Gaseous impurity detector employing corona discharge phenomenon

Abstract

A method .[.is disclosed.]. of detecting gaseous impurities, particularly halogens, in an ambient atmosphere by repeatedly pulsing a pair of electrodes disposed in that atmosphere with a voltage sufficient to cause a corona discharge in the continuous corona region, and detecting the average (d.c.) current component of such discharge, changes in which correspond to changes in the concentration of such gaseous impurities. Apparatus .[.is disclosed.]. for detecting such impurities in concentrations as low as 1 ppm.

We claim: .[.1. A method of detecting gaseous impurities in an ambient atmosphere, comprising applying voltage pulses across a pair of electrodes disposed in such atmosphere, the voltage being sufficient to cause a corona discharge across said electrodes in the continuous corona region; and detecting the mean corona current of said discharge, which current varies with impurity concentration..]. .[.2. A method of detecting gaseous impurities in an ambient atmosphere, comprising applying voltage pulses across a pair of electrodes disposed in such atmosphere, the voltage thereof being sufficient to cause a negative corona discharge across said electrodes in the continuous corona region and said pulses being between about 1 to 300 microseconds in length at a pulse rate greater than 10/second, but not so great as to exceed 10 percent duty cycle; and detecting the mean corona current of said discharge, which current varies with impurity concentration..]. .[.3. A method of detecting gaseous impurities in an ambient atmosphere comprising applying voltage pulses across an asymmetrical electrode pair sufficient in magnitude to cause a corona discharge thereacross in the continuous corona region; and measuring the peak true corona discharge current, which is representative 
     
        of such impurity concentration..]. 4. Apparatus for detecting .[.gaseous.]. .Iadd.halogen .Iaddend.impurities in an ambient atmosphere comprising: an asymmetrical electrode pair disposable in such ambient atmosphere;   a .Iadd.portable battery-operable .Iaddend.source of voltage pulses .Iadd.including an oscillator .Iaddend.connected to the electrode pair, the voltage of said pulses being sufficient to cause a .Iadd.negative .Iaddend.corona discharge across the electrode pair in the continuous corona region; and   means for indicating the mean corona current of said discharge, which is   
     
     
        representative of the concentration of such impurity. 5. Apparatus as defined in claim 4 including a limiting resistor for preventing spark breakdown under all impurity .[.concentration.]. .Iadd.concentrations .Iaddend.occurring in such ambient atmosphere. .[.6. Apparatus for detecting gaseous impurities in an ambient atmosphere comprising: an asymmetrical electrode pair disposable in such ambient atmosphere, one electrode of said electrode pair being pointed;   a source of voltage pulses connected to the electrode pair, the voltage of said pulses being sufficient to cause a corona discharge across the electrode pair in the continuous corona region and said pulse source providing negative-polarity pulses to the pointed electrode having a pulse width of about one to 300 microseconds at a pulse rate greater than 10/second but not so great as to exceed 10 percent duty cycle; and   means for indicating the mean corona current of said discharge, which is representative of the concentration of such impurity..]. .[.7. Apparatus as defined in claim 6 wherein said indicating means includes an R-C circuit in series with the electrode pair for providing an output voltage proportional to the time-average discharge current..]. .[.8. Apparatus as defined in claim 7 wherein said indicating means includes a voltage-controlled multivibrator connected to drive a speaker and connected to be controlled by said output voltage, whereby the frequency of the speaker output is indicative of impurity concentration..]. .[.9. Apparatus as defined in claim 7 wherein said indicating means includes an active amplifier responsive to said output voltage, connected in circuit with an indicating meter for indicating impurity concentration..].   
     
     
        .Iadd.  .  Apparatus for detecting halogen impurities in an ambient atmosphere comprising: an asymmetrical electrode pair disposable in such ambient atmosphere;   a source of voltage pulses connected to the electrode pair, the voltage of said pulses being sufficient to cause a negative corona discharge across the electrode pair in the continuous corona region; and   means for indicating the mean corona current of said discharge, which is representative of the concentration of such impurity; wherein   said indicating means includes an R-C circuit in series with the electrode pair for providing an output voltage proportional to the time-average discharge current, said source of voltage pulses being connected to the electrode pair to produce a negative corona discharge thereacross;   said asymmetrical electrode pair includes a pointed electrode disposed opposite a substantially hemispherical electrode provided with openings to admit the atmosphere under test into the corona region; and   said source of voltage pulses includes a blocking oscillator having an output transformer, said output transformer including an output winding, one side of said output winding being connected in circuit with the pointed electrode and the other side of said output winding being connected in circuit with the substantially hemispherical electrode through said R-C circuit..Iaddend. .Iadd.11. Apparatus as defined in claim 10 wherein the voltage pulses produced by said source thereof have a voltage between about 1800 and 2700 volts peak..Iaddend. .Iadd.12. Apparatus as defined in claim 10 wherein the substantially hemispherical electrode has an interior radius of about 3/32 inch and the pointed electrode is formed of a fine wire..Iaddend.