where DP is the measure of depth in feet 



K is a constant number of feet represented by the voltage C, - ZC 



D is the datum point 



ZC is the sensor zero-depth voltage 



Cj is the most positive calibration voltage 



In regard to the sensors at the submarine; including submarine depth, fine and coarse 

 cable scope, and cable tension, ail require readouts that start from a zero position and 

 increase positively. Therefore, a data reduction equation in the form of Equation (6) is used 

 for reducing data from these channels. 



EVALUATION EXPERIMENTS 



To evaluate properly the pitch measurement channel, the differences between it and a 

 conventional measurement channel should be understood. In any measurement system, the 

 accuracy of the recorded data is a function of instrument and sensor stability and sensor 

 accuracy. Since no recording system maintains perfect stability, a means of monitoring or 

 eliminating the effect of instrumentation zero and sensitivity shifts is required. 



In the evaluation measurement system, the sensor and calibration network are inter- 

 connected to form a single unit. A circuit diagram of the electrical calibration network for 

 the potentiometer-type sensor is shown in Figure 8. With a common voltage source supplying 

 input to both the sensor and calibration network, an interrelationship exists between the 

 electrical-calibration readings and the sensor-output signal such that the amplitude of the 

 calibration steps is a direct measure of sensor sensitivity. This arrangement permits physical 

 calibration of a sensor in the early stages of system development, since the sensor with asso- 

 ciated calibration network are the only components of the total system required for the 

 physical calibration. Transmitting electronics and other signal conditioning components 

 which will be added to complete a measurement system are not required for this calibration. 

 Even the final readout device for the completed system may be selected or changed at a later 

 date. Two additional advantages of this design over conventional designs are: 



1 . The accuracy of recorded data is not affected by a long-term variations of sensor- 

 excitation voltage. 



2. The accuracy of data is not affected by long-term zero or sensitivity shifts within 

 the signal transmitting electronics or recording instrumentation. 



To illustrate that long-term variations in the sensor excitation voltage have no effect on 

 the accuracy of sensor output, typical cases are shown for the pitch measurement channel. 

 The same analyses apply, of course, to other channels using the same resistive-types of sensors. 



The schematic diagram in Figure 1 1 shows the arrangement of the pitch-angle potentiom- 

 eter and the resistors of the calibration network for the four switch positions previously 



30 



