal level changes significantly along with the sensitivity, making it difficult to perform correct digital photometry. It was extremely difficult to obtain quantities. The present invention has been made for the purpose of solving the above-mentioned disadvantages in the prior art and providing a photometric amount conversion device that eliminates temperature effects and obtains a digital amount that is accurately proportional to the amount of incident light.

The gist of the present invention is to provide a means for blocking the light of the measurement object that enters the photoelectric conversion means, and a means for irradiating the photoelectric conversion means with a constant amount of light regardless of the blocking means, and further, the blocking means The amount of digital signal obtained at the step where light is blocked and the amount of digital signal obtained at the step where light is not blocked are subtracted by the digital amount, and the amount of light added by the constant light amount irradiation means is 1cif! A: To kill. The present invention will be described in detail below based on a preferred embodiment of the present invention.

FIG. 1 is a functional explanatory diagram showing a preferred embodiment of the present invention.

A photoelectric conversion means 10 consisting of a photoelectric conversion element 12 such as a photomultiplier tube, an amplifier 14, a power supply to the photoelectric conversion element 12 (not shown), etc. detects incident light and converts the amount of light into an amount of electricity such as voltage. and input it to the A-D converter 30. A-
D converter 30 converts the input voltage into a digital quantity and provides it to digital storage device 40 . On the other hand, the light beam 50 to be measured out of the light incident on the photoelectric conversion element 12 is blocked by a shutter 54 driven by a drive device 52 composed of, for example, a rotary solenoid or a motor. In FIG. 1, the light beam 50 is not blocked at the position of the shutter 54 shown by the solid line, and the light beam 50 is blocked at the position shown by the dotted line. Further, the light from the light source 90 irradiates the photoelectric conversion element 12 with a constant amount of light regardless of the position of the shutter 54. Therefore, at the position where the shutter 54 is indicated by a dotted line, only a constant amount of light from the light source 90 is incident on the photoelectric conversion element 12, and at the position where the shutter 54 is indicated by a solid line, the constant amount of light from the light source 90 and the measurement target are incident on the photoelectric conversion element 12. light 5
0 enters the photoelectric conversion element 12. Whether or not the shutter shutter 54 is blocking the light 50 to be measured is determined by the driving device 52 or a shutter position detector (not shown), and the discrimination signal generating device 56 is driven.
The discrimination signal generator 56 sends a signal indicating whether or not the shutter 54 is blocking the light 50 to be measured to the address register 6.
0, the address register 60 controls the storage address of the digital storage device 40 based on the signal, and the address register 60 controls the storage address of the digital storage device 40 based on the signal.
The digital photometric signals inputted from the converter 30 are stored in different addresses of the digital storage device 40 depending on whether or not the light 50 to be measured is in a blocked state.
The digital calculation device 70 reads out the photometric digital signal S in which the light 50 to be measured is not blocked and the photometric digital signal z in which the light 50 to be measured is blocked, which are stored in the digital storage device 40, and outputs (S-Z). The result is output to and displayed on the display device 80. According to one embodiment of the present invention, the digital quantity (S-Z) obtained from the digital arithmetic unit 70 is obtained by canceling the constant light amount signal added by the light source 90 or the offset voltage added to the photometric signal in the amplifier 14 or the like. However, it is possible to obtain a digital absolute value proportional to the amount of incident light.

Since the amount of light incident on the photoelectric conversion element 12 is always larger than the constant amount of light from the light source 90, the voltage input to the A-D converter 30 is a voltage above a certain level even if the light to be measured is weak light, and as described above. It is possible to eliminate malfunctions when the A-D converter is input at low levels, and the A-D converter 30 can always be operated in a region with good linearity, so the light 50 to be measured is extremely weak. Even in such cases, it is possible to stably obtain a digital amount that is faithfully proportional to the amount of light. In addition, the photometric value converted into a digital quantity by the A-D converter 30 includes the dark current of the photoelectric conversion element 12, which occurs regardless of whether or not the light 50 to be measured is blocked. Although the offset voltage of the amplifier 14 is included, it is also possible to obtain the feature that these quantities are canceled out during subtraction in the digital arithmetic unit 70. Furthermore, the shutter 54 is a member that blocks only the light to be measured 50, and in addition to the constant light from the light source 90, it also detects undesirable leakage light that enters from the outside through a light shielding part (not shown) as a constant light amount. incident on the vessel.

