138 INSTRUMENTATION IN SCIENTIFIC RESEARCH [Chap. 1 



A considerable number of variations of the basic system have been 

 described in the literature. 1 The hygroscopic material is either 

 deposited on impervious insulating surfaces, on fibers or fabrics, or 

 on porous ceramics. A great number of hygroscopic materials have 



R,M? 



Fig. (1-7)1. Resistive humidity 

 transducer; the hygroscopic salt 

 layer B is deposited between the 

 two electrodes A A. 



Fig. 



[1- 



Electrode 



arrangement of a resistive 

 humidity transducer. 



Fig. (1-7)3. Resistive humidity transducer (courtesy 

 of El-Tronics, Inc., May field, Pa.). 



also been described or suggested, e.g., sulfuric acid, phosphoric acid, 

 lithium chloride, calcium chloride, zinc chloride, solutions of the 

 tetrachlorides of the metals tin, zirconium, hafnium, or lead, and 

 many others. 



The resistance of a sensing element of the described type varies for 

 a humidity variation from zero to 100 per cent by large orders of 



1 Wexler, loc. cit. 



