JPH0720584Y2 - UV detector - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a UV detector, and more particularly to a UV detector for liquid chromatography (LC) or flow injection (FIA).

[Prior Art] For example, in a UV detector for LC, the reference light intensity that does not pass through the flow cell and the sample light intensity that passes through the flow cell are detected by light receiving elements, and the ratio of the reference light intensity and the sample light intensity is calculated. The light source intensity is time-compensated and further logarithmically converted to obtain an output proportional to the absorbance (actually, the logarithm of the control light intensity and the sample light intensity is taken first and the difference between them is obtained). Conventionally, the logarithmic conversion of the reference light intensity and the sample light intensity is performed by a logarithmic circuit that uses the forward current-voltage characteristics of the diode, and the difference is calculated by a subtraction circuit that uses an OP amplifier. The signal processing from the light receiving element to the output terminal (for recorder and integrator) was performed in analog system.

[Problems to be solved by the invention] However, in these analog circuits, the conversion accuracy changes due to the temperature change due to the large temperature dependence of the circuit component characteristics such as the diode of the logarithmic circuit. It is easy to operate, and trying to obtain stable accuracy with respect to temperature changes leads to high costs and increase in adjustment points.In addition, the characteristics of diodes etc. change over the years, so periodic adjustments are required to maintain device reliability.・ Part conversion was required. Further, even the OP amplifier has a drawback that it takes time and effort to adjust the gain and the offset.

Further, the absorbance data output from the UV detector is supplied to the recorder and the integrator. Generally, the input voltage range of the integrator is a negative number of 10mV to + 1V,
There is almost no margin on the negative side.

For this reason, when the absorbance itself is DA converted and analog output is performed, for example, the so-called baseline shifts to the negative side due to drift during measurement or changes in the eluent, and when the degree is large, it falls outside the input voltage range of the integrator and measurement is impossible. Itself may occur. Similarly, since a sample without absorption is detected by the indirect absorbance method (implied absorbance method), even if an absorbent substance is added to the eluent and you want to detect the sample as a negative peak, the integrator will detect a large peak. The input voltage range of may be out of range.

Furthermore, the final calculation result is output as an analog signal to an output device such as a recorder or integrator, but since the resolution required by each output device is different, if the same analog signal is output as is, one output There is also a problem that the device cannot output with high precision, and the recorder side requires an expensive attenuator for the recorder, which is composed of a precision resistor, resulting in high cost and complicated adjustments.

In view of the drawbacks of the prior art, an object of the present invention is to obtain stable detection accuracy regardless of temperature change and age, to reduce the number of adjustment points, and to prevent the data supplied to the integrator from becoming invalid. In addition, it is possible to output analog signals of different resolutions to different output devices, and devices such as attenuators are unnecessary,
An object is to provide a UV detector that has a simple structure and is inexpensive.

[Means for Solving the Problems] In order to achieve the above-mentioned object, in the present invention, a detection unit for detecting a reference optical signal and a sample optical signal, and the control optical signal and the sample detected by the detection unit A / D that digitizes optical signals
A conversion unit, a setting unit for setting the level shift amount for an integrator, and a value proportional to the absorbance based on the reference light data and the sample light data output from the A / D conversion unit, and A digital operation processing unit for adding the level shift amount set to the calculated value to calculate integrator output data, the value before addition of the level shift amount calculated by the digital operation processing unit, and the integrator. The output data for use is converted into an analog signal of two or more systems with different bit precisions and output.

[Embodiment] An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a UV detector for LC according to the present invention.

The light emitted from the light source 10 is separated into monochromatic light having a predetermined wavelength (wave number) by the spectroscope 12, and then is irradiated onto the flow cell 16 via the beam splitter 14. The wavelength of the spectroscope 12 is set under the control of the microcomputer unit 40 described later.

In the flow cell 16, the sample temporally separated on the liquid chromatography side flows. The sample substance absorbs light according to the concentration, and the sample light flux leaving the flow cell 16 is detected by the photodiode 18
Incident on. In the photodiode 18, a current proportional to the amount of incident light is generated.

A current / voltage converter 20 is connected to the output side of the photodiode 18, converts the current signal generated by the photodiode 18 into a voltage signal, and outputs it as an analog sample light signal SAMPA.

On the other hand, the reference light flux that has not passed through the flow cell 16 separated by the beam splitter 14 enters the photodiode 22, and a current proportional to the amount of incident light is generated in the photodiode 22. A current / voltage converter 24 is connected to the output side of the photodiode 22, converts the current signal generated by the photodiode 22 into a voltage signal, and outputs an analog reference optical signal RE.
Output as FA.

The output sides of the current / voltage converters 20 and 24 are connected to the three input terminals of the analog switch 26 together with the ground level. The analog switch 26, under the control of the microcomputer section 40, periodically switches three input signals (for example, 50 msec cycle) and outputs them to the A / D converter 28 connected to the output side.

The A / D converter 28 is an 18-bit conversion circuit, and the analog switch 26
Sample optical signal SAMPA, reference optical signal REFA, and ground signal GA sent from the A / D converter, and each digital sample optical signal SAMP
D, a reference light signal REFD, and a ground signal GD are output to the microcomputer unit 40.

The gains of the current / voltage converters 20 and 24 can be switched in four steps, for example, and immediately after setting the wavelength,
Controlled by the microcomputer unit 40, the same gain is switched and set in conjunction with each other, and the magnitude of the reference optical signal REFA is set to A /
The optimum input level to the D converter 28 (the maximum level within the range not exceeding the dynamic range of the A / D converter 28) is set.

The microcomputer unit 40 includes a CPU 42, R connected to the bus.
Includes OM44 and RAM46. The CPU 42, according to a predetermined program stored in the ROM 44, sets the wavelength for the spectroscope 12, the time constant of the time constant circuit 54 described later, the gain setting for the current / voltage converters 20 and 24, the switching control for the analog switch 26, As will be described later, it controls the time variation of the light source intensity by calculating the ratio of the control light intensity and the sample light intensity and the logarithmic conversion, and the calculation of the absorbance, the sensitivity setting, the level shift and the like.

The operation unit 48 is connected to the microcomputer unit 40, and when the sensitivity setting and response setting for the wavelength setting recorder and the level shift amount setting for the integrator are made, each set value is input to the microcomputer unit 40. To do.
The CPU 42 performs control, calculation, etc. according to the value set by the operation unit 48.

The output side of the microcomputer section 40 is connected to an output section 50 capable of outputting two systems, one for a recorder and the other for an integrator. First, the line for the recorder receives the calculation result for the recorder in the microcomputer unit 40 in 12 bits.
A D / A converter 52 for A / A conversion is provided. D / A converter 52
An amplifier 56 is connected to the output side of the via a time constant circuit 54, and the output side of this amplifier 56 is the output terminal OU for the recorder.
It is T1. The time constant circuit 54 can switch the time constant in three stages under the control of the microcomputer unit 40. This makes it possible to adjust the response speed of the UV detector.

The reason why the D / A converter 52 is 12 bits is as follows. The ratio of the pen thickness of the recorder (pen recorder) to the full scale is about 1/10.
Estimating to 00, the resolution required for output is 10 ³ , which is about 10 bits. Therefore, it is set to 12 bits with some margin.

On the other hand, in the line for the integrator, first, the calculation result for the integrator in the microcomputer unit 40 is
A D / A converter 58 for receiving D / A conversion at t is provided. D
An amplifier 62 is connected to the output side of the / A converter 58 via a time constant circuit 60.
Is connected, and the output side of the amplifier 62 is connected to the output terminals OUT2 and OUT3 for the two-stage integrator through the voltage dividing circuit.

The reason why the D / A converter 58 is 20 bits is as follows. Generally, the minimum detection voltage of the integrator is 1μV,
From the maximum input voltage of 1V, the resolution required for the integrator output is 1 (V) / 1 (μV), which is 10 ⁶ . This is equivalent to less than 20 bits without the number of bits. Therefore, looking at many margins, 20b
as it is.

The detection processing operation by the CPU 42 will be described below with reference to the flowchart of FIG. Operation unit in advance
It is assumed that the measurement wavelength, the sensitivity and response for the recorder, and the level shift amount for the integrator are set in 48.

The CPU 42 first controls the spectroscope 12 to set the wavelength based on the wavelength data specified by the operation unit 48 when setting the predetermined wavelength, and controls the time constant circuit 54 to set the time constant based on the response data. Perform (step 70, step 71).

Then, switching control of the analog switch 26 is started, the current / voltage converters 24 and 20 are switched to the minimum gain, and the A / D converter 28
The optimum gain is determined on the basis of the magnitude of the output of the reference optical signal REFD output from, and the current / voltage converters 24 and 20 are switched and controlled. Thereafter, the gain does not change until the wavelength setting is changed (steps 72 to 75).

In this way, when the preparation process is completed, the CPU 42 executes the next process while the analog switch 26 performs one switching scan. That is, when the analog switch 26 is switched to the ground side and the A / D converter 28 outputs the ground signal GD, the CPU 42 stores the offset data OFS in the read RAM 46 (step 76).

