Sensing the arc

Citation

Spencer, J.W. (2003), "Sensing the arc", Sensor Review, Vol. 23 No. 1. https://doi.org/10.1108/sr.2003.08723aaa.002

Sensing the arc

Sensing the arc

Joseph W. Spencer

Keywords: Gas discharges, Plasma, Arcs, Sensors

The importance of sensors, data processing and information extraction tools were discussed at the Fourteenth International Conference on Gas Discharges and their Applications (Liverpool, 2-6 September 2002). They were shown to be a vital component in the understanding of the fundamental processes within such discharges and plasmas. Furthermore, the number of different types of plasma and their numerous applications to a wide range of industrial processes highlighted that such sensing and monitoring techniques used in this area are transportable across technology boundaries and may benefit other technology areas.

Electrical discharges and plasmas are complex structures with many interrelated variables such as power input, temperature, pressure, gas flow etc. In general, electrical discharges and plasmas and their applications are vital tools in a modern technology based society. Applications for which they are used are varied. Some examples of their applications are:

• •

  processing and manufacture of the latest semiconductor processor for use in the personal computer or in the latest mobile phone;

• •

  processing of pure metals for aerospace use;

• •

  environmental conditioning, e.g. sterilisation of rooms and equipment, air purification; and

• •

  disconnection of fault currents in power systems.

Due to the close coupling of the variables within plasmas they, and the applications to which they are applied, must be treated as forms of complex systems. As such their monitoring requires the use of a variety of sensors, signal conditioning methods, data processing, information extraction tools and information interpretation algorithms. The latter is vital for connecting the sensed data to the prevailing conditions within the complex system. However, there are many instances where conventional sensors and processing tools are not appropriate and therefore new and novel sensors, data processing methods and information extraction tools are developed. These have been presented at previous conferences and some are being used successfully for nonplasma applications.

Sensors used for monitoring electrical discharges and plasmas are fundamental tools by which information is gathered.

This is primarily useful to scientists and engineers in order to provide a basic understanding of the fundamental processes within the plasma and for the optimisation of the application of the plasma for a particular technological use. However, the deployment of these sensors often leads to a compromise between, on one hand, the need to know the value of a parameter at that point in the system and, on the other, the difficulties relating to the environment in which the sensor is to function. Some plasma environments are chemically and thermally aggressive and all are electrically hostile (e.g. RFI arising from radio frequency induced plasmas; plasmas with currents in excess of 60 kA; rapid voltage transients of many kV/μs arising from fast electrical breakdowns ~ 300 ps). Without careful consideration of the system and the environment into which the sensor is placed, the sensor itself may either significantly distort the very parameter to be measured or it may itself be subjected to interference. In either case the data from the sensor may appear normal whilst it may have been corrupted giving a false indication of the condition of the discharge/plasma or of the condition of the process to which the plasma is applied. It is therefore imperative that the functionality of the sensor and the application to which it is deployed are readily understood and the data carefully validated before being accepted.

No matter what type of sensor is used, in essence data taken from a sensor is a measure of that sensor’s response to the reality pertaining to the environment of the application and how this might change spatially or temporally. As such the data from the sensor and signal conditioning processes in one sense is meaningless until it is deconvolved within the context of the measurement environment. The information arising from this deconvolution is the closest that one can get to understand the reality of the environment in which the sensor is operating. The subsequent interpretation of the information by a scientist or engineer provides knowledge and understanding of the complex system.

Papers chosen for publication in this special edition of Sensor Review highlight some of the sensing techniques reported recently at the conference. These may have applications to other technology areas.