AEROGRAPHER'S MATE 3 & 2 



the pen is not being held back by drag. If 

 the pen is still not on zero, adjust the mechanical 

 zero of the recorder by moving the ZERO 

 ADJUSTMENT lever on the bottom of the case 

 in the direction toward which the pen needs 

 to be moved. Frequent, gentle tapping of the 

 chart will eliminate pen drag. 



INDICATOR CONTROLS. — Controls (fig. 

 5-19) used in normal operation of the indicator 

 of the transmissometer set are as follows: 



1. TRANSMISSION METER. Indicates inper- 

 cent the atmospheric transmission between the 

 projector and receiver. 



2. POWER SWITCH. Connects (ON position) 

 or disconnects (OFF position) power to indicator 

 units. 



3. BACKGROUND SWITCH. In TEST po- 

 sition, shuts off projector lamp to determine 

 the amount of background illumination. 



4. ZERO SWITCH. In TEST position, shorts 

 input signal to ground for check on electrical 

 zero of the indicator. 



5. CALIBRATE SWITCH. In CALIB position 

 introduces line frequency to calibrate circuit. 



6. RANGE SWITCH. Selects HIGH or LOW 

 sensitivity range of indicator, actuates marker 

 pen, which indicates sensitivity range on roll 

 chart. (When RANGE switch is in HIGH position, 

 sensitivity is five times as great as when 

 switch is in LOW position.) 



7. ZERO AD JUSTMENT POTENTIOMETER. 

 Provides adjustment of electrical zero of indi- 

 cator and recorder. Clockwise rotation causes 

 needle of transmission meter and recorder pen 

 to move up-scale. 



8. CALIBRATION ADJUSTMENT POTEN- 

 TIOMETER. Provides adjustment so that trans- 

 mission meter and recorder will read 90 when 

 the pulse rate of the signal it is receiving 

 is 3,600 pulses per minute with range switch 



Figure 5-19. — Transmissometer indicator control panel. 



96 



209.137 



