JPH087141B2 - Sample atomizer heating device - Google Patents

Description

Detailed Description of the Invention a. TECHNICAL FIELD The present invention relates to a heating device for a graphite tube sample atomization furnace used for flameless atomic absorption spectrometry.

B. Prior Art A graphite tube atomization furnace has a structure as shown in FIG. In this figure, 1 is a graphite tube, and holes for dropping the sample solution are formed on the upper surface. Electrode rings 2 made of tungsten or the like are attached to both ends, and a large current is passed through the electrode ring for a short time to the graphite tube. The dropped sample is dried, ashed, and vaporized. The current at that time is controlled so as to increase sequentially in the three stages of drying, ashing, and evaporation of the sample, and the current is controlled so that the specified temperature is reached in each stage of drying, ashing, and evaporation. Has been done.

The current control described above has been conventionally performed as follows. That is, make a small hole in the cylinder wall of the graphite tube,
The light emitted from this small hole is detected by a photodetector. Since this detection signal is a function of the temperature in the small hole of the graphite tube, the output of this photodetector is compared with a reference value and the output of the comparator is used for current control. The temperature programmer changes it over time.

C. Problems to be Solved by the Invention In a conventional current control circuit in a graphite tube sample atomization reactor, a phenomenon that an excessive current flows often occurs. The cause of this phenomenon is the apparent decrease in photodetection sensitivity due to the contamination of the light receiving optical path of the photodetector, and the higher the temperature of graphite, the lower the electric resistance, so in the case of energization heating, if there is temperature unevenness, the temperature If the contact resistance between the end surface of the graphite tube and the electrode ring is not uniform around the entire tube end surface, it tends to increase the unevenness. However, it is considered that there occurs a situation in which the temperature of the portion where the photodetector looks through the small hole of the graphite tube does not reach the target temperature.

In any case, when such an excessive current flows, the tube holder or the like makes an abnormal sound, and conventionally, the operator notices the sound abnormally and shuts off the power source to investigate the defective portion. However, if the state in which such an abnormal current flows is repeated, the electrical system of the device will be damaged early.

Therefore, the present invention is intended to prevent the occurrence of a state in which an abnormal current flows as described above.

D. Means for solving the problem In addition to the conventional current control system in the current heating device of the graphite tube sample atomization furnace, a current detection means and a current breaker are provided in the current circuit of the graphite tube, and the output of the current detection means is provided. Compare with a reference value with a comparator,
When the reference value is exceeded, the current breaker is operated by the output of the comparator.

E. Action When the excessive current does not flow, the current control means operates to control the current according to the temperature program set in the temperature plug lammer. When a current larger than the reference current, which is considerably larger than the current expected to flow by the temperature program, flows, the current breaker by the output of the comparator operates to cut off the graphite tube, and the excessive current flows. To prevent.

F. Embodiment FIG. 1 shows an embodiment of the present invention. Reference numeral 1 is a graphite tube, 2 is an annular electrode fitted to both ends, 3 is a graphite tube current circuit, and 4 is a heating power supply circuit.
The power supply circuit 4 receives power from a commercial AC power supply, steps down the voltage with a step-down transformer, and controls the conduction phase of the thyristor to adjust the graphite tube current. A current breaker 5 is inserted in the current circuit 3. 6 is a current circuit 3
Is a current sensor attached to. The output of the current sensor 6 is applied to the comparator C1 via the amplifier 7 and compared with the reference voltage sent from the temperature programmer 8. When the output of the amplifier 7 exceeds the reference voltage, the current breaker 5 is activated by the output of the comparator C1 and the graphite tube current circuit 3 is opened.

Reference numeral 9 is a photodetector for detecting the temperature inside the graphite tube, the output of which is an amplifier 10 and a changeover switch.
It is applied to the error amplifier C2 via 11 and the temperature programmer 8
The output of the error amplifier C2 is sent to the heating power supply circuit 4 after being compared with the reference voltage from the above, and the graphite tube current is adjusted so that the output of the error amplifier C2 becomes zero.

The temperature of the graphite tube is controlled so as to gradually increase in the order of sample drying, ashing, and evaporation, but the changeover switch 11 is in contact with the contact b side as shown in the figure in the low temperature region, and the error amplifier C2 The signal from the current sensor 6 is applied and compared with the signal from the temperature program 8 to heat at a constant current. In the high temperature region, the switch 11 is switched to the contact a side by a signal from the temperature plug rama 8. Therefore, the signal from the photodetector 9 is applied to the error amplifier C2 and compared with the signal from the temperature programmer 8. At the same time, the signal from the current sensor 6 is also applied to the comparator C1 and compared with the signal from the temperature programmer 8. To be done. If an excessive current flows in the graphite tube current circuit 3 because the resistance between the two annular electrodes drops significantly,
A signal is output from C1 to activate the current breaker 5 to cut off the graphite tube current.

FIG. 2A shows the relationship between current and temperature in the graphite tube. B in the figure is the upper limit current set for the temperature of the graphite tube.
The current breaker 5 is activated when the current value exceeds the current value shown by the line.

Although the above-described embodiment is configured to monitor and limit only the upper limit side of the current, two comparators are used, one is C1 of the above-mentioned embodiment, the other is for setting the lower limit of the current, and the lower limit current is the second. It can be set as shown in FIG. C so that an alarm is issued or the current breaker is activated even when the current is below this lower limit. The reason why the graphite tube current cannot increase above the lower limit is considered to be poor contact between the graphite tube 1 and the electrode ring 2 or wear or cracks due to multiple uses of the graphite tube itself, so a function for monitoring the lower limit of the current is also added. Then, together with the upper limit monitoring, it is possible to contribute to the determination of the replacement time of the graphite tube and the like.

In the embodiment shown in FIG. 1, the current breaker 5 can be activated and the alarm device can be activated.

G. Effect The graphite tube material nuclear reactor heating device of the present invention performs overcurrent monitoring as described above, and prevents the flow of a current exceeding the specified value, so that damage to the device due to excessive current can be avoided, and device malfunction can occur early. It can be found and the maintenance of the device becomes easy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a graph showing the relationship between temperature and current in a graphite tube, and FIG. 3 is a vertical sectional view of a graphite tube sample atomization furnace. is there. 1 ... Graphite tube, 2 ... Electrode ring, 3 ... Graphite tube current circuit, 4 ... Heating power supply circuit, 5
...... Current breaker, 6 ... Current sensor, 8 ... Temperature programmer, 9 ... Photo detector, C1 ... Comparator, C2 ... Error amplifier.

Claims (1)

[Claims] 1. A graphite tube current circuit supplied with current from a heating power source, wherein a current breaker is inserted and current detection means is attached, and the output of the temperature detection means of the graphite tube is compared with the output of the temperature programmer. The heating power source is controlled, and the current breaker is activated when the output of the current detecting means exceeds a reference value preset according to each temperature step controlled by the temperature programmer. A device for heating a sample atomization furnace, characterized by: