298 THE SPERRY GYRO-COMPASS IN SERVICE. 



to be properly impregnated for protection against moisture and heat and to 

 conform to the Navy's Specification for Auxihary Electrical Appliances. 

 The storage battery provided as auxiliary supply for 20- volt service shall be 

 capable of supplying the azimuth motor, relay and all repeaters for a period 

 of not less than ten hours. To be furnished with each set there shall be a 

 complete folio of correct drawings of the instruments and three sets of instruc- 

 tions. The contractors are also required to furnish a full set of spare parts, 

 accessories and tools, packed in a suitable and convenient case. 



A rigid system of tests is provided for all instruments for determining 

 whether or not the sets furnished conform to the specifications. These tests 

 include the following : — 



(a) Continuous running under conditions of heavy rolling, pitching and 

 yawing for six days, during which time the deviation of the master or indi- 

 cations of the repeater compasses shall not exceed one-half degree from the 

 correct indication ; and during this time the vacuum shall not fall more than 

 one and one-half inches. 



(6) Continuous operation for forty-eight hours under condition of no 

 vacuum, without excessive heating of any part and without any material 

 increase in deviation from correct indication of the master or repeating 

 compasses. 



(c) Continuous, operation for four hours at the critical speed, that is, 

 at the speed where the natural period of the instrument synchronizes with 

 the period of the wheel, thus causing vibrations. (On all of the latest instru- 

 ments no critical speed has been found.) 



(d) Speed test of the rotor of 10,000 revolutions per minute for two 

 hours without effect upon the balance of the wheel. If the maximum speed 

 that can possibly be given by the motor-generator equipment on board ship 

 exceeds 10,000 revolutions per minute, then the speed tests shall be run at 

 that maximum speed. The contractors shall certify that the rotor was run 

 at least 12,000 revolutions for two hours before being finally balanced. 



Contractors are required to furnish an engineer [to supervise the instal- 

 lation and make adjustments on the sets installed. The instruments are to 

 be guaranteed against any defects or imperfections for a period of one year. 



Under the supervision of the Bureau of Navigation, the compass has 

 been thoroughly tested on board the U. S. S. Worden and at the electrical 

 laboratory of the Navy Yard of New York. During these tests several 

 curves of the operation of the Sperry gyro-compass have been developed 

 and these curves are publishedwiththepermissionof the Bureau of Navigation. 



Figure 13, Plate 1 08, is a time and speed curve, showing the rate at which 

 the gyro wheel is accelerated when starting. This figure also shows a decel- 



