JPS6161611B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photometer having a hot cathode discharge tube as a light source, and more particularly to a photometer equipped with a zero adjustment circuit.

Liquid chromatography is a useful tool for separating and analyzing trace mixture components. In order to increase the detection sensitivity of trace components, it is necessary to make the photometer used as a detector highly sensitive.

In a conventional photometer of this type, electrical signals from photoelectric conversion elements on the sample side and reference side are adjusted to a specified magnitude using a variable resistor of an amplifier, and outputted as a logarithmic difference voltage using an absorbance converter. The output of this absorbance converter is selected in an appropriate range in a voltage dividing circuit and recorded in a recorder.

On the other hand, in a photometer, the sample light and standard light are generally not the same. This is due to factors such as the wavelength used, dirt on the flow cell, and the type of solvent flowing.
The type of eluent that is passed through the separation column varies depending on the purpose of analysis.If the eluent is aqueous, the eluent itself will have almost no absorption in the ultraviolet range of 200 nm to 350 nm, but if the eluent is methanol, for example, it will absorb depending on the wavelength. 1/
Therefore, the above-mentioned variable resistor of the photometer used as a detector must be able to be adjusted over a wide range to increase the sensitivity by 10 or 100 times. However, the wider the adjustment range of the variable resistor, the more difficult it becomes to match it in a highly sensitive range. In such conventional photometers, there is a sensitivity difference of 1000 times between 0.001 absorbance full scale and 1 absorbance full scale, and the adjustment work using a variable resistor for zero adjustment during high-sensitivity measurements is troublesome and lacks accuracy.

Therefore, the inventors of the present invention invented a circuit configuration that allows the zero adjustment operation to be performed easily and accurately, and filed a patent application on March 5, 1981. A photometer with this new configuration is equipped with a zero adjustment circuit that accepts the output from the absorbance converter and a switch section that provides a start signal to this zero adjustment circuit. The output voltage is applied to one end of the input of the summing amplifier, the output voltage of the DA converter is applied to the other end of the input of the summing amplifier, and the output voltage of the DA converter is equal to the output voltage of the absorbance converter at the summing point. Zero compensation is performed so that the magnitudes are equal and the polarities are opposite.

However, if the photometer is equipped with a hot cathode discharge tube as a light source, even if the above-mentioned zero adjustment circuit is applied, the first adjustment must be made manually after the power is turned on and before the hot cathode discharge tube is turned on. After turning on the zero adjustment circuit start switch and confirming that the hot cathode discharge tube is turned on even after the discharge is turned on, the
The zero adjustment circuit start switch must be turned on for the first time, which is cumbersome to operate. Moreover, until the zero adjustment circuit is operated in the two states of lighting and lighting, the absorbance converter outputs an undefined voltage, which causes the recorder to swing out in the positive or negative direction, often causing damage to the recorder. be.

The present invention was made in order to improve a photometer having a hot cathode discharge tube by applying the above-mentioned zero adjustment circuit. To provide a photometer capable of preventing the recorder from running out even when using a photometer.

The features of the present invention include an adding circuit that takes the output of the absorbance converter as one of its inputs, and a zero adjustment circuit that gives an output that is equal in magnitude and opposite in polarity to the output of the absorbance converter as another input of the adding circuit. The zero adjustment circuit is automatically driven when the power is turned on, and the zero adjustment circuit is automatically driven at the same time as the discharge of the hot cathode discharge tube is turned on. The purpose is to prevent the effects of unsteady voltage.

Prior to describing embodiments of the present invention, a photometer to which a zero adjustment circuit, which has been improved by the present invention, is applied will be described with reference to FIG.

The discharge tube lighting circuit 1 includes a hot cathode discharge tube 2. When the switch 5 is on the NC contact side by the delay relay 10, the filament voltage of the discharge tube 2 is
Since the base current flows through the PNP transistor 9 and the PNP transistor 9 is in the ON state, the voltage of the low voltage rectifier circuit 7 is directly applied to the filament and heats the filament. The high voltage rectifier circuit 3 charges the capacitor 4 with the wavelength value of the AC voltage.

