12 



input to the amplifier. In short, the follow-up system is arranged so as to 

 balance the sum of the transformer voltages to zero. 



If greater pen deflections are desired for a given transducer signal, 

 it is only necessary to tap off a smaller portion of the output of the balance 

 transformer's secondary since this will require the motor to drive the core of 

 the balance LVDT through a greater distance in order to null the system; and 

 of course, the pen motion is directly proportional to the core motion. 



The primaries of both transformers are connected in series, likewise 

 the secondaries. This insures freedom from disturbances due to changes in 

 line voltage; since line voltage changes will affect each transformer equally, 

 the net change will be zero. 



Figure 4 shows the location of the balance LVDT's and the adjusting 

 screws for manually moving their cores in order to center the corresponding 

 pen on the chart . The screws marked "ADJ RANGE" permit adjusting the sensi- 

 tivity of the several channels. The amplifiers, one for each channel, may be 

 seen in Figure 5 • 



Detailed circuit diagrams and operation instructions are given in 

 Appendix 2 . 



DISCUSSION AND EVALUATION 



In discussing the instrumentation it will be appropriate to discuss 

 the recorder and the transducers separately since they are, in fact, complete 

 in themselves. 



The recorder and transducers were installed on the Coast Guard 

 weathership USCGC CASCO, a vessel 310 feet in length, while on a duty tour in 

 the North Atlantic from 11 March to 12 April 1951, a total of 32 days. The 

 equipment was operating during this entire trip except for a day's interrup- 

 tion due to failure of a relay, which has since been replaced by a more rugged 

 unit. The performance of all units was entirely satisfactory during this 

 trip — especially when one considers that it was the first time the equipment 

 had been given a service test. The maximum measured values during this voyage 

 were: Roll of 37-5 degrees double amplitude, pitch 18 degrees double ampli- 

 tude, heaving acceleration 0.8 x gravity, pitching acceleration 0.5 radians/ 

 sec 2 , and rolling acceleration 0.20 radians/sec 2 . All of these are double 

 amplitude or peak-to-peak values. The voyage may be considered to have pro- 

 vided rolling, heaving, and pitching conditions of the maximum order of magni- 

 tude to be expected. 



