JPH05264352A - Spectorophotometer - Google Patents

Abstract

PURPOSE:To provide a simple and inexpensive construction by integrating an output signal of a photosensor, by computing an optimum time for integration from an integrated value and by controlling the time for integration on the basis of it. CONSTITUTION:A light of a light source 1 which is passed through a slit 4a is condensed by a lens 2 and applied to a sample 3. The light transmitted through the sample 3 is passed through a slit 4b, separated its spectral components by a grating 5 and detected by an array 6. The array 6 is driven by a driving circuit 7. An output of the array 6 is passed through an integrating circuit 8, selected then by a multiplexer 9, converted into a digital signal by an A/D converter 10 and latched by an arithmetic processing part 11. The processing part 11 computes an optimum time for integration from a value obtained by the A/D conversion and a target value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output signal processing method for a photosensor of a spectrophotometer, and more particularly to a spectrophotometer used for biochemical examination.

[0002]

2. Description of the Related Art In a spectrophotometer, light from a light source is dispersed by a grating, a prism or the like, and the light is detected by a photosensor array or the light selected by an interference filter is detected by a photosensor. FIG. 4 shows an output example when light from a halogen lamp is dispersed by a grating and detected by a photosensor array. Based on the emission characteristics of the halogen lamp and the sensitivity characteristics of the photo sensor, a wavelength of 340 to 800 nm
It can be seen that there is a difference of two orders of magnitude in the output current between the two. Further, a spectrophotometer used in a biochemical test usually has to detect a light quantity change of about three digits at the same wavelength.
Therefore, an amplifier and an AD converter having a 5-digit input range in total are required. Also, a resolution of two significant figures is required for each measured value.

FIG. 5 shows the structure of a conventional spectrophotometer.
Since it is difficult to set the input range of the logarithmic converter to 5 digits, in the conventional method, the logarithmic converter is separately used for each wavelength and each wavelength is adjusted so as to have the optimum input range.
Further, as the AD converter, a 5-digit, 17-bit type is used in order to provide a measurement value with a resolution of 2 significant digits.

[0004]

In the prior art, since the input range of the logarithmic converter is constant, the measurable range is narrowed if the light source lamp deteriorates and the light amount of the light source decreases. It was

Further, since the amount of incident light greatly varies depending on the wavelength, one logarithmic converter cannot obtain data of all wavelengths, and an expensive logarithmic converter is required for the number of measurement wavelengths. The AD converter is also required to have a high resolution of only (measurement range + resolution), which has a drawback that the configuration is complicated and the cost is high. The object of the invention is to eliminate the above-mentioned drawbacks.

[0006]

In order to achieve the above object, a spectrophotometer according to claim 1 of the present invention comprises an integrator for integrating an output signal of a photosensor and an optimum integration time from the integrated value. Is provided to control the integration time. Further, the arithmetic processing unit calculates the amount of light incident on the photosensor from the integrated value and the integration time.

In the second aspect, a circuit or program for measuring the integration time is added, integration is performed until the integration value reaches a predetermined value, and the amount of light incident on the photosensor is obtained from the integration time taken at that time.

According to a third aspect of the present invention, a drive pulse generating circuit for the charge storage type photosensor array, an output current detecting circuit for the photosensor, and an AD for converting the output into a digital signal.
A converter and an arithmetic processing unit for calculating an optimum driving frequency from the value are provided. As is well known, in the charge storage type photo sensor array, the cycle of the drive pulse is proportional to the integration time of the detected light amount. The pulse frequency of the drive pulse generating circuit can be freely controlled by the arithmetic processing unit. The arithmetic processing unit obtains the amount of light incident on the linear image sensor from the output current value of the linear image sensor and the driving frequency.

[0009]

The light amount measuring method in the present invention will be described below.

When the output current of the photo sensor is integrated for a fixed time T, and the integrated value at that time is S, the amount of light incident on the photo sensor is obtained by the following equation.

Incident light amount = K ₁ · S / T (Equation 1) Here, K ₁ is a constant and can be obtained by the sensitivity of the photosensor and the gain of the amplifier.

Like the absorbance used in biochemical tests,
To obtain the amount of change with respect to a certain reference light amount, use K
The value of ₁ need not be determined as shown below. That is, the number 1 when the reference light amount I ₀ is I ₀ = K ₁ · S ₀ / T ₀ (Equation 2) The number 1 when the light amount Is at the time of absorbance measurement is Is = K ₁ · Ss / Ts If the equation 3) is used, the required absorbance is: absorbance = Is / I ₀ = (Ss · T ₀ ) / (S ₀ · Ts) (Equation 4), which is irrelevant to K ₁ .

