JP5117180B2 - Power supply device for deuterium discharge tube, control method thereof and analysis device - Google Patents

Description

  The present invention relates to a power supply device for a deuterium discharge tube and a control method thereof, and also relates to an analyzer using the same.

  A deuterium discharge tube is used as a light source for ultraviolet wavelength region analysis in a spectrophotometer. Along with the improvement of analysis accuracy, there is a demand for improvement in the stability of the amount of light emitted from the light source.

  In order to improve the light quantity stability, it is necessary to improve the discharge current stabilization accuracy of the deuterium discharge tube.

  Patent Document 1 discloses a deuterium discharge tube power supply device provided with a trigger voltage generation circuit for starting discharge and a constant current circuit for continuing the discharge current.

  Patent Document 2 discloses a deuterium discharge tube power supply device that detects the discharge current and controls the voltage.

JP-A-5-93752 JP 2001-85186 A

  The constant current circuit in the deuterium discharge tube lighting device disclosed in Patent Document 1 is insufficient for stabilizing the discharge current.

  In Patent Document 2, since the amount of light is proportional to the discharge current of the discharge tube, proportional control is performed by negative feedback that detects the discharge current and reduces the difference from the target signal. By this proportional control, when the amount of current is smaller than the target value, the discharge current is increased by increasing the output voltage of the power supply. Conversely, when the current amount is larger than the target value, the discharge current is decreased by decreasing the output voltage of the power supply. Act on. This effect is realized because the load characteristic is a positive resistance.

  However, in the case of a deuterium discharge tube, the characteristics of the anode voltage applied between the anode (anode) and the cathode (cathode) and the discharge current flowing from the anode to the cathode become negative resistance. For this reason, even if the accuracy of proportional control is increased in order to improve the stability of the discharge current, the accuracy does not increase. In addition, this results in positive feedback control, which may oscillate, stop discharging, and turn off.

  FIG. 3 is a graph showing an example of changes in the voltage between the anode and the cathode of the deuterium discharge tube and changes in the discharge current in the prior art. As is apparent from the figure, after the initial state after the trigger voltage is applied, the negative feedback control system oscillates without being stable due to the negative resistance in the low current control period, and finally the discharge current is It has disappeared and has gone out.

  In addition, even if the light does not turn off, the oscillation causes a decrease in stability.

  FIG. 4 is a graph showing an example of a change in the voltage between the anode and the cathode of the deuterium discharge tube and a change in the discharge current in the oscillation state of the prior art. Although the discharge state of the deuterium discharge tube continues, as is apparent from the figure, the anode voltage is increased or decreased with the increase or decrease of the discharge current, and the stability is greatly reduced.

  An object of the present invention is to reliably turn on a deuterium discharge tube suitable as a light source for an analyzer such as a spectrophotometer or a liquid chromatograph, and to improve the stability of the amount of light emitted from the lighted deuterium discharge tube. It is.

  Another object of the present invention is to provide an analyzer such as a spectrophotometer or a liquid chromatograph using a deuterium discharge tube with improved stability of radiant light quantity as a light source.

  In a preferred embodiment of the present invention, a relatively high discharge start trigger voltage is applied between the anode and the cathode of the deuterium discharge tube at the start of discharge, and a relatively low discharge continuation voltage is applied during the subsequent discharge. A deuterium discharge tube power supply device comprising a control device for controlling a discharge continuation current of the deuterium discharge tube to a predetermined value, a resistor on a common line supplying both the discharge start trigger voltage and the discharge continuation current When viewed from the power source side, the anode-cathode of the deuterium discharge tube and the series circuit of the resistors are set to have positive resistance characteristics in voltage-current characteristics. That is, by connecting a resistor in series with the discharge tube and adding a positive resistance characteristic by the resistor to the negative resistance characteristic of the deuterium discharge tube, the load characteristic viewed from the power source is corrected to the positive resistance characteristic. is there.

  In a preferred embodiment of the present invention, there is provided means for switching the resistance value of the resistor between an initial state of discharge start and a stable control state of discharge current. In other words, since it has a larger negative resistance characteristic in the glow discharge state at the beginning of the discharge, a relatively large resistor is connected, while a relatively small negative resistance characteristic is present in the arc discharge state where the discharge current is stably maintained. Therefore, it is corrected by connecting a relatively small resistor.

