Ionization device and method of operating same

A method of detecting small concentrations of volatile organic compounds in ambient air, the method comprising the steps of:

• (a) providing a sensor having a lamp assembly and a gas sampling chamber assembly which is operatively associated with the lamp assembly, the gas sampling chamber assembly having an ionization chamber and an electrode assembly, the electrode assembly comprising a sensing electrode, a counter electrode, and, at least one auxiliary electrode, and the sensing, counter, and at least one auxiliary electrodes being positioned within the ionization chamber and being separated from one another along at least one wall, wherein the at least one auxiliary electrode is positioned between the sensing electrode and counter electrode;
• (b) applying a voltage difference to the sensor and counter electrodes to create an electric field across at least the sensor and counter electrodes;
• (c) controlling an electrical potential of the at least one auxiliary electrode to be substantially equal to an electrical potential of the counter electrode;
• (d) measuring/estimating a current at the sensing electrode and at the at least one auxiliary electrode;
• (e) determining a difference between the current at the sensing electrode and the current at the at least one auxiliary electrode;
• and
• (f) correcting the current at the sensing electrode by using the difference.

A sensor for detecting small concentrations of volatile organic compounds in ambient air, the sensor comprising:

• a lamp assembly having a lamp housing and a window, the window being connected to the lamp housing;
• a gas sampling chamber assembly having an ionization chamber and an electrode assembly,
• the ionization chamber being defined by at least one wall having first and second ends, the at least one wall being formed of a hydrophobic, non-conductive material, the first end of the ionization chamber being operatively associated with the window to allow ultra-violet light to enter the ionization chamber from the lamp housing via the window,
• the electrode assembly comprising a sensing electrode, a counter electrode, at least one auxiliary electrode and circuitry, the sensing, counter, and at least one auxiliary electrodes being positioned within the ionization chamber and being separated from one another along the at least one wall, wherein the at least one auxiliary electrode is positioned between the sensing electrode and counter electrode, the circuitry configured to
• apply a voltage difference to the sensing and counter electrodes to create an electric field across at least the sensing and counter electrodes,
• control an electrical potential of the at least one auxiliary electrode to be substantially different from an electrical potential of each of the sensing and counter electrodes,
• measure/estimate a current at the sensing electrode and at the at least one auxiliary electrode,
• determine a difference between the current at the sensing electrode and the current at the at least one auxiliary electrode, and
• correct the current at the sensing electrode by using the difference.