98 BELL SYSTEM TECHNICAL JOURNAL 



make the grid less negative, thereby reducing the resistance shunted 

 across the field winding. 



A somewhat similar arrangement can readily be applied to regulate 

 the voltage delivered by a battery. Fig. 78 illustrates such a circuit. 

 An increase in E\ raises the grid potential, thereby increasing the 

 current through the tube and the resistance r 3 . By a choice of regu- 

 lating tube and resistances such that 



ri-{-r 2 dE g 



r * = -Jr* 



r x alp 



it may readily be shown that the voltage E 2 remains constant. Since 

 the regulation effected by this circuit is independent of frequency it 



Supply 



Fig. 78 



may also be applied to a generator supply for elimination of commuta- 

 tor noise as well as voltage fluctuations due to changes in speed. 



59. The Ionization Manometer. When gas is present in a three- 

 electrode tube in quantities not sufficient to seriously affect the 

 activity of the filament, and the plate voltage exceeds a value suffi- 

 cient to produce ionization by collision, it has been found that the 

 number of ions produced is proportional both to the pressure of the 

 gas and to the electron current passing through the gas to the anode. 48 

 If now a small negative potential be applied to the grid, a certain 

 fraction of the positive ions will be drawn to it and their number can 

 be accurately measured by the current flowing in the grid circuit. 

 The best arrangement is to apply the positive potential, not to the 

 plate in the usual fashion, but to the grid, and apply the negative 

 potential to the plate making it the collector of the positive ions. 

 Dimensions of a satisfactory tube are given in Fig. 79. The values 

 £ g = 110 volts and E p =—2 volts have been found to give very satis- 

 factory results, the electron current being .02 ampere, and K being 

 equal to 0.10 for nitrogen and having approximately this value for air. 

 The gauge equation may be put in the form, 



P-Kg. 



in which P is the pressure, K a constant depending upon the design 

 «0. E. Buckley, Procd. Nat. Acad., Vol. 2, p. 683, 1916. 



