JP4055678B2 - Flame atomic absorption photometer - Google Patents

Description

  The present invention relates to an atomic absorption photometer, and more particularly to a flame atomic absorption photometer using a flame in which a gas is burned as a heat source for atomizing a sample.

  In the flame type atomic absorption photometer, a sample liquid is sprayed on a combustible gas, and the mixed gas is burned on a burner head to form a flame. In this flame, the sample is heated to high temperature and atomized, and the absorbance is measured by passing measurement light through the atomic vapor. As the combustible gas, for example, a mixture of an auxiliary combustion gas such as air and a fuel gas such as acetylene is used.

  In such a flame atomic absorption spectrophotometer, flame extinction may occur due to various causes such as depletion or supply failure of the fuel gas or auxiliary gas, the type of sample to be sucked, strong wind, and the like. Since it is a safety problem that the flammable gas continues to be ejected from the burner while the flame is extinguished, the flame type atomic absorption photometer has conventionally been provided with a flame monitoring means for monitoring the extinction of the flame ( (See Patent Documents 1 and 2).

  For example, in the device described in Patent Document 1, a phototransistor is provided as a light detection unit in the vicinity of a flame formed on a burner head, the emitter terminal of the phototransistor is grounded, and the collector terminal is pulled up with a load resistor. is doing. When there is a flame, a current flows through the phototransistor (the phototransistor is turned on), and the collector terminal becomes “L” level. On the other hand, when there is no flame, no current flows through the phototransistor (the phototransistor is turned off), and the collector terminal becomes “H” level. Therefore, by comparing the potential of the collector terminal with a predetermined reference potential (determination criterion), it is possible to determine the presence or absence of a flame and detect the extinction of the flame.

  Such an optical flame monitoring means ideally detects only the light from the flame, so that it is possible to prevent undesired background light (sunlight, illumination light, etc.) other than the flame light as much as possible. Design considerations have been made. However, since it is difficult to completely block the background light, depending on the background light conditions (for example, the position of illumination), the background light may be misrecognized as flame light, and the flame is extinguished even though the flame is extinguished. If there is, there may be a wrong decision.

  As a countermeasure against such a false detection of a flame, in some frame-type atomic absorption photometers, a light shielding plate is installed so that the flame monitoring means (strictly, the light detection unit) does not detect background light. Due to structural reasons, such a light shielding plate is often attached to a hood (sometimes called a chimney or the like) provided so as to surround the burner. However, such a hood can be easily removed by a measurer and is often forgotten to be worn during measurement. When such a hood is removed, a lot of background light is incident on the flame monitoring means, and the flame may be erroneously detected as described above.

Japanese Patent Laid-Open No. 11-23453 JP-A-11-183376

  The present invention has been made to solve such a problem, and a first object is to prevent erroneous detection of a flame by an optical flame monitoring means when the influence of background light other than flame light is large. Thus, an object of the present invention is to provide a frame-type atomic absorption photometer that can ensure high safety. Further, the second object of the present invention is to improve the flame detection accuracy by optical flame monitoring means and ensure high safety even when there is an influence of background light other than flame light. The object is to provide an absorptiometer.

The present invention was made in order to solve the above Symbol challenge, samples were atomized in a flame formed by burning combustible gas, measuring the absorbance due to the atoms by passing a measurement light to the atom vapor In the frame type atomic absorption photometer
a) flame monitoring means for detecting light emitted from the flame and judging the presence or absence of flame by comparing the detection signal with a predetermined criterion value;
b) Detection standard setting means for detecting a level of a detection signal by the flame monitoring means before ignition of the flame and changing the determination reference value according to the level;
It is characterized by having.

Embodiments and effects of the invention

In the flame type atomic absorption photometer according to the present invention, at any time before starting combustion, the determination reference setting means reads the level of the detection signal of the flame monitoring means, and the flame monitoring means Change the criterion value for determining the presence or absence. Specifically, if the background light is relatively high and the level of the detection signal is high before ignition, the judgment reference value is increased by that much so that it is not judged that there is a flame when there is no flame. To do.

