| 摘要 |
<p>A gas jet generating apparatus has a container with an electric arc chamber from which the gas jet is to issue, two arc electrodes are provided in the chamber, and at least one of the electrodes has a metallic portion defining a foot-point locality for the arc. The combination of a protective device has near at least one of the electrodes, a vaporizable means of material different from that of said electrode portion so as to effect, when burning off, a change in spectral distribution of the gas jet. Also provided is a signal generating arrangement that is responsive to the spectral distribution for deriving a signal from the change.</p> |
