TM No. 377 



where Kp is a proportionality constant o 



The individual voltage traces in figure II-7 show sinusoidal-like pulses 

 and not really sharp spikes » This is due to the induction factor d< Pn» /dtr 

 which varies with time as the magnet approaches, passes _. and moves away from 

 the fixed eoilo In other words, the closer the magnet approaches, the more 

 lines of magnetic flux cut per unit area per unit t.ime<> Thus.,, for each 

 passage of a coil by the magnet, a voltage peak always occurs having a sign 

 associated with the sense of w„ 



The peak or maximum value of E^0( designated by £m ) can therefore be 

 used to estimate the instantaneous value of U)CO ° 



coC*)* T' W*) J (n-32) 



where K B = IT 1 - 



The amplitude of the voltage (either positive or negative) can supply a 

 velocity value for the time of occurrence of the peak (see figure 11-7)° This 

 is, in fact, an amplitude modulated vector Measuring the frequency and the 

 amplitude of the voltage passes with time,, thus ijroviies two indicators of 

 the direction and magnitude of flow through the impellers 



Further mention of the use of the voltage amplitude modulation to 

 portray wave motions is made in chapter V. 



Summary of Dynamic Characteristics of the Wave Meters 



Various tests and calibrations were made,, including steady state towing 

 at various angles with respect to flow direction, and accelerative and 

 oscillatory tests „ The following summary of the characteristics of the 

 wave meters is based on results of these tests and calibrations , (Table II-5 

 lists some of the more important system characteristics „ ) 



lo The ducted meters have a linear response for impeller rotation 

 frequency with speed of flow up to at least 200 cm sec~i« 



2 The impeller response time is about 65 millesecondSe 



3. The impeller system is simple in geometry and easy to build. Hence, 

 it can be fabricated to give essentially identical calibrations „ 



k a The electronics (consisting of magnets and a coil) are the antithesis 

 of the very expensive and complex photographic or digitizing electronics used 

 with Savonius rotor systems The system is free flooding,, requiring no pres- 

 sure case or protected electronics „ No power is needed and no pre-amplifica- 

 tion is required prior to the strip chart recording of the signalo 