Next, when the analog switch 26 is switched to the REF side and the A / D converter 28 outputs the reference optical signal REFD, this is read and subtracted by the offset data OFS to subtract the true reference optical signal REFD '.
(Step 77). As a result, an accurate signal value can be obtained even if there is an offset at the input of the analog switch 26 and the magnitude of the offset changes over time. On the other hand, manually removing the offset of the current / voltage converter is troublesome, costly, and susceptible to aging.

Next, the CPU 42 performs logarithmic calculation of the 18-bit data of the reference optical signal REFD 'to obtain logarithmic conversion reference optical data LREFD (step 7
8). For the logarithmic conversion, a logarithmic conversion table is provided in the ROM 44, and the table is referred to, arithmetic operation is performed by a so-called series expansion method, or dedicated digital arithmetic operation is performed.
You may go with an IC attached.

Next, when the analog switch 26 is switched to the SAMP side and the A / D converter 28 outputs the sample optical signal SAMPD, the CPU 42 reads it and subtracts the offset data OFS to obtain the true sample optical signal SAMPD '(step 79). ). Then, the logarithmic calculation of the 18-bit data of the sample light signal SAMPD 'is performed to obtain the logarithm-converted sample light data LSAMPD (step 80).

Next, the CPU 42 calculates (logarithmic conversion reference light data LREFD)-(logarithmic conversion sample light data LSAMPD) to obtain absorbance data PD (step 81).

Then, the CPU 42 divides the absorbance data PD by the set sensitivity K preset by the operation unit 48 (step 82), and the predetermined 12
Output bit data PD 'to D / A converter 52 (step
83).

Further, the CPU 42 adds the level shift amount SF preset by the operation unit 48 to the absorbance data PD, and outputs a predetermined 20-bit data PD ″ to the D / A converter 58 (steps 84, 8).
Five).

Sensitivity is set by digital input using a numeric keypad, such as 0.32 (ABU) and 0.01 (ABU). The D / A converter 52 is
D / A conversion is performed so that the output of amplifier 56 is 10 mV per set sensitivity. The output of the amplifier 56 is sent to the recorder as an analog absorbance signal (for recorder) RECPA.

The level shift amount SF is also set as a + value by digital input with a numeric keypad or the like. The D / A converter 58 performs D / A conversion of the level-shifted 20-bit data PD ″ and a time constant circuit.
It is output to the amplifier 62 via 60 so that the output after amplification becomes 1V / ABU. The output of amplifier 62 is output terminal OUT2 or OUT as analog absorbance signal (for integrator) INTPA
It is sent from 3 to the integrator.

Here, the reason why the level of the absorbance data is shifted to the integrator is as follows.

That is, in general, the input voltage range of the integrator is −
It is several tens of mV to + 1V, and there is almost no margin on the-side. On the other hand, when the absorbance data PD itself is D / A converted and analog-outputted, for example, the so-called baseline shifts to the − side due to drift during measurement or changes in the eluent, and the input voltage range of the integrator when the degree is large. There is a case that it is out of the range and measurement is impossible. Similarly, a sample with no absorption is detected by the indirect absorption method (differential absorption method), so if you want to detect the sample as a negative peak by adding an absorbing substance to the eluent, the integrator will detect a large peak. The input voltage range of may be out of range. However, if a value is added to the absorbance data PD and then D / A conversion is performed, even in the above case, it can be easily accommodated within the input voltage range of the integrator, and measurement can be performed.

Upon completion of the above processing in response to the switching operation to the ground side, the reference light side, and the sample light side by the A / D converter 28, the CPU 42 repeats the same operation from step 76 again. Therefore, every time the analog switch 26 performs one switching scan, the absorbance data PD ′, PD ″ is calculated and analogly output to the recorder and the integrator.

In this embodiment, the control optical signal and the sample optical signal are converted into an A / D converter 28
After being digitized by, the microcomputer 40 performs digital processing such as logarithmic conversion and difference to perform highly accurate and stable absorbance calculation that is not affected by temperature changes and does not change over time. It is not necessary to use an expensive log amplifier using a diode such as the one described above, and the OP amplifier can be used in a small amount. Therefore, the configuration can be relatively inexpensive, and temperature compensation adjustment, gain adjustment of the OP amplifier, etc. The effort is also reduced.

Further, in the microcomputer unit 40, the spectroscope 12, current /
Since other processing such as control of the voltage converters 20 and 24 and the time constant circuit 54 can be performed, it is extremely advantageous in terms of cost.

Further, before the measurement, the gains of the current / voltage converters 20 and 24 are switched and set so that the input levels of the reference optical signal and the sample optical signal to the A / D converter 28 are optimized,
A / D conversion accuracy can be increased. Also, analog switch 26
Is also switched to the ground side to detect the ground level and the offset included in the reference light signal and the sample light signal is removed by calculation, so there is no need to adjust the offset in the analog signal system, and it is accurate regardless of age. It can perform various signal processing.