  According to the preferred embodiment of the present invention, the lighting of the deuterium discharge tube can be reliably continued and the stability of the amount of radiated light can be improved.

  Moreover, according to another desirable embodiment of the present invention, it is possible to provide an analyzer such as a spectrophotometer or a liquid chromatograph with improved measurement accuracy.

  Other objects and features of the present invention will be clarified in the embodiments described below.

  In a preferred embodiment of the present invention, a plurality of resistors are connected to form a maximum resistance value required at the start of discharge, and immediately after the start of discharge, a part of the connected resistors is short-circuited, A resistance value is formed in accordance with the continuous discharge state.

  FIG. 1 is an electric circuit configuration diagram of a power supply device for a deuterium discharge tube according to an embodiment of the present invention.

  A DC voltage is input to the power input terminal 1. The power converter 2 is a DC chopper that controls the voltage applied to the primary coil 301 of the transformer 3 with the pulse width by performing pulse width modulation on the input DC voltage. Of course, a PWM inverter can also be used, but in this embodiment, a DC chopper is used and a simple configuration with one switching element is realized.

  When the pulse width of the DC chopper is kept constant and the pulse width is widened, the current flowing through the coil 301 increases. When the pulse width is narrowed, the current flowing through the coil 301 decreases. A pulse voltage proportional to the current flowing through the primary coil 301 is generated in the secondary coil 302 of the transformer 3.

  On the output side of the triple voltage rectifier circuit 4, when the switch by the transistor 11 is in an open state, a no-load state occurs, and a DC high voltage that is three times the peak voltage of the pulse voltage generated in the secondary coil 302 is generated. In this embodiment, the voltage is tripled, but can be doubled or quadrupled as necessary. The output voltage of the triple voltage rectifier circuit 4 is smoothed by the LC filter circuit including the reactor 7 and the capacitor 8, and a smooth DC high voltage is obtained.

  This DC high voltage is output by the voltage dividing resistor 18 to a signal proportional to the magnitude of the DC high voltage and transmitted to the anode of the diode 19. The cathode of the diode 19 is connected to the cathode of the diode 20, and is transmitted to the cathode only when the anode voltage of the diode 19 is larger than the anode voltage of the diode 20, and is compared with the set (command) value, and the difference is PWM controlled. It is transmitted to the device 21. That is, a high-order priority circuit is formed by matching the diodes 19 and 20.

  The difference output signal between the set value and the negative feedback value is transmitted to the PWM control device 21 and performs PWM pulse width control so as to reduce the difference. As a result, the direct current voltage charged in the capacitor 8 or the discharge current value of the deuterium discharge tube 24 is controlled to be equal to the set value. That is, while the voltage of the capacitor 8 of the LC filter is high, the AVR control system is configured, and when the voltage of the capacitor 8 is low, the discharge current detection value becomes relatively large. The system automatically shifts to the ACR control system.

  A voltage corresponding to the current flowing in the primary coil 301 is also generated in the secondary coil 303 of the transformer 3. This voltage is rectified by the diode 16 and charged in the capacitor 15 to generate a DC voltage across the capacitor 15. Reference numeral 22 denotes a heater circuit for the cathode of the deuterium discharge tube 24.

  When a voltage is applied to the lighting start signal input terminal 25, a current flows through the light emitting diode in the photocoupler 14 to emit light, and the phototransistor in the photocoupler 14 is turned on. As a result, a DC voltage generated at both ends of the capacitor 15 is applied between the gate and source of the transistor 11, and the transistor 11 is turned on. Therefore, the DC high voltage charged in the capacitor 8 is applied between the anode and the cathode of the deuterium discharge tube 24 through the connection terminal 23 to the deuterium discharge tube 24, and the deuterium discharge tube 24 is connected to the DC high voltage. Discharge starts with voltage.

  The discharge current at the start of discharge passes through the resistor 9 and the resistor 10 and flows into the deuterium discharge tube 24. The resistance between the anode and the cathode of the deuterium discharge tube 24 at the start of discharge changes from the open state before the start of discharge to about several Ω in several μs. For this reason, when the discharge current suddenly increases and the output current from the power supply increases, the DC high voltage charged in the capacitor 8 decreases due to the discharge, and the voltage in the triple voltage rectifier circuit 4 is charged by the triple voltage. The electric charge that generated the voltage is also discharged, and the output voltage decreases.

