A Safety Shutoff for Your Plasma Torch Box

Abstract

Since the introduction of inductively coupled plasma atomic emission spectrometry (ICP-AES) as an analytical technique, the associated instrumentation has undergone numerous changes. From simple radio-frequency generators, homemade matching network, and a monochromator, the inductively coupled plasma atomic emission spectrometer has evolved into a fully automated computer-controlled analysis system. Modern ICP-AES systems are not only capable of determining the elemental makeup of a sample but they can also monitor their own performance and can correct or avoid many problems. There exist, however, a large number of commercial instruments built before the new self-monitoring generation that lack some of the more basic safety devices. One of the most damaging situations that can occur is the continued operation of the radio-frequency generator at excessively high reflected powers. This can occur if the plasma is extinguished but the rf generator is left operating. A high reflected power forces the power amplifier tube of the rf generator to dissipate as heat the energy that would otherwise be transferred to the plasma. Continued excessive heating of the power amplifier tube in the rf generator will greatly degrade the performance of the tube and severely shorten its usable lifetime.