F-4 



SILICON 



DIODE 



PHOTRAN 



(PNPN) 



SWITCH 



TYPE 



3PI5 



313 

 LAMP 



HB-4 



SILICON 



DIODE 



MFD 



I 15V 

 TANTALUM 



~_1_A 



ANEMOMETER CONVERTER 



SQUARE 



WAVE 



GENERATOR 



Fig. 3- An electrical circuit design for converting anemometer output. 



DYNAMIC CALIBEATIOH 



When observing a cup anemometer in the labora- 

 tory it is immediately noticeable that the cups 

 will accelerate rapidly in response to a sudden 

 draft of air but will continue to coast for a 

 relatively long time in still air when the 

 driving force has been removed. This raises the 

 possibility that the angular acceleration of the 

 cups in response to an increasing wind velocity 

 differs from the deceleration in response to a 

 decrease in wind velocity of the same magnitude. 

 Furthermore, it can be expected that the angular 

 acceleration of the cups will be larger; that is, 

 the cups will respond faster to the same magni- 

 tude of velocity change at higher mean wind 

 velocities. Thus, it is at least possible that 

 the dynamic response of the cups is dependent 

 on both the mean wind velocity and the sense of 

 velocity change. 



One way to evaluate the overall response of 

 any transducer is to subject it to a step change 

 of the variable to be measured while observing 

 the output from the transducer. The technique is 

 highly developed for purely electrical measure- 

 ments and much of the existing technique may be 

 applied directly in evaluating transducers of 

 various kinds. The apparatus for simulating a 

 step function in the wind tunnel is shown sche- 

 matically in Fig. k. A variable speed motor 

 mounted on a hinged support drives a circular 

 puck on the end of a long shaft . The puck may 

 be engaged against the anemometer upper cap by 

 forcing the motor to swing upward by means of a 

 push bar extending through the floor of the wind 

 tunnel. The angular velocity of the cups may 

 now be regulated by adjusting the motor speed to 

 be either greater or less than the wind speed. 

 Upon release of the push bar the motor and puck 

 assembly is pulled rapidly back to its retracted 

 position. Thus, so far as the anemometer is con- 

 cerned, it experiences a realistic step change 



151 



