JPS6024411B2 - Photometric conversion device - Google Patents

Abstract

PURPOSE:To obtain a digital quantity, which is correctly proportional to the quantity of incident light, even in the case of weak light by effecting conversion to the digital quantity with the use of an AD converter after a preset quantity of electric signals are added to the either signals which are produced by photoelectric converting means.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a neck light amount converting device that converts a light amount into a digital amount, and particularly to a leg light amount converting device that provides a digital amount that is accurately proportional to the incident light amount even when the incident light amount is weak.

For example, in a device such as a spectrophotometer that uses light to analyze a sample, the amount of light is converted into an electrical signal by a photoelectric conversion means (for example, a phototube or a semiconductor photodetector), and the electrical signal processing is performed to analyze the sample. The transmittance and absorbance of the light are determined.

However, with the development of digital technology in recent years, it is sometimes more convenient to handle the above-mentioned electrical signal processing in digital quantities rather than using analog circuits, and it has become necessary to convert the amount of attention to digital quantities. Light amount conversion has come into widespread use. 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 to a digital amount. Counting type and comparison type converters are often 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, it is necessary to calculate the absolute value proportional to the amount of light. It is necessary to obtain digital quantities. Furthermore, particularly in absorbance measurement of high-concentration samples, Raman spectroscopy, fluorescence spectroscopy, etc., a wide dynamic range is required, and even weak light is required to be converted with good linearity. In this way, in response to the request,
The conventional A/D converters have some disadvantages as follows. Particularly when dealing with weak light, good linearity is required at weak signal levels.
In general, A-D converters often have poor linearity when the input is small, such as in commonly used voltage-to-frequency converters. The range of good linearity of an A-to-D converter using a voltage single-frequency rotor converter depends on the frequency of the converted pulses and is up to about 1% of the full scale of the input. Further, the range in which the double integral type A-D converter has good linearity depends on the accuracy of the level comparator, and is about 0.5% to 5% of the full scale of the input. That is, full
In an A-○ converter with a scale of 10V, the range of good linearity is about 1 hV to 10V, and a weak signal of 1 hV or less cannot be accurately converted into a digital electrical signal. Furthermore, when weak light is converted into an electrical signal using, for example, a photomultiplier tube, the electrical signal obtained from the photoconversion means contains a lot of noise due to noise generated by the photoelectric conversion element itself and noise in peripheral circuits. There are times when I am.
On the other hand, an A-D converter that handles positive electrical signals ignores electrical signals that are close to the zero bell and contain a lot of noise, and therefore ignores electrical signals that are below the zero bell. Digital quantities cannot be obtained. Note that the noise signal level varies depending on the conditions, but is about lmV to I
It is V. In addition, because A-○ conversion is performed including negative electrical signals, an A-○ converter that applies a bias to the input can obtain a digital signal that faithfully contains noise, but has the disadvantage that it is not proportional to the amount of light. arise. Furthermore, when comparing the sawtooth voltage and the input voltage and measuring the time until the two match, such as in a one-time voltage conversion type A-D converter, or when inputting the input voltage after integrating it with an integrator for a certain period of time, When applying a reference voltage with the opposite polarity to the integrator and measuring the time it takes for the output voltage to return to the reference level, the input signal may drop during A-to-D conversion due to noise and do not exceed the level. Sometimes the bell detector does not work, which is a serious inconvenience.

Further, an undesirable DC signal component is superimposed on the electric signal obtained from the photoelectric conversion means.

