WO2008072318A1

WO2008072318A1 - Emission analyzer

Info

Publication number: WO2008072318A1
Application number: PCT/JP2006/324834
Authority: WO
Inventors: Haruki Osa
Original assignee: Shimadzu Corporation
Priority date: 2006-12-13
Filing date: 2006-12-13
Publication date: 2008-06-19
Also published as: JP4919104B2; CN101558291B; JPWO2008072318A1; CN101558291A

Abstract

After a switching element (13) is turned on, a charge control section (16) makes a decision whether a current detected at an exciting current detecting section (15) has reached a predetermined level or not, and turns the switching element (13) off if the predetermined level has been reached. When the exciting current is controlled to a constant level, exciting energy stored in a flyback transformer (12) also becomes constant and that constant energy is stored in a capacitor (22) every time when the switching element (13) is turned off. A charge control section (16) repeats the on/off operation of the switching element (13) by a predetermined number of times at a predetermined interval before stopping the charging operation. Consequently, a constant energy is held in the capacitor (22) when the charging operation stops and the time from the start to the end of charging also becomes constant. Conditions for repeating spark discharge are thereby satisfied and an analysis precision and reproducibility are enhanced.

Description

Specification

Luminescence analyzer

Technical field

[0001] The present invention relates to an emission analysis device using spark discharge.

Background art

In a spark discharge type emission spectrometer, energy stored in a capacitor is applied to a discharge electrode to generate a spark discharge between the electrode and a metal sample, thereby evaporating elements in the metal sample and discharging. This element is excited by plasma. Since an element excited in the plasma emits light at a specific wavelength, the element can be quantified by measuring the light intensity at the wavelength by analyzing the emitted light. If the contained element is unknown, qualitative analysis can be performed by obtaining an emission spectrum in a predetermined wavelength range and examining the wavelength at which the line spectrum exists. Generally, spark discharge is repeatedly performed at a period of several tens to several hundreds of Hz, and the measurement accuracy is improved by integrating the photometric values obtained for each discharge.

In such an emission analyzer, it is necessary to charge a capacitor with a voltage of about several hundred volts in a relatively short time in order to perform a spark discharge. For this purpose, switching type capacitor charging circuits have been widely used in recent years (see, for example, Patent Document 1). Fig. 3 is a block diagram of an emission analyzer using a conventional switching capacitor charging circuit.

[0004] In this emission analyzer, the light emitting section includes a capacitor charging circuit 1, a capacitor circuit 2, an igniter circuit 3, and a light emitting stand 4. The capacitor charging circuit 1 includes a DC power source 11, a flyback transformer 12 having primary and secondary windings, a switching element 13 such as an FET, and a charging control unit 14 for driving the switching element 13. The capacitor circuit 2 includes a rectifier diode 21, a discharge capacitor 22 that stores electrical energy for discharge, and a charge voltage detection unit 23 that detects a charge voltage of the discharge capacitor 22. The igniter circuit 3 includes an igniter transformer 31 having a primary winding and a secondary winding, and an igniter driving unit for generating a high voltage at the secondary winding of the igniter transformer 31. Includes 32. The light emitting stand 4 includes a discharge electrode 41 and a sample (usually a metal) 42 which is an analyte.

In the capacitor charging circuit 1, the primary power wire of the flyback transformer 12 and the switching element 13 are connected in series at both ends of the DC power supply 11, and the switching element 13 is turned on (conducted by the charging control unit 14). ), A direct current flows through the primary winding of the flyback transformer 12 and the excitation energy is stored in the flyback transformer 12. The charging control unit 14 turns on the switching element 13 for a preset time, and when the switching element 13 is turned off, a back electromotive force is generated in the secondary winding of the flyback transformer 12. As a result, the excitation energy force capacitor circuit 2 stored in the flyback transformer 12 immediately before that is supplied to the discharge capacitor 22 through the rectifier diode 21 and the discharge capacitor 22 is charged.

The switching element 13 is on / off controlled as shown in FIG. 4, and every time the switching element 13 is turned off, the charging voltage of the discharging capacitor 22 is determined by the excitation energy stored in the flyback transformer 12 immediately before the switching element 13 is turned off. Goes up step by step. The charging voltage detection unit 23 monitors the charging voltage of the discharging capacitor 22, and the charging control unit 14 determines whether or not the charging voltage exceeds a predetermined voltage VI based on the monitored value. The charging control unit 14 repeats the on / off control of the switching element 13 until the charging voltage exceeds the predetermined voltage VI. When the charging voltage exceeds the predetermined voltage VI, the on / off operation of the switching element 13 is stopped so that the discharging capacitor 22 Stop charging.

