288 WET SUITS 



were considered within a reasonable range to obtain good configuration flexibility, adequate 

 strength, and minimal bulkiness when incorporated into the laminated insulating material. 



The resistance required for a body-region circuit is determined by the supply voltage, the 

 wire length, and the power required for heating the area. The resistances for body-region 

 circuits were given in Table 40. The resistance-wire circuit design includes parallel heating 

 wires in each area and the area circuits connected together in parallel. Single resistance 

 wires for some body areas would require, within a reasonable range of wire gages, a lower 

 resistivity than found in any commercially available alloy. 



A general approach was taken for the design of all body- region circuits, with the exception 

 of the hands and feet, which were treated specially. The generalized configuration was designed 

 as follows. 



1. Assume a configuration which is periodic, will permit stretch, and has a wire separa- 

 tion, X. Let X be the wavelength of the periodicity. Then: 



lA = CjXandA/x = C^x^ 



where Cj and C2 are constants depending on the configuration, L is the wire length, and A is 

 the area to be heated. We then have that: 



L/A = Cix/Cjx^ = C/x where C = Cj/Cj. 



Rewriting, we have L = CA/x, which is the wire length to cover the area in the chosen 

 configuration. 



2. The supply voltage is applied across parallel heating circuits. The resistance for each 

 body area circuit is: R = E-/P, where E is the supply voltage and P is the power. 



3. The resistivity of the wire is given by (R/L) j = R/L if the circuit consists of only one 

 heater wire. For parallel wires of the same material emitting equal heat power, we have that: 



(R/L)i = n2(R/L)i 



arising from 



1/Ri = i;(l/Ri) = n/Ri and L = nL; 

 i = i 

 where the subscript, i, denotes an individual heater wire. 



4. Writing the expression for resistivity, we have: 



(R/L)j = p- 

 where j denotes specific diameter and material. 



5. Introducing a requirement for an allowable power deviation, R ± e = E Vp ± € , which 

 can also be written as: 



[n2(R/L)i - pJ/[n2(R/L)i] ^e . 



6. Compute the values of the expression given in step 5 for n = 1 to 20 (number of parallel 

 heaters). 



7. Choose the value of n which satisfies the permissible deviation, E. 



8. If no value of n satisfies the permissible deviation, alter the configuration and/or spac- 

 ing by using the value of n corresponding to the minimum e . The new spacing constant is 

 given as 



x' = CjA/n^R. 



