Knife-edge washers

Figure 32 Schematic of cross section of arrangement used with knife-edge PTFE washer for definition of sample area. A represents the PTFE washer, B represents the sample, C represents the assembly, including the backing plate that generally is screwed against the sample to press it against the PTFE washer, and D represents the insulated electrical contact.

Fig. 33) in which a cylinder of PTFE is forced onto the top of a generally cylindrical sample. The Stern-Makrides washer suffers from same problems as does the knife-edge, but to a greater degree due to the larger surface area involved. 

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