[0007] Since the charging is completed by this, if a high voltage is subsequently generated in the igniter transformer 31 by the igniter driving unit 32 in the igniter circuit 3, a spark discharge is generated between the discharge electrode 41 and the metal sample 42. At this time, the surface of the metal sample 42 is locally heated and the elements present on the sample surface evaporate. At the same time, the energy stored in the discharge capacitor 22 moves between the discharge electrode 41 and the metal sample 42 (gap) to form plasma, and the evaporated elements are excited by electrons in the plasma. When the excited element returns to a stable state, light having a wavelength corresponding to the energy difference is emitted. The photometry unit 5 including a spectroscope and a light detector measures emitted light having a wavelength peculiar to this element, and collects information on the elements contained in the metal sample 42. [0008] As described above, in the capacitor charging circuit 1 using the conventional switching method, the electric energy required for the discharging capacitor 22 is stopped by a method in which charging is stopped when the charging voltage of the discharging capacitor 22 exceeds a predetermined voltage VI. To store.

However, the capacitor charging circuit 1 as described above has the following problems. That is, since the time during which the switching element 13 is turned on is constant, when the voltage of the DC power supply 11 changes, the amount of excitation energy stored per on / off operation of the switching element 13 changes. Further, the capacitance of the discharge capacitor 22 fluctuates due to the temperature rise of the discharge capacitor 22 and the like. As described above, when the accumulated amount of excitation energy in the flyback transformer 12 or the capacitance of the discharge capacitor 22 fluctuates, the switching element 13 that is required to charge the discharge capacitor 22 to a certain constant voltage V 1 is turned on. / The number of OFF operations will change. Then, as shown in FIG. 5, the timing at which the charging voltage of the discharging capacitor 22 exceeds the threshold voltage VI varies, and the switching element 13 is turned on / off at most once for the charging voltage of the discharging capacitor 22 when charging is stopped. Variation in voltage corresponding to operation occurs. As a result, the energy stored in the discharging capacitor 22 varies.

[0010] In addition, since the charge stop control is performed by the monitor value of the charging voltage of the discharging capacitor 22, if the capacitance of the discharging capacitor 22 itself changes as described above, the final charging voltage is temporarily Even if it is constant, the energy held in the capacitor 22 will change.

[0011] If the energy stored in the discharge capacitor 22 is not constant during spark discharge, the plasma generation state changes during discharge. As a result, even if the amount of elements contained in the metal sample 42 is constant, the emission intensity varies, which may cause a decrease in analysis accuracy and reproducibility.

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-333323 (paragraphs 0004-0007, FIG. 5)

Disclosure of the invention

Problems to be solved by the invention

[0013] That is, in order to improve the analysis accuracy and reproducibility of a spark discharge type emission spectrometer, it is important to keep the accumulated energy of the capacitor just before discharge constant, but the conventional apparatus Then, it was difficult to make the stored energy constant. Main departure Is designed to solve these problems, and the purpose of this is to improve the stability of the stored energy of the discharge capacitor for generating spark discharge, and to An object of the present invention is to provide an emission analyzer capable of stabilizing the light emission of an element.

Means for solving the problem

[0014] The present invention, which has been made to solve the above problems, stores a discharge electrode disposed with a predetermined gap between a sample, an igniter circuit connected to the discharge electrode, and electrical energy for discharge. In a light emission analyzer comprising a capacitor and a capacitor charging circuit that charges the capacitor, the capacitor charging circuit comprises:

a) DC power supply,

b) a flyback transformer in which a primary feeder is connected to the DC power source, and electric energy is supplied to the capacitor from the secondary feeder;

c) switching means for on-Z-off controlling the exciting current supplied from the DC power source to the primary winding of the flyback transformer;

d) current detection means for detecting the current value of the excitation current;

e) An on / off operation of turning off the switching means when the current value detected by the current detection means reaches a predetermined value after turning on the switching means is repeated a predetermined number of times at predetermined time intervals. Control means for controlling the operation of the switching means;

It is characterized by having

In the emission analysis apparatus according to the present invention, the control means turns on the switching means and then supplies the excitation current supplied to the primary winding of the flyback transformer at a certain constant value. -Turn off the switching means to stop. Since the excitation energy accumulated in the flyback transformer depends on the inductance of the winding and the current flowing in the winding, control is performed so that the supply of that current stops when the excitation current reaches a certain value. If this is done, the excitation energy stored in the flyback transformer per on / off operation of the switching means will be constant regardless of the DC power supply voltage. Furthermore, the control means repeats the ON / OFF operation of the switching means for a fixed number of times, thereby condensing the condenser. Since the capacitor is charged (that is, the excitation energy stored in the flyback transformer is transferred to the capacitor), the energy held in the capacitor when charging stops is also constant.

