An arc plasma generator for the atomic emission analyzer with digitally controlled discharge parameters

Subject and Purpose. The subject of the work is atomic emission spectral analysis of substances using the most affordable arc and spark sources widely accepted in both laboratory and industrial practice. The aim is to improve solution principles of some technical problems in the field of construction of power supplies of arc and spark discharges with predetermined properties and to study their parameters.

Methods and Methodology. Traditional methods of producing spark and arc discharges are used. Several designs are proposed for discharge current and discharge gap breakdown power supplies, modeled using a computer program of circuit simulation and tested on the existing prototypes. The developed generator was put through tests and compared with a production analog of it in terms of statistical analysis of spectrum measurement results. 

Results. The microprocessor-controlled arc plasma generator "TsUG-2" has been developed and performed. The discharge current generation unit was constructed on the principle of digital-to-analog converter (DAC) with current summation. The discharge gap breakdown unit was performed on the semiconductor circuitry basis without any gas spark gaps. A unit was added for generating the initial pulse of discharge current, which made it possible to extend the spectrum excitation range, provide the sampling process control and improve the discharge combustion stability. A parameter control unit was developed to create and maintain the protective gas environment in the discharge chamber. The control over the operating modes of the generator and its synchronization with the spectrum recording equipment is exerted through an external interface. The manual control is carried out via a stand-alone control panel. The created generator "TsUG-2" produces discharge gap breakdown pulses of up to 12 kV amplitudes and arc pulses spanning a discharge current range as wide as 1...47 A. On them, additional current pulses of up to 150 A amplitudes can be superimposed, which significantly increases the rate of discharge current rise. The highest frequency of the discharge excitation pulses is 800 Hz. Comparison tests of the developed generator "TsUG-2" and a production generator "UGE-4" have been carried out.

Conclusion. The measurement results show that the standard deviation (RMS) of the photometric data of plasma formations obtained from the developed arc plasma generator "TsUG-2" is, on the average, three times less than from a production generator "UGE-4.