The Measurement Of Humidity Based On The Dark Current From The Field Ionization Of A Needle-needle Electrode

The humidity is closely related to people’s life and production activities. And the existing moisture measurement method does not guarantee the accurate measurements of humidity in dramatic changes environments. This study proposes a method to measure atmospheric relative humidity by corona discharge dark current, which can solve the measurement of humidity quickly and accurately in a wide range of rapid change environment.Corona discharge is one of the basic form of uneven gas discharge. It is not only related to the atmospheric humidity, but also closely related to temperature, pressure, discharge, environmental pollution, the air flow and so on. The theory mechanism of corona discharge are analyzed in this paper, and established a symmetrical needle-needle electrode discharge experimental model by thompson discharge theory and streamer discharge theory, and deduced the theoretical formula of corona discharge dark current with the humidity. The highly uneven field of needle electrode structure ensures the stability of the corona discharge, and be helpful to experimental research. To reduce the air flow and the impurity on discharge interference, the electrodes are placed in the transparent container which embedded with the titanium plate.This paper studies the influence of corona discharge dark current with the input DC voltage, air pressure, temperature, relative humidity, and discharge time. And the analysis focuses on the influence of relative humidity on the dark current when the other parameters remain unchanged. The experimental results accord with the change tendency of gas discharge theory. The fitting curve characteristics by the dark current theoretical formula obtained by the matlab software, are complete accord with the change rule of experimental value.The experimental and theoretical results show:when the discharge occurs, the dark current increases with the voltage increases until the air gap breakdown electrodes; when the relative humidity is high, the dark current decreases from fast to slow with the temperature increases, and when the relative humidity is low, the dark current increased from slow to fast with the temperature increases; when the temperature and pressure remain unchanged, the dark current increases as the relative humidity increases. And the higher relative humidity range, the dark current rapidly increases with the humidity rises. And the lower relative humidity range, the dark current increases slowly. The dark current relationship with the relative humidity changes exponentially. The main reason is that:with the increase of relative humidity, the content of water molecules in the air of the discharge gap increase, and the average ionization energy of air molecules decrease, and the probability of impact ionization increase, and the charge density in the discharge channel increase, so the dark current of corona discharge increases.When the relative humidity is high, the water molecule concentration is high. The air molecules and water molecules of inter-electrode gap are ionized more easily. And the lower air density of air causes a collision kinetic energy increase. The probability of collision ionization increases. Under the high relative humidity, the corona discharge dark current increased dramatically with the relative humidity rises.