[0016] In addition, since the number of times the switching element is turned on / off and the time interval (the time required for one on / off operation of the switching element) are determined, the time from the start of charge to the end of charge is It becomes constant. If the time from the end of charging to the operation of the igniter circuit is constant, the time to operate the charging start force igniter circuit is also constant. For example, the energy consumption by the circuit that detects the charging voltage of the capacitor, etc. The amount (loss) is also constant. Therefore, the energy stored in the capacitor immediately before the spark discharge is generated by operating the igniter circuit is constant.

[0017] It should be noted that the accumulated energy of the capacitor during discharge depends on the number of repetitions of the on / off operation of the switching means, so that the number of repetitions can be set from the outside. It is also possible to set a predetermined value for determining the current value of the excitation current from the outside in order to turn off the switching element.

The invention's effect

[0018] According to the emission analysis apparatus according to the present invention, the accumulated energy of the discharge capacitor is kept constant when spark discharge is generated without being affected by fluctuations in the voltage of the DC power supply or the capacitance of the capacitor. Can be. As a result, the generation of plasma due to discharge can be performed stably and almost under the same conditions, and the emission of the target element in the plasma can also be performed stably. Thus, it is possible to improve the accuracy and reproducibility of the emission analysis.

Brief Description of Drawings

FIG. 1 is a block configuration diagram centering on a light emitting unit of an emission analyzer according to an embodiment of the present invention.

FIG. 2 is a main timing chart in the light emission part of the emission spectrometer according to the present embodiment.

FIG. 3 is a block configuration diagram centering on a light emitting portion of a conventional emission analyzer.

FIG. 4 is a waveform diagram of the main part of a light emission part of a conventional emission spectrometer.

FIG. 5 is an explanatory diagram of variation in charging voltage in a light emitting unit of a conventional emission spectrometer.

Explanation of symbols

[0020] 1 ... Capacitor charging circuit 11-… DC power supply

12-… flyback run

13-… Switching element

15-… Excitation current detector

16-… Charge controller

2--'Capacitor circuit

21-… Rectifier diode

22-… Discharge capacitor

23-… Charging voltage detector

3.

31-ignitorance

32-… Dydanita Drive

4.

41-■ · · Discharge electrode

42-… Metal sample

5

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of an emission analyzer according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram centering on the light emitting part of the emission analyzer according to the present embodiment, and FIG. 2 is a main timing diagram. The same components as those of the conventional emission analyzer described in FIG. 3 are denoted by the same reference numerals, and detailed description thereof is omitted.

In the light emission part of the emission analyzer according to the present embodiment, in the capacitor charging circuit 1, an excitation current detection part 15 is connected in series with the primary winding of the flyback transformer 12 and the switching element 13. The current value detected by the current detection unit 15 is input to the charge control unit 16. The charging control unit 16 determines the on / off operation timing of the switching element 13 based on the current detection value from the excitation current detection unit 15 instead of the voltage detection value from the charging voltage detection unit 23. In FIG. 1, the charging voltage detection unit 23 is also provided. For example, this can check whether or not the discharging capacitor 22 is normally charged, It is provided to prevent overcharging or to detect that the discharge has been completed.

[0023] The operation of the light emitting unit will be described step by step. When the switching element 13 is turned on by the charging control unit 16, a direct current excitation current flows from the direct current power source 11 to the primary winding of the flyback transformer 12, and excitation energy is accumulated in the flyback transformer 12. At this time, the excitation current increases substantially linearly during the ON period of the switching element 13 as shown in FIG. The current value of the excitation current is detected momentarily by the excitation current detection unit 15, and the charge control unit 16 determines whether or not the current value has reached a predetermined threshold value il. When it is detected that the current value of the excitation current has reached the threshold value il, the charging control unit 16 quickly drives the switching element 13 off. As a result, the supply of excitation current is cut off. When the switching element 13 is turned off, a back electromotive force is generated in the secondary winding of the flyback transformer 12. As a result, the excitation energy stored in the flyback transformer 12 immediately before is supplied to the discharging capacitor 22, and the discharging capacitor 22 is charged.