  FIG. 2 is a circuit diagram of the triple voltage rectifier circuit 4 in one embodiment of the present invention. In the figure, C is a capacitor, D is a diode, and since it is known, its description is omitted.

  Now, returning to FIG. 1, the pulse voltage output from the secondary coil 302 of the transformer 3 is rectified by the diode 5, flows into the reactor 7 and the capacitor 8 of the LC filter, charges the capacitor 8, and deuterium discharge tube 24 discharge current is supplied.

  When the pulse output from the secondary coil 302 of the transformer 3 changes from the ON state to the OFF state, the reactor 7 releases a current close to the current that flows before turning OFF. This current is charged into the capacitor 8 and supplied as a discharge current of the deuterium discharge tube 24, passes through the current detection circuit 17, passes through the diode 6, and returns to the reactor 7.

  As a result, a current signal proportional to the discharge current is output from the current detection circuit 17 and transmitted to the anode of the diode 20 of the high priority circuit. On the other hand, since the anode voltage of the other diode 19 of the high priority circuit decreases for the above-described reason, the current signal passing through the diode 20 is automatically compared with the set value and the difference is transmitted to the PWM control circuit 21. Switch. The difference output signal between the set (command) value and the negative feedback value is transmitted to the PWM control circuit 21 and performs control to increase / decrease the output voltage of the DC chopper 2 so as to reduce the difference.

  FIG. 5 is a graph showing changes in voltage and current, which are lighting start characteristics of a deuterium discharge tube in a deuterium discharge tube power supply device according to an embodiment of the present invention. Comparing the lighting start characteristic of FIG. 5 with the lighting start characteristic in the prior art of FIG. 3, it can be seen that the discharge current is stably controlled from the transient state at the start of discharge to the set current value without an oscillation phenomenon.

  According to this embodiment, the discharge current reaches the set value of 0.3 (A) when 200 μs has elapsed from the start of lighting. Further, the current peak value immediately after the start of lighting of the lighting start characteristic in the prior art of FIG. 3 exceeded 10 (A). However, in the lighting start characteristic in one embodiment of the present invention of FIG. The current peak value of is about 3 (A). This is a result of the current being limited by the sum of the resistor 9 and the resistor 10. The large negative resistance characteristic of the deuterium discharge tube 24 in the process in which the discharge current reaches the set value of 0.3 (A) is discharge-corrected by the sum of the resistor 9 and the resistor 10, and the load as viewed from the power source The characteristic is a positive resistance characteristic. For this reason, the oscillation phenomenon which occurred conventionally by proportional control by negative feedback does not occur.

  When a voltage is applied to the lighting start signal input terminal 25, a current flows through the light emitting diode in the photocoupler 14 to emit light, and the phototransistor in the photocoupler 14 is turned on, so that the delay circuit 13 is generated at both ends of the capacitor 15. Applied DC voltage. In this embodiment, the voltage passing through the delay circuit 13 after 500 μs closes the switch by the transistor 12. As a result, both ends of the resistor 10 are short-circuited, and only the resistor 9 is connected in series with the deuterium discharge tube 24. Immediately after the start of discharge, the change region of the discharge current is several amperes, and it is necessary to correct a wide range of negative resistance characteristics. However, the fluctuation range of the discharge current after reaching the set current is 1 (mA) or less. become. For this reason, the correction region of the negative resistance is greatly narrowed, and it becomes possible to correct the negative resistance characteristic only by the resistor 9. In this embodiment, the resistor 9 is about 40Ω and the resistor 10 is about 100Ω.

  FIG. 6 is a graph showing a negative resistance characteristic of a deuterium discharge tube according to an embodiment of the present invention and a correction characteristic by a resistor. The figure shows the pre-correction characteristics in the stable arc discharge continuation state and the characteristics after correction using only the resistor 9. Therefore, the difference voltage between the two is a correction voltage applied to both ends of the resistor 9. The corrected characteristic is a positive resistance characteristic that rises to the right, and the discharge current can be made equal to the set (command) current value and stabilized by a proportional control system using negative feedback.

  FIG. 7 is a schematic functional configuration diagram of a spectrophotometer which is an analyzer using a power supply device for a deuterium discharge tube according to an embodiment of the present invention. The deuterium discharge tube 24 is used as a light source for ultraviolet wavelength region analysis in a detector for an analyzer such as a spectrophotometer or a liquid chromatograph. An example of an apparatus (FIG. 7) equipped with a discharge tube power source serving as a lighting power source is shown below.

