CALIBRATION 



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

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

 section. ) 



The MB Vibration Pickups were calibrated on the NKF Scotch 

 Yoke Calibrator. This calibrator is a motor driven shaker. The im- 

 pressed amplitude was t 50 mils. A variable speed control provides 

 the frequency adjustment. A range of 1 to 20 cps was used during the 

 calibrations . 



The transducer outputs were fed into the electronics shown on 

 Figure 4. A convenient technique was used for maintaining calibration 

 of this system throughout the calibration runs and the actual test runs . 

 With the application of a known signal from the oscillator, monitored 

 by the vacuum tube voltmeter, the signal size on the oscillograph chart 

 is maintained constant by a simple adjustment of the sensitivity dial on 

 the Edin Amplifier. Thus checks are possible after each run and any 

 variation in gain of the system, can be readily compensated. 



Figures 8 and 9 show the calibration curves for the pickups 

 used. 



The calibration factor is used to determine the amplitude of 

 vibration by insertion in the following expression: 



. -,■.■,+ 1 D.A. X Attenuation Setting 



Amplitude _ mils = ^ -, ., —. = — 7 °- 



'^ Calibration Factor 



Where: 



D.A. = double amplitude in millimeters, as measured 

 on the oscillograph record 



Attenuation setting = attenuation setting of the Edin 

 Amplifier as used on any particular run. 



42 