Therefore, according to the flame type atomic absorption photometer according to the present invention, even if there is a certain amount of background light, the accuracy of detecting the presence or absence of flame by the flame monitoring means is improved, and the disappearance of the flame is reliably detected. By doing so, high safety can be ensured.

Further, in the flame type atomic absorption photometer according to the present invention, even when the determination reference value is changed by the determination reference setting means based on the level of the detection signal of the flame monitoring means before the ignition of the flame, Determination means for determining whether or not the determination of the presence or absence of flame by the monitoring means cannot be performed normally, and flame ignition when the determination means determines that the determination of the presence or absence of flame is not normally performed It is preferable to further include an ignition control unit that is not permitted.
In this configuration, at any time before the start of combustion, the determination means reads the level of the detection signal of the flame monitoring means, and determines whether or not the flame monitoring operation by the flame monitoring means can be performed normally. . Specifically, the criterion value was changed when the background light was too much due to, for example, the positional relationship between the device and the illumination being bad or the light shielding plate to be originally mounted was not mounted. However, there is a high possibility that the flame monitoring operation cannot be normally performed after the flame ignition. In such a case, there is a possibility of missing the flame, so the ignition control means disallows flame ignition.
That is, if the influence of the background light is abnormally large and the possibility of causing a malfunction in the monitoring operation of the flame monitoring means is high, the ignition is not permitted, but the background light exists even if the possibility is not high. If it is clear, the determination reference value for the presence or absence of flame is changed in accordance with the level of the detection signal before flame ignition while permitting ignition. Thereby, higher safety can be ensured.

Hereinafter, a frame type atomic absorption photometer which is an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic configuration diagram of a main part of a flame type atomic absorption photometer according to the present embodiment. A burner 10 for forming a flame (frame) 15 is connected to a fuel gas pipe 11 and an auxiliary combustion gas pipe 13, and a fuel gas electromagnetic valve 12 that opens and closes the pipe is connected to the fuel gas pipe 11. The tube 13 is provided with an auxiliary combustion gas solenoid valve 14 for opening and closing the pipeline. For example, the fuel gas is acetylene, and the auxiliary combustion gas is air or dinitrogen monoxide, but is not limited thereto. The burner 10 is provided with an ignition unit 16 that performs ignition (ignition), and a detection unit 17 that constitutes a part of flame monitoring means for detecting the presence or absence of the flame 15 is installed near the formation position of the flame 15. Has been. The detection unit 17 includes an optical sensor such as a phototransistor or a photodiode, receives light emitted from the flame 15, and outputs a detection signal corresponding to the received light intensity. A cylindrical hood 18 is detachably provided so as to surround the flame 15 for the purpose of ensuring the safety of the measurer and preventing the strong wind from hitting the flame. The hood 18 also functions as a light shielding plate that shields the outside light from the detection unit 17.

  The control unit 20 is mainly composed of a microprocessor, and is connected to a memory 25 for storing a control program corresponding to an analysis procedure, various parameters necessary for analysis, or data. The A / D conversion unit 24 converts the analog detection signal from the detection unit 17 into a digital signal and supplies the digital signal to the control unit 20. In addition, an operation unit 26, a display unit 27, an output drive unit 28, and the like are connected to the control unit 20, and the output drive unit 28 controls the electromagnetic valves 12, 14 and the ignition unit 16 in accordance with instructions from the control unit 20. To do. The control unit 20 executes various control operations in accordance with the control program, and includes characteristic units such as a pre-ignition level determination unit 21, an in-ignition level determination unit 22, and an ignition / extinguishment control unit 23 as characteristic functions. . Note that these functions centering on the control unit 20 can be realized using a general-purpose personal computer.

