JPS5885143A - Heating control device for atomic absorption analysis - Google Patents

Abstract

PURPOSE:To obtain heating characteristics that have good reproductivity by providing a circuit means to calibrate the output of a current sensor for temperature control in the stages of drying and ashing by means of output of a temperature sensor for temperature control in the stage of atmizing. CONSTITUTION:The output from a temperature sensor for a heating furnace is compared with a reference voltage Vr that corresponds to the maximum temperature of the heating furnace by means of a comparator 30 via a preamplifier 18. When the output exceeds the reference voltage Vr, a display device 31 is lighted to display, and when it is equal to Vr, it flickers. The output Vi of an electric current sensor for furnace heating current is inputted to an error amplifier 20 via a preamplifier 15 and a change-over switch 19, and compared with a reference voltage Er (Er=Vr) from a temperature programmer 21 and the heating current is controlled by the difference of the outputs. The output Vt of the preamplifier 18 is compared with Er in the same way by changing over the switch 19 to the B side. If Vi is not equal to Vt, the gain regulator 32 is adjusted to control the heating current until the display device 32 flickers. Accordingly heating characteristics with good reproductivity are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating control device for atomic absorption spectrometry, and particularly to a heating control device for atomic absorption spectrometry in a frameless atomic absorption spectrometer.

Some flameless atomic absorption spectrometers use Joule heat or arc heat to heat a sample and atomize it. 1st
The figure shows the principle of a flameless atomic absorption spectrometer that uses Joule heat. In this flameless atomic absorption spectrometer, a sample 5 is injected into a heating tube, such as a graphite tube 1, through an inlet 2, and a current for heating the sample is passed through the graphite tube 1 from a heating power source 4.

By controlling this current value, the sample 6 is heated in three stages: drying, ashing, and atomization, and is decomposed and atomized.

When atomized, the light from the hollow cathode lamp 5 is absorbed, and the amount of light absorbed is measured from the light flux passing through the spectroscope 6 to quantify the element. In this case, the heating temperature of the graphite tube 1 needs to be optimally controlled depending on the type of target element to be quantified and the properties of the sample.

Therefore, the temperature sensor 7 is installed near the graphite tube 1.
is arranged so that the entire temperature of the graphite tube 1 can be detected and the heating temperature can be controlled.

In such a flame Rene atomic absorption spectrometer, there are many factors to consider in order to increase the reliability of atomic absorption spectrometry, and ensuring reproducibility of addition/4' and tin Ji is one of them.

However, conventional flameless heating control devices for atomic absorption spectrometry perform drying and drying using the output of a single temperature sensor.
Since it is difficult to fully control the weighted temperature at each stage of ashing and atomization, that is, from 0° to 3000'C, in addition to the temperature sensor, we installed a basket E sensor that detects the current of the heating power source.・In the low-temperature heating overhead for ashing, this current sensor detects the current of the heating power source, and a signal according to the output heavy flow is returned to the heating power source to control the power [1 heat control C' ton current control]. Do.

High-temperature heating for atomization (1000'C to 3000°C)
Only the temperature sensor detects 1MLPik of the heating tube, and a signal corresponding to this detection output is returned to the entire heating power source to perform an assist control and a huge temperature control.

The heating control using the temperature sensor is always controlled depending on the temperature itself, so there is no problem, but heating control using the current sensor has a problem in reproducibility. In other words, no matter how much you control the heating current to a constant value, the heating temperature of the graphite tube will change due to variations in the resistance value of the graphite tube and variations in the flow rate of atmospheric gas and cooling water.
The drawback was that the temperature could not be controlled to a constant value.

The purpose of this invention is to eliminate the drawbacks of the conventional heating control device for atomic absorption spectrometry as described above, to control heating in the low temperature region of drying and ashing using a current sensor, and to control the heating only in the high temperature region of atomization using a temperature sensor. It is an object of the present invention to provide a heating control device for atomic absorption spectrometry, which has high reproducibility of heating temperature even when heating is controlled by heating.

In order to achieve the above object, the heating control device for atomic absorption spectrometry of the present invention uses a temperature sensor output for temperature control during the atomization stage, that is, high-temperature heating, and a temperature sensor output for temperature control during the drying/ashing stage, that is, low-temperature heating. The present invention is characterized in that circuit means 91 for calibrating the dual-use current sensor output can be implemented.

The present invention will be described in detail below with reference to an embodiment shown in one drawing.

