JPS5892917A - Spectrophotometer - Google Patents

Abstract

PURPOSE:To provide a simple and less-expensive spectrophotometer, wherein a high precision of measurement is ensured through a compensation for the drift of the light source intensity, by a process having the steps of determining the mean values of the base-line signals for respective time sections of a suitable time interval, calculating the rate of change of the base-line signal in relation to time from the mean values of base- line signals of three successive time sections, and making a base-line correction by estimating the mean value of the base-like signals in the fourth time section. CONSTITUTION:The spectrophotometer has a photometer PM, pre-amplifier PA, subtractor SUB, signal processing unit S and a display unit D for displaying the measured value after a base-line correction. The photometric output derived from the pre-amplifier PA is transmitted to the subtractor SUB in which a base-line correction value is subtracted from the photometric output to produce a corrected photometric output. The photometric output is then delivered to the signal processing unit S which processes the photometric output into, for example, an absorbance, the result of which is put on display in the display unit D. A base-line correction signal generating circuit CG produces the correction value which is delivered to the subtractor SUB as a negative value. The essence of this invention resides in the construction of the base-line signal generator CG.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spectroscopic analyzer, and more particularly to a baseline correction device in a spectroscopic analyzer.

In absorption spectroscopy, a temporal drift in the light source intensity appears as a baseline drift in the measurement results. A double-beam spectrophotometer is required to correct the baseline drift in this measurement result. That is, the light from the light source is divided into two beams, one beam passes through the sample cell, the other beam passes through the control cell, and the sensitivity of the photometric circuit is controlled so that the photometric output of the light beam that passes through the control cell is constant. . However, the equipment of the double beam spectrophotometer is complicated and expensive. Furthermore, in emission analysis, a drift in the baseline of the measurement results occurs due to output drift of the sample excitation source.

If it were possible to correct such baseline drift using a single-beam spectrophotometer, it would be very advantageous because it would allow highly accurate analysis with inexpensive equipment. From this viewpoint, the present invention provides a baseline correction means for a single beam spectrophotometer.

The present invention calculates the average value of the baseline signal for each time interval taken at appropriate time intervals, and calculates the temporal change rate of the baseline signal from the baseline signal average value in three successive intervals. Then, assuming that the temporal change rate of this baseline signal is maintained in the fourth interval following the above three successive intervals, the baseline signal average value of the same interval is extrapolated. The present invention provides an apparatus that performs baseline correction by calculating. The present invention will be explained below with reference to Examples.

FIG. 1 provides an overview of one embodiment of the invention. PM is a photodetector, FA is a preamplifier, SUB is a subtracter, S is a signal processing unit, and D is a display device, on which baseline-corrected measured values are displayed. The output of the preamplifier FA is the raw photometric output, and the subtracter SUB subtracts the baseline correction value from this raw photometric output to obtain the corrected photometric output.This photometric output is subjected to signal processing. In the section S, processing such as conversion into an absorbance value is performed, and the result is displayed on the display section. Ca is the baseline correction signal generator and its output signal is the subtracter SUB
is applied as a subtractive number to . The main part of the present invention lies in the configuration of this baseline correction signal generator.

FIG. 2 shows the configuration of the baseline correction signal generator CG. The output of the preamplifier FA is input to the first integrator 1. So is a reset switch of the integrator and is turned on for a short time at constant time intervals Δt to clear integrator 1. This operation is performed in SO and 1 in the time chart in Figure 3.
Indicated by Therefore, since the integrator 1 integrates the raw photometric output within the time period Δ, that is, the photometric output including the baseline fluctuation, the output of the integrator 1 at the end of Δt is the average value of the baseline signal within the time interval Δ. shows. The output of this process 1 is So
The signal is input to the first memory (sample and hold circuit) M1 through the memory switch S1, which is turned on at a timing slightly earlier than the timing at which the signal is turned on, and is stored therein. A time chart of this operation is shown in FIG. 381. M2. M3 is the second. It is a third memory, B2 is a memory switch that connects Ml and M2, 83 is a memory switch that connects M2 and M3, and in the time chart of FIG. 3, 82.
As shown by B3, 83 is turned on at the quickest timing, 82 is next, Sl is the next, and so on from 83 to 81 and then to SO in order. Therefore, at the timing when B2 turns on, memory M1 has not yet received the new output from integrator 1, and holds the average value of the baseline signal of the previous time interval, which is transferred to M2. Read. Similarly, M3 stores the average baseline signal of one more previous time interval. In the time chart of FIG. 3, the intervals are given identification codes such as j J j-1rj2. Using this code, the memory M3 stores the average baseline Bj-2 of j-2, and M2 stores the average baseline Bj-2 of j-2.
-1, and Ml stores the average baseline Bj at j. Since the above operation is performed continuously, j in this S is 1, 2 at a time interval of Δt.
．． 3. ...and it changes. SC is a switch control unit that turns on and off the switches So and 81 to S3 by the above-mentioned dimming. 5UBI and 5UB2 are respectively the first
and a second subtractor (different from SUB in Figure 1), 5
UB1 calculates Xj-Bj-(Bj-1), and 5UB2
calculates (Xj-1)-(Bj-1)-(Bj-2). The output X of 5UBI is input to the 2 multiplier SQ.