[0024] The charging control unit 16 previously stores the length of a period of one on / off operation of the switching element 13 (the time interval from when the switching element 13 is turned on to when it is turned on) and the on / off movement. The number of repetitions of the work is set. Therefore, the charging control unit 16 stops the charging by executing the on / off operation of the switching element 13 for the number of repetitions in the on / off operation period length.

[0025] When the voltage of the DC power supply 11 fluctuates, the slope of the increase in excitation current when the switching element 13 is on changes. For example, in Fig. 2, the slope of the increase in excitation current is gentle in (B) because the voltage of DC power supply 11 is lower than in (A). On the other hand, since the switching element 13 is kept on until the exciting current reaches the threshold value il, the on-time of the switching element 13 is not always constant, and switching is performed when the increase of the exciting current is gentle. The on-time of the element 13 is increased. However, as described above, the length of one ON-Z OFF operation is fixed (does not vary), so if the ON time becomes longer, the OFF time becomes shorter accordingly.

[0026] The excitation energy E stored in the flyback transformer 12 is equal to the winding inductance less excitation current I. E = (l / 2) -LI

Therefore, when the excitation current I is constant, the excitation energy is also constant. Therefore, every time the switching element 13 is turned off, the same amount of excitation energy is transferred from the flyback transformer 12 to the discharging capacitor 22. Since the number of on / off operations of the switching element 13 is also determined, the energy stored in the discharging capacitor 22 is constant when charging is stopped.

When the charging of the discharging capacitor 22 is completed as described above, a high voltage is generated from the igniter driving unit 32 to the igniter transformer 31 in the igniter circuit 3 under the control of a control circuit (not shown), and the light emitting stand Spark discharge is generated between the discharge electrode 41 of 4 and the metal sample 42. Thereby, the elements present on the surface of the metal sample 42 evaporate, and light emission derived from the elements occurs in the plasma formed between the discharge electrode 41 and the metal sample 42.

[0028] The length of the ON / OFF operation period of the switching element 13 and the number of repetitions thereof are constant (they are not changed during the analysis of at least one sample). The time required from the start of charging to the completion of charging is constant. A charging voltage detector 23 is connected to the discharging capacitor 22 in parallel. In addition, a bleeder resistor is also connected in parallel to the discharging capacitor 22 for ensuring safety. These leak the electric charge held in the discharge capacitor 22, that is, consume a small part of the stored electric energy. However, since the required time is constant as described above, the amount of energy consumed is constant. Is also constant. Furthermore, since the time from the start of charging to the execution of discharging, that is, the operation of the igniter circuit 3 is also constant, the electrical energy accumulated in the discharging capacitor 22 at the time of discharging can be made constant.

[0029] Thereby, when the spark discharge is repeatedly executed, for example, the conditions for the spark discharge between the discharge electrode 41 and the metal sample 42 and the light emission in the plasma can be made uniform, and unnecessary photometry. Analysis accuracy and reproducibility can be improved by suppressing variation in values.

[0030] As is clear from the above description, if the number of repetitions of the on-Z-off operation of the switching element 13 is changed, the stored energy in the discharge capacitor 22 at the time of discharge execution Is different. Therefore, for example, if you want to change the discharge conditions depending on the type of sample or the discharge atmosphere, change the number of repetitions of the on / off operation. ,

Further, the above-described embodiment is an example of the present invention, and it is apparent that the present invention is encompassed in the scope of the present application even if appropriate modifications, additional calories and corrections are made within the scope of the present invention.

Claims

The scope of the claims

[1] A discharge electrode arranged with a predetermined gap between the sample, an igniter circuit connected to the discharge electrode, a capacitor for storing electric energy for discharge, and a capacitor charging circuit for charging the capacitor , The capacitor charging circuit comprises:

a) DC power supply,

c) switching means for controlling on / off of the exciting current supplied from the DC power source to the primary winding of the flyback transformer;

An emission analysis apparatus comprising:

[2] The luminescence analyzer according to [1], wherein the number of repetitions of the on / off operation of the switching means can be set from the outside.