A hydrocyclone is a particle separation device widely used in chemical and allied process industries in which a particle-fluid mixture is injected tangentially creating a strong swirling, recirculation flow. The particle separation efficiency increases by suppressing the air core, so online prediction of air core formation has significant importance in the industrial operations. Performance of hydrocyclone is greatly influenced by shape and size of air core. A novel type of senor technique has been developed to identify and predict the air core diameter from online live data using data acquisition card. The true signal amplitudes change as a function of the time was used with noise interruption for random changes in amplitude. Noises are eliminated by using moving average technique. The slope of the curve is continuously tracked to determine sudden or abrupt change and indicates the formation of air core. It has been observed that a strong air core of diameter 0.95 cm to 1.2 cm was formed during experimentation and matched with predicted values over an entire flow regime. The experimental and finally an alarm is designed which gives alerts once air core is formed and calculates air core diameter. For calculating air core diameter a polynomial equation is fitted between pressure difference and the pressure transmitter reading. A simple moving average with a smooth width of 10 was used for prediction of air core. Experimental results indicate that the digital signal sensor techniques identify the air core and measure air core diameter very accurately and can be used in many mining and mineral based chemical and allied process industries. (C) 2010 Elsevier B.V. All rights reserved.