Therefore, it is possible to obtain the feature that these undesirable amounts of leaked light are also canceled out by the subtraction in the digital arithmetic unit 70. FIG. 2 is a circuit explanatory diagram showing an embodiment of an A-D converter which is a component of the photometric amount converter according to the present invention, and the A-D converter circuit is a so-called double integral type A-D converter. A vessel is used. Analog input A of photoelectric conversion means
ln passes through a resistor R1 and is integrated by an integrator 31. After integrating the input voltage to the integrator 31 for a certain period of time, the control circuit 33 switches the switch SWl to control the integrator 31 by the voltage supplied to the integrator 31 from the constant voltage source 32 having the opposite polarity to the input voltage through the resistor R3. Inversely integrate. The comparator 34 detects that the analog input voltage integrated by the integrator 31 returns to zero potential through inverse integration at a constant rate by the constant voltage source 32, and generates a signal. The gate 36 opens only while the integrator 31 is inversely integrating according to the signals from the control circuit 33 and the comparator 34, and sends a constant frequency clock pulse from the oscillator 35 to the counter 37. Digital output D proportional to analog input voltage by counting clock pulses. You can get ut. In the embodiment shown in FIG. 2, the offset voltage at the amplifier and comparator 34 used in the integrator 31 is constant regardless of whether or not the light 50 to be measured from the light source conversion means 10 is blocked. , can be canceled in subtraction after digital conversion. FIG. 3 is a functional explanatory diagram showing another embodiment of the present invention.

The same reference numerals as in FIG. 1 indicate the same parts, and description thereof will be omitted. The light 50 to be measured is interrupted by a chopper 100, the amount of light is converted into an electrical signal such as a voltage by a photoelectric conversion means 10, and the converted signal is input to an AD converter 30. An A-D converter 30 converts the input voltage into a digital quantity and stores it in a digital storage device 40.
give to On the other hand, the Chiyotsuba 100 has a part that blocks the light 50 to be measured and a part that transmits it, as shown in FIG. Intermittent at regular intervals. This intermittent state is between the light source 104 and the phototransistor 106.
A discrimination signal indicating whether the light is blocked or not is sent to the address register 60. The address register 51 is, for example, a flip-flop circuit, and controls the storage address of the digital storage device 40 based on the discrimination signal. The data are stored in different addresses of the digital storage device depending on whether the data is present or not. Of the photometric signals stored in the digital storage device 40, the digital calculation device 70 reads out a photometric digital signal S in which the light 50 is not blocked and a photometric digital signal Z in which the incident light is blocked,
Performs subtraction of S-Z and outputs the result. In this way, the digital quantity (S
-Z) can cancel out the voltage added from the light source 90 or the offset voltage added to the photometric signal by the amplifier 14, etc., and obtain a digital absolute value proportional to the amount of incident light, and the result can be displayed on a display device, for example. 80 etc. The input voltage to the A-D converter 30 is input to the amplifier 11.
Since it is a voltage obtained by adding a constant voltage to the output voltage of 0 by the adder 20, it can be operated in a region with good linearity even with the A-D converter 30, and a digital amount that is faithfully proportional to the amount of incident light can be obtained. be able to. Digital storage device 40 and address register 6 in each of the above embodiments
0. The digital arithmetic device 70 can be easily achieved by using, for example, a digital calculator.

As described above, according to the present invention, it is possible to obtain a digital quantity with an absolute value that is linearly proportional to the amount of incident light, and furthermore, it is possible to eliminate undesirable direct current components generated by photoelectric conversion means and their temporal fluctuations. It is possible to operate the A-D converter stably, and the influence of undesirable interfering light such as external leakage light can be removed.

[Brief explanation of the drawing]

FIG. 1 is a functional explanatory diagram showing a preferred embodiment of a device for converting a light quantity into a digital electrical quantity according to the present invention, and FIG. 2 shows an embodiment of an A-D converter which is a component of the present invention. FIG. 3 is a functional diagram showing another embodiment of the present invention, and FIG. 4 is a front view showing an example of a light blocking means which is another component of the present invention. 10...Photoelectric conversion means, 30...A-
D converter, 40...Digital storage device, 54
...Shutta, 70...Digital arithmetic device, 90...Light source, 100...Chiyotsupa.

Claims (1)

[Claims] 1. A first means for converting incident light into an electrical signal, a second means for converting the electrical signal outputted by the first means into a digital quantity, and a method for converting the light to be measured that is incident on the first means. a third means for blocking, a fourth means for irradiating a certain amount of light to the first means without being blocked by the third means, and a fourth means for irradiating the first means with a certain amount of light that is not blocked by the third means; a fifth means for storing digital signals respectively corresponding to a state in which the means blocks the light of the object to be measured from the first means and a state in which it does not block the light of the object to be measured from the first means; A sixth circuit that calculates the difference between the respective digital signals.
A device for converting an amount of light into a digital amount of electricity, characterized by comprising means for converting an amount of light into a digital amount of electricity.