  In order to light the deuterium discharge tube 24, the ON signal of the heater ON / OFF signal 31 from the microcomputer 39 that controls the entire apparatus, and the ON signal of the lamp ON / OFF signal 40 after about 20 seconds, respectively, are discharged from the discharge tube power supply 30. Is output. When the deuterium discharge tube 24 is lit, an ON signal of the lighting status signal 41 is output from the discharge tube power supply 30 to the microcomputer 39.

  The measurement wavelength designated by the operator is set by driving the diffraction grating 32 by a wavelength setting signal 46 from the microcomputer 39.

  Radiated light from the deuterium discharge tube 24 is split by the diffraction grating 32, and the operator-designated wavelength light is irradiated to the half mirror 33, and the reference light (R light) 35 serving as reference light and the cell 34 in which the measurement sample is present. It is divided into the irradiation light. The reference light (R light) 35 is converted into an analog electric signal via the R light detector 36 and the R light preamplifier 37, digital data is generated by the R light AD converter 38, and is input to the microcomputer 39.

  On the other hand, the sample light (S light) 42 that has passed through the cell 34 and has not been absorbed by the sample is irradiated to the S light detector 43, and is sent to the microcomputer 39 via the S light preamplifier 44 and the S light AD converter 45. Entered. Here, the microcomputer 39 performs absorbance calculation based on the digital data of the reference light (R light) 35, the sample light (S light) 42, and outputs the result as measurement data of the apparatus.

  According to the present embodiment, light source fluctuation noise in absorbance data can be reduced in an analyzer such as a spectrophotometer or a liquid chromatograph.

It is an electric circuit block diagram of the power supply device of the deuterium discharge tube by one Example of this invention. It is a circuit diagram of the triple voltage rectifier circuit 4 in one Example of this invention. It is a graph which shows the example of the change of the voltage between the anodes and cathodes of a deuterium discharge tube, and the change of discharge current in a prior art. It is a graph which shows the example of the change of the anode-cathode voltage of the deuterium discharge tube in the said oscillation state of a prior art, and the change of discharge current. It is a graph which shows the change of the voltage and electric current which are the lighting start characteristics of the deuterium discharge tube in the power supply device for deuterium discharge tubes by one Example of this invention. It is a graph which shows the negative resistance characteristic of the deuterium discharge tube by one Example of this invention, and the correction characteristic by a resistor. It is a schematic functional block diagram of the spectrophotometer which is an analyzer which used the power supply device for deuterium discharge tubes by one Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Input terminal of power supply, 2 ... Power converter (DC chopper), 3 ... Transformer, 301 ... Primary side coil, 302 ... Secondary side coil, 303 ... Secondary side coil, 4 ... Triple voltage rectifier circuit, 5, 6, 16, 19, 20 ... diode, 7 ... reactor, 8, 15 ... capacitor, 9, 10 ... resistor, 11, 12 ... transistor, 13 ... delay circuit, 14 ... photocoupler, 17 ... current detection circuit, DESCRIPTION OF SYMBOLS 18 ... Voltage detection voltage dividing resistor, 21 ... PWM controller, 22 ... Heater circuit, 23 ... Deuterium discharge tube connection terminal, 24 ... Deuterium discharge tube, 30 ... Discharge tube power supply, 32 ... Diffraction grating, 33 ... Half mirror, 34 ... cell, 35 ... reference light (R light), 36 ... R light detector, 37 ... R light preamplifier, 38 ... R light AD converter, 39 ... microcomputer, 42 ... sample light (S light), 43 ... S light detector, 44 ... Optical pre-amplifier, 45 ... S optical AD converter.

