JPS593227A - Direct ratio photometric type spectrophotometer - Google Patents

Abstract

PURPOSE:To enable a highly accurate measurement with high S/N ratio preventing the lowering of the computation accuracy in a weak signal area by controlling the integrated time of a measuring sample photometry signal depending on the magnitude of a reference sample photometry signal. CONSTITUTION:While a reference sample transmission light is being emitted from a spectrometer 1, a sampling circuit 4 fetches a output of an amplifier 3 or while a measuring sample transmission light is being emitted sampling circuit 5 does so. Outputs of the circuits 4 and 5 are counted with counters 10 and 11 respectively through A/D converters 6 and 7, AND gates 8 and 9. Then, an integrated value A of the counter 10 is compared 13 with the set value C and according to a comparison output (a), the integration operation of the counters 10 and 11 is switched ON or OFF while a latch pulse (b) and a reset pulse (c) are outputted from a control pulse generation circuit 15. An integrated value B of the counter 11 is divided 12 by the integrated value A and output is latched with a circuit 16 by the pulse (b).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a direct photometry type spectrophotometer in which a photometric signal for a measurement sample is divided by a photometric signal for a base sample, and the ratio of optical signals on both sides is determined.

In a ratio recording method spectrophotometer, the reference sample of the measurement sample]
As a method for measuring the transmittance of the light, a standard test method is used. Negative feedback methods such as controlling O or the sensitivity of the detector (dynode feedback control when using a photomultiplier), or controlling the slit width of the optical system, and negative feedback control. There is a direct ratio photometry method in which the photometric signal of the measurement sample is directly divided by the photometric signal of the reference sample.

This direct ratio photometry method does not require a special negative feedback circuit or gain or sensitivity variable adjustment elements, so it has the advantages of a simpler equipment configuration and better stability than the negative feedback method, making it very useful. However, on the other hand, it has the disadvantage that when the absolute amount of the signal is small, the measurement sample signal and the reference sample signal are small, so it is difficult to realize a calculation means that achieves a predetermined accuracy. That is, when the above-mentioned division is implemented using an analog electric circuit, the problem is that the dynamic range of the denominator is narrow, usually on the order of -digits, which guarantees the accuracy of the analog divider, and when using a digital calculation method, , so-called bit loss (bit drop), which reduces the effective data resolution in A/D conversion
For example, if we are dealing with 8-bit data, 20Jj:
8 binary digits, but the same 3 significant digits], O, O, i
d: 4 digits in binary), measurement 1i'i once cannot be secured. In addition, in the negative feedback method, a method that controls electrical gain, and a direct ratio photometry method, when the amount of measured signal decreases, the S/N ratio worsens because the detector and amplifier's original sound d is constant. The dynode feedback method has the characteristic that when the photomultiplier increases the sensitivity, the noise tends to increase, but it does not increase in proportion to the sensitivity, so the S/N ratio does not decrease much even in the case of a weak signal. However, the equipment is more expensive than the direct specific photometry method.

As mentioned above, all of the various types of ratio recording spectrophotometers that have been used in the past have problems.

These problems can be summarized as calculation accuracy, S/N ratio at 2-weak signal, and equipment cost.

The present invention has been made with the aim of obtaining a ratio recording type spectrophotometer that harmoniously solves these problems.By adopting the direct ratio photometry method, the cost of the device can be reduced and the signal can be integrated. To provide a ratio recording type spectrophotometer which prevents deterioration of calculation accuracy in the case of a weak signal and also improves the S/N ratio by performing division.

The direct photometry spectrophotometer of the present invention integrates a photometric signal for a measurement sample (referred to as a sample signal) and a photometric signal for a standard sample (referred to as a reference signal), and when the integrated output of the reference signal exceeds a predetermined level. The feature is that both integrations are stopped when j~ is reached, and the integrated output of the sample signal is divided by the integrated output of the reference signal. In this case, the timing for stopping the integration of the signal does not necessarily depend on when the integrated output of the reference signal matches a predetermined constant level, but it may be stopped after reaching a certain level.

In this way, if the signal is handled continuously, it is possible to find the point in time when the integral output exactly matches a predetermined constant level, but by sampling the signal in a time-sharing manner and integrating the
This is because when performing integration in the form of ~, it is generally impossible for the integral output to match an appropriately determined constant value. It can be applied to any case. The present invention will be explained in the following examples.

