described. A constant input voltage, E, is provided as excitation to the sensor and calibration 

 network. Assuming that the potentiometer arm is physically located at any arbitrary point 

 on the 2000-ohm potentiometer, the resistance of that portion of the potentiometer between 

 the lower end of the network and the potentiometer arm is 2000-A where < A < 1 . The 

 output voltage, e^, for each switch position is calculated in Figure 1 1 . For these calculations, 

 the external load impedance is neglected since it is greater than 100 times the network output 

 resistance. From Equation (5), the general expression for the pitch angle is 



K (D - ZC) 



C - c 



For the arbitrary points, the pitch angle 6 is obtained by substituting the expressions for e^ 

 shown in Figure 1 1 into Equation (5) since D, ZC, Cj , and Cj are all represented by the 

 output voltages from the various switch positions. Thus, the pitch angle 



K [EA - 0.5E] 



0.75E - 0.25E 

 - K (2A - 1) 



is independent of long-term variations in the excitation voltage and depends only on the 

 value of K and the position of the potentiometer arm. The only requirement is that the 

 excitation voltage remains constant during the calibration sequence. 



To illustrate that long-term zero or sensitivity shifts within the transmitting electronics 

 or the recording instrumentation have no effect on the accuracy of the data, typical cases 

 are shown for the pitch-angle channel. The same analyses apply to other channels using the 

 same resistive-type sensors. In the absence of any zero or sensitivity shifts, the measured 

 pitch angle at a particular towing condition is: 



K (D - ZC) 



Assume a zero shift of an arbitrary amount AZ. This will shift all points in the calibration 

 sequence and also the datum point by AZ. In addition, assume an arbitrary change in sensi- 

 tivity of X percent, where — <» < X < + oo but X =^ 0. With these assumptions, the measured 

 pitch angle at the same towing condition is: 



32 



