INSTRUMENTATION 



(Note: If the standard instrument package available from the Maritime 

 Administration is used, a standard write-up will be provided for this 

 section. ) 



Figure 4 shows the block diagram of the electronic instrumen- 

 tation used on this survey. 



The MB Vibration Pickup is an electromagnetic seismic 

 instrument which generates a voltage proportional to the velocity of 

 vibration. As shown on Figure 4, this voltage is passed through an 

 NKF Integrator to convert velocity to displacement, and amplified 

 by the Ballantine Decade Amplifier. This displacement signal is 

 then recorded through the Edin Amplifier and Oscillograph. 



Two types of MB pickups were used: the type 120 and the type 

 124. These pickups are similarly constructed and have the same nominal 

 sensitivity of 94. 5 mv per inch/ sec. The type 120 has a natural frequency 

 of 2. 25 cps, as compared with a frequency of 4. 75 cps for the type 124. 

 Thus, the type 120 would be useable at a lower frequency. 



A brief description of each component of the electronic instru- 

 mentation follows: 



1. MB type 120 Velocity Pickup 

 Velocity sensitivity = 94.5 mv/in/sec. 

 Flat Frequency from 5 to 1000 cps. 

 Electro-magnetic damping = 0.65 critical. 



2. MB Type 124 Vibration Pickup 

 Velocity sensitivity = 94.5 mv/in/sec. 

 Flat Frequency from 8 to 1000 cps. 

 Electro -magnetic damping = 0.65 critical. 



3. NKF Selector Switch - provides means for switching 

 any of 12 different input signals into either of two record- 

 ing channels . 



4. NKF Integrator - provides two channels of either 

 single or double integration. 



5. Ballantine Decade Amplifier Model 220B - is used to 

 amplify the transducer output voltage before integration. 

 This amplifier can be set to either lOx or lOOx amplifica- 

 tion. An amplification of lOx was used during this survey. 



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