According to the first aspect, in order to effectively use the input range of the AD converter, the measurement is performed by the following procedure. First, the output current of the photosensor is integrated for a certain period of time, and the integration time T ₀ is calculated back based on the integration value S at that time so that the integration value becomes a value suitable for the input range of the AD converter. next,
The output current of the photo sensor is integrated at the obtained integration time Ts. From the integration value S ₀ and the integration time T ₀ measured the second time, it is possible to measure highly accurate data that effectively uses the input range of the AD converter.

In the second aspect, the integration value S is integrated until it becomes a constant value A suitable for the input range of the AD converter, and the integration time T required at that time is measured to obtain the amount of light incident on the photosensor. In this case, the incident light quantity is given by the following equation.

Incident light amount = K ₂ / T (Equation 5) K ₂ is a constant and can be determined by the sensitivity of the photosensor and the gain of the amplifier. Again, it is not necessary to determine K ₂ in the absorbance measurement for the same reason as shown in equation 4.

In the third aspect, when the output value of the AD converter when measured at a certain driving frequency F is S, the incident light quantity is obtained by the following equation.

Incident light amount = K ₃ · S · F (Equation 6) K ₃ is a constant and can be determined by the sensitivity of the photosensor and the gain of the amplifier. In the case of usage in which the detected wavelength differs depending on the position on the photosensor array, K ₃ has a different value depending on the position on the array, but here again it is not necessary to obtain K ₃ in the absorbance measurement.

In order to effectively use the input range of the AD converter, first, measurement is performed at a certain standard driving frequency, and the measured value is set to a value suitable for the input range of the AD converter based on the measured value at that time. The drive frequency F ₀ is determined so that next,
Equation 6 is obtained by re-measurement at the newly determined drive frequency. In the case of the charge storage type photo sensor array, the charge storage time is inversely proportional to the drive frequency (proportional to the period). The weak light has a long storage time, and the strong light has a short storage time, so that an optimum measurement with a good S / N ratio and no output saturation can be performed.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration example of the spectrophotometer according to claim 1. In this device, the light of the light source 1 that has passed through the slit 4a is condensed by the lens 2 and the light is applied to the sample 3. The transmitted light that has passed through the sample 3 is dispersed by the grating 5 through the slit 4b and detected by the photodiode array 6. The photodiode array 6 is driven by the drive circuit 7. The output of the photodiode array 6 passes through the integrating circuit 8 and is then screened by the multiplexer 9 to obtain the AD converter 1
When it is 0, it is converted into a digital signal and taken into the arithmetic processing unit 11. The arithmetic processing unit 11 calculates the optimum integration time from the AD-converted value and the target value.

Now, assume that the amount of light when there is no sample is considered as the reference amount of light and the measurement is performed with an integration time of 1 ms. It is assumed that the AD converter input at that time is 2V. When the input range of the AD converter is 0 to 10 V, it is desirable that the input voltage is about 8 V in order to consider the fluctuation of the light emission amount of the light source and effectively use the resolution of the AD converter. Therefore, the arithmetic processing unit controls the integration circuit so that the integration time is set to, for example, 8 V / 2 V = 4 times 4 ms.

The procedure for measuring the absorbance is summarized as follows.

(1) First, in the state where there is no sample (reference light amount = incident light amount), is the integrated value (=
AD converter input voltage) S is obtained.

(2) The optimum integration time T ₀ (= A · T, A = S ₀ / S) is calculated from the value of S so that the integrated value becomes the target value.

(3) Measure again at the integration time T ₀ . The reference light amount I ₀ is I ₀ = K ₁ · S ₀ / T ₀ K ₁ : constant (Equation 7) (4) A sample is placed and measured at the integration time T ₀ . Transmitted light amount Is is Is = K ₁ · Ss / T ₀ (Equation 8) (5) Absorbance is absorbance = transmitted light amount / incident light amount = Is / I ₀ = (K ₁ · Ss / T ₀ ) / (K ₁ · S ₀ / T ₀ ) = Ss / S ₀ (Equation 9)

In order to effectively utilize the input range of the AD converter when obtaining the amount of transmitted light, there is also a method of obtaining the optimum integration time B · T ₀ after the procedure of (4) and then performing remeasurement. Is = K ₁ · Ss / (B · T ₀ ) ... (Equation 10) Therefore, the absorbance is: absorbance = Is / I ₀ = (K ₁ · Ss / T ₀ ) / (K ₁ · S ₀ / (B · T ₀ )) = B · Ss / S ₀ (Equation 11)

