Section VIII. MODIFICATION OF STRIP-CHART RECORDER SPEED 



The slowest speed of the chart on the recorder as received from the 

 manufacturer is 5 millimeters per second or about 12 inches per minute. 

 To conserve chart paper and lengthen the time between visits to the wave 

 recording station, it is desirable to change the chart speed to a lower 

 value. 



Three lower chart speeds can be provided for the recorder with 

 fairly simple changes in the gears. These changes will provide a basic 

 chart speed of 2.5 millimeters per second, 1.25 millimeters per second, 

 or 1.0 millimeter per second. 



Recorder paper comes in rolls 300 feet long on GSA schedule from 

 Judson Bigelow, Inc., 12-12 44th Avenue, Long Island City, New York, 

 Chart No. RA-2911-30 JB. With the recorder operating for 7 minutes each 

 4 hours and the reduced chart speed of 2.5 millimeters per second, a 

 300-foot roll will last about 14 days. If different frequency recording 

 periods are desired, the time span for one roll may be calculated. 



If the recorder is modified to a slower chart speed, wave crests 

 will appear closer together on the chart. A sample of wave periods, 

 using sine waves, on a recorder chart with speeds of 2.5 millimeters, 

 1.25 millimeters, and 1.0 millimeter per second are shown on Figures 

 51, 52, and 53. 



To modify the recorder chart speed, proceed as follows: 



a) Fabricate the required gear assemblies and parts for the 

 selected chart speed as shown on Figures 54 through 56. 



b) Remove the recorder pen. 



c) Remove the chart platen. 



d) Remove the chart payout guide and paper tear-off unit . 



e) Remove the chart driving roller, taking care not to lose the 

 two brass spacers on the ends of the roller. 



f) Remove the chart speed-shift knob assembly. A thin knife blade 

 "in the side of the main drive-shaft slot will accomplish this. 



g) Remove the snap spring on the main drive shaft. Observe the 

 spacing between the spring and the recorder frame, and retain 

 this distance when recorder is re-assembled. 



101 



