JPS6058811B2 - spectrophotometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spectrophotometer, and more particularly to a spectrophotometer in which detector output is processed by a digital computer.

Electrical control such as wavelength drive in a spectrophotometer or signal processing such as calculation of transmittance and absorbance using a digital computer has become relatively easy due to the progress of integration due to recent developments in semiconductor technology. It has become like that. In such cases, it is necessary to convert the detector output from analog to digital (hereinafter referred to as A-D conversion) and input it into a digital computer as a digital quantity.
One method that is often used as an A-D converter is a one-time voltage conversion type A-D converter. For example, an integral type that compares the sawtooth wave voltage and the input voltage and measures the time until the two match, or an integral type that integrates the input voltage using an integrator for a certain period of time, and then integrates the reference voltage with the opposite polarity to the human voltage using the integrator. An example of this is a double-integrating type A/D converter that measures the time required for the output voltage to return to the reference level in addition to the output voltage. When such a voltage-time conversion type AD converter is used in a two-beam spectrophotometer, there is a problem that the time required for AD conversion varies depending on the input voltage. In a dual-beam spectrophotometer, the spectral transmittance of the sample is determined by comparing the reference light amount and the sample light amount, so when measuring a sample with low transmittance, the two light amounts are significantly different, and in addition to the reference light and sample light, In the case of a two-beam spectrophotometer with a step of blocking the beam to obtain a zero signal, the input signal level to the A/D converter will vary significantly periodically. In a two-beam spectrophotometer, a rotating sector mirror (for example, a rotating sector mirror (for example, a A time-series division or combination method is often used.
In a two-beam spectrophotometer that uses such a time-series light velocity splitting or combining means, A-D conversion must be performed based on the phase of the beam splitting or combining means. If the time is not constant, if an attempt is made to notify the digital computer of the completion of A/D conversion by an interrupt, the interrupt request will occur extremely non-periodically, which is very inconvenient in terms of programming. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a spectrophotometer with A-D conversion timing suitable for control of the spectrophotometer and signal processing by a digital computer.

The key point of the present invention is to start A-D conversion based on the phase information of the time-series two-beam splitting or combining means, and to generate an interrupt request to the digital computer in synchronization with the A-D conversion. This is to import the D conversion results. That is, the A-D converted detector output signal is held until the next photometry step such as time-sequential two-beam splitting or combining means, and is input to the digital computer immediately before or after the start of the photometry step. become. The present invention will be described in detail below based on preferred embodiments of the present invention.

FIG. 1 is a functional diagram showing a preferred embodiment of the present invention.

Light from a light source 1 is separated by a spectrometer 2 and monochromatic light is extracted. The sector mirrors 3, 3'' and the reflectors 4, 4'' split the monochromatic light from the spectrometer 2 into two beams, and separate them into a reference object 5 and a sample 5.
The reference light amount R and the sample light amount S converted into electrical signals by the detector 6 are amplified by an amplifier 7 and then A-D converted. In this embodiment, a double integral type A-D converter 8 is used as an example.The output voltage of the amplifier 7 is integrated by an integrator 80 through a resistor R1. After integrating the input voltage to the integrator 80 for a certain period of time, the control circuit 88 switches the switch 82 to control the integrator 8, 0 by the voltage supplied through the resistor R2 from the constant voltage source 81 having the opposite polarity to the input voltage. On the other hand, the phase of the rotation of the sector mirrors 3, 3'' is detected by the phase discriminator 10, which triggers the monostable multivibrator 12 to generate a pulse with a constant time width, and at the same time sends an interrupt request to the digital computer 9. Occur. The constant time width pulse from the monostable multivibrator 12 is sent to the control circuit 88;
This fixed time width pulse determines the integration start timing and integration time of the integrator. Comparator 83 is integrator 8
A signal is generated by detecting that the input voltage integrated to zero returns to zero potential through inverse integration at a constant rate by the constant voltage source 81. AND gate 85 connects control circuit 88 and comparator 83
The integrator 80 opens the gate only while inverse integration is being performed by the signal from the oscillator 84, and sends a constant frequency clock pulse from the oscillator 84 to the counter 86, which counts this clock pulse. A digital value proportional to the voltage can be obtained. The digital computer 9 generates an A-D result capture command signal 92 based on the interrupt request signal 91 from the phase discriminator 10, opens the gate circuit 87, and captures the digital value of the counter 86. FIG. 2 shows the timing relationship of the above operations. a
b is the output signal of the detector 6, and the signals of the reference light R and sample light S are obtained alternately in synchronization with the rotation of the rotating sector mirrors 3, 3''.b is the output signal of the monostable multivibrator 12. , c is the output signal of the integrator 80, d is the AND gate 85
The counting pulse signal e from , and e indicates the generation timing of the interrupt request signal.A-D conversion starts at time Tl, t4 in synchronization with the time when the interrupt request is generated, that is, the phase of the sector mirrors 3, 3''. , t7, etc., periodically. On the other hand, the end of A-D conversion is at time T3, t6, etc., and the A-D conversion time (T3-t1) (T6-T4) depends on the amount of light.
) are different. An interrupt request to the digital computer 9 is generated every cycle 1/2Tsect0r of the rotating sector mirror,
When the digital computer 9 receives an interrupt request, that is, at times Tl, ti, t7, etc., it reads the digital value of the counter. The digital value read at this time is 112Tse
This is the detector output before ct0r. That is, the sample light SO)A-
What is read at the D conversion start time T4 is the value of the reference light R, and what is read at the A-D conversion start time of the reference light R is the value of the sample light S. Since the time at which an interrupt request is generated is periodic, the digital computer 9 reads the A-D conversion value by accepting the interrupt request, and at the same time reads the wavelength synchronized with the sector cycle by, for example, driving the wavelength of the spectrometer. It is possible to drive
It can also be used as a timing device and easily used to determine time intervals for other controls. The above description has been given by exemplifying a double integral type A-D converter, but in the above-mentioned integral type A-D converter that compares the sawtooth wave voltage and the input voltage, the counter The above method is inconvenient because the value of 86 changes.

In such a case, for example, a monostable multivibrator for a fixed time delay may be arranged immediately before the monostable multivibrator 12 in FIG. 1, and the interrupt request generation and A-D conversion start time may be slightly shifted. The method described above can be carried out without impairing the effects of the present invention. The invention can also be implemented in dual wavelength spectrophotometers in exactly the same way. A dual-wavelength spectrophotometer is a device that alternately irradiates a sample with light of two different wavelengths using a rotating sector mirror, etc., and measures the difference in absorbance at both wavelengths, in order to form different types of light in a time-series manner. The present invention can be implemented in exactly the same manner as the above-mentioned two-beam spectrophotometer by using a phase signal of a rotating sector mirror that intersects two wavelengths. As described above, according to the present invention, the A/D conversion results can be read by generating periodic interrupt requests depending on the phase of the sector mirror, so that programming of a digital computer can be facilitated.

[Brief explanation of drawings]

FIG. 1 is a functional explanatory diagram showing a preferred embodiment of the present invention;
FIG. 2 is a timing diagram illustrating the function of FIG. 1.

Claims (1)

[Claims] 1 a light source, a first means for forming at least two types of light in chronological order from the light emitted by the light source, a detector for detecting the light from the first means, and an output signal of the detector. In the spectrophotometer, the spectrophotometer is equipped with an analog-to-digital converter that converts the digital signal into a digital signal, and an arithmetic device that performs digital arithmetic processing on the digital signal.
a second means for generating a signal for causing the analog-to-digital converter to start analog-to-digital conversion based on the phase information of the means; and generating an interrupt request signal to the arithmetic unit in synchronization with the second means. Provide a third means,
A spectrophotometer characterized in that the digital signal held in the analog-to-digital converter is configured to be input into the arithmetic unit based on the interrupt request signal.