FIG. 2 shows a block diagram configuring a heating control device for atomic absorption spectrometry, which is a premise for carrying out this invention.9. This corresponds to a conventional heating control device for atomic absorption spectrometry. In the figure, the AC signal applied to the source terminals 11a and 11b is passed through the heating power transformer 12 to the graphite tube 1.
3, graphite
A heating current is caused to flow through the tube 16 in accordance with an applied signal. Secondary side 12b of heating source track 12
A current sensor 14 is coupled to the current sensor 14 .
detects the heating current and is connected to a preamplifier 15 for signal amplification according to the detected current.

Still in the vicinity of the graphite tube 16, a temperature sensor 16 composed of, for example, a solar cell is arranged. The temperature sensor 16 detects the heating temperature of the graphite tube 13 by receiving light emitted when the graphite tube 16 is heated to a high temperature. The graphite tube 16 and the temperature sensor 16 constitute a sample heating furnace 17.
The temperature sensor 16 is connected to a preamplifier 18 that amplifies a signal corresponding to the detected temperature. The preamplifier 15 derives an output voltage Vi according to the detected current, and this output voltage V
i is connected so that it is applied to terminal A of the current control/temperature control changeover switch 19. On the other hand, the preamplifier 18 derives an output voltage Vt according to the detected temperature, and the common terminal C of the current control and temperature control j is connected to one end of the input of the error amplifier 20. At this input terminal of the error amplifier 2D.

Current control - temperature control switch 19 is terminal A (current control)
When it is tilted to the side, the output Vi of the preamplifier 15 is
On the other hand, when the terminals are turned to the terminal B (temperature control) side, the output Vt of the preamplifier 18 is applied to each terminal. At the other end of the input of the error amplifier 20.

It is connected to receive a reference voltage Er from the temperature programmer 21. The reference voltage Er from the temperature programmer 21 depends on the target element and the properties of the sample.

The value can be arbitrarily set continuously or in stages according to each stage of drying, ashing, atomization, etc.

The error amplifier 2o generates a voltage V which is the difference between the reference voltage Er and the output voltage Vi (or Vc) of the preamplifier 15 (or 18).
O is applied to the trigger pulse generation circuit 22. The trigger pulse generation circuit 22 generates a trigger pulse P at a timing corresponding to the differential voltage VO, and transmits this pulse P to the heating power supply transformer 1.
2, the firing angle of the triac 23 is determined by the differential voltage vO.
I try to control it accordingly.

Now, about heating graphite tube 13.

In the case of drying and ashing, assuming low-temperature region heating,
Heating control is under current control. That is, the current control/temperature control switching switch 19 is pushed to the terminal A side. Therefore, the heating current is detected by the current sensor 14, and the signal voltage Vi corresponding to this detected current is applied to the current control/temperature control switching switch.
Terminal A of switch 19.

It is added to one end of the input of the error amplifier 2o via the common terminal C. Then, when the signal voltage Vi is larger than the reference voltage Er, the heating current becomes smaller.

Conversely, if the signal voltage Vi is smaller than the reference voltage Er,
In order to increase the heating current, a trigger pulse P is generated at a timing corresponding to the voltage difference Vo between the signal voltage Vi and the reference voltage Er.
is added to TRIAC 23.

That is, a signal corresponding to the signal voltage Vi is fed back to the heating power source side. When performing the atomization stage, ie high temperature region heating, the heating control is under temperature control.

In this case, the current control-temperature control changeover switch 19 is connected to terminal B.
thrown to the side. Therefore, a signal voltage Vt corresponding to the temperature detected by the temperature sensor 16 is applied to one end of the input of the error amplifier 20 via the terminal B of the current control/temperature control switching switch 19 and the common terminal C.

Then, when the signal voltage Vt is larger than the reference voltage Er, the heating temperature is lowered, and conversely, when the signal voltage Vt is smaller than the reference voltage Er, the heating temperature is set higher. The heating temperature is controlled by applying a trigger pulse P at a timing corresponding to the reference voltage ErO differential voltage Vo to the triac 23 and controlling the heating current by changing the firing angle.

FIG. 3 is a circuit block diagram showing the main parts of an embodiment of the heating control device for atomic absorption spectrometry according to the present invention.

This circuit is additionally connected to the circuit shown in FIG. The same numbers as those shown in FIG. 2 refer to the same circuits. In the figure, the output terminal of the preamplifier 18 to which the temperature detection signal from the temperature sensor 16 is input is connected to the terminal B of the current control-temperature control changeover switch 19, and also to the comparator 30.
The comparator 30 is connected to one input end of the comparator 30, and is connected to the other input end of the comparator 30 so that a reference voltage Vr for calibration is applied thereto. This reference voltage Vr is selected to be a voltage corresponding to the highest temperature (for example, 1000° C.) in the current-controlled temperature range. Comparator 60 is preamplifier 1
When the output signal voltage Vt of 8 is higher than the reference voltage Vr, no output signal is derived;
The output terminal is connected to the display 31 so that the output signal voltage is applied to the display 31. The display 31 shows the signal voltage V
If t is smaller than the reference voltage Vr, it will not turn on, but if the signal voltage vtO is larger, it will turn on, and if the signal voltage Vt and the reference voltage Vr are equal, it will blink. Also, a preamplifier 15 to which a detection signal from the current sensor 14 is input.
A gain adjuster 32 is provided.

