JPH11166923A - Element analyzing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an element analyzing method capable of saving high-frequency output (power) to a minimum which is excessively supplied and improving analysis accuracy. SOLUTION: An extracting gas G of an element contained in a sample S is introduced from a sample extracting furnace 1 to a detecting part 4, and the outputs (a) and (b) of the detecting part 4 are processed at a computation control part 2. By this, the concentration of the above-mentioned element is quantitatively analyzed in an element analyzing method. At the time when the concentration of the extracting gas reaches set concentration P1 and P2, a signal is transmitted from a computation control part 2 to restrict power supply to the sample extracting furnace 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an elemental analysis method for quantitatively analyzing elements such as carbon and sulfur contained in samples such as metals and ceramics.

[0002]

2. Description of the Related Art For example, as an elemental analyzer for quantitatively analyzing elements such as carbon (C) and sulfur (S) contained in a sample such as steel or ceramics, a sample in a crucible is burned as an extraction gas. There is one that generates an oxidizing (combustion) gas and analyzes the oxidizing gas by an infrared absorption method.

As a device used in this elemental analyzer, there is, for example, a high-frequency induction heating device as shown in FIG. This apparatus has a high-frequency combustion furnace (also referred to as an induction combustion furnace) provided with a work coil 81 for burning a sample (which may contain an auxiliary agent) S in a crucible A to which a high-frequency voltage is applied. ) 82, and an air cylinder (not shown) that moves vertically while holding the crucible A under the high-frequency combustion furnace 82, and the crucible A containing the sample S is placed on the air cylinder. The sample S in the crucible A is set by setting the crucible table, raising the air cylinder, inserting the crucible A into the work coil 81, and applying a high-frequency voltage to the work coil 81 under O ₂ gas supply. Generates heat and burns. The supply of O ₂ gas is carried out via the O ₂ gas supply lance provided in the upper portion of the combustion furnace main body of the high-frequency combustion furnace 82. And, for example, a carrier gas (for example, O
Oxidizing gas G is introduced into the infrared detector 83 as a detection portion by the carrier gas introduced from ₂ gas) inlet holes. The detection signal (output of the detection unit) detected here is
The CPU as an arithmetic control unit calculates the instantaneous flow rate, concentration, integrated value, etc., divides by the sample weight, and displays the final result on the display 84. FIG. 8 shows a waveform 86 of a detection (CO ₂ concentration every moment) detected by a CO ₂ detection signal, for example.
7 shows a waveform 87 (a momentary SO ₂ concentration) detected by the SO ₂ detection signal.

[0004]

In the meantime, although the combustion state in the high-frequency induction heating system may be easily influenced by the kind of the auxiliary agent and the composition of the sample S, conventionally, the oscillation circuit of the high-frequency induction heating apparatus has conventionally been used. Is supplied to the sample S in an O ₂ gas atmosphere, and as a result, for example, carbon (C) in the sample S is extracted as a CO ₂ concentration. Output), and the CO ₂ concentration was not actively controlled by the high frequency output. Therefore, there were the following problems.

That is, the CO ₂ concentration varies widely depending on the content of carbon (C) in the sample S and the weight of the sample. For example, as shown in FIG. 8, the detected waveform 86 has a sharp peak. , The height of which is a momentarily detected amount. This is also true for the detection waveform 87 of the SO ₂ concentration. For this reason, in order to ensure analysis accuracy and reproducibility, a detector with good linearity over a wide range is required to avoid a non-linear error of the detector due to a wide dynamic range. It needs to be corrected. Also, since it supplies only a certain high frequency output,
The sample S burns at once, or the sample S bumps, resulting in abnormal analysis values and poor analysis accuracy. In addition, a detection error due to the sample weight also occurred. In addition, wasteful use of energy has frequently occurred, such as providing a high-frequency output similar to the case where the concentration of the extracted gas is originally low.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems, and has as its object to reduce the amount of high-frequency output (electric power) supplied excessively to a necessary minimum and to improve the analysis accuracy. It is intended to provide a way.

[0007]

In order to achieve the above object, an element analysis method according to the present invention introduces an extraction gas of an element contained in a sample from a sample extraction furnace to a detector, and calculates an output of the detector. In the element analysis method in which the element is quantitatively analyzed by processing in the control unit, when the extraction gas concentration reaches a set concentration, a signal is sent from the arithmetic control unit to supply electric power to the sample extraction furnace. I am trying to limit it.

The present invention is characterized in that the power supplied to the sample extraction furnace is controlled so that the concentration of the extracted gas is kept substantially constant every moment. That is, when the present invention is applied to, for example, a high-frequency induction heating method, as shown in FIG. (High-frequency) output control means (specific configuration will be described later) 2 for controlling (supply power) is provided, and feedback is performed mainly based on the output of the infrared detector 4 as a detection unit of the extraction gas G. ing. That is, a detection signal of a specific element contained in the sample S (for example, a CO ₂ detection signal a, or
The output of the SO ₂ detection signal b, etc.) is fed back to the output control means 2 to limit the high-frequency output so that the concentration of the extracted gas is kept substantially constant every moment. As a result, instead of obtaining the detection waveforms 86 and 87 having steep peaks as shown in FIG. 8, an almost trapezoidal shape in which the instantaneous extracted gas concentration is constant and the momentary extraction gas concentration is prevented as shown in FIG. Detection waveforms 3B, 3
C is obtained. In FIG. 1, the same reference numerals as those used in FIG. 7 indicate the same or corresponding elements, and reference numeral 5 denotes a display. FIG. 5 corresponds to FIG.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 2 to 4 show a first embodiment of the present invention in which elements such as carbon (C) and sulfur (S) contained in a sample S are quantitatively analyzed using a high-frequency induction heating apparatus. In this embodiment, a crucible table that moves in a vertical direction so as to enter and exit the high-frequency combustion furnace is used. 2 to 4, FIG.
The same reference numerals as those used in the above denote the same or corresponding parts.

First, in FIG. 2, a crucible A made of a material such as ceramic contains a sample S such as steel or ceramic, and the crucible A is vertically moved by an air cylinder (not shown). Is placed on a crucible base 6 that can be moved.

The high-frequency combustion furnace 1 burns a sample S in a crucible A by high-frequency induction heating, and has, for example, a cylindrical combustion furnace main body 6a and a work coil 7 therein. The work coil 7 is connected to a high-frequency oscillation circuit (hereinafter referred to as an oscillation circuit) 8 for supplying a high-frequency output (power) as supply power to the work coil 7. 9
Is a gas through hole provided in the combustion furnace main body 6a for letting out oxidizing gas W such as CO ₂ and SO _2, and is a carrier gas (O _{2 in} this embodiment) provided in the combustion furnace main body 6a.
Gas) The oxidizing gas W is used as an analysis gas by the CO ₂ analyzer 11 and the SO ₂ by the carrier gas Z introduced from the introduction hole 10.
₂ Sent to analyzer 12 and the like. 14 is a crucible A
In order to burn the sample S in the inside by high-frequency induction heating under the supply of O ₂ gas, an O provided at the upper part of the combustion furnace main body 6a is provided.
₂ Gas supply lance. Reference numeral 15 denotes a valve for supplying and stopping the O ₂ gas.

Hereinafter, an example of a power supply circuit of the high-frequency induction heating apparatus will be described in detail with reference to FIG. In addition,
3, the same reference numerals as those used in FIGS. 2 and 1 indicate the same or corresponding components.

The oscillating circuit 8 includes an oscillating tube 20 composed of a triode vacuum tube, a choke coil 21 connected to a plate of the oscillating tube 20, and a cascade coil 21 connected in series between the plate of the oscillating tube 20 and a grid. And two capacitors 22 and 23.

Reference numeral 24 denotes a DC power supply unit for supplying a variable DC current to the oscillation circuit 8; a transformer 25; and a phase control element (for example, a triac) 26 disposed on the primary side of the transformer 25. Is provided on the secondary side of the transformer 25, and the output side is connected to the oscillation tube 2 via the choke coil 21.
And a rectifying bridge 27 connected to zero.

The DC power supply 24 is connected to the input terminals 28 and 29 via, for example, an AC 200 V (50/60).
(Hz) AC power supply 30 is connected.

The rectifying bridge 27 has an oscillation tube 20.
Ammeter 31 for monitoring the plate current I _p of the plate
Is connected.

The phase control element 26 controls the phase of the high-frequency output output from the oscillation circuit 8. In the power supply circuit employed in this embodiment, the phase control element 26 A DC signal is provided as a trigger signal via the insulating circuit 32.

That is, the insulating circuit 32 is constituted by, for example, a photocoupler including a light emitting element 32a and a light receiving element 32b, and a trigger circuit 34 coupled to the DC signal circuit 33 by the insulating circuit 32 is provided with two resistances. 35 and 36 and the light receiving element 32b are connected in series. The DC signal circuit 33 includes the light emitting element 32
a, a resistor 37, a transistor 38 as a switching element, a controller 39 for outputting a control signal to the transistor 38 at a predetermined timing, and a DC 24, for example.
And a V power supply 40. The controller 39 is connected to a CPU (microcomputer) 41 as an arithmetic and control unit for controlling the entire high-frequency induction heating apparatus, and the controller 39 has a detection output of the plate ammeter 31, that is, an oscillation. The plate current _{Ip of the} tube 20 is input.

In the power supply circuit having the above structure, the transistor 38 is controlled by the control signal from the controller 39.
Is turned on, and the conduction of the transistor 38 causes a DC signal of a certain level to be supplied as a trigger signal to the phase control element 26 via the insulating circuit 32, whereby the phase control element 26 is turned on at a predetermined firing angle. The current is ignited and the current of the AC power supply 30 is switched by the phase control element 26 which is ignited at a predetermined ignition angle, and is supplied to the oscillation circuit 8 via the transformer 25 and the rectifying bridge 27. Then, a high-frequency output whose phase has been controlled is supplied from the oscillation circuit 8 to the work coil 7.

As described above, by continuously changing the on / off timing of the transistor 38 in the DC signal circuit 33, the plate current _Ip of the oscillation tube 20 can be continuously changed. The value of _p is detected by the monitor, and this is
In addition to controlling the high-frequency output by feedback, the present invention further controls the high-frequency output by feeding back the extracted gas detection signals a and b provided from the infrared detectors of the analyzers 11 and 12. For example,
(1) The high-frequency output is controlled so that the CO ₂ concentration is kept constant by the CO ₂ detection signal a, and the CO
_2. A substantially trapezoidal detection waveform 3A having a constant concentration is obtained (see FIG. 5), and after the CO ₂ extraction, a high-frequency output of the SO ₂ detection signal b is set so that the SO ₂ concentration is kept constant every moment. By performing the control, a substantially trapezoidal detection waveform 3C (see FIG. 5) in which the SO ₂ concentration is constant every moment is obtained.
In addition, the present invention utilizes the fact that the value of the plate current _Ip can be detected by a monitor, and
₂ , so that it can cope with the case where the SO ₂ concentration is so low that it does not reach the set concentration values P ₁ and P ₂ (see FIG. 5). That is, when the CO ₂ and SO ₂ concentrations are low, the plate current I
_The high frequency output is controlled by _p .

As a configuration for achieving the above (1) and (2), the output control means 2 is introduced in the present invention. The output control means 2 is mainly composed of a CPU 41, and detects a plate current I _p , a CO ₂ detection signal a and a SO ₂ detection signal b detected by a monitor.
Is fed back to the CPU 41. Note that FIG.
In the figure, 60 is a display, and 61 is a printer.

The CPU 41, as shown in FIG.
A function of calculating the O ₂ detection signal a and the SO ₂ detection signal b into the density, a function of comparing the reference voltage C _REF corresponding to the set density value P ₁ with the obtained CO ₂ density detection signal 43a, Has a function of comparing the reference voltage S _REF corresponding to the value P ₂ with the obtained SO ₂ concentration detection signal 43b, and further has an _Ip detection signal 43c,
It has the function of an OR circuit that outputs one of a and 43b. Reference numeral 44 denotes a control signal for controlling the firing angle of the phase control element 26.
9 is output. The reference voltages C _REF , S _REF and the reference current I _{(p) REF} of the plate current I _p may be set / adjusted separately or may be set / adjusted collectively. Further, the set density values P, P ₁ and P ₂ may be fixed, or may be set by a control signal from the CPU 41.