The output Y of SQ is Xj. DV is a divider and L=
Calculate Xj2/(j-1). L is section 1, 2.・・・
- In j-2, j-1, L j+1+..., it is calculated for each interval from the fourth interval. Step 2 is a second integrator that integrates the above values obtained for each section. The VR is a volume that appropriately attenuates the output of the second controller, and the output of the same volume is the baseline correction signal and the first
It is applied as a subtractor to the subtracters SU and B in the figure.

The meaning of the above arithmetic operation in the circuit of FIG. 2 will be explained with reference to the graph of FIG. 4. In the figure, l is the output of the preamplifier 7FA. Bl, B2. ... is for each section 1. Thanks...
The output of the first integrator 1 is indicated by the average value of j at .

B3-B2=X3. Let B2-Bl=X2. In general, Bj-(Bj-1)=Xj, (Bj-1)-(Bj-2
)=Xj-1 equals 4. Similarly, the average slope d3 between sections 2 and 3 is a3=(Ba-Bz)7Δt=x37Δ, and the average slope d2 between sections 1 and 2 is d2=X2/Δt. Generally speaking, considering dj=xd, 1-1, K=
cL3/42, and the predicted value d4 of the average slope between sections 3 and 4 is as follows. The change x4 in the average value of j between sections 3 and 4 is Δ1
．． It is Xd4. If d4 is rewritten using X3 etc., d4 = (X3/jt)/(X2/, (t) = (X3)
/X2·Δt, so X4:(X3)/X2. The divider DV performs this operation. The baseline correction signal is section 4
It is obtained only when , and thereafter it is obtained for each section.

Since Xj is the change in the interval average of j, the value of j for each interval is obtained by integrating this.

The second integrating circuit 2 performs this integration, and since the integration starts from section 4, the baseline correction signal becomes C7. By subtracting this from l using the subtractor 1111UB, baseline correction will be performed after interval 4.The meaning of assuming dj = Kdj-1 in the above calculation is that the baseline time Approximating the differential function by an exponential function.It is always possible to approximate the derivative of the baseline between three consecutive intervals by an exponential function, and this exponential function always approximates each interval by an exponential function. It is determined based on actual measurements of the previous two sections, so there is no possibility that approximation errors will accumulate.

Of course, it is also possible to apply a quadratic equation as an approximation method. In this case, the difference between the average slope dj and dj-1 corresponds to the second derivative, and this is regarded as a constant, so dj
-1-1=2dj-(dj-1)-c's, Xj+1
=2! It is given by xj-(xj-1).

In Fig. 2, the switch Sw is a switch that turns on and off the baseline correction operation, and when it is turned off, the switch So
, 81 to S3 are turned on, the first integrator 1 and the first to third memorandums IJMI to M3 are cleared, and when the SW is turned on, the correction operation is restarted. After the lapse of 13 sections, the baseline correction signal is output. begins to be output. During this time, the baseline correction signal before the correction operation is stopped is held in the second integrator 2, and the sample measurement is performed while the switch Sw is temporarily turned off. The switch S4 is a switch that clears the second integrator 2.

The spectrophotometer of the present invention has the above-described configuration, and even if it is a single-beam spectrophotometer, it can correct for drifts in light source intensity, etc., so the device is simple and inexpensive, and a double-beam spectrophotometer is used. This makes it possible to perform measurements with the same degree of precision.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an overview of an embodiment of the device of the present invention, FIG. 2 is a block diagram showing details of the correction signal generator in the above, FIG. S is a time chart explaining the operation of the above device, and FIG. FIG. 4 is a graph explaining the calculation operation. SUB...Subtractor, CG...2 baseline correction signal generator, PM...Detector, S...Signal processing unit, D...
...Display device. Agent: Patent attorney Kosuke Agata = 8'-

Claims (1)

[Claims] A subtracter and a baseline correction signal generator are provided, and the raw photometric output is applied to the subtractor as a minuend, and the output of the baseline correction signal generator is applied as a subtrahend, and the above-mentioned The baseline correction signal generator calculates the average value of the raw photometric output for each different time interval with an appropriate time width, and extrapolates the photometric output of the next interval from the above average value of the past multiple intervals. A spectrophotometer characterized in that the spectrophotometer is configured to output an output signal.