This DC signal component is a dark current in a phototube or a photomultiplier tube, and has a clear resistance in a photoconductive element such as a Pumpkin cell, and changes due to temperature conversion. Additionally, intensifiers have offset voltages and temperature drifts. Incidentally, the temperature change in the floor resistance is 20 to 30% for a temperature change of 10 qo. This DC signal component makes it impossible to obtain a digital signal that is accurately proportional to the amount of light. The present invention has been made for the purpose of solving the above-mentioned disadvantages and providing a side light amount conversion device that obtains a digital amount that is accurately proportional to the amount of incident light.
The key point of the present invention is to add a certain amount of signal to the electric signal input to the A-D conversion means, and then convert it into a digital quantity by the A-D conversion means, so that even in the case of weak light, the signal is always A - In order to use the D conversion means in a region with good linearity, to avoid the unstable operation region in the low-level input signal region mentioned above, and to obtain a digital amount that is faithfully proportional to the amount of incident light, A means for blocking light is provided, and the digital signal amount obtained in the step in which the incident light is blocked by the blocking means and the digital signal amount obtained in the step in which the incident light is not blocked are converted into digital quantities. The method is to cancel the added electric signal of a certain amount by subtracting the electric signal.

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 element 1 1 such as a photoelectron intensifier tube, an amplifier 12,
A photoelectric conversion means 1 including a power supply to a photoelectric conversion element 11 (not shown) detects incident light, converts the amount of light into an electrical amount such as voltage, and inputs the converted amount to an adder 2. The adder 2 adds a constant voltage to the input voltage from the constant voltage source +V through the resistor R2, and inputs the added voltage to the AD converter 3. A-D converter 3
converts the input voltage into a digital quantity and provides it to the digital storage device 52. On the other hand, incident light 10 to the photoelectric conversion element 11
is a shutter 41 driven by a drive device 42 composed of, for example, a rotary solenoid or a motor.
Due to this, Koto is cut off. In FIG. 1, the light east 10 is in a non-blocking state at the position of the shutter 41 shown by a solid line, and the light east 10 is in a blocked state at a position shown by a dotted line. The shutter 41 prevents incident light 10 from entering the photoelectric conversion element.
It is determined by the driving device 42 or a shutter thinness detector (not shown), etc., and the discrimination signal generating device 43 is driven. The discrimination signal generator 43 gives a signal indicating whether or not the shutter 41 is blocking the incident light 10 to the address register 51, and the address register 51 controls the storage address of the digital storage device 52 based on the signal. The digital side optical signals input from the D converter 3 are stored in different addresses of the digital storage device 52 depending on whether or not the incident light 10 is in a blocked state. The digital arithmetic unit 53 reads out the side light digital signal S in a state in which the incident light 10 is not blocked and the footlight digital signal Z in a state in which the incident light 10 is blocked, which are stored in the digital storage device 52. -Z) and outputs the result. According to one embodiment of the present invention, the digital quantity (S-Z) obtained from the digital arithmetic unit 53 is applied to the voltage summed by the adder 2 or the parent value in the amplifier 12 or the like.

By canceling out the offset voltage applied to the optical signal, it is possible to obtain a digital absolute value proportional to the amount of incident light. The voltage added by the adder 2 is determined by the current of the photoelectric conversion element 11, the offset voltage or drift of the intensifier 12, and the range of good linearity of the A-D converter. If an A-D converter has an input voltage scale of 10V and the range of good linearity is from 1 hV to 10V, the added voltage may be 10 hV or more. Since the input voltage to the A-D converter 3 is the output voltage of the amplifier 2 plus a constant voltage by the adder 2, the above-mentioned A-D
It is possible to eliminate malfunctions when the converter is input at low levels, and it is also possible to always operate the A-D converter 3 in a region with good linearity, so even when the incident light 10 is extremely weak, the amount of incident light can be controlled. It is possible to stably obtain a digital quantity that is faithfully proportional to . In addition, the leakage light value converted into a digital quantity by the A-D converter 3 includes the information current of the photoelectric conversion element 11 and the amplifier 12, which are generated regardless of whether or not the incident light 10 is blocked. , offset voltage, etc. are also included, but it is also possible to obtain the feature that these amounts are canceled out during subtraction in the digital arithmetic unit 53. Figure 2 shows the wolf of the present invention.

