2N700 



-° -6V 



"l^W* °SV- 



820 



IN— ^i — ► OUT 



GAIN = lOdb/STAGE 

 BAND = TO 30 mc 



Fig. 9- Amplifier circuit. 



a major improvement in the accuracy and relia- 

 bility of pulsed velocimeters . These ideas are 

 now being applied to a new instrument incorpo- 

 rating all of these improvements . The amplifier 

 circuit shown in Fig. 9 wa s designed to pass any 

 of these pulses without distortion. The band- 

 width of this amplifier can easily be adjusted 

 by changing the feedback network values . Present 

 indications are that the bandwidth required is 

 only about 10 Mcps with the pulses shown. The 

 use of the wider amplifier bandwidth does how- 

 ever yield a smaller electronic time delay and, 

 therefore, reduces the nonlinearity of the cali- 

 bration. The amplifier shown has a delay of less 

 than 100 nanoseconds. 



CONCLUSIONS 



A pulsed type velocimeter requires an acoustic 

 pulse with a fast rise time and one in which the 

 first rise is greater than any succeeding cycle. 

 The attenuation caused by changes in water tem- 

 perature and other factors introduces a time 

 error in measurement which limits the accuracy 

 obtainable unless a means of compensation is 

 introduced. Methods for generating suitable 

 wide-band pulse forms and for making loop gain 

 compensation have been discussed. Unfortunately 

 there are no adequate standard testing facilities 

 available for determining over environmental 

 extremes the success of these corrective measures. 

 Until such facilities become available, the only 

 way to estimate the accuracy of these instru- 

 ments is by careful quantitative consideration 

 of all the individual factors which control the 

 accuracy of the instrument . 



ACKNOWLEDGMENTS 



Mr. Paul West performed all the physical tests 

 and took the excellent photographs which con- 

 tribute so much to the understanding of the vari- 

 ous phenomena. 



161 



