Air Ion Counter Design Using Gerdien Condenser

Air is a mixture of gases including nitrogen, oxygen, water vapour, carbon dioxide etc. which are ionized. We live in the ocean of air ions. Actually ions are nothing but atoms or molecules which have lost or gained electrons. These ions are counted with the help of new model based on cylindrical capacitor designed by Gerdien. We have designed and developed air ion counter using operational amplifier AD549JH which has very low input current and low input offset voltage. The fan fixed at one end of the cylinder sucks the air then similar charged ions are repelled by the outer electrode. Further, these ions travel towards the central electrode to form a very small current of the order of pA. The current measured is proportional to the air ion concentration. Particularly, to calibrate and measure air ion concentration, the current to voltage converter is used. The complete instrumentation necessary to measure ions consists of Gerdien condenser associated electrometer and bias voltage supply. Data acquisition is done with the help of digital voltmeter, personal computer by using Rishcom software. This instrument gives opportunity for comprehensive measurement of air ions. It is low cost instrument and can be used to measure positive and negative ions for different atmospheric conditions.