JPS5925449B2 - Photometric conversion device - Google Patents

Abstract

PURPOSE:To obtain an absolute digital value, which is highly linerarly proportional to the quantity of incident light, by interrupting the incident light upon a photoelectric converter in a preset period, by guiding the interrupted light into the photoelectric converting element, by amplifying the electric signals and by eliminating the DC component which is generated by the converting means. CONSTITUTION:Optical converting means 1, which is composed of a supply power source for a photoelectric converting element 11 such as a photoconductive element, detects incident light 10, which is interrupted by a chopper 71, so that the quantity of the light may be converted into electric signals of voltage, which are fed to an amplifier 2. This amplifier 2 eliminates the DC component of the input signals and selectively amplifies only the AC component, which is then fed to an adder 3. This adder 3 adds a preset DC voltage to the AC component to generate a positive monopolar voltage, which is fed to an A/D converter 4. This converter 4 converts the input voltage into digital quantities, which are then fed to a memory device 5. On the other hand, the chopper 71 is turned by a drive motor 72 to interrupt the incident light in a preset period. Thus, it is possible to stably operate the A/D converter.

Description

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

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 direction, and photometric quantity conversion, which converts photometric quantities to digital quantities, is often used. I've come to be able to do it. In such a case, the analog electrical signal amount from the photoelectric conversion means described above is converted into a digital amount.
A digital converter (hereinafter abbreviated as an A-D converter) is used. Counting type and comparison type converters are often used as A-D converters to meet the required accuracy and simplicity of the circuit, but in both cases, in order to handle the amount of light, it is necessary to calculate the absolute value proportional to the amount of light. It is necessary to obtain digital quantities. 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 good linearity. Considering this point of view, the photometric quantity conversion using the conventionally used A/D converter has several disadvantages as described below. In particular, when dealing with weak light, good linearity in the weak signal range is necessary, but generally speaking, linearity is poor at low inputs, such as in voltage-frequency converters commonly used in A-D converters. There are many 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 below zero level that contain many miscellaneous tubes, so it is not properly proportional to the amount of light. cannot obtain digital quantities. In addition, when comparing the sawtooth voltage and the input voltage and measuring the time until they match, such as with a voltage-time conversion type A-D converter, or when measuring the time until the two match, or after integrating the input voltage with an integrator for a certain period of time, the input voltage If a method is used in which a reference voltage of opposite polarity is applied to the integrator and the time required for the output voltage to return to the reference level is measured, the input signal may drop to zero level during A-D conversion due to noise etc. If the level is not exceeded, a malfunction occurs in which the level detector does not operate, which is extremely inconvenient. In addition to the above-mentioned problems with the A-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 vorticity drift have a serious adverse effect. Furthermore, in a photoconductive element such as a PbS cell, the change in dark resistance due to depth is extremely large, 20 to 30% for a 10°C change in depth, and the DC signal level changes markedly with the sensitivity. It has been extremely difficult to obtain digital photometric quantities. The present invention has been made for the purpose of solving the above-mentioned problems 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 main point of the present invention is to intermittent light incident on a photoelectric conversion element at a certain period, guide the intermittent light to the photoelectric conversion element, and amplify the electric signal from the photoelectric conversion element with AC, so that DC signals caused by temperature changes, etc. By removing undesirable DC signal components such as level changes and dark current, and adding a certain amount of DC signal to the obtained AC signal, input it to an A-D converter and convert it into a digital quantity. Even in the case of light, it is important to always use the A-D converter in a region with good linearity, to avoid unstable operation in the low-level input signal range mentioned above, and to use a digital quantity that is correctly proportional to the amount of incident light. In order to obtain the digital signal amount, the amount of digital signal obtained at the step where the incident light is blocked in response to the intermittent incident light and the amount of digital signal obtained at the step where the incident light is not blocked, are expressed as a digital amount. By subtracting at , the added constant amount of DC signal is canceled out, and a digital amount that is correctly proportional to the amount of incident light is obtained. 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.

