CHAPTER 



13 



Electrical Measurements 



Many biologists prefer to make their measurements electrically when- 

 ever it is possible. Much of the information obtained in biological ex- 

 periments is indirect information anyway. If the possibility exists of 

 converting this indirect information into an electrical signal of some 

 sort, several advantages accrue. The measurement can be made more-or- 

 less automatically, which often reduces the chances of human error. 

 The electrical devices can produce permanent records, as on strips of 

 chart paper, and these records can be examined and re-examined as 

 needed. The electrical instruments usually respond very rapidly, so 

 some responses too fast for the human senses can be detected easily. 

 Electrical quantities are rather easily converted from one form to another. 

 Certainly there are disadvantages, too. Electrical and electronic equip- 

 ment can fail, and sometimes does at the most awkward moments. 

 The operator must be able to recognize faulty performance and, ideally, 

 should know what to do about it. The electrical instrument measures 

 only indirectly, necessitating the assumption that the electrical signal 

 is some unvarying mathematical function of the biological response. 

 Electrical instruments usually are expensive and require maintenance. 

 In many kinds of experiments, however, the advantages outweigh the 

 disadvantages. 



Electrical theory 



Current electricity, as opposed to static electricity, is used almost ex- 

 clusively in electrical instrumentation. This fact somewhat simplifies the 



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