FIG. 2 shows a structural example of the spectrophotometer according to claim 2.
is doing. In this device, after the integrating circuit 8 of the device of FIG.
Is added with the comparator 12. This COMPARE
When the integrator circuit output reaches a preset value,
Notifying the arithmetic processing unit so that the integration time can be calculated
ing. Sequential AD converter monitors the value, and the target value
This time, it measures the time until
It is also possible to implement the functions of the
It The arithmetic processing unit waits until the preset value is reached.
The amount of incident light is calculated from the integration time of. Summarizing the procedure (1) Reference light intensity I₀To the preset value
The integration time until₀ Then I₀And T₀connection of
Is I₀= K₂/ T₀K₂: Constant ... (Equation 12) (2) Integration time of Ts
At this time, the amount of transmitted light Is is Is = K₂/ Ts (Equation 13) (3) Absorbance is the same as in Equation 9 Absorbance = transmitted light amount / incident light amount = Is / I₀= (K₂/ T₀) / (K₂/ Ts) = T₀/ Ts ... (Equation 14) becomes a very simple formula.

FIG. 3 shows an example of the structure of the spectrophotometer of claim 3. In this device, a function that the driving pulse of the linear image sensor 6 can be controlled by the arithmetic processing unit 11 is added. In this example, the frequency of the drive pulse corresponds to the integration time of claim 1. Now, drive a sample to drive frequency 1
Assume that the measurement is made in MHz. The AD converter input at that time is 2
Suppose it was V. Input range of AD converter is 0-10
When the voltage is V, it is desirable to set the input voltage to about 8V in order to consider the fluctuation of the input light and effectively use the resolution of the AD converter. Therefore, the arithmetic processing unit 11 controls the drive circuit 7 so that the drive frequency becomes 250 kHz, which is 2V / 8V = 1/4 times. The procedure is summarized as follows: (1) A when the reference light amount I ₀ is measured at the standard frequency F
The input voltage S of the D converter is measured.

(2) The drive frequency F ₀ is calculated from the value of S so that the input voltage of the AD converter becomes the optimum value.

(3) I ₀ is remeasured at F ₀ .

I ₀ = K ₃ · F ₀ · S ₀ K ₃ : constant (Equation 15) (4) Put a sample and measure at F ₀ .

Is = K ₃ · F ₀ · Ss (Equation 16) (5) Absorbance is absorbance = amount of transmitted light / amount of incident light = (K ₃ · F ₀ · Ss) / (K ₃ · F ₀ · S ₀ ). = Ft · St / F ₀ · S ₀ (Equation 17)

After the procedure of (4), the driving frequency Fb (= B) is set again so that the value of Ss becomes the optimum input value of the AD converter.
There is also a method of obtaining F ₀ ) and then measuring again. At this time, the absorbance is as follows: absorbance = (K ₃ · B · F ₀ · Sb) / (K ₃ · F ₀ · S ₀ ) = (B · Sb) / S ₀ (Equation 18).

[0033]

According to the present invention, the time for integrating the output of the photosensor and the storage time for the charge storage type photosensor array are adjusted according to the amount of incident light. There is no drawback that the measurable dynamic range is narrowed. Further, since the dynamic range of the integrator can be reduced and the input level of the AD converter is controlled to a substantially constant value, the required resolution can be improved to about two digits, and the configuration is simple and inexpensive.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a spectrophotometer according to claim 1 of the present invention.

FIG. 2 is a diagram showing an embodiment of the spectrophotometer according to claim 2 of the present invention.

FIG. 3 is a diagram showing one embodiment of a spectrophotometer according to claim 3 of the present invention.

FIG. 4 is a diagram showing an output example of a photo sensor array.

FIG. 5 is a diagram showing an example of a conventional spectrophotometer.

[Explanation of symbols]

1 ... Light source, 2 ... Lens, 3 ... Sample, 4a, 4b ... Slit, 5 ... Grating, 6 ... Photosensor, 7 ...
Photosensor driving circuit, 8 ... Integrating circuit, 9 ... Analog multiplexer, 10 ... A / D converter, 11 ... Arithmetic device,
12 ... Comparator, 13 ... Threshold value, 14 ... Output current detection circuit, 15 ... Logarithmic converter.

Claims (3)

[Claims] 1. A light source and an optical mechanism for splitting the light of the light source, a photosensor for converting the split light into an electric signal and its driving circuit, an AD conversion circuit for converting the electric signal of the photosensor into a digital signal, In a spectrophotometer including an arithmetic device for arithmetically processing a signal from the AD conversion circuit, a spectrophotometer characterized by integrating the output signal of the photosensor and changing the integration time according to the output signal level of the photosensor. Photometer. 2. The spectrophotometer according to claim 1, wherein the integration time is changed until the integration value becomes a constant value. 3. In the above spectrophotometer, when the photosensor is a charge storage type photosensor array (linear image sensor, etc.), the frequency of the drive clock of the photosensor array is changed according to the output level of the photosensor array. Is a spectrophotometer.