JPS6148101B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plasma light source stabilization device for a high frequency inductively coupled plasma emission spectrometer.

Conventionally, in the above-mentioned emission spectrometer, the light source is stabilized by detecting the high frequency wave power incident on the load using a pass-through power type and performing negative feedback control to keep this power constant. However, the impedance of the load changes depending on the flow rate of the gas supplied to the plasma, and also changes even when the sample is introduced, so even if the frequency of the high-frequency power source is kept constant, the matching state between the power source and the load will shift and reflected waves will occur. Therefore, even if the incident wave power is controlled to be constant, there is no guarantee that the power absorbed by the load will be constant. Also, as a characteristic of plasma, when power consumption decreases, plasma becomes inductive, so if the impedance between the power supply and the load matches in a certain state, the plasma flame becomes inductive from that state. When such a change occurs, as reflected waves are generated and power consumption is reduced, the plasma becomes more inductive and mismatching becomes more severe, and eventually the plasma disappears because there is no longer enough power to maintain it. Therefore, it is difficult to stabilize the plasma flame by controlling only to keep the incident wave power constant, and a separate control to accurately maintain matching between the power source and the load is required.

In view of the above-mentioned current situation, the present invention was made in an attempt to make it possible to stabilize a high frequency inductively coupled plasma light source with a simpler system. In accordance with this purpose, the present invention detects the incident wave power Pf to the load and the reflected wave power Pr from the load, and calculates the absorbed power Pp of the load = Pf
-Provide a control device that keeps Pr constant. The present invention will be explained below with reference to Examples.

The figure shows an apparatus for implementing the invention. 1 is a high frequency power supply circuit, 2 is a load, and 3 is a pass-through wattmeter. The high frequency output from the high frequency power supply 1 passes through the pass-through wattmeter 3 and is supplied to the load 2. The pass-through power meter 3 has two output terminals, one of which receives the incident wave power Pf.
The detected value of the reflected wave power Pr from the load 2 is outputted to the other output terminal. A subtraction circuit 4 performs a subtraction operation corresponding to Pf-Pr on the two output signals of the pass-through wattmeter 3. The output of this subtraction circuit 4 is applied to a comparison circuit 6 via an amplifier 5 and compared with a reference signal, and the output of the high frequency power supply circuit 1 is controlled by the output of the comparison circuit 6, so that the output of the comparison circuit 6 becomes 0. controlled so that

The device of the present invention has the above-described configuration and operates so that the power consumed by the load is always constant regardless of load impedance fluctuations, so even if the load matching state drifts during long-term use, the influence of the drift will be minimized. The long-term stability of the analysis is improved, and even when the load condition is changed, such as when changing the plasma gas flow rate or the type of sample solvent, There is no need to re-match the load and power supply, and the stability of the plasma flame is improved compared to conventional models, so the tuning range in which the plasma can be lit stably is widened, making it easier to tune. Furthermore, no other control device for stabilizing the plasma is required.

Note that the device of the present invention does not actively return the load to a matching state, so if the matching state of the load deviates significantly, the high frequency power supply circuit will be forced to produce a very large output. Therefore, in order to avoid putting an undue burden on the high-frequency power supply circuit, the reflected wave power detection output of the pass-through power meter 3 shown in the figure is monitored, and the above-mentioned control operation is performed until the reflected wave power reaches a certain level. Even if the reflected wave power increases beyond this level, the high frequency output may be clamped so as not to increase.

[Brief explanation of the drawing]

The drawing is a block diagram showing the configuration of an apparatus according to an embodiment of the present invention. 1... High frequency power supply circuit, 2... Load, 3... Pass-through wattmeter, 4... Subtraction circuit, 6... Comparison circuit.

Claims (1)

[Claims] 1 Using a pass-through wattmeter, detect the incident wave power to the load and the reflected wave power from the load, and control the high-frequency power supply so that the difference between the incident wave power and the reflected wave power is constant. High frequency inductively coupled plasma stabilizer.