accuracy of at least 0.1 percent of full scale. This arrangement is shown in Figure 9. During 

 calibration of the pendulum sensor a small vibrator is attached to the tilt table to reduce 

 static friction in the bearing; its use is justified because the buoy towing environment is also 

 vibratory. A tabulation of the electrical-calibration sequence (Zero Check, Cal 1, Cal 2, and 

 Data position) from the DVM is made using the electrical calibration network. With the tilt 

 table set at zero degrees, the pendulum sensor is rotated so that the output voltage coincides 

 with the voltage from the zero check calibration step. The zero check voltage is used in 

 referencing the zero degree pitch angle in the data reduction process described later. Once 

 the sensor zero is established, the pendulum is locked in position on the tilt table and a 

 physical calibration is begun. The electrical-calibration sequence is repeated and the resulting 

 voltage outputs tabulated. A tabulation of the sensor output voltage is made while the sensor 

 is incrementally rotated from degrees to minus 20 degrees to plus 20 degrees, and back to 

 degrees. A second electrical-calibration sequence is tabulated. This procedure should be 

 repeated several times to establish repeatability of readings. 



To analyze a complete set of calibration data, each known incremental angle and the 

 resulting measured voltage is tabulated and may be plotted on linear graph paper or a least- 

 squares fit may be obtained through use of a computer and the Government Services Adminis- 

 tration (GSA) Computer Program available to all government services. The GSA program 

 entitled CURFIT^ will print out a comparison of a least-squares fit of the calibration data to 

 the equation of a straight line, y = mX + b, and will print out the angle in degrees, represented 

 by each of the electrical calibration steps, i.e., Zero Check, Cal 1, and Cal 2. The printout 

 also lists sensor sensitivity (the factor m above), percent deviation from the straight line, and 

 the index of determination where the number 1 represents a perfect curve fit and a number 

 less than 1 indicates the degree of deviation from a straight line. A straight-line curve indi- 

 cates sensor linearity, the slope of the curve indicates sensor sensitivity, and if the increasing 

 angle curve coincides with the decreasing, angle curve, there is no hysteresis. A comparison 

 of the first calibration sequence to the second yields the following information; if the two 

 zero-check points match, there was no instrument zero drift during the calibration; if the 

 differences between the calibration steps (C, - C2) in both sequences match, there was no 

 change in excitation voltage or instrumentation sensitivity during the calibration. 



The physical zero of the pitch pendulum is again adjusted when the sensor is placed in 

 the buoy. The buoy is positioned to zero degrees pitch and the pendulum is rotated so that 

 its electrical output exactly matches the zero-check voltage from the calibration network. 



Applications Library Operating Instructions," Federal Data Processing Center, Atlanta, Georgia (1973). 



24 



