When both the zero position and sensitivity calibration have been established for the 

 pitch sensor, no variance can be caused by electrical drift and/or sensitivity change within the 

 instrumentation external to the sensor and electrical calibration network. So long as the 

 datum-point recording, zero check, and calibration steps are within the bounds of the record, 

 a valid datum point is obtained. 



The following discussion deals with the relationship between the physical calibration 

 data and the electrical-calibration voltage steps. The type of calibration employed in this 

 system is referred to as a "voltage substitution circuit" where fixed voltages from a resistor 

 divider network are substituted for voltages from the sensor, and each voltage relates to some 

 fixed position or angle of the sensor. A graph of the pitch calibration curve of angular dis- 

 placement versus voltage output is plotted and presented in Figure 10. The abscissa is a 

 scale of angular displacement, 9, and the ordinate is a scale of sensor output voltage, D. The 

 equation of the physical calibration curve is: 



D = m,0 + b (1) 



where D is sensor output voltage 

 d is the pitch angle 

 b is the voltage intercept, where 9=0 

 m, is the slope of the curve, representing sensor sensitivity 



The voltage intercept, b, is the voltage output of the pitch sensor when it is at zero 

 degrees. Furthermore, this same voltage equals the zero check voltage of the calibration 

 sequence, since the sensor was physically rotated at zero degrees so its output and the zero 

 check output would coincide. Therefore, ZC may be substituted for b in Equation (1) which 

 yields 



D = m,0 + ZC (2) 



where ZC is the output voltage for 9=0. 



If the voltage values of the calibration sequence (ZC, Cj and C2) are plotted on the 

 voltage axis D of the calibration graph, ZC will fall on the curve at the D intercept as men- 

 tioned above. If the calibration voltages C, and Cj are projected to the calibration curve at 

 0p Cj and ^2' arid Cj, the following relationships may be concluded: 



C2 = mj ^2 + ZC 



26 