In addition, since the output section 50 has two systems and the sensitivity adjustment for the recorder is performed by digital calculation, an expensive attenuator for the recorder composed of a precision resistor is not required, and multistep switching is easy. Since the time constant of the time constant circuit 54 can be switched, the response speed of the UV detector can be changed freely.

Further, since the level of the absorbance output signal for the integrator can be shifted, the integrator input can be easily set within the required input range, and the scale-over in the integrator can be avoided in advance. Moreover,
By performing the level shift of the absorbance output signal by digital calculation, multi-stage shift can be performed accurately, no adjustment is required as in the case of shifting with an analog adder circuit, and the shift amount does not change over time.

A phototube or a photomultiplier tube may be used instead of the photodetection photodiode, and a current / voltage converter may be used.
It is also possible to enable arbitrary multi-step switching of more than one step, and the method of determining the optimum gain is also performed by referring to the magnitude of the light source monitor signal detected separately from the reference light signal and the sample light signal, or by the wavelength. You may carry out by program control. Furthermore, the gain of the current / voltage converter may be fixed, a variable gain amplifier may be provided on the output side, and this gain may be switched to optimize the input level to the A / D converter.

Also, the response speed on the integrator side may be changed by changing the time constant of the time constant circuit as in the recorder side. Furthermore, every time the analog switch scans once, the absorbance data P
Instead of obtaining D ′, PD ″ and outputting it to the D / A converter,
The absorbance data PD obtained each time the analog switch scans is integrated for a plurality of times (m times), the absorbance data PD ′, PD ″ is obtained from the integrated value, and D / A is obtained every time the analog switch scans m times. The response speed may be output to the converter. In this case, the response speed can be changed digitally by changing the number of integrations while the time constant of the time constant circuit is fixed, and the time and effort of adjusting the time constant circuit and the time Eliminate the effects of change.

[Advantage of Device] In the UV detector according to the present invention, the reference light signal and the sample light signal detected by the detector are detected from the light before and after passing through the flow cell.
Stable detection that is less affected by temperature changes and less likely to change over time by digitizing with an A / D converter, calculating at least the absorbance with the calculation processing unit, and outputting the calculation result from the output unit Accuracy can be obtained,
In addition, a UV detector that requires less adjustment can be obtained.

The control light signal before and after passing through the flow cell is detected by the detection unit and the sample light signal is digitized by the A / D converter, and then the calculation unit calculates a value proportional to the absorbance and the setting unit. The level shift amount set in step 1 is added to this value and the calculation result is output from the output section, so there is no absorption even if the so-called baseline shifts to the negative side due to drift during measurement or changes in the eluent. Even when an absorbing substance is added to the sample as the eluent and the sample is detected as a negative peak, the output of the output section can be input to the integrator by setting an appropriate level shift amount in the setting section. The data supplied to the integrator can be prevented from being invalidated, and the level shift with respect to the absorbance can be performed digitally, so that the ambient temperature can be maintained. Accurately perform a level shift without performing independent and cumbersome adjustment of changes and aging.

Further, since the output section is adapted to convert and output to two or more analog signals having different numbers of bits, it is possible to output optimum analog signals to a plurality of output devices such as recorders and integrators having different resolutions. . Moreover, an attenuator or the like is not required, and the structure is simple and the cost is low.

[Brief description of drawings]

FIG. 1 is a block diagram of a UV detector for LC according to an embodiment of the present invention, and FIG. 2 is a flow chart showing the operation of the microcomputer section in FIG. 18, 22: Photodiode 28: A / D converter 40: Microcomputer section 42: CPU 44: ROM 46: RAM 48: Operation section 50: Output section 52, 58: D / A converter (bits for conversion) Accuracy is different)

 ─────────────────────────────────────────────────── --- Continued from the front page (56) References JP-A-50-85254 (JP, A) JP-A-52-117181 (JP, A) JP-A-61-110002 (JP, A) JP-A-56- 138226 (JP, A)

Claims (1)

[Scope of utility model registration request] 1. A detector for detecting a reference optical signal and a sample optical signal, an A / D converter for digitizing the reference optical signal and the sample optical signal detected by the detector, and an integrator. A setting unit for setting the level shift amount of the, and a value proportional to the absorbance based on the control light data and the sample light data output from the A / D conversion unit, and set to the calculated value. A digital operation processing unit for adding the level shift amounts thus calculated to calculate integrator output data; and a value before the level shift amount addition and the integrator output data calculated by the digital operation processing unit, respectively. A UV detector for liquid chromatography or flow injection, comprising: an output unit that converts and outputs two or more analog signals with different bit precision. Producer.