FIG. 2 is a circuit explanatory diagram showing an embodiment of an addition circuit and an AD converter that are one component of a light amount conversion device, and the AD conversion circuit uses a so-called double integral type AD converter. The analog input Ain from the photoelectric conversion means is passed through the resistor R,
A constant voltage from a constant voltage source of 10 V passes through a resistor 2 and is added and integrated by an integrator 31. The control circuit 33 is an integrator 31
After integrating the input voltage for a certain period of time, switch SW is switched to connect the constant voltage source 32, which has the opposite polarity to the input voltage, to the resistor R.
3 to the integrator 31 by the voltage supplied to the integrator 31 through 3.
Inversely integrate 1. The comparator 34 detects that the analog input voltage integrated by the integrator 31 returns to a drop potential due to 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. By counting these clock pulses, a digital output D proportional to the analog input voltage can be obtained. As in the embodiment of FIG. 2, the adder circuit 2 can be very easily achieved in combination with an A/D converter. In the example in FIG.
The offset voltage in the amplifier and comparator 34 used in the integrator 31 is constant regardless of whether the incident light 10 to the photoelectric conversion means 1 is blocked or not, so it can be canceled out in the subtraction after digital conversion. I can do it. FIG. 3a is a functional explanatory diagram showing an embodiment of a light blocking means which is a component of the spotlight amount converting device according to the present invention.

The light incident on the photoelectric conversion element 11 is interrupted at regular intervals by the chopper 44, and then enters the photoelectric conversion element 11. The chopper 44 is provided with a part that blocks the incident light 10 and a part that transmits the incident light 10, as shown in a side view in FIG.
Intermittent. In this way, the incident light 10' enters the photoelectric conversion element 11 intermittently at a constant period, but this intermittent state is detected by, for example, the light source 46 and the photoelectric element 47 (for example, a phototransistor or the like is used), and a discrimination signal is generated. It controls the address register as well as the control circuit 33 in FIG. 2 to control the timing of integration and inverse integration in the integrator. In the embodiment shown in FIG. 3, the incident light 10 to the photoelectric conversion element 11 can be interrupted at regular intervals, and subtraction can be performed in the digital arithmetic unit each time. It is possible to always compensate for the drift of the amplifier used in the amplifier 1, the drift of the integrator used in the adder 2 and the AD converter, etc., and it is possible to obtain a digital quantity that is faithfully proportional to the amount of incident light. The digital storage device 52, address register 51, and digital arithmetic device 53 in FIG. 1 can be easily achieved by using, for example, a digital calculator.

As described above, according to the present invention, even in the case of weak light, it is possible to obtain a digital amount with an absolute value that is linearly proportional to the amount of light, and furthermore, it is possible to obtain a digital amount with an absolute value that is linearly proportional to the amount of light, and furthermore, it is possible to obtain a digital amount with an absolute value that is linearly proportional to the amount of light. It is possible to compensate for drifts and the like occurring in the A-D converter, and to operate the A-D converter stably.

[Brief explanation of the drawing]

FIG. 1 is a functional explanatory diagram showing a preferred embodiment of the side light amount conversion device according to the present invention, and FIG. 2 is a circuit diagram showing an embodiment of an adding means and an A-D converter which are one component of the present invention. 3A is a functional explanatory diagram showing an embodiment of a light blocking means which is another component of the present invention, and FIG. 3B is a side view of the chopper in FIG. 3A. 1...Photoelectric conversion means, 2...Adder,
3... A-D converter, 41... Shirtless, 44... Chopper, 53... Digital calculation device. Younger brother/Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. In the photometric quantity conversion device comprising a photoelectric conversion means for converting a light quantity into an electrical signal, and an analog-to-digital conversion means for converting the electrical signal from the photoelectric conversion means into a digital quantity, means for adding a certain amount of signal to the electrical signal input to the digital conversion means; a light blocking means for blocking light incident on the photoelectric conversion means; and a light blocking means among the output signals of the analog-to-digital conversion means. A photometric amount conversion characterized by comprising means for subtracting a signal amount obtained while the light blocking means is blocking light and a signal amount obtained while the light blocking means is not blocking light. Device. 2. The photometric amount conversion device according to claim 1, wherein the light blocking means is a light interrupter that interrupts the light incident on the photoelectric conversion means at a constant cycle. Device.