Claims (8)

While a relatively high discharge start trigger voltage is applied between the anode and cathode of the deuterium discharge tube at the start of discharge, and a relatively low discharge continuation voltage is applied during the subsequent discharge, the discharge of the deuterium discharge tube is continued. In a deuterium discharge tube power supply device equipped with a control device for controlling the current to a predetermined value,
A power converter with adjustable output voltage;
First and second resistors having different resistance values connected in series in a circuit for applying an output voltage of the power converter between an anode and a cathode of the deuterium discharge tube;
Of the two resistors, a short-circuit switch means connected in parallel to the first resistor having the larger resistance value;
Based on the lighting start signal, glow discharge is started by applying the output voltage of the power converter between the anode and cathode of the deuterium discharge tube via the two resistors with the short-circuit switch means open. Starting switch means
After a predetermined short time after the activation switch means is turned on, the short-circuit switch means is turned on to short-circuit the first resistor having the larger resistance value, and the second resistor having the smaller resistance value is turned on. Switching means for applying an output voltage of the power converter via the anode and cathode of the deuterium discharge tube to continue arc discharge,
A control device for controlling the power converter so that the output voltage of the power converter or the discharge current of the deuterium discharge tube is negatively fed back to a set value;
As viewed from the power converter, the voltage-current characteristic of the series circuit of the first and second resistors between the anode and the cathode of the deuterium discharge tube during the glow discharge and the first and second resistors is a positive resistance characteristic. Resistance values of the first and second resistors are set, and
When viewed from the power converter, the voltage-current characteristic of the series circuit of the second resistor having the smaller resistance value between the anode and the cathode of the deuterium discharge tube during the arc discharge becomes a positive resistance characteristic. As described above, the deuterium discharge tube power supply device is characterized in that the resistance value of the second resistor is set . 2. The deuterium discharge according to claim 1, further comprising negative feedback value switching means for switching a voltage detection value applied to the series circuit or a detection value of the discharge current to perform negative feedback to the negative feedback control system. Pipe power supply. 3. The high feedback circuit according to claim 2 , wherein the negative feedback value switching means inputs a voltage detection value applied to the series circuit or a detection value of the discharge current, and outputs the detected value to the control device of the power converter. A power supply device for a deuterium discharge tube. 4. The deuterium discharge tube power supply device according to claim 1, wherein the power converter is a chopper. In any one of claims 1 to 4, wherein the applied output voltage of the power converter to the primary side, the secondary side and a transformer connected to multiple voltage doubler rectifier circuit having more than doubled, the multiples A power supply device for a deuterium discharge tube, wherein an anode-cathode of the deuterium discharge tube and a series circuit of the resistor are connected to an output side of the pressure rectifier circuit. An analyzer for analyzing the data relating to the sample by calculating the absorbance by dispersing the radiated light from the power supply device for the deuterium discharge tube according to any one of claims 1 to 5 into reference light and irradiation light to the sample. While a relatively high discharge start trigger voltage is applied between the anode and cathode of the deuterium discharge tube at the start of discharge, and a relatively low discharge continuation voltage is applied during the subsequent discharge, the discharge of the deuterium discharge tube is continued. In the control method of the power source for the deuterium discharge tube for controlling the current to a predetermined value,
A first resistor and a second resistor having different resistance values are connected in series in a circuit for applying an output voltage of a power converter capable of adjusting an output voltage between an anode and a cathode of the deuterium discharge tube,
A short-circuit switch means is connected in parallel with the first resistor having the larger resistance value of the two resistors.
At the time of start-up, the short-circuit switch means is kept open, and the start-up switch means is turned on so that the output voltage of the power converter is supplied to the anode of the deuterium discharge tube via the first and second resistors. A glow discharge step applied between the cathodes;
After a predetermined short time after the activation switch means is turned on, the short-circuit switch means is turned on to short-circuit the first resistor having the larger resistance value, and the second resistor having the smaller resistance value. An arc discharge step of applying an output voltage of the power converter between an anode and a cathode of the deuterium discharge tube via
Controlling the power converter so that the output voltage of the power converter or the discharge current of the deuterium discharge tube is negatively fed back to a set value,
During the glow discharge, when viewed from the power converter, the voltage-current characteristics of the series circuit of the first and second resistors between the anode and the cathode of the deuterium discharge tube become positive resistance characteristics. , Setting resistance values of the first and second resistors,
During the arc discharge, when viewed from the power converter, the voltage-current characteristic of the series circuit of the second resistor having the smaller resistance value between the anode and the cathode of the deuterium discharge tube is a positive resistance characteristic. The control method of the power source for the deuterium discharge tube is characterized in that the resistance value of the second resistor is set . 8. The negative feedback control system according to claim 7 , wherein the step of controlling the power converter switches between a voltage detection value applied to the series circuit and a detection value of the discharge current with respect to the set command value. A method for controlling a power source for a deuterium discharge tube, characterized by performing negative feedback.

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