Photoelectric conversion elements such as phototubes and photoconductive elements 11. Power supply 12 to a preamplifier and photoelectric conversion element 11 (not shown)
The photoelectric conversion means 1 , which consists of the like, detects the incident light 10 interrupted by the chopper 71 , converts the amount of light into an electrical signal such as a voltage, and inputs the electrical signal to the AC amplifier 2 . AC amplifier 2
removes the DC component from the human input signal, selectively amplifies only the AC component, and inputs it to the adder 3. Since the human input signal of adder 3 is an AC signal, it has both positive and negative polarity components.
is made into a positive unipolar voltage by adding a constant DC voltage thereto, and inputted to the AD converter 4. The A/D converter 4 converts the input voltage into a digital quantity and provides it to the digital storage device 5. On the other hand, the chopper 71 has a portion that blocks the incident light 10 and a portion that transmits the incident light 10, as shown in FIG. Intermittent. This cutoff state is detected by the light source 73 and the phototransistor 74, and a discrimination signal indicating whether or not the incident light is cut off is sent to the address register 51. The address register 51 is, for example, a flip-flop circuit, and controls the storage address of the digital storage device 5 based on the discrimination signal, and the digital photometry signal inputted from the A-D converter 4 indicates that the incident light 10 is in a blocked state. They are stored at different addresses in the digital storage device depending on whether or not the data is stored. Of the photometric signals stored in the digital storage device 5, the digital arithmetic unit 6 reads out a photometric digital signal S in which the incident light 10 is not blocked and a photometric digital signal Z in which the incident light is blocked. -Z is subtracted and the result is output. In this way, the digital quantity (S-Z) obtained from the digital arithmetic unit 6 cancels out the voltage added by the adder 3 or the offset voltage added to the photometric signal in the AC amplifier 2, etc., and becomes a digital absolute value proportional to the amount of incident light. can be obtained, and the results are displayed on, for example, the display device 61. The input voltage to the A-D converter 4 is added to the output voltage of the amplifier 2 by the adder 3.
Since the voltage is a voltage to which a constant voltage is applied, it is possible to operate in a region with good linearity even with the A-D converter 4, and it is possible to obtain a digital amount that is faithfully proportional to the amount of incident light.

In addition, malfunctions of the A-D converter described above during low-level human power can also be eliminated. FIG. 3 is a signal waveform diagram showing the state of the operating signal at each point in FIG. 1, and FIG.
indicates the conversion characteristic of the X-D converter 4, and e indicates the digital value after A-D conversion. The output voltage of the photoelectric conversion means 1 has undesirable DC components 13 such as dark current of the photoelectric conversion element 1 and offset voltage of the amplifier, which are generated regardless of whether or not the incident light is blocked. In the figure, this undesirable DC component 13 is shown as a positive voltage, but when a photoconductive element or the like is used, for example, this DC component changes greatly depending on the degree of mud, and may even become a negative voltage.
This undesirable DC component is removed in the AC amplifier 2. Furthermore, as shown in c in the same figure, since a constant voltage +VO is added in the adder 3, the input voltage to the A-D converter 4 is always a positive voltage, and the region of good linearity of the A-D converter is used. It is possible to obtain an accurate digital output e. The added voltage in the adder 3 is A-D, where R is the duty during the time when the incident light 10 is not blocked.
When the input voltage range of the converter is made equal to the voltage multiplied by R, the A/D converter can be used with a wide dynamic range. In the above explanation, the incident light 1
0 is periodically interrupted by the shutter 71, but the interruption of the incident light does not necessarily have to be periodic. It is also possible to block the incident light intermittently, and even such a method can be implemented without impairing the effects of the present invention at all.

Further, the digital storage device 5, address register 51, and digital arithmetic device 6 in FIG. 1 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 human light, and furthermore, it is possible to remove undesirable DC components and their temporal fluctuations generated in photoelectric conversion means, etc. It is possible to operate the AD converter stably.

[Brief explanation of the drawing]

FIG. 1 is a functional explanatory diagram showing a preferred embodiment of the photometric amount conversion device according to the present invention, FIG. 2 is a front view showing an example of a chopper which is a component of the present invention, and FIG. FIG. 3 is a diagram illustrating the operation of the embodiment. 1...Photoelectric conversion means, 2...AC amplifier, 3...Adder, 4...A-D converter, 5... ...Digital storage device, 6...
・Digital arithmetic device, 71...Chiyotsupa.

Claims (1)

[Scope of Claims] 1. A light intermittent means for periodically intermittent light, a photoelectric conversion means for detecting the disconnected light and converting it into an electrical signal, and an alternating current signal among the electrical signals from the photoelectric conversion means. an amplifier that selectively amplifies the signal, an adder circuit that adds a certain amount of electrical signal to the output signal of the amplifier, and an adder circuit that adds the output signal of the adder circuit at a time interval corresponding to the optical intermittent period of the optical intermittent means. an analog-to-digital converter for converting into a digital quantity, the signal quantity obtained in the period in which the light intermittent means is blocking light, and the signal amount obtained in the period in which the light intermittent means is not blocking light; A photometric quantity converting device, characterized in that the signal quantity is converted into a digital quantity by the analog-to-digital converter and then subtracted. 2. In the photometric amount conversion device according to claim 1, the amount of electrical signals added in the adding circuit is the input operating range of the analog-to-digital converter multiplied by the light intermittent duty of the light intermittent means. A photometric amount conversion device characterized in that the amount is approximately equal to the amount.