Here, when heating current I is passed through the graphite tube 13 and the relationship between the heating temperature T and the passage of one hour is determined, as shown in Fig. 5, the temperature T rises as time passes and then settles down to a constant temperature. . This settled moisture corrosion becomes more severe as the current flow increases. Conversely, if other conditions do not change and the current value rIIf is the same, the temperature will naturally settle down to the same. However, as mentioned above, in conventional heating control devices, even if the heating current is the same, there are variations in the resistance of the graphite tube, atmospheric gases not shown in the diagram,
The temperature T is not constant due to factors such as differences in the flow rate of cooling water.

For example, even if a heating current of 1 is applied, the characteristic curves of the heating temperature T for 9 hours depending on the heating furnace condition are, for example, 11a and 11b shown in FIG.

It will look like 11c. The characteristic curve shown in FIG.
(2) ib is Tu and 11c is Td, indicating that they have different heating characteristics. In this way, even if the same heating current is applied, it is not possible to always obtain the same heating temperature, so in the heating control device shown in Fig.
) It is difficult to confirm the reproducibility of N. Therefore, the circuit shown in FIG. 6 is added, the gain regulator 62 is adjusted, and the current sensor output is calibrated using the temperature sensor output.

Calibration is performed with the temperature programmer 21 outputting a reference voltage Er equal to the calibration reference voltage Vr, and with the current control/temperature control changeover switch 19 turned to the terminal A (current control) side.

Now, the standard state is such that the temperature of the graphite tube 13 when the heating current 1 is applied is Tr, and the output voltage Vi of the preamplifier 18 corresponding to this temperature is Vt=Vr. In this case, the output voltage Vi of the preamplifier 15 corresponding to the detected current of the heating current generator 1 is also equal to Vr. When the heating control device is in such a standard state, that is, in the state of the characteristic curve 11a in FIG. 6, it is in a stable state.

9. The output voltage VL of the preamplifier 18 and the calibration reference voltage Vr are equal. Since the comparator 30 derives the output voltage and the 1 indicator 61 blinks, there is no need to particularly adjust the gain adjuster 32.

Next, when the heating temperature T of the heating electric current 1 becomes higher than the temperature Tr in the standard state, for example, the characteristic curve 1 in FIG.
Assuming the state of ib, the output voltage VL of the preamplifier 18 corresponding to the thermal temperature Tu is larger than the calibration reference voltage Vr, so the 1 indicator 61 is turned on. Therefore, the gain regulator 32 is adjusted to increase the gain and lower the heating current until the indicator 31 is in a blinking state. Assuming that the display 31 blinks when the heating current is 0 as a result of lowering the current, the same heating temperature characteristics as when the heating current 11 is applied in the standard state can be obtained when the heating current is 0. That is, it is calibrated. Conversely, when the heating temperature T becomes p lower than the temperature Tr in the standard state with respect to the heating current 1, for example, considering the state of the characteristic curve 11c in FIG. 6, the output voltage Vt1d of the preamplifier 18 corresponding to the heating temperature TdK
Since it is smaller than the calibration reference voltage Vr, the comparator 6
0 is output type 8. is not derived, so the display 61 does not light up. Therefore, adjust the gain adjuster 32 to reduce the gain and increase the heating current until the display 31 flashes.If the heating current 2 causes the display 31 to flash, then With the current (2), heating temperature characteristics equivalent to those obtained when the heating current (1) is applied in the standard state can be obtained.That is, the heating temperature characteristics are calibrated.

In the embodiment shown in FIG. 6, the display 61 employs a three-stage display of lighting, 9 blinks, and non-lighting.

This may be a display in other forms, such as a color-based display. Furthermore, a digital display may also be used.

Although the current control system is still manually calibrated using the display and gain adjuster in the embodiment shown in FIG.
Alternatively, the circuit shown in FIG. 4 may be used to automatically complete one bite.

The circuit shown in Fig. 421 is also implemented by being added to the heating control device shown in Fig. 2, and the same numbers as those in Fig. 2 refer to the same circuits. The output terminal of the preamplifier 18 is connected to the terminal B of the current control/temperature control switching nut 19, and
It is connected to one end of the input of the comparator 30, and further connected so that the calibration reference voltage Vr is applied to the other end of the input of the comparator 30. The output terminal of the comparator 30 is connected so that its output is applied to the temperature programmer 65. The temperature proger 5, 733 receives the signal from the comparator 30 and sets the reference voltage Eri.
The signal is changed and applied to the other end of the input of the error amplifier 20.

Calibration in the embodiment circuit shown in FIG. 4 is performed by outputting a reference voltage Er equal to the calibration reference voltage Vr from the temperature programmer 33, and at the same time outputting a reference voltage Er equal to the calibration reference voltage Vr.
This is done with the terminal turned to the terminal A (current control) side. In the standard state where the temperature is Tr when the heating current 11 is applied,
Since the output voltage vt of the preamplifier 18 is equal to the calibration reference voltage Vr, the temperature programmer 53 that receives the output voltage from the comparator 30 does not change the reference voltage Er and directly uses it as the reference voltage Er in the current control to the error amplifier 20.
Add to.

Next, when the heating temperature for the heating electric current 1 becomes higher than the temperature Tr in the standard state, for example, the characteristic curve 11 in FIG.
In a case like state b.

Output voltage V of the free amplifier 18 corresponding to the heating temperature Tu
Since t is larger than the calibration reference voltage Vr.

Comparator 30 provides a signal indicating Vj)Vr to temperature programmer 33. The temperature programmer 66 is V t )
When receiving a signal indicating V r f, the level of reference voltage E' r is lowered until V t = V r. and Vt
The reference voltage Er when = Vr is set as the calibrated reference voltage in current control. Conversely, when the heating temperature for the heating current generator 1 is lower than the temperature Tr in the standard state, the output voltage V of the preamplifier 18 corresponding to the heating temperature Td
Since t will be less than the calibration reference voltage Vr, the comparator 30 will not derive an output. Therefore, the temperature programmer 33 increases the level of the reference voltage Er until the heating temperature rises and V t == V r. And V L
= Vr, the reference voltage Er stops rising and the reference voltage Er at that time is used as the calibrated reference voltage in current control.

As described above, the heating control device for atomic absorption spectrometry of the present invention uses the temperature sensor output for temperature control during the atomization stage to perform drying and
Since it is equipped with circuit means to calibrate the current sensor output for temperature control during the ashing stage, even if the heating characteristics vary due to variations in the resistance of the heating tube or other factors, the current control with temperature calibration will still work. , it is possible to obtain heating characteristics with good reproducibility.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the basic configuration of the Flame Rene atomic absorption spectrometer, Fig. 2 is a block diagram showing the configuration of the heating control device for atomic absorption spectrometry, which is a premise for implementing this invention, and Fig. 3
The figure is a block diagram showing the main circuit parts of a heating control device for atomic absorption spectrometry according to one embodiment of the present invention, and FIG. 4 shows the main circuit parts of a heating control device for atomic absorption spectrometry according to another embodiment of the invention. A block diagram, FIG. 5 is a diagram showing the time-heating temperature characteristic in FIG. 2, and FIG. 6 is a diagram showing the time-heating temperature characteristic and heating temperature characteristic shown in FIGS. 3 and 4 to explain the calibration operation of the embodiment circuit. - It is a diagram showing comparator output characteristics. 12: Heating power transformer, 13: Graphite tube, 14: Current sensor. 15/18: Preamplifier, 16: Temperature sensor 17:
Heating furnace, 19: Current control-temperature control changeover switch,
20: Error amplifier. 21/33: Temperature programmer, 22:) Trigger pulse generator, 23:) Liac. 30: Comparator, 31: Display. 32 = Gain adjuster patent applicant Shimadzu Corporation Representative Patent attorney Shigeru Nakamura Shin No. 1 Closed Figure 3 T Collection 5 Figure C Entrance

Claims (1)

[Claims] (1) A heating tube into which a sample is injected and a current applied from a heating power source to the sample to perform three-step heating of drying, ashing, and atomization, and a temperature sensor that detects the temperature of this heating tube. A current sensor detects the current of the heating power source, and the output of the current sensor is fed back to the heating power source during the low temperature heating stage of drying and ashing, and the output of the temperature sensor is fed back to the heating power source during the high temperature heating stage of atomization. A heating control device for atomic absorption spectrometry, comprising a control circuit section that returns to a heating power source and controls the temperature of the heating tube. A heating control device for atomic absorption spectrometry, comprising means for calibrating the current sensor output with the output of the temperature sensor.