When the filament of the discharge tube 2 is heated for about 10 seconds after the power is turned on, the delay relay 10 is operated and the switch 5 is switched to the NO contact side. This starts the discharge of the discharge tube 2, and the discharge current flows to the constant current circuit 6 through the NO contact. The switch 5 also controls the start of discharge and also changes the filament voltage. When the switch 5 changes to the NO contact, no base current flows through the PNP transistor 9, so the PNP transistor 9 turns off and the filament is heated by the output voltage of the constant voltage circuit 8. In this way, from now on, the constant current circuit 6 controls the discharge current, and the constant voltage circuit 8 controls the filament voltage, so that the brightness is stabilized.

The light from the hot cathode discharge tube 2 enters the spectroscope 11, and one of the monochromatic lights thus separated is absorbed by the sample cell 12 containing the sample liquid and enters the sample-side photoelectric conversion element 14. The other side of the monochromatic light is the standard side photoelectric conversion element 15
to go into. The photocurrents of the photoelectric conversion elements 14 and 15 are converted into absorbance values by an absorbance converter 16, and are recorded by a recorder 26 via a summing amplifier 19 of a signal processing circuit 13. The output end 20 of the summing amplifier 19 is branched into two, one end being connected to the analog signal input end of the zero adjustment circuit 12 and the other end being connected to the voltage dividing resistor 24 . The voltage of the voltage dividing resistor 24 is determined by the sensitivity selector switch 2.
5 is selected.

The output of the absorbance converter 16 is connected to the first input terminal 17 of the summing amplifier 19, and the analog signal output of the zero adjustment circuit 21 is connected to the second input terminal 18. If the voltage at the first input terminal 17 is -V ₁ ,
When the zero adjustment circuit 21 is activated, the second input terminal 18
A compensation voltage +V ₁ is applied to .

Now, when the sample cell 12 is filled with solvent and the output voltage of the absorbance converter 16 is _-V1 , the operation of the zero adjustment circuit is as follows.

When the trigger switch 23 for the zero adjustment circuit 21 generates a negative logic pulse, the zero adjustment circuit 21 starts operating, and the analog output voltage of the zero adjustment circuit 21 changes so that the output voltage of the summing amplifier 19 becomes 0V. , when the analog output voltage reaches +V ₁ , the comparator in the zero adjustment circuit operates and zero adjustment is completed. From then on, unless a negative logic pulse is applied again by the trigger switch 23, the analog output voltage +
Works to continue outputting V ₁ .

As mentioned above, when the output voltage of the summing amplifier 19 is 0
If so, the recorder also records a zero point, and thereafter the output voltage of the summing amplifier 19 changes in proportion to the change in the output voltage of the absorbance converter 16, and can be recorded on the recorder.

Although such a device eliminates the need to manually adjust the variable resistor to zero, it does require manual operation of the zero adjustment circuit twice, before and after the hot cathode discharge tube is turned on. In the first state from when the power is turned on until the discharge tube lights up, even if the signal processing circuit 15 is in an operable state, the light source is not lit, so the output current of the photoelectric conversion elements 14 and 15 is 0. It is. At this time, the absorbance converter 16 outputs a voltage determined by the offset voltage of the built-in operational amplifier. This is because the offset voltages of the operational amplifiers in the absorbance converter 16 vary, so the output voltage of the absorbance converter also does not take a constant value. At this time, the recorder 26 swings completely in the positive or negative direction, so the trigger switch 23 is turned on manually to perform the first zero adjustment.

Next, the delay relay 10 operates and the hot cathode discharge tube 2
When lit, a photocurrent flows through the photoelectric conversion elements 14 and 15, and the absorbance converter 16 outputs another voltage. Since this varies depending on the type of solvent and the wavelength of light, the recorder 26 can also swing in the positive or negative direction. Therefore, after confirming that the discharge tube is lit, the second zero adjustment is performed manually in this state.

Next, one embodiment of the present invention will be described with reference to FIG. Components that are the same as those in FIG. 1 are given the same reference numerals. In this example, the first trigger circuit 3 generates a negative logic trigger pulse to drive the zero adjustment circuit.
0 and a second trigger circuit 40 are added. The output ends of both trigger circuits 30 and 40 are zero adjustment circuit 2
Connected to 1.

When the power is turned on, the switch 5 becomes an NC contact state by the delay relay 10, and the hot cathode discharge tube 2
filament is heated, and at the same time, the first trigger pulse generation circuit 30 operates.

At the moment when the power supply voltage of the first trigger circuit is supplied by turning on the power, the voltage across the capacitor 32 is 0V, so the transistor 34 is OFF and the collector is at a high level. capacitor 32
As charging progresses and the voltage increases, the transistor 34
Base current flows to turn ON, and the collector becomes low level. When the input of the inverter 35 changes from a high level to a low level, the output changes from a low level to a high level, and when the input of the monostable multivibrator 36 changes from a low level to a high level, it outputs a positive logic pulse, and the inverter 37 with an open collector outputs a positive logic pulse. Then, a negative pulse is generated. As a result, the zero adjustment circuit 21 is operated at the same time as the power is turned on, and the influence of an undefined voltage from the absorbance converter 16 is prevented.

The second trigger circuit 40 is a negative logic pulse generation circuit for performing zero adjustment when the discharge tube 2 is turned on. When the hot cathode discharge tube 2 lights up, a voltage is generated across the resistor 41 connected in series with the constant current circuit. The photocoupler 42 is driven with this voltage. Photocoupler 4
When current flows through the photodiode No. 2, the phototransistor 50 is turned on. Phototransistor 50
When turned on, the transistor 45 turns off and the collector changes from low level to high level. When the input of the monostable multivibrator 46 changes from a low level to a high level, it generates a positive logic pulse, and the open collector inverter 47 generates a negative logic pulse. As a result, the zero adjustment circuit 21 is operated simultaneously with the lighting of the hot cathode discharge tube 2.

As described above, according to this embodiment, the first trigger circuit 30 operates at the same time as the power is turned on, generates a negative logic trigger pulse to execute the first automatic zero adjustment operation, and then the hot cathode The second trigger circuit 40 operates simultaneously with the lighting of the discharge tube 2, generates a trigger pulse of negative logic, and executes the second automatic zero adjustment operation.

According to the present invention, the photometer can be easily handled because manual operation for zero adjustment is not necessary just by turning on the power. Further, since the zero adjustment circuit operates immediately when the power is turned on and when discharge starts, even when using a recorder, it is possible to prevent the recorder from running out.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic configuration of a photometer that is an object of improvement according to the present invention, and FIG. 2 is a diagram showing a schematic configuration of an embodiment of the present invention. 2... Hot cathode discharge tube, 11... Spectrometer, 14,
15...Photoelectric conversion element, 16...Absorbance converter,
19...Summing amplifier, 21...Zero adjustment circuit, 26
...Recorder, 30, 40...Trigger circuit.

Claims (1)

[Claims] 1 A discharge tube lighting circuit having a hot cathode discharge tube, an optical system that irradiates a sample with light from the hot cathode discharge tube and receives transmitted light from the sample at a light receiving section, and detects the signal from the light receiving section by absorbance. In a photometer equipped with a signal processing circuit that outputs an absorbance value from a converter, the signal processing circuit includes an addition circuit that takes the output of the absorbance converter as one of its inputs, and a signal processing circuit that outputs the output of the absorbance converter as one of its inputs. a zero adjustment circuit that provides an output of equal magnitude and opposite polarity as another input of the adder circuit, and a first pulse generation circuit that provides a drive pulse to the zero adjustment circuit when the power is turned on; A photometer equipped with a zero adjustment circuit, characterized in that a second pulse generation circuit is provided for detecting the start of discharge of a hot cathode discharge tube with a discharge current detection section and applying a driving pulse to the zero adjustment circuit.