/I CLOCK-CONTROLLED TUNING PORK 



151 



turlHil aiul a chronograpli record taki-ii of tlic rt.a(ljiistim-iit. This 

 will i^ivc the [x^rioil of tlie oscillation, if any, and the amount of 

 damping. 



Fig. 3 shows one of theso records. The chronograpli was con- 

 ncctinl in the circuit as shown in Fig. 1 and a record was taken over a 

 pericxl of alxnit 20 minutes after starting the fork. This record 

 shows the length of time in each half second that the control relay was 

 operateti. At starting this period is about .11 second. After about 

 8 minutes it becomes a maximum equal to .2 second and there is no 

 appreciable change over the next 5 minutes, showing a permanent 

 condition has been reiiched. Accordingly we may conclude from 

 this recoid that any oscillation about the mean value of the control 



Fig. 3 — Chronograph Record of Fork After First Starting 



is almost if not quite critically damped. Several other records 

 taken with even greater phase displacements bear out this conclusion. 

 This practically precludes hunting after the phase angle has been 

 once adjusted. 



Accuracy of the Clock-Controlled Fork 



The accuracy of the fork has been checked in two ways For long 

 periods of time, chronograph records have been taken at inters'als 

 over a period of 8 hours and the maximum variation of the fork from 

 the clock in this period has been found to be less than .02 second, or 

 one cycle. Smaller periods of tim.e cannot be measured accurately 

 on the chronograph used. If we are dealing with periods of time of 