FIG. 1 shows an embodiment of the invention. Reference numeral 1 denotes a spectroscope, from which light transmitted through a measurement sample and light transmitted through a reference sample are alternately emitted and incident on a photodetector 2 . An amplifier 3 amplifies the output of the photodetector 2. Reference numerals 4 and 5 denote sampling circuits, and the sampling circuit 4 operates as the amplifier 3 while the reference sample transmitted light is being emitted from the spectrometer 1 by the synchronization signal sent from the spectrometer 1.
The sampling circuit 5 takes in the output of the amplifier 3 while the measurement sample transmitted light is being emitted from the spectrometer 1. That is, the sampling circuit 4 samples the reference signal, and the sampling circuit 5 takes in the sampled signal. The configuration up to this point is the same as the basic configuration of a conventional double beam spectrophotometer. 6. '7 is an A/D converter, which is of the voltage frequency conversion type in this embodiment, and converts the DC smoothed reference signal and sample signal into a pulse train proportional to the input signal by the sampling circuits 4 and 5. There is. This pulse train is input to the next stage counter 1.0.11 through the AND gate 8.9 and counted. This counting operation is the aforementioned photometric signal integration operation, and the counters 10 and 1.1 correspond to integrators. AND gates 8 and 9 are normally open, and the count output of the counter 10, which is the integral output of the sample signal, is compared with a constant value preset in the setting device 14 by the digital comparator 13, and the count output of the counter 0 is When the relationship A>C is established for a value C preset in the setting device 14, the output of the comparator 13 changes from 1" to 10", and the AND gates 8 and 9 change the output of this comparator 13 to "1". ”
Since it is open at `0'' and closed at '0'', the integrating operation by the counters 10 and 11 stops when A>C.

Figure 2 is a time chart of one cycle of the operation of the device in Figure 1, where a is the output of the digital comparator and t is A>
This is the point when it becomes C. ], 5 is a control pulse generation circuit that generates the signal shown in Fig. 2, c, which generates the first pulse signal at the falling edge of the output of the two one-shot circuits. A second pulse signal C is output at the falling edge of the signal S. Returning to FIG. 3, 12 is a digital divider, which divides the count output B of the Carantaco], ie, the integral value of the sample signal, by the count output A of the Calantaco-00, ie, the integral value A of the reference signal, ]- 6
When the pulse signal b (FIG. 2b) is applied to the data latch circuit, the output of the divider 2 at that time is latched. At the falling edge of the signal shown in FIG. 2C, the counters 10, 1 .
] is cleared, and at the same time the output of converter tacho 3 is ]”
Returning to , gates 8 and 9 are opened and integration is restarted.

In this device, the integration time is decreased or increased depending on the magnitude of the reference signal, and when the reference signal increases by 17M, the integration time increases by M times. If the noise contained in the sample signal and reference signal is constant regardless of the signal size, the signal will be multiplied by M by multiplying the integration time, but the random noise will only be multiplied, so the signal strength will be If the S/N ratio is 19 when the signal strength is 1, then the S/N ratio is 17 when the signal strength is 1.7M.
M, and when the M times time integral is 1~, the signal strength is 1. Since the noise is convex, the S/N ratio becomes "/convex," and when the signal strength reaches 17 M, the S/N ratio becomes l.
This means that the S/N ratio has been improved by 0 times when it should have been /M.

In the above embodiment, the timing at which the integral value of the reference signal becomes equal to or greater than a certain value is used as the timing to end one photometry operation (integral operation), but conversely, the integral value of the sample signal becomes equal to or greater than a certain value. Timing may also be used, but this is not relevant to the essence of the invention. It is of course also possible to implement the invention in an analog manner.

The spectrophotometer of the present invention has the above-mentioned configuration, and inherits the advantages of the north light method, which does not require any gain control elements, and has features such as good stability, and has no restrictions on the dynamic range. Highly accurate measurement is possible even in the weak signal range without compromising accuracy, and S/N is still high even in the weak signal range.
This has the effect of suppressing a decrease in the ratio.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention, and FIG. 2 is a time chart showing a part of the operation of the apparatus according to the embodiment. ]... Spectrometer, 2... Photodetector, 4, 5... Sampling circuit, 6, 7... A/D converter, 10,
11. ...Counter as an integrator,]2...Digital divider,]3...Digital comparator,]
, 4... constant value setter, 5... control pulse generation circuit, 16... data latch. Agent Patent Attorney Hiroshi Hiru Keidai Futamata

Claims (1)

[Claims] Means for integrating the photometric signal for the measurement sample (sample signal) and the photometric signal for the reference sample (reference signal), and comparing the output of either of the integrating means with a predetermined constant value, and determining whether the output of the integrating means is the same. means for stopping the integrating operation of both of the integrating means when the value exceeds a certain value;
and dividing means for dividing the output of the sample signal integrating means at that time by the output of the reference signal integrating means.