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Electrical Potentials of the Brain /5 : 3 



The thermostat operates only in an on-off, that is, all-or-none, 

 manner. If, instead of the thermostat, one uses a thermocouple, or 



External 

 Influences 



Sensing 

 Element 



Comparator 



Reference 



Control 

 Device 



(a) 



(b) 



Heat Loss 

 to Outside 



(c) 

 Figure 3. (a) General scheme of negative feedback control 

 loop (servomechanism). Large cross-hatched arrows indicate 

 variable elements, (b) Block diagram of negative feedback 

 loop to keep amplifier output constant. Such amplifiers can 

 be used to present subjects with speech of constant (average) 

 sound pressure level, (c) Negative feedback control loop used 

 to regulate room temperature. In practice, an additional 

 loop is used to keep furnace below some set temperature. 



thermistor bridge circuit, it is possible to obtain a voltage proportional 

 to the error in temperature from the 68°F at which the system is set. 