With the crucible A containing the sample S set on the crucible base 6, the crucible base 6 is raised, and the crucible A is inserted into the work coil 7. Is supplied, the sample S in the crucible A generates heat, melts, ignites, and further burns.

The carbon (C) contained in the sample S
₂ and SO due to sulfur and sulfur (S) respectively
₂ is generated and when the amount of carbon (C) and sulfur (S) contained in the sample S is determined, the optimum extraction temperature of carbon (C) is different from that of sulfur (S).
_{(2) The} high frequency output is controlled so that the CO ₂ concentration is kept constant every moment by the detection signal a. That is, when the CO ₂ concentration detection signal 43a reaches the reference voltage C _REF (set concentration value P ₁ ), the control signal 44 is output via the controller 39. Thereby, a substantially trapezoidal detection waveform 3A (see FIG. 5) in which the CO ₂ concentration is constant every moment is obtained.

After the CO ₂ extraction, the SO ₂
The high-frequency output is controlled so that the SO ₂ concentration is kept constant every moment by the detection signal b. That is, when the SO ₂ concentration detection signal 43b reaches the reference voltage S _REF (set concentration value P ₂ ), the control signal 44 is output via the controller 39. As a result, a substantially trapezoidal detection waveform 3B (see FIG. 5) in which the SO ₂ concentration is constant every moment is obtained.

Before completion of the extraction of CO ₂ , SO ₂
May be switched to the output control based on the above. Alternatively, the output control may be performed using only the larger one of the density detection signals 43a and 43b.

[0027] In the case _above, if a case was shown CO 2, SO ₂ concentration is high, low, i.e., if not reach the set levels, I _p detected signal 43c by the control signal 4
4 can be output, and the combustion state can be optimized.

FIG. 6 shows a state in which a metal sample S is charged into a graphite crucible A, an inert gas such as Ar or He is supplied as a carrier gas, and a large current is applied between the upper and lower electrodes 51 and 52. A second embodiment of the present invention using a resistance heating furnace 50 configured to dissolve the gas and introduce the gas generated at that time into the infrared detector 53 is shown.

In this embodiment, a heating power supply (for example, A
A voltage variable control means 56 corresponding to the output control means 2 in the first embodiment is provided between the C200V) 54 and the transformer 55. 5 is a display.

[0030]

As described above, according to the present invention, when the concentration of the extracted gas reaches the set concentration, a signal is sent from the arithmetic and control unit to limit the power supplied to the sample extraction furnace. is there. Therefore, the following effects are obtained.

An excessively supplied high-frequency output (power) can be saved. Since the dynamic range of the detector is not required more than necessary, detection can be performed in the optimum sensitivity range of the detector. Thereby, the analysis accuracy and the reproducibility can be improved. Detection errors due to sample weight can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a principle of supply power control according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a main part configuration in the embodiment.

FIG. 3 is an explanatory view of the overall configuration in the embodiment.

FIG. 4 is an explanatory diagram of a main part configuration in the embodiment.

FIG. 5 is a characteristic diagram showing detection waveforms of two extracted gases obtained in the embodiment.

FIG. 6 is a diagram for explaining the principle of supply power control according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a conventional example.

FIG. 8 is a characteristic diagram showing detection waveforms of two extracted gases obtained in a conventional example.

[Description of Signs] 1 ... Sample extraction furnace, 2 ... Output control means, 4 ... Detection unit, 44
... Control signal, G ... Extracted gas, a, b ... Output of detection unit, P
₁ , P ₂ … Set concentration value.

Claims (1)

[Claims] An element analysis method wherein an extraction gas of an element contained in a sample is guided from a sample extraction furnace to a detection unit, and an output of the detection unit is processed in an arithmetic and control unit to quantitatively analyze the element. 2. The element analysis method according to claim 1, wherein when the concentration of the extracted gas reaches a set concentration, a signal is sent from the arithmetic and control unit to limit the power supplied to the sample extraction furnace.