In this video we are going to see the working principle of ionization gauge. so here is the diagram which consists of triode tube consisting of cathode filament positive potential grid and negative potential plate. heated filament emits electrons which are accelerated at high speed to positive charge grid. as electron move towards grid they ionize gas molecules by collision. positive ions are attracted and collected towards negative potential plate and produce plate current Ip. electrons and negative ions are collected by grid producing grid current Ig. using Empirical relation. unknown pressure p is calculated, by putting values of Ip and Ig, where k is sensitivity of gauge.