AUTOMATIC TESTING IN TELEPHONE MANUFACTURE 



1149 



Fig. 8 — Film scale calibrator, 



feet long. It has sprocket holes and is moved by a standard movie 

 sprocket. The required precision of each calibration mark is ±2 kc. Two 

 resonant devices are included in the circuit to permit checking and ad- 

 justing two widely separated points on the scale, 100 kc and 7,266 kc. 

 Considering the output frequency as a function of scale setting, one of 

 the two adjustments controls the lateral displacement of the curve and 

 the other its average slope. By design the curve approaches linearity 

 but not closely enough to permit less than a uniciue calibration for each 

 oscillator manufactured. 



Fig. 8 shows the machine which performs the calibration, with an 

 oscillator connected, and the control cabinet. The oscillator is shown in 

 its shipping frame. An unexposed photographic film to be calibrated is 

 mounted in a camera so that it can be driven by a sprocket. The sprocket 

 is connected by gears to a drive motor which also drives the take-up reel 

 and, through a flexible shaft, the cavity tuner and sprocket in the oscil- 

 lator itself. The gear arrangement is such that the peripheral speeds of 

 the two sprockets are the same. 



A positive master film is provided which has a scale similar to the one 

 to be made for the product except that it is very precisely hnear. A por- 

 tion of the master is shown in Fig. 9(b). The master film passes over a 

 sprocket which is driven by a servo motor. A lamp illuminates and shines 

 through that portion of the master which is in front of an aperture at 



