charged with respect to filaments 24 although not shown input output i o pins are connected to the grid conductors for providing a voltage potential to helical coil grid anode 28 the input output pins are shown in cross section in fig4 a and 4b designated as 40 a and 40 b it will be understood that fig1 shows one example of an ionization gauge there are many other types of ionization gauges in which the anode cathode and ion collector have configurations different than the configuration shown in fig1 for example an ultrahigh vacuum uhv nude bayard alpert gauge may be used to measure pressure below 2 u00d7 10 u2212 11 torr this lower limit is achieved by modifying two elements of a standard bayard alpert gauge first the diameter of the collector is reduced the smaller cross sectional area reduces the probability that x rays created at the grid will strike the collector second the helical grid structure is replaced with a fine wire mesh grid structure and there is also a fine wire structure across both ends of the grid the fine grid wires provide a more transparent grid for longer electron path lengths and the grid ends confine the positive ions for better ion collection together these two modifications cause a higher gauge sensitivity returning to fig1 at an end distal from grid insulator posts 12 a 12 b tubular housing 18 includes a right angle bend that continues the tubular section of housing 18 and.