  In FIG. 1, the description of the flow rate adjustment unit, the gas pressure monitoring unit, the sample introduction unit, and the optical system for measuring absorbance is omitted.

  Next, a flame monitoring operation will be described with reference to FIGS. 2 and 3 as a characteristic operation in the frame-type atomic absorption photometer according to the present embodiment. FIG. 2 is a control flowchart regarding the flame monitoring operation, and FIG. 3 is a conceptual diagram of signal levels for explaining the operation.

  When an operation such as start of analysis (or ignition instruction) is performed by the operation unit 26, the control unit 20 determines that there is an ignition instruction (Y in step S1) and starts processing related to ignition. That is, the control unit 20 reads the signal level of the detection unit 17 via the A / D conversion unit 24 immediately before the start of combustion, that is, prior to flame ignition, and stores it in the memory 25 (step S2). Let this detection value be La. Next, the pre-ignition level determination unit 21 determines whether or not the detected value La exceeds a predetermined first determination reference value T1 (step S3). It is determined that there are too many light shielding plates (that is, the hood 18) is not attached. In this case, even if there is no flame after the flame ignition, there is a high possibility that it is determined that there is a flame, so flame ignition is not permitted (step S4).

  The ignition / extinguishment control unit 23 does not execute the ignition sequence when ignition is not permitted, and causes the display unit 27 to display an error message related to the impossibility of ignition, for example, “There is too much light from the outside” (step S5). Accordingly, the operator can quickly know that there is too much external light for some reason or that the hood 18 provided with the light shielding plate is not attached.

  On the other hand, if the detected value La is equal to or smaller than the determination reference value T1 in step S3, ignition is permitted, and the ignition / extinguishment control unit 23 executes an ignition operation (step S6). That is, according to a predetermined ignition sequence, the solenoid valves 12 and 14 are opened and the ignition unit 16 is operated to burn a mixed gas of fuel gas and auxiliary combustion gas to form a flame 15 on the burner 10.

  During combustion after ignition, the level determination unit 22 during ignition reads the signal level from the detection unit 17 every time a predetermined time (for example, 0.1 second) elapses (steps S7 and S8). Let this detection value be Lb. Then, it is determined whether or not the detection value Lb exceeds a predetermined second determination reference value T2 and an addition value (T2 + La) of the pre-ignition detection value La stored in the memory 25 (step S9). If the detected value Lb exceeds the added value (T2 + La), it is determined that there is a flame (step S12), and then it is determined whether there is a fire extinguishing instruction (step S13). If there is no fire extinguishing instruction, the process returns to step S7 to continue combustion. If there is a fire extinguishing instruction, the ignition / fire extinguishing control unit 23 executes a predetermined fire extinguishing sequence (step S14) and ends the process.

  If the detected value Lb is equal to or less than the added value (T2 + La) in step S9, it is determined that the flame has disappeared. In that case, both the solenoid valves 12 and 14 are closed, and the supply of these two gases to the burner 10 is stopped (step S10). At this time, for example, an error message notifying that the flame has disappeared is displayed on the display unit 27 (step S11). Thus, the operator can quickly know that the flame has disappeared.

  The conditions for disabling ignition in step S3 will be described with reference to FIG. When the background light is small enough to be ignored, the signal level by the detection unit 17 is assumed to be in the state shown in FIG. At this time, the pre-ignition detection value La (which is equivalent to the detection value when the flame goes out after ignition) is sufficiently lower than the second determination reference value T2 for determining the presence or absence of the flame after ignition. It should be possible to reliably detect the presence or absence of a flame after ignition.

  On the other hand, the background light is very large. For example, as shown in FIG. 3A-2, a state in which the signal level is significantly increased by the background light before ignition is considered. As described above, when determining the presence or absence of the flame after ignition, the determination reference value is raised by adding the pre-ignition detection value La to the second determination reference value T2, but the signal level originally has an upper limit Lmax. Therefore, there is a limit to the level at which accurate determination is possible even if the determination reference value after ignition is changed. That is, in the state shown in FIG. 3A-2, when the detection value La is added to the second determination reference value T2, the value approaches the upper limit Lmax as shown in FIG. It is impossible to determine whether there is a flame after ignition. Therefore, ignition is not permitted in such a state, and the first determination reference value T1 may be set so that the detection value La in such a state can be detected.

  On the other hand, although background light exists, as shown in FIG. 3 (b-2), the increase in signal level due to background light is not so large before ignition and is considered to be lower than the first determination reference value T1. At this time, as shown in FIG. 3 (b-3), between the determination reference value for the presence or absence of the flame after ignition raised by adding the pre-ignition detection value La to the second determination reference value T2 and the upper limit Lmax Has a sufficient margin, and the detection value Lb when there is a flame and the detection value La when there is no flame can be discriminated without any problem on the basis of the added value (T2 + La). Thus, even if there is a certain amount of background light, it is possible to reduce the influence of the background light and detect the presence or absence of a flame with high accuracy.

  According to the above configuration, when there is a high possibility that a flame is erroneously determined despite the fact that there is a lot of background light and no flame, the flame ignition itself is not performed, and to some extent the background light Even if there is a flame, the presence / absence of the flame after ignition is determined in consideration of the presence of the background light, so that the extinction of the flame can be detected with high reliability.

  In the above description, the detection signal of the detection unit 17 is described as being configured such that the signal level increases as the amount of received light increases, but conversely, the signal level decreases as the amount of received light increases. Even if configured in this manner, it is easy for the control unit 20 to invert and process the upper and lower relations, so that the same control is naturally possible.

  For example, when the function of the present invention is added to the existing frame type atomic absorption photometer as described above, generally only the addition of the A / D conversion unit 24 and the software change in the control unit 20 are performed. Correspondence is possible. Therefore, there is an advantage that it can be implemented with minor changes to the existing apparatus, that is, without significant increase in cost.

  The above-described embodiment is an example of the present invention, and it is apparent that the present invention is encompassed by the present invention even if appropriate modifications, corrections and additions are made within the scope of the present invention.

The schematic block diagram of the principal part of the flame | frame type atomic absorption photometer by one Example of this invention. The control flowchart of the flame monitoring operation | movement of the flame | frame type atomic absorption photometer by a present Example. The conceptual diagram of the signal level for demonstrating the flame monitoring operation | movement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Burner 11 ... Fuel gas pipe 12 ... Fuel gas solenoid valve 13 ... Auxiliary combustion gas pipe 14 ... Auxiliary combustion gas solenoid valve 15 ... Flame 16 ... Ignition part 17 ... Detection part 18 ... Hood 20 ... Control part 21 ... Pre-ignition level judgment part 22 ... Level determining unit during ignition 23 ... Ignition / extinguishing control unit 24 ... A / D conversion unit 25 ... Memory 26 ... Operation unit 27 ... Display unit 28 ... Output drive unit

Claims (2)

In a flame type atomic absorption photometer that atomizes a sample in a flame formed by burning a combustible gas and measures the absorbance by passing the measurement light through the atomic vapor,
a) flame monitoring means for detecting light emitted from the flame and judging the presence or absence of flame by comparing the detection signal with a predetermined criterion value;
b) Detection standard setting means for detecting a level of a detection signal by the flame monitoring means before ignition of the flame and changing the determination reference value according to the level;
A frame-type atomic absorption photometer characterized by comprising: 2. The flame type atomic absorption photometer according to claim 1, wherein even when the determination reference value is changed by the determination reference setting means based on the level of the detection signal of the flame monitoring means before ignition of the flame, the flame Determination means for determining whether or not the determination of the presence or absence of flame by the monitoring means cannot be performed normally, and flame ignition when the determination means determines that the determination of the presence or absence of flame is not normally performed A flame-type atomic absorption photometer, further comprising: an ignition control means for disapproval.

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