JPS6059532B2 - spectrophotometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a variable light attenuation method that changes the amount of light attenuation due to a measurement sample placed in one of two light beams and the amount of light attenuation caused by a measurement sample placed in the other light beam.

The variable dimmer is balanced by a variable dimmer and measures the transmittance of a sample from the amount of light attenuation of the variable dimmer, and is particularly suitable for digital data processing. This invention relates to a spectrophotometer that can directly read out the amount of light attenuation as a digital amount. A type of spectrophotometer is a type of spectrophotometer in which the amount of light attenuation due to the measurement sample placed in one of the two light beams is balanced by a variable attenuator placed in the other beam, and the amount of light attenuation of the variable attenuator is calculated from the amount of light attenuation of the sample. There are optical nulling spectrophotometers that measure the transmittance of . As shown in FIG. 1, this includes a light source 10,
A sample 12 placed in one beam from the light source 10 and a willow blade 1 placed in the other beam from the light source 10.
6, a light flux illuminator 18 having a region where one of the two light fluxes is alternately incident on the spectroscope 20, and a light flux illuminator 18 that monochromates the incident light and outputs it to the detector 22 as light with only a specific wavelength. an amplifier 24 that AC amplifies the output of the detector 22; a synchronous rectifier 26 that rectifies the output of the amplifier 24 in synchronization with the synchronization signal 19 of the beam illuminator 18; a drive circuit 28 that amplifies the error signal 27 output from the synchronous rectifier 26 in accordance with the difference and its positive/negative nature; and a servo motor 30 that drives the willow blade 16 of the variable dimmer 14 while being controlled by the drive output 29 thereof. has. In such a conventional optical nulling method spectrophotometer, the light beam from the light source 10 is divided into two parts, passes through the sample 12 and the variable attenuator 14, and is sent to the light beam illuminator 18. One of the light beams is alternately incident on the spectrometer 20.

The spectrometer 20 monochromates the incident light and outputs it to the detector 22 as light having only a specific wavelength. When the amount of light attenuation by the comb blades 16 of the sample 12 and the variable attenuator 14 is equal, the cross-illumination light incident on the detector 22 has the same light intensity and is balanced. After that, the error signal 27 extracted in synchronization with the synchronization signal 19 from the beam illuminator 18 becomes a zero signal. If there is an intensity difference between these two beams, the error signal 27 will be a positive or negative signal,
This error signal 27 is amplified by the drive circuit 28, rotates the servo motor 30 in a direction in which the difference in intensity between the light beams disappears, and automatically adjusts the amount of light attenuation of the variable dimmer 14. When the comb blade 16 of the variable dimmer 14 moves in the direction of arrow A to block part of the luminous flux, the amount of movement corresponds to the amount of light attenuation, and therefore the position of the comb blade 16 at equilibrium and the transmission of the sample 12 The rate will also correspond. Such an optical nulling method spectrophotometer is a type of spectrophotometer that optically balances the light intensity of two light beams to zero, and is a type of spectrophotometer that uses low light source energy and does not require high-speed response. It is widely used for external spectroscopy. On the other hand, in recent years, as in other fields, there has been a growing demand for spectrophotometers to digitally process data using microcomputers and the like.

In the conventional optical nulling spectrophotometer as described above,
In order to obtain a digital output, a reference voltage from a constant voltage power supply 32 is applied as shown in FIG. The potentiometer 34 is connected to the variable dimmer 14 to obtain a voltage signal 35 corresponding to the position of the comb blade 16, which is supplied to an analog-to-digital converter (hereinafter referred to as an A-D converter) 36. By doing so, a digitized output signal 37 is obtained. there was.

Therefore, in conventional optical nulling spectrophotometers that can obtain digital output, there are limits to reliability, lifespan, linearity, etc. when converting the displacement of the comb blade 16 into voltage or current form. A mechanical potentiometer and meter must be used,
Furthermore, the analog signal obtained by the potentiometer must be converted from analog to digital by an AD converter.

Therefore, there was a possibility that errors would occur in each of them. The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional method, and is a spectrometer that allows the amount of light attenuation of a variable attenuator used in the optical zeroing method, that is, the transmittance of a spectrophotometer, to be directly obtained digitally. The purpose is to provide a photometer.

The present invention balances the amount of light attenuation due to a measurement sample placed in one of the two light beams with a variable attenuator placed in the other light beam, and adjusts the amount of light attenuation of the sample from the amount of light attenuation of the variable attenuator. In a spectrophotometer that measures transmittance, the difference between the amount of light attenuation of the measurement sample and the amount of light attenuation of the variable dimmer detected by a bidirectional rotating pulse motor that drives the variable attenuator and a detector. The above object is achieved by comprising a drive pulse generation circuit that generates drive pulses that rotate the pulse motor in positive and negative directions depending on whether the pulse motor is positive or negative, and a reversible counter that counts the drive pulses output from the drive pulse generation circuit. This has been achieved.

Further, the drive pulse generation circuit generates pulses in the direction of increasing or decreasing the amount of light attenuation of the variable dimmer, depending on the positive or negative of the unbalanced signal between the two luminous fluxes obtained by synchronously rectifying the output of the detector. It is designed to generate drive pulses that rotate the motor.

Alternatively, when the absolute value of the unbalance signal between the two luminous fluxes obtained by synchronously rectifying the output of the detector by the drive pulse generation circuit is equal to or higher than a certain threshold value, the light is variablely attenuated depending on the positive or negative of the signal. generating a drive pulse that rotates the pulse motor in a direction that increases or decreases the amount of light attenuation of the device, and when the absolute value of the unbalanced signal is less than or equal to the certain threshold;
By not generating drive pulses regardless of whether they are positive or negative,
This prevents hunting of the pulse motor.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In this embodiment, as shown in FIG. 2, the comb blade 40 of the variable dimmer 14 has a transparent part 42 for calibration in a part thereof, and the comb blade 40 is a bidirectional rotatable type. The synchronous rectifier 26 is driven by the pulse motor 44 of
The drive pulse generation circuit 46 is provided with a drive pulse generation circuit 46 that generates a drive pulse 47 for rotating the pulse motor 44 in positive and negative directions in accordance with an output error signal 27.
A reversible counter 48 for counting output drive pulses is provided, a calibration light source 50 and a calibration detector 52 are provided, and the calibration transparent portion 42 of the comb blade 40 is detected by the calibration detector 52. In this case, the difference from the conventional example shown in FIG. 1 is that the digital signal 49 of the reversible counter 18 is calibrated to be a constant amount. In the figure, reference numeral 54 denotes a drive circuit that generates a drive output 55 for driving the pulse motor 44 in response to the drive pulse 47 output from the drive pulse generation circuit 46. The other points are the same as those of the conventional example, so the explanation will be omitted. As shown in FIG. 3, the drive pulse generation circuit 46 generates an error signal 2 of the output of the synchronous rectifier
7, a pair of comparators 60 and 62 each having a non-inverting side input terminal and an inverting side input terminal and the other input terminal being grounded, and a pair of comparators 60 and 62 connected between the output terminals of the comparators 60 and 62 and the ground, respectively. Limiting diode 6
4, 66, a square wave oscillator 68, and the square wave oscillator 68
a one-shot circuit 70 that converts the output into a pulse signal; and an output of the one-shot circuit 70 and the first comparator 60.
A first AND circuit 72 that performs logical product with the output, and the output of the one-shot circuit 70 and the second comparator 62.
and a second AND circuit 74 that takes a logical product with the output, the output of the first AND circuit 72 is used as a positive direction drive pulse 73, and the output of the second AND circuit 74 is used as a negative direction drive pulse 75. It is said that The operation will be explained below.

The rectified output from the synchronous rectifier 26 obtained in the same manner as before is input to the drive pulse generation circuit 46, which generates either the positive direction drive pulse 73 or the negative direction drive pulse 75 depending on the polarity of the error signal 27. It occurs or it does not occur at all. The positive direction drive pulse 73 and the negative direction drive pulse 75 are input to the reversible counter 48 and the drive circuit 54, respectively. Therefore, the drive output 55 of the drive circuit 54 output
For example, in a 4-phase 1-2 phase excitation system, the pulse motor 44 is rotated in both forward and reverse directions, and the amount of dimming of the variable dimmer 14 is adjusted by moving the comb blade 40 connected to the pulse motor 44. By counting the output of the drive pulse generation circuit 46 using a reversible counter 48, a digital signal 49 is obtained in accordance with the amount of light attenuation of the variable dimmer 14. The operation of the drive pulse generation circuit 46 will be explained in more detail.

The synchronously rectified error signal 27 is sent to two comparators 6.
0 and 62 are input to the non-inverting input terminal and the inverting input terminal, respectively. Since the other input terminal of each of the comparators is grounded, when the error signal 27 is a positive voltage, the output of the comparator 60 becomes the logical value "゜1゛" and generates a positive voltage detection signal. When 27 is a negative voltage, the output of the comparator 62 has a logical value of "1", and a negative voltage detection signal is output. On the other hand, a one-shot circuit 70 connected to a rectangular wave oscillator 68 generates a pulse train of a constant period, and two AND circuits 72, 7
4 is supplied. Therefore, when the output signal of the comparator 60 is "1", the first AND circuit 72 is turned on and the forward drive pulse 73 is generated.On the other hand, when the output signal of the second comparator 62 is "46r" is the second AN
The D circuit 74 is turned on and a negative direction drive pulse 75 is generated. In this way, the drive pulse generation circuit 46 drives the pulse motor 44 in the forward or reverse direction depending on the voltage polarity of the error signal 27, and adjusts the variable dimmer 14 so that the unbalanced component between the two beams becomes O. Since the comb blade 40 is controlled, if these two types of driving pulses 73 and 75 are constantly counted by the reversible counter 48, the counting result becomes a digital signal 49.

In this embodiment, the comb blade 40 of the variable dimmer 14 is provided with a transparent part 42 for calibration, and the comb blade 40 of the variable dimmer 14 is
For example, only when the light flux on the dimmer side is completely blocked, the light from the calibration light source 50 enters the calibration detector 52 and fights against it, and then the calibration signal 53 output from the calibration detector 52 is The contents of the reversible counter 48 are reset, and the reversible counter 4
The initial value may be 8.

Thereby, a digital signal 49 corresponding to the calibrated transmittance can be obtained as the output of the reversible counter 48. Drive pulse generation circuit 80 in the second embodiment of the present invention
is shown in Figure 4.

In this embodiment, a squaring circuit 82 is installed in parallel with the two comparators 60 and 62 in the first embodiment, and
A third comparator 86 is provided to compare the magnitude relationship between the output of the square circuit 82 and the reference voltage source 84, and the logic between the output of the third comparator 86 and the output of the one-shot circuit 70 similar to that of the first embodiment is provided. A third AND circuit 88 that takes the product is provided, and this is connected to the one-shot circuit 70 and the first and second AN
It differs from the first embodiment in that it is inserted between the inputs of D circuits 72 and 74. The other points are the same as those of the first embodiment, so the explanation will be omitted. In this embodiment, due to the action of the square circuit 82 and the third comparator 86, no pulse train is generated when the square of the absolute value of the error signal 27 is less than the reference voltage ■τ of the reference voltage source 84. , Therefore, pulse motor drive pulses 73 and 75 are not generated.

Therefore, a dead zone is provided in the optical nulling servo system, which prevents over-correction of the variable dimmer and suppresses hunting of the digital output 49 due to noise components of the servo system. As explained above, the present invention balances the amount of light attenuation due to the measurement sample placed in one of the two light beams with the variable dimmer placed in the other beam, and the amount of light attenuation of the variable dimmer In a spectrophotometer that measures the transmittance of a sample from
A bidirectional rotary pulse motor drives the variable dimmer, and the pulse motor is rotated in the positive and negative directions depending on the sign of the difference between the amount of light attenuation of the measurement sample and the amount of light attenuation of the variable dimmer detected by the detector. Since it is equipped with a drive pulse generation circuit that generates drive pulses to rotate the dimmer, and a reversible counter that counts the drive pulses output from the drive pulse generation circuit, the only mechanical means required is to drive the variable dimmer using a pulse motor. Control is all electronic, without the need for limited and inaccurate potentiometers, increasing reliability, linearity, longevity, and performance.

Further, since expensive potentiometers, A/D converters, etc. are not required, a digitalized spectrophotometer can be provided at low cost. Furthermore, since the electronic control part can be easily replaced with a microcomputer, etc., a spectrophotometer with a built-in microcomputer does not need to add an electronic control circuit, and has excellent effects such as being inexpensive. have

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional optical zeroing spectrophotometer, and FIG. 2 is a block diagram showing the overall configuration of a first embodiment of the spectrophotometer according to the present invention. , FIG. 3 is a circuit diagram showing the drive pulse generation circuit in the first embodiment, and FIG. 4 is a circuit diagram showing the drive pulse generation circuit in the second embodiment of the spectrophotometer according to the present invention. It is a diagram. 10... Light source, 12... Sample, 18...
・・・・Light flux commensator, 20・・・・Spectrometer, 22・
...Detector, 24...Amplifier, 26...
...Synchronous rectifier, 27...Error signal, 40.
... Comb blade, 44 ... Pulse motor, 46
, 80... Drive pulse generation circuit, 47...
... Drive pulse, 48 ... Reversible counter, 49.
...Digital signal, 73...Positive direction drive pulse, 75...Negative direction drive pulse.

Claims (1)

[Claims] 1. The amount of light attenuation due to a measurement sample placed on one of the two beams,
In a spectrophotometer that measures the transmittance of the sample from the amount of light attenuation of the variable attenuator, which is balanced by a variable attenuator placed in the other beam, a bidirectional rotary pulse motor that drives the variable attenuator and , a drive pulse that generates a drive pulse that rotates the pulse motor in a direction that increases or decreases the amount of light attenuation of the variable dimmer, depending on the sign or negative of the difference between the amount of light attenuation of the measurement sample and the amount of light attenuation of the variable dimmer. A spectrophotometer comprising: a generating circuit; and a reversible counter that counts drive pulses output from the drive pulse generating circuit and directly provides a transmittance value. 2. In claim 1, when the absolute value of the difference between the two amounts of light attenuation is greater than or equal to a certain threshold, the drive pulse generation circuit controls the amount of light attenuation of the variable dimmer depending on the positive or negative sign of the difference. A drive pulse is generated to rotate the pulse motor in the direction of increasing or decreasing the light intensity, while when the absolute value of the difference between the two light attenuation amounts is less than the certain threshold value, no drive pulse is generated and the variable dimmer is turned off. A spectrophotometer that